1. A molecular probe for use in the detection of myelin in a subject comprising the general formula: ##STR00030## wherein R1 and R2 are each independently selected from the group consisting of H, NO2, NH2, NHCH3, N(CH3)2, OH, OCH3, COOCH3, SH, SCH3, alkyl derivatives thereof, a halo group, a radiolabel, a chelating group, and a near infrared group; wherein X1 is a double or triple bond; each R4-R9 are independently H, wherein R10 and R11 and/or R12 and R13 are each independently H or linked to form a cyclic ring, wherein the cyclic ring is aromatic, alicyclic, heteroaromatic, or heteroalicyclic; or a pharmaceutically acceptable salt thereof, wherein the molecular probe upon administration to the subject binds to myelin of the subject.
3. The molecular probe of claim 1, is a double bond, and R10 and R11 are linked to form a heterocylic ring.
6. The molecular probe of claim 1, further comprising a chelating group or a near infrared imaging group.
9. A method of detecting myelin in vivo in an animal, the method comprising: (i) administering to the animal a molecular probe including the general formula: ##STR00031## wherein R1 and R2 are each independently selected from the group consisting of H, NO2, NH2, NHCH3, N(CH3)2, OH, OCH3, COOCH3, SH, SCH3, alkyl derivatives thereof, a halo group, a radiolabel, a chelating group, and a near infrared group; wherein X1 is a double or triple bond; each R4-R9 are independently H, wherein R10 and R11 and/or R12 and R13 are each independently H or linked to form a cyclic ring, wherein the cyclic ring is aromatic, alicyclic, heteroaromatic, or heteroalicyclic; or a pharmaceutically acceptable salt thereof; (ii) visualizing the myelin in the animal using an in vivo imaging modality.
12. The method of claim 9, further comprising the step of administering the molecular probe to the animal parenterally.
14. The molecular probe of claim 9, is a double bond, and R10 and R11 are linked to form a heterocylic ring.
17. The method of claim 9, wherein the molecular probe further comprises a chelating group or a near infrared imaging group.
[0001] This application claims priority from U.S. Provisional Application No. 61/101,299, filed Sep. 30, 2008, the subject matter, which is incorporated herein by reference.
[0003] The present invention relates to molecular probes and to methods of their use, and particularly relates to molecular probes that readily enter the brain and selectively localize in the myelinated regions.
[0004] Myelin is a specialized membrane that ensheathes neuronal axons, promoting efficient nerve impulse transmission (Morell and Quarles (1999) Basic Neurochemistry: molecular, cellular, and medical aspects. In Siegel G J, ed. Myelin Formation, Structure, and Biochemistry. Lippincott-Raven Publishers, 79-83). Due to its important biological functions in the normal central nervous system (CNS) and its vulnerability in disease, several techniques have been developed to visualize and characterize myelin histopathology. These can be broadly divided into those based upon antibody immunohistochemistry (IHC) (Horton and Hocking (1997) Cereb. Cortex 7:166-177) and more traditional histochemical procedures. The classic histochemical stains include luxol fast blue MBN (Kluver and Barrera (1953) J Neurosci Methods 153: 135-146; Presnell and Schreibman (1997) Humanson's Animal Tissue Techniques, 5th ed.; Kiernan (1999) Histological and Histochemical Methods: Theory and practice, 3rd ed.; Bancroft and Gamble (2002), Theory and Practice of Histological Techniques, 5 ed. and Sudan Black B (Lison and Dagnelie (1935) Bull. d'Histologie Appliquee 12: 85-91). Traditional chromogenic methods also include the Palweigert method ((Weigert (1884) Fortschr Deutsch Med 2: 190-192, (1885) Fortschr Deutsch Med 3:236-239; Clark and Ward (1934) Stain Technol 54:13-16), the Weil stain (Weil (1928) Arch Neurol Psychiatry 20:392-393; Berube et al. (1965) Stain Technol 40:53-62)), the Loyez method (Cook (1974) Manual of Histological Demonstration Methods, 5th ed.), and a method based on horse serum followed by subsequent reaction with diaminobenzidine (McNally and Peters (1998) J Histochem Cytochem 46:541-545). In addition, modified silver stains including the Gallyas method (Pistorio et al. (2005) J Neurosci Methods 153: 135-146) and Schmued's gold chloride technique (Schmued and Slikker (1999) Brain Res 837:289-297) have also been used as simple, high-resolution histochemical markers of myelin. More recently, fluoromyelin (Kanaan et al. (2005) Am J Physiol Regul Integr Comp Physiol 290:R1105-1114) and NIM (Xiang et al. (2005) J Histochem Cytochem 53:1511-1516) were introduced as novel myelin dyes, which enable quick and selective labeling of myelin in brain tissue sections. Although these myelin-staining techniques are widely used in vitro, none can be applied in vivo due to impermeability of the blood-brain barrier (BBB). The lack of in vivo molecular probes has limited the progress of myelin imaging and hindered efficacy evaluation of novel myelin repair therapies during their development.
[0005] The present invention relates to molecular probes for use in the detection of myelin in a subject. The molecular probes include a compound having the general formula:
[0007] In one aspect of the invention, R1 and/or R2 can be selected from the group consisting of H, NO2, NH2, NHCH3, N(CH3)2, OH, OCH3, COOCH3, SH, SCH3, and alkyl derivatives thereof and each R4-R13 is H. The molecular probe in accordance with the present invention can readily enter the brain following systemic or parenteral administration and bind to myelin membranes.
[0008] In another aspect of the invention, R1 and R2 are each independently selected from the group consisting of H, NO2, NH2, NHCH3, N(CH3)2, OH, OCH3, COOCH3, SH, SCH3, and alkyl derivatives thereof, X1 is a double bond, and R10 and R11 are linked to form a heterocylic ring.
[0009] The present invention also relates to a method of detecting myelin in vivo in an animals's tissue. The method includes administering in vivo to the animal a molecular probe that includes a compound having the general formula:
[0011] In one aspect of the invention, R1 and/or R2 can be selected from the group consisting of H, NO2, NH2, NHCH3, N(CH3)2, OH, OCH3, COOCH3, SH, SCH3, and alkyl derivatives thereof and each R4-R13 is H. The molecular probe in accordance with the present invention can readily enter the brain following systemic or parenteral administration and bind to myelin membranes.
[0012] In another aspect of the invention, R1 and R2 are each independently selected from the group consisting of H, NO2, NH2, NHCH3, N(CH3)2, OH, OCH3, COOCH3, SH, SCH3, and alkyl derivatives thereof, X1 is a double bond, and R10 and R11 are linked to form a heterocylic ring.
[0013] The present invention further relates to a method of detecting a myelin related disorder in a subject. The method includes labeling myelin in vivo in the animal's tissue by administering to the animal a molecular probe that includes a compound having the general formula:
[0015] The present invention further relates to a method of monitoring the efficacy of a remyelination therapy in an animal. The method includes labeling myelin in vivo in the animal's brain tissue with a molecular probe having the general formula:
[0017] The present invention further relates to a method of screening the myelination effects of an agent in an animal. The method includes labeling myelin in vivo in the animal's tissue with a molecular probe having the general formula:
[0019] The foregoing and other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which:
[0021] FIG. 2 illustrates plots of the concentrations of free, unbound 6 and 7 following incubation with isolated myelin fractions and non-myelin pellets based upon a spectroscopic assay. In these assays, 10 μM of 6 and 7 was added to each solution containing myelin fractions or non-myelin pellets at various concentrations ranging from 0-2.5 μg per tube. Each data point was repeated in triplicate and an average was used.
[0022] FIG. 3 illustrates saturation and scatchard plots of [3H]BMB binding to isolated myelin fractions. [3H]BMB displayed one-site binding. High-affinity binding with dissociation constant (Kd) values in a nanomolar range was obtained (Kd)) 1.098 nM.
[0023] FIG. 4 illustrates plots of competition binding assays of test compounds using [3H]BMB as the radioligand in isolated myelin fractions. The concentrations that inhibited 50% of specific binding of [3H]BMB (IC50 values) were converted to inhibition constant (Ki). Ki values were calculated using the Cheng-Prusoff equation: Ki=IC50/(1+[L]/Kd), where [L] is the concentration of [3H]BMB used in the assay. Data are means of three independent measurements done in duplicate.
[0025] FIG. 6 illustrates photographs of in situ staining of myelin sheaths in the cerebellum of mouse brain.
[0027] FIG. 8 illustrates structures of coumarin derivatives that have been screened for myelin staining.
[0030] FIG. 11 illustrates quantification of the fluorescent intensity as determined in the same corpus callosum region following MBP staining (A) and chemical staining (B). The data were analyzed using the GraphPad Prism. (A) P=0.0393, n=3, Unpaired t-test; (B) P=0.0393, n=3, Unpaired t-test.
[0032] The present invention relates to molecular probes that upon administration to a mammal (e.g., systemic, parenteral, or intravenous administration) can readily and selectively localize to myelinated regions of the brain, central nervous system, and peripheral nervous system. The molecular probes can bind to myelin membrane and do not bind to a component of degenerating myelin fragments. The molecular probes can also be readily visualized using conventional visualization techniques to indicate myelinated regions of the brain, central nervous system, and peripheral nervous system. The molecular probes can be used in a method of detecting a level of myelination in vivo in a subject, a method of detecting a myelin related disorder in a subject, a method of monitoring the remyelination effects of an agent in an animal, and a method of screening the myelination effects of an agent in an animal.
[0033] The molecular probe can include a fluorescent trans-stilbene derivative or a pharmacophore thereof (e.g., coumarin pharmacophore) that is less than about 700 daltons and has a relatively high binding affinity (Kd) (e.g., at least about 1.0 nM) to isolated myelin fractions but a relatively low binding affinity (Kd) to isolated non-myelin fractions.
[0034] In an aspect of the invention, the molecular probe can include a fluorescent trans-stilbene derivative having the following formula:
[0036] The phrase "having the formula" or "having the structure" is not intended to be limiting and is used in the same way that the term "comprising" is commonly used.
[0037] The term "alkyl" refers to a branched or unbranched saturated hydrocarbon group typically although not necessarily containing 1 to about 24 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, octyl, decyl, and the like, as well as cycloalkyl groups, such as cyclopentyl, cyclohexyl, and the like. Generally, although again not necessarily, alkyl groups herein contain 1 to about 18 carbon atoms, preferably 1 to about 12 carbon atoms. The term "lower alkyl" intends an alkyl group of 1 to 6 carbon atoms. Substituents identified as "C1-C6 alkyl" or "lower alkyl" can contain 1 to 3 carbon atoms, and more particularly such substituents can contain 1 or 2 carbon atoms (i.e., methyl and ethyl). "Substituted alkyl" refers to alkyl substituted with one or more substituent groups, and the terms "heteroatom-containing alkyl" and "heteroalkyl" refer to alkyl in which at least one carbon atom is replaced with a heteroatom, as described in further detail infra. If not otherwise indicated, the terms "alkyl" and "lower alkyl" include linear, branched, cyclic, unsubstituted, substituted, and/or heteroatom-containing alkyl or lower alkyl, respectively.
[0038] The term "alkenyl" refers to a linear, branched or cyclic hydrocarbon group of 2 to about 24 carbon atoms containing at least one double bond, such as ethenyl, n-propenyl, isopropenyl, n-butenyl, isobutenyl, octenyl, decenyl, tetradecenyl, hexadecenyl, eicosenyl, tetracosenyl, and the like. Generally, although again not necessarily, alkenyl groups can contain 2 to about 18 carbon atoms, and more particularly 2 to 12 carbon atoms. The term "lower alkenyl" refers to an alkenyl group of 2 to 6 carbon atoms, and the specific term "cycloalkenyl" intends a cyclic alkenyl group, preferably having 5 to 8 carbon atoms. The term "substituted alkenyl" refers to alkenyl substituted with one or more substituent groups, and the terms "heteroatom-containing alkenyl" and "heteroalkenyl" refer to alkenyl in which at least one carbon atom is replaced with a heteroatom. If not otherwise indicated, the terms "alkenyl" and "lower alkenyl" include linear, branched, cyclic, unsubstituted, substituted, and/or heteroatom-containing alkenyl and lower alkenyl, respectively.
[0039] The term "alkynyl" refers to a linear or branched hydrocarbon group of 2 to 24 carbon atoms containing at least one triple bond, such as ethynyl, n-propynyl, and the like. Generally, although again not necessarily, alkynyl groups can contain 2 to about 18 carbon atoms, and more particularly can contain 2 to 12 carbon atoms. The term "lower alkynyl" intends an alkynyl group of 2 to 6 carbon atoms. The term "substituted alkynyl" refers to alkynyl substituted with one or more substituent groups, and the terms "heteroatom-containing alkynyl" and "heteroalkynyl" refer to alkynyl in which at least one carbon atom is replaced with a heteroatom. If not otherwise indicated, the terms "alkynyl" and "lower alkynyl" include linear, branched, unsubstituted, substituted, and/or heteroatom-containing alkynyl and lower alkynyl, respectively.
[0040] The term "alkoxy" refers to an alkyl group bound through a single, terminal ether linkage; that is, an "alkoxy" group may be represented as --O-alkyl where alkyl is as defined above. A "lower alkoxy" group intends an alkoxy group containing 1 to 6 carbon atoms, and includes, for example, methoxy, ethoxy, n-propoxy, isopropoxy, t-butyloxy, etc. Preferred substituents identified as "C1-C6 alkoxy" or "lower alkoxy" herein contain 1 to 3 carbon atoms, and particularly preferred such substituents contain 1 or 2 carbon atoms (i.e., methoxy and ethoxy).
[0041] The term "aryl" refers to an aromatic substituent containing a single aromatic ring or multiple aromatic rings that are fused together, directly linked, or indirectly linked (such that the different aromatic rings are bound to a common group such as a methylene or ethylene moiety). Aryl groups can contain 5 to 20 carbon atoms, and particularly preferred aryl groups can contain 5 to 14 carbon atoms. Exemplary aryl groups contain one aromatic ring or two fused or linked aromatic rings, e.g., phenyl, naphthyl, biphenyl, diphenylether, diphenylamine, benzophenone, and the like. "Substituted aryl" refers to an aryl moiety substituted with one or more substituent groups, and the terms "heteroatom-containing aryl" and "heteroaryl" refer to aryl substituent, in which at least one carbon atom is replaced with a heteroatom, as will be described in further detail infra. If not otherwise indicated, the term "aryl" includes unsubstituted, substituted, and/or heteroatom-containing aromatic substituents.
[0042] The term "aryloxy" as used herein refers to an aryl group bound through a single, terminal ether linkage, wherein "aryl" is as defined above. An "aryloxy" group may be represented as --O-aryl where aryl is as defined above. Preferred aryloxy groups contain 5 to 20 carbon atoms, and particularly preferred aryloxy groups contain 5 to 14 carbon atoms. Examples of aryloxy groups include, without limitation, phenoxy, o-halo-phenoxy, m-halo-phenoxy, p-halo-phenoxy, o-methoxy-phenoxy, m-methoxy-phenoxy, p-methoxy-phenoxy, 2,4-dimethoxy-phenoxy, 3,4,5-trimethoxy-phenoxy, and the like.
[0043] The term "alkaryl" refers to an aryl group with an alkyl substituent, and the term "aralkyl" refers to an alkyl group with an aryl substituent, wherein "aryl" and "alkyl" are as defined above. Exemplary aralkyl groups contain 6 to 24 carbon atoms, and particularly preferred aralkyl groups contain 6 to 16 carbon atoms. Examples of aralkyl groups include, without limitation, benzyl, 2-phenyl-ethyl, 3-phenyl-propyl, 4-phenyl-butyl, 5-phenyl-pentyl, 4-phenylcyclohexyl, 4-benzylcyclohexyl, 4-phenylcyclohexylmethyl, 4-benzylcyclohexylmethyl, and the like. Alkaryl groups include, for example, p-methylphenyl, 2,4-dimethylphenyl, p-cyclohexylphenyl, 2,7-dimethylnaphthyl, 7-cyclooctylnaphthyl, 3-ethyl-cyclopenta-1,4-diene, and the like.
[0044] The term "cyclic" refers to alicyclic or aromatic substituents that may or may not be substituted and/or heteroatom containing, and that may be monocyclic, bicyclic, or polycyclic.
[0045] The terms "halo" and "halogen" are used in the conventional sense to refer to a chloro, bromo, fluoro or iodo substituent.
[0046] The term "heteroatom-containing" as in a "heteroatom-containing alkyl group" (also termed a "heteroalkyl" group) or a "heteroatom-containing aryl group" (also termed a "heteroaryl" group) refers to a molecule, linkage or substituent in which one or more carbon atoms are replaced with an atom other than carbon, e.g., nitrogen, oxygen, sulfur, phosphorus or silicon, typically nitrogen, oxygen or sulfur. Similarly, the term "heteroalkyl" refers to an alkyl substituent that is heteroatom-containing, the term "heterocyclic" refers to a cyclic substituent that is heteroatom-containing, the terms "heteroaryl" and heteroaromatic" respectively refer to "aryl" and "aromatic" substituents that are heteroatom-containing, and the like. Examples of heteroalkyl groups include alkoxyaryl, alkylsulfanyl-substituted alkyl, N-alkylated amino alkyl, and the like. Examples of heteroaryl substituents include pyrrolyl, pyrrolidinyl, pyridinyl, quinolinyl, indolyl, pyrimidinyl, imidazolyl, 1,2,4-triazolyl, tetrazolyl, etc., and examples of heteroatom-containing alicyclic groups are pyrrolidino, morpholino, piperazino, piperidino, etc.
[0047] By "substituted" as in "substituted alkyl," "substituted aryl," and the like, as alluded to in some of the aforementioned definitions, is meant that in the alkyl, aryl, or other moiety, at least one hydrogen atom bound to a carbon (or other) atom is replaced with one or more non-hydrogen substituents. In addition, the aforementioned functional groups may, if a particular group permits, be further substituted with one or more additional functional groups or with one or more hydrocarbyl moieties such as those specifically enumerated above. Analogously, the above-mentioned hydrocarbyl moieties may be further substituted with one or more functional groups or additional hydrocarbyl moieties such as those specifically enumerated.
[0048] When the term "substituted" appears prior to a list of possible substituted groups, it is intended that the term apply to every member of that group. For example, the phrase "substituted alkyl, alkenyl, and aryl" is to be interpreted as "substituted alkyl, substituted alkenyl, and substituted aryl." Analogously, when the term "heteroatom-containing" appears prior to a list of possible heteroatom-containing groups, it is intended that the term apply to every member of that group. For example, the phrase "heteroatom-containing alkyl, alkenyl, and aryl" is to be interpreted as "heteroatom-containing alkyl, substituted alkenyl, and substituted aryl."
[0049] "Optional" or "optionally" means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not. For example, the phrase "optionally substituted" means that a non-hydrogen substituent may or may not be present on a given atom, and, thus, the description includes structures wherein a non-hydrogen substituent is present and structures wherein a non-hydrogen substituent is not present.
[0050] In one aspect of the invention, R1 and/or R2 can be selected from the group consisting of H, NO2, NH2, NHCH3, N(CH3)2, OH, OCH3, COOCH3, SH, SCH3, and alkyl derivatives thereof and each R4-R13 is H.
[0051] In one example of the invention, the molecular probe can include a fluorescent stilbene derivative having the following formula:
[0053] In a further aspect the, the molecular probe can be selected from the following general structures:
[0055] In another aspect of the invention, the molecular probe can include a fluorescent coumarin derivative that is a pharmacophore of trans-stilbene. In an aspect of the invention, R1 and R2 are each independently selected from the group consisting of H, NO2, NH2, NHCH3, N(CH3)2, OH, OCH3, COOCH3, SH, SCH3, and alkyl derivatives thereof, X1 is a double bond, and R10 and R11 are linked to form a heterocylic ring.
[0056] In one example, the fluorescent coumarin derivative can a pharmacophore of trans-stilbene having the following formula:
##STR00009## [0057] wherein R1 and R2 are each independently selected from the group consisting of H, NO2, NH2, NHCH3, N(CH3)2, OH, OCH3, COOCH3, SH, SCH3, and alkyl derivatives thereof; and pharmaceutically acceptable salts thereof.
##STR00010## [0059] wherein R1 and R2 are each independently selected from the group consisting of H, NO2, NH2, NHCH3, N(CH3)2, OH, OCH3, COOCH3, SH, SCH3, and alkyl derivatives thereof; and pharmaceutically salts thereof.
[0060] In a further example, the fluorescent coumarin derivative can be a pharmacophore of stilbene having the following formula:
[0062] The foregoing formulae represent the general structures of fluorescent trans-stilbene compounds found to be effective molecular probes for labeling myelin in vivo as well as in vitro as described in the examples below. They are characterized by their ability to be administered to a mammal or subject parenterally and selectively localize to myelinated regions in the brain, central nervous system, and peripheral nervous system via direct binding to myelin membranes and not bind to degenerating myelin fragments. The molecular probes are unique in that they exhibit negligible toxicities as demonstrated in both preclinical and clinical settings, making them suitable candidates for clinical imaging modalities and translational studies. For example, once radiolabelled with positron-emitting radionuclide, they can be used for positron emission tomography to detect and quantify myelin contents in vivo.
[0063] When referring to the terms "fluorescent trans-stilbene" or "fluorescent trans-stilbene derivative" or "fluorescent trans-stilbene compound" in the specification and the claims, it is intended that the terms encompass not only the specified molecular entity but also its pharmaceutically acceptable, pharmacologically active analogs, including, but not limited to, salts, esters, amides, prodrugs, conjugates, active metabolites, and other such derivatives, analogs, and related compounds.
[0064] By "pharmaceutically acceptable" is meant a material that is not biologically or otherwise undesirable, i.e., the material may be incorporated into a pharmaceutical composition administered to a patient without causing any undesirable biological effects or interacting in a deleterious manner with any of the other components of the composition in which it is contained. When the term "pharmaceutically acceptable" is used to refer to a pharmaceutical carrier or excipient, it is implied that the carrier or excipient has met the required standards of toxicological and manufacturing testing or that it is included on the Inactive Ingredient Guide prepared by the U.S. Food and Drug administration. "Pharmacologically active" (or simply "active") as in a "pharmacologically active" derivative or analog, refers to a derivative or analog having the same type of pharmacological activity as the parent compound and approximately equivalent in degree.
[0065] As used herein, the term "pharmaceutically acceptable salts" or complexes refers to salts or complexes that retain the desired biological activity of the parent compound and exhibit minimal, if any, undesired toxicological effects. Nonlimiting examples of such salts are (a) acid addition salts formed with inorganic acids (for example, hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid, and the like), and salts formed with organic acids such as acetic acid, oxalic acid, tartaric acid, succinic acid, malic acid, ascorbic acid, benzoic acid, tannic acid, palmoic acid, alginic acid, polyglutamic acid, naphthalenesulfonic acids, naphthalenedisulfonic acids, and polygalacturonic acid; (b) base addition salts formed with cations such as sodium, potassium, zinc, calcium, bismuth, barium, magnesium, aluminum, copper, cobalt, nickel, cadmium, sodium, potassium, and the like, or with an organic cation formed from N,N-dibenzylethylene-diamine, ammonium, or ethylenediamine; or (c) combinations of (a) and (b); e.g., a zinc tannate salt or the like.
[0066] Typically, the molecular probe can be formulated into solution prior to use. In one example, a molecular probe solution includes a 10 mM molecular probe solution. A molecular probe solution can also contain saline, DMSO, and HCL. One skilled in the art can utilize the molecular probe with pharmaceutical carriers and/or excipients in varying concentrations and formulations depending on the desired use.
[0067] In some embodiments of the present invention, the molecular probe can be radiolabeled to aid in the detection of the molecular probe once it binds to myelin. A `radiolabel` as used herein is any compound that has been joined with a radioactive substance. Examples of radiolabels include positron emitting 3H, 125I, 11C, and 18F radiolabels.
[0068] In an embodiment of the invention, the molecular probe can be coupled to a chelating group (with or without a chelated metal group) to improve the MRI contrast properties of the molecular probe. In one example, as disclosed in U.S. Pat. No. 7,351,401 which is herein incorporated by reference in its entirety, the chelating group can be of the form W-L or V--W-L, wherein V is selected from the group consisting of --COO--, --CO--, --CH2O-- and --CH2NH--; W is --(CH2)n where n=0,1,2,3,4, or 5; and L is:
[0070] ##STR00014## [0071] or a myelin binding, chelating compound (with or without a chelated metal group) or a water soluble, non-toxic salt thereof of the form:
[0073] The chelating group can be coupled to at least one terminal benzene groups or the R1 or R2 groups. In one example, the chelating group can be coupled to terminal amino R1 and/or R2 group through a carbon chain link. The carbon chain link can comprise, for example about 2 to about 10 methylene groups and have a formula of, for example, (CH2)n, wherein n=2 to 10.
[0076] In another example, the molecular probe with the chelating group can have the following formula:
[0078] In another example, the molecular probe with the chelating group can have the following formula:
[0080] In another embodiment, the molecular probe can be coupled to a near infrared group to improve the near infrared imaging of the molecular probe. Examples of near infrared imaging groups that can be coupled to the molecular probe include:
[0082] The near infrared imaging group can be coupled to at least one terminal benzene groups, or the R1 or R2 groups. In one example, the near infrared imaging group can be coupled to at least one terminal benzene group.
[0083] In one example, the molecular probe with the near infrared imaging group can have the following formula:
[0085] In another example, the molecular probe with the near infrared imaging group can have the following formula:
[0089] In certain embodiments of the present invention, the molecular probes described herein can be contacted with an animal's brain tissue central nervous system, and/or peripheral nervous system and utilized for labeling and detecting myelinated regions of an animal's brain tissue, central nervous system, and/or peripheral nervous system. Myelinated regions of an animal's brain are typically found in the white matter of the brain in the myelin sheaths of neuronal axons. Myelin is an outgrowth of glial cells, more specifically oligodendrocytes, which serve as an electrically insulating phospholipid layer surrounding axons of many neurons. For purposes of the present invention, an animal's brain tissue is typically a mammal's brain tissue, such as a primate, e.g., chimpanzee or human; cow; dog; cat; a rodent, e.g., guinea pig, rat, mouse; rabbit; or a bird; reptile; or fish.
[0090] In some embodiments, the molecular probes described herein can be used for the in vivo detection and localization of myelinated regions of an animal's brain, central nervous system, and/or peripheral nervous system. The molecular probe can be administered to the animal as per the examples contained herein, but typically through intravenous injection. "Administered", as used herein, means provision or delivery molecular probes in an amount(s) and for a period of time(s) effective to label myelin in an animal's brain central nervous system, and/or peripheral nervous system. The molecular probes can be administered to the animal can be enterally or parenterally in a solid or liquid. Enteral route includes oral, rectal, topical, buccal, and vaginal administration. Parenteral route includes intravenous, intramuscular, intraperitoneal, intrasternal, and subcutaneous injection or infusion.
[0091] An example of a dosing regimen is to administer about 40- about 50 mg/kg by weight to the animal. In one example at 5 min, the brain concentration of probe can range between about 4% to 24% ID/g to ensure sufficient visualization of the myelinated regions of the brain, central nervous system, and/or peripheral nervous system.
[0092] The molecular probes of the present invention can be used for neuroanatomical or neuropathological studies. Researchers studying normal brains can employ this method to examine the morphology and distribution of myelinated tissue in an animal. "Distribution" as used herein is the spatial property of being scattered about over an area or volume. In this case the "distribution of myelinated tissue" is the spatial property of myelin being scattered about over an area or volume included in the animal's brain, central nervous system, or peripheral nervous system tissue. Researchers interested in neurotoxicology and neuropathology can also use this method in several ways. One way is to infer demyelination by the absence of the molecular probe labeling compared to normal control tissue (e.g., normal brain). A second way is to study morphological changes in the myelin such as a fragmented or beaded appearance of the myelin sheath. In yet another embodiment of the present invention, one skilled in the art can assess and quantify changes in myelin content in vivo.
[0093] In other aspects of the present invention, myelin in an animal's brain, central nervous system, and/or peripheral nervous system can be visualized and quantified using an in vivo imaging modality. The molecular probe may be visualized any time post administration depending on the application as typical molecular probes embodied in the present invention have a low clearance rate due to specific binding in the myelinated regions (e.g. at 60 min, the brain concentration of probe can be ≦50% of 5 min value to ensure that half time retention in normally myelinated brain is 60 min or longer).
[0094] An in vivo imaging modality as used herein is an imaging modality capable of visualizing molecular probes described herein in vivo (within a living organism). An example of an in vivo imaging modality is positron emission tomography (PET). PET is a functional imaging technique that can detect chemical and metabolic change at the molecular level. To function as a PET imaging molecular probe, embodiments of the present invention must meet a set of biological requirements known to the skilled artisan, some of which may include lipophilicity, binding affinity, binding specificity, brain uptake, retention, and metabolism. Another example of an in vivo imaging modality is MicroPET. MicroPET is a high resolution positron emission tomography scanner designed for imaging small laboratory animals. Other examples of imaging modalities that can be used in accordance with the present invention include magnetic resonance imaging (MRI), near infrared (NIR) imaging, fluorescent microscopy, and mutiphoton microscopy.
[0095] For directly monitoring myelin changes in the white matter of a subject, embodiments of the invention can readily penetrate the blood-brain barrier (BBB) and directly bind to the myelinated white matter in proportion to the extent of myelination. Radiolabeled molecular probes of the present invention can be used in conjunction with PET as imaging markers to directly assess the extent of total lesion volumes associated with demyelination. This can provide a direct clinical efficacy endpoint measure of myelin changes and identify effective therapies aimed at protection and repair of axonal damages.
[0096] The molecular probes of the present invention can also be used to diagnose a myelination related disorder in an animal through the use of in vivo myelin labeling. Thus, in certain embodiments of the present invention, solutions containing the molecular probes describe herein can be used in the detection of myelin related disorders in an animal.
[0097] Methods of detecting a myelin related disorder include the steps of labeling myelin in vivo in the animal's brain tissue with a molecular probe described herein, visualizing a distribution of the molecular probe in the animal's brain tissue as described above and in the examples, and then correlating the distribution of the molecular probe with a myelin related disorder in the animal. In one example of detecting a myelin related disorder, the methods described herein can be used to compare myelinated axonal regions of the brain in the normal tissues of control populations to those of a suspect animal. If the suspect animal has a myelin related disorder, myelin may be virtually absent in lesioned areas thus indicating the presence of a myelin related disorder.
[0098] Myelination disorders can include any disease, condition (e.g., those occurring from traumatic spinal cord injury and cerebral infarction), or disorder related to demylination, remylination, or dysmyelination in a subject. A myelin related disorder as used herein can arise from a myelination related disorder or demyelination resulting from a variety of neurotoxic insults. Demyelination is the act of demyelinating, or the loss of the myelin sheath insulating the nerves, and is the hallmark of some neurodegenerative autoimmune diseases, including multiple sclerosis, transverse myelitis, chronic inflammatory demyelinating polyneuropathy, and Guillain-Bane Syndrome. Leukodystrophies are caused by inherited enzyme deficiencies, which cause abnormal formation, destruction, and/or abnormal turnover of myelin sheaths within the CNS white matter. Both acquired and inherited myelin disorders share a poor prognosis leading to major disability. Thus, some embodiments of the present invention can include methods for the detection of neurodegenerative autoimmune diseases in an animal and more specifically the detection of multiple sclerosis in an animal.
[0099] Another embodiment of the present invention includes a method of monitoring the efficacy of a remyelination therapy in an animal. Remyelination is the repair of damaged or replacement of absent myelin in an animal's brain tissue. The methods described include the steps of labeling myelin in vivo in the animal's brain tissue with a molecular probe described herein, then visualizing a distribution of the molecular probe in the animal's brain tissue (e.g. with a in vivo imaging modality as described herein), and then correlating the distribution of the molecular probe as visualized in the animal's brain with the efficacy of the remyelination therapy. It is contemplated that the labeling step can occur before, during, and after the course of a therapeutic regimen in order to determine the efficacy of the therapeutic regimen. One way to assess the efficacy of a remyelination therapy is to compare the distribution of the molecular probe before remyelination therapy with the distribution of the molecular probe after remyelination therapy has commenced or concluded.
[0100] Remyelination therapy as used herein refers to any therapy leading to a reduction in severity and/or frequency of symptoms, elimination of symptoms and/or underlying cause, prevention of the occurrence of symptoms and/or their underlying cause, and improvement or remediation of damage related to demyelination. For example, a remyelination therapy can include administration of a therapeutic agent, therapies for the promotion of endogenous myelin repair, or a cell based therapy (e.g., a stem-cell based therapy).
[0101] In another embodiment of the present invention, methods are provided for screening for a myelination response in an animal's brain tissue to an agent. The method includes the initial step of administering an agent to the animal. Myelin in the animal's brain tissue is labeled in vivo with a molecular probe in accordance with the present invention. A distribution of the molecular probe in the animal's brain tissue is then visualized using a conventional visualization modality. Finally, the distribution of the molecular probe with the myelination response in the animal's brain tissue is correlated to the agent. One way to assess the myelination response in the animal's brain tissue is to compare the distribution of the molecular probe in an animal's brain tissue, which has been treated with a suspect agent with the distribution of the molecular probe in the brain tissue of a control population. "Control Population" as used herein is defined as a population or a tissue sample not exposed to the agent under study but otherwise as close in all characteristics to the exposed group as possible.
[0102] The molecular probes described herein can be used to determine if an agent of interest has the potential to modulate demyelination, remyelination, or dysmyelination of axonal regions of an experimental animal's brain tissue.
[0103] We have identified a series of stilbene derivatives that displayed promising in vitro and in situ properties for imaging of myelinated white matter. Compared to previously reported myelin-imaging probes, these compounds showed improved solubility and binding affinity. The synthesis and biological evaluation of trans-stilbene derivatives is described below.
[0104] Synthesis of stilbene derivatives was achieved through Horner-Wittig reaction as shown below.
[0105] In this study, 4-nitrobenzaldehyde and 4-dimethylamino-benzaldehyde were employed to react with a Horner-Wadsworth-Emmons reagent, (p-nitrobenzyl)-phosphonic acid diethyl ester (1), to yield (E)-4,4'-dinitro-stilbene (2) and (E)-dimethyl-{4-[2-(4-nitro-phenyl)-vinyl]-phenyl}-amine (5). Further reduction of the nitro groups of 2 and 5 in the presence of SnCl2 in ethanol, furnished (E)-4,4'-diamino-trans-stilbene (3) and (E)-dimethyl-{4-[2-(4-amino-phenyl)-vinyl]-phenyl}-amine (6). Reduction of 2 also yielded a less polar, semi-reduced compound, 4-[2-(4-nitro-phenyl)-vinyl]-phenylamine (4) that was successfully separated and characterized by HNMR and HR-MS. Compound 4 was further protected with trifluoroacetic anhydride. Subsequently, methylation with iodomethane in the presence of potassium carbonate followed by hydrolysis and reduction yielded the monoalkylated compound, N-methyl-4-[2-(4-amino-phenyl)-vinyl]-phenyl}-amine (7), which was purified by flash chromatography. In addition, an iodinated compound, 4-[2-(4-Iodo-phenyl)-vinyl]-phenylamine (9) was also synthesized through Horner-Wittig reaction (see Scheme 2).
[0106] 4-Iodo-benzaldehyde readily reacted with 1 in DMF in the presence of NaH. Subsequent reduction with SnCl2 yielded Compound 9. Compounds 3, 6 and 7 are fluorescent compounds and soluble in EtOH, CH2Cl2, DMSO and other organic solvents. The excitation and emission spectra of 3, 6 and 7 (1 μM in DMSO), as recorded using a Cary Eclipse Fluorescent Spectrophotometer, are shown in FIG. 1. The maximal excitation wavelengths were found at 347 nm, 350 nm and 363 nm, and the maximal emission wavelengths were determined at 415 nm, 415 nm and 419 nm for 3, 6, and 7, respectively.
[0107] Compound 9 was selected for radiolabelling with 125I. The radiolabeling precursor, 4-[2-(4-tributylstannanyl-phenyl)-vinyl]-phenylamine (10), was first synthesized directly from the cold standard compound 9, in which the iodo group was replaced with a tributyltin group in the presence of Pd(PPh3)4. Iododestannylation reaction using no-carrier-added sodium [125I] iodide in the presence of hydrogen peroxide as the oxidant yielded [125I]9 (Scheme 2).
[0108] The radiochemical identity of [125I]9 was verified by co-injection with cold standard Compound 9. Following HPLC purification, [125I]9 was obtained in 70% radiochemical yield with a radiochemical purity of >98% and a specific activity of 80 TBq/mmol As monitored by HPLC, [125I]9 was found stable to be kept at room temperature for up to 8 hrs and in the refrigerator for up to 2 months.
[0109] Binding affinities of newly synthesized compounds 6 and 7 were determined based on spectrophotometry. Myelin sheaths and non-myelin pellets were extracted from rat's brain homogenates according to subcellular fraction protocol (Martenson, R. E.; Deibler, G. E.; Kies, M. W. Extraction of rat myelin basic protein free of other basic proteins of whole central nervous system tissue. An analysis of its electrophoretic heterogeneity. J Biol Chem 1969, 244, 4268-4272). Briefly, the homogenates were successively mixed with different concentrations of sucrose and spun in a Beckman ultracentrifuge. Myelin sheaths and non-myelin containing pellets were well separated according to their different densities and located in different layers of sucrose. The proteins were then collected and washed thoroughly with Colman buffer (10 mM). The desired proteins were aliquoted and frozen at -80° C. for up to 6 months without noticeable change in its properties determined by electrophoresis (data not shown). Prior to binding assays, the protein fractions (myelin and pellet) were thawed and diluted with PBS (10 mM, pH 7.0). A series of concentrations of the protein fractions were incubated with tested compounds (6 and 7, 12.5 μM) for 1 h at room temperature. The free and bound tested compounds were then separated by centrifuging at 6000 rpm for 10 min and quantified.
[0110] As shown in FIG. 2, when incubated with non-myelin pellet, the concentrations of free, unbound 6 and 7 were not reduced despite the increased concentration of non-myelin pellet. The concentrations of free 6 and 7 remained constant and close to the total concentration (10.47 μM for 6 and 10.53 μM for 7) initially used, suggesting there was no binding to the non-myelin fractions. In contrast, when incubated with myelin fractions, the concentrations of unbound 6 and 7 decreased proportionally when the concentrations of myelin fractions were increased, suggesting that specific binding interactions exist between the test compounds and the myelin fractions.
[0111] In vitro binding assay using radioligand is the most sensitive techniques available to quantitatively determine the binding affinities of compounds to certain proteins. Our previous studies have shown that BMB binds to myelin sheaths with high affinity and specifity (Stankoff, B.; Wang, Y.; Bottlaender, M.; Aigrot, M. S.; Dolle, F. et al. Imaging of CNS myelin by positron-emission tomography. Proc Natl Acad Sci USA 2006, 103, 9304-9309). For this reason, tritiated BMB was custom synthesized by American Radiolabeled Chemicals Inc. (St Louis, Mo.) and was used as the radioligand for binding assays. This allowed us to determine the binding affinities of the newly synthesized compounds using isolated rat myelin fractions. Saturation experiment was first conducted using [3H]BMB. As shown in FIG. 3, [3H]BMB displayed saturable binding with isolated myelin fractions of rats and approximately 30% of [3H]BMB binding to isolated rat myelin was displaced by 1.0 μM unlabeled BMB. Transformation of the saturation binding of [3H]BMB to Scatchard plots gave linear plots, suggesting that it involved single population of binding sites (FIG. 3). The dissociation constant (Kd value) was 1.098±0.20 nM and Bmax value was 17.61 pmol/mg under the assay condition, respectively. Competitive binding assays were also conducted using [3H]BMB as radioligand. The stilbene derivatives competed effectively with [3H]BMB binding sites on rat myelin fractions at affinities of low micromole concentrations. As shown in FIG. 4, the Ki values estimated for 3, 6, 7 and 9 were 370 nM, 119 nM, 126 nM and 494 nM, respectively. These Ki values suggested that all these derivatives of stilbene had relatively high binding affinity for myelin fractions in the order of 7>6>3>9.
[0112] We then evaluated the myelin-binding properties of the newly synthesized compounds 3, 6, and 7 through in vitro staining of mouse brain tissue sections. Both myelinated corpus callosum and cerebellar regions were then examined by fluorescent microscopy. At 10 μM concentration, compounds 3, 6, and 7 selectively labeled both corpus callosum and cerebellum (FIG. 5), exhibiting a staining pattern that were virtually identical to the pattern observed in immunohistochemical staining of MBP (Wu, C.; Tian, D.; Feng, Y.; Polak, P.; Wei, J. et al. A novel fluorescent probe that is brain permeable and selectively binds to myelin. J Histochem Cytochem 2006, 54, 997-1004).
[0113] Following our in vitro tissue staining studies, we then evaluated the brain permeability and subsequent myelin-binding properties of 6 and 7 in the mouse brain. A dose of 6 or 7 (20-80 mg/kg) was administered via tail vein injection into wild-type mice. Three hours post injection, the mouse brains were perfused with saline followed by 4% paraformaldehyde (PFA) and removed. The fresh frozen brains were then sectioned. Fluorescent staining of myelinated regions such as the cerebellum were then directly examined under a microscope. As shown in FIG. 6, fluorescent compounds 6 and 7 readily entered the mouse brain and selectively labeled myelinated cerebellum.
[0115] Encouraged by the aforementioned studies, we further evaluated the permeability of [125I]9 across the blood brain barrier. Following bolus tail vein injection of [125I]9 (0.2 ml, 0.185 MBq), the radioactivity concentration of [125I]9 in the brain was determined at 2, 30, and 60 min post injection. As shown in Table 1, [125I]9 displayed rapid brain entry at early time intervals. The initial brain entry was 2.29±0.66% ID/g at 2 min post injection. At 30 min post injection, the brain radioactivity concentration reached its peak level (2.65±0.27% ID/g). The radioactivity concentration slowly decreased to 1.12±0.23% ID/g at 120 min post injection. These results indicated that [125I]9 readily entered the brain. Retention of [125I]9 at later time points was likely due to binding to myelin membranes as indicated by aforementioned in vitro and in situ staining studies.
[0116] To further evaluate the binding specificity of [125I]9 to myelin sheaths in the brain, in vitro autoradiography was carried out in mice. As shown in FIG. 7, a distinct labeling of myelinated regions such as corpus callosum and cerebellum were observed after the mouse brain tissue sections (sagittal) were exposed to [125I]9. The result indicated that the autoradiographic visualization was consistent with the histological staining of myelinated regions (i.e. corpus callosum and cerebellum).
[0119] Under Ar, (4-nitro-benzyl)-phosphoric acid diethyl ester (1, 1.81 g, 6.6 mmol) and 4-nitrobenzaldehyde (1.00 g, 6.6 mmol) were dissolved in DMF (10 mL) and EtOH (10 mL). Then NaOCH3 (2.3 mL, 4.37 M) in MeOH was added and the suspension was stirred for another 3 hours. The solid was filtered and dried in vacuum to give 1.50 g (yield: 83%) of 4,4'-dinitro-trans-stilbene. 1H NMR (300 MHz, CDCl3): 8.28 (d, J=8.4 Hz, 4H), 7.94 (d, J=8.4 Hz, 4H), 7.69 (s, 2H).
[0120] To a solution of compound 2 (0.10 g, 0.4 mmol) in THF (20 mL) was added SnCl2 (1.50 g) dissolved in 1N HCl (10 mL). The reaction mixture was stirred overnight at room temperature. The acidic solution was then neutralized using 1N NaOH and extracted with ethyl acetate (3×20 mL). The combined organic phases were washed with water and brine, dried over Na2SO4, and concentrated. Purification with flash column (HE:EA=2:1 to 1:1) yielded 4,4'-diamino-trans-stilbene (3, 0.03 g, 40%) and 4-[2-(4-nitro-phenyl)-vinyl]-phenylamine (4). 1H NMR of 3 (300 MHz, CDCl3): 7.31 (d, J=8.4 Hz, 4H), 6.86 (s, 2H), 6.68 (d, J=8.4 Hz, 4H). HR-ESIMS of 3: m/z calcd for C14H14N2 (M+H.sup.+): 211.1230, found 211.1225. Melting point of 3: 206.1˜207.3° C. 1H NMR of 4 (300 MHz, CDCl3): 8.22 (d, J=8.0 Hz, 2H), 7.59 (d, J=6.86 Hz, 2H), 7.41 (d, J=8.57 Hz, 4H), 7.22 (d, J=17.14 Hz, 1H), 6.97 (d, J=12.57 Hz, 1H), 6.72 (d, J=10 Hz, 2H).
[0121] To a solution of 4-dimethylamino-benzaldehyde (2.24 g, 15 mmol) and (4-nitro-benzyl)-phosphoric acid diethyl ester (1, 4.10 g, 15 mmol) in DMF (20 ml) and EtOH (20 mL) was added to NaOCH3 (1.62 g, 30 mmol). The suspension was stirred and refluxed for 3 hrs. After cooled to room temperature, the precipitate was filtered and washed thoroughly with ethanol to give dimethyl-{4-[2-(4-nitro-phenyl)-vinyl]-phenyl}-amine (5, 2.55 g, 65%) as red solid, 5 was used without further purification.
[0122] To a solution of 5 (2.55 g, 9.5 mmol) in EtOH (100 ml) was added to SnCl2 (8.58 g, 38 mmol). The resulting mixture was refluxed for 4 hrs. The solvent was then removed under vacuum and NaOH (2 mol/L, 40 mL) was added to the residue. The crude solid was filtered and suspended in ethyl acetate (200 ml). The precipitates were then filtered to give dimethyl-{4-[2-(4-amino-phenyl)-vinyl]-phenyl}-amine (6, 1.45 g, 64%) as gray solid. 1H NMR (300 MHz, CDCl3): 7.40 (d, J=8.62 Hz, 2H), 7.33 (d, J=8.40 Hz, 2H), 6.86 (d, J=5.92 Hz, 2H), 6.76 (d, J=8.34 Hz, 2H), 6.69 (d, J=8.22 Hz, 2H), 2.99 (s, 6H). HR-ESIMS: m/z calcd for C16H18N2 (M+H.sup.+): 239.1543, found 239.1542. Melting point: 167.7˜168.5° C.
[0123] To a solution of 4 (50 mg, 2 mmol) dissolved in THF (5 mL) under argon was added to Et3N (1 mL). The solution was stirred for 4 hrs. The solvent was evaporated under vacuum and the protected product was then used without further purification.
[0124] To the solution of the above protected product dissolved in DMF (5 mL) were added NaH (0.10 g) and iodomethane (1 mL). The vial was sealed and stirred overnight. Then the solution was diluted with methanol (8 mL) and 1M NaOH solution (2 mL). After stirred for another 2 hours, the solution was extracted with ethyl acetate. The combined organic layer was washed with water and brine and dried over Na2SO4. Following concentration, the reduced product was then subsequently used without further purification.
[0125] To the suspension of the above compound in acetic acid (10 mL) was added tin (II) chloride (1.0 g). The suspension was heated to reflux for 2 hrs. After concentration, the residue was dissolved in ethyl acetate, washed with 2 N NaOH solution, water, and brine. Dried over Na2SO4, the solution was concentrated and purified by flash column (Hexanes: ethyl acetate=2:1 to 1:1) to give 15 mg of 7 (0.6 mmol, 35% yield for the above three steps). 1H NMR (400 MHz, CDCl3): 7.36 (d, J=8.3 Hz, 2H), 7.32 (d, J=8.2 Hz, 2H), 6.87 (AB, J=18.7 Hz, 16.5 Hz, 2H), 6.69 (d, J=8.2 Hz, 2H), 6.62 (d, J=8.3 Hz, 2H), 3.92 (br, 3H), 2.88 (s, 2H). HR-ESIMS: m/z calcd for C15H16N2 (M+H.sup.+): 225.1386, found 225.1385. Melting point: 143.7˜144.7° C.
[0126] To a solution of diethyl 4-nitrobenzylphosphate (0.44 g, 1.61 mmol) dissolved in DMF (10 mL) was added NaH (0.07 g, 1.75 mmol). The suspension was stirred for 1 hour followed by addition of 4-iodo-benzaldehyde (0.35 g, 1.51 mmol). The suspension was stirred for another 2 hours. Water was added and the solid was collected by filtration to give 8 (0.40 g, 1.14 mmol, yield: 75%). 1H NMR (400 MHz, CDCl3): 8.24 (d, J=8.65 Hz, 2H), 7.88 (d, J=8.68 Hz, 2H), 7.80 (d, J=8.19 Hz, 2H), 7.49 (m, J=8.2 Hz, 4H).
[0127] To a suspension of Compound 8 (0.20 g, 0.57 mmol) in ethanol (10 mL) was added Tin (II) chloride (1.00 g, 5 mmol) and heated to reflux for 4 hours under argon. The ethanol was evaporated under vacuum. The residue was dissolved in ethyl acetate, washed with 1 N NaOH, water, and brine. Dried over Na2SO4, the solution was concentrated and purified by flash column (Hexanes:ethyla acetate=2:1 to 1:1) to give 9 (0.18 g, quant. yield). 1H NMR (400 MHz, CDCl3): 7.66 (d, J=8.25 Hz, 2H), 7.35 (d, J=8.34 Hz, 2H), 7.04 (d, J=15.73 Hz, 1H), 6.71 (d, J=16.26 Hz, 1H), 6.70 (d, J=8.29 Hz, 2H). HR-ESIMS: m/z calcd for C14H12IN (M+H.sup.+): 322.0087, found 322.0084. Melting point: 213.4-215.2° C.
[0128] Under Ar, the substrate 9 (0.05 g, 0.15 mmol) was mixed with (Bu3Sn)2 (1 mL), Pd(PPh3)4 (0.02 g) and Et3N (5 mL). The mixture was sealed in a vial and heated to 80° C. for 1 day. The solvent was evaporated in vacuum and the residue was purified by column to give 10 (44 mg, 0.09 mmol, yield: 60%). 1H NMR (400 MHz, CDCl3): 7.42 (s, 4H), 7.33 (d, J=7.87 Hz, 2H), 7.03 (d, J=16.18 Hz, 1H), 6.89 (d, J=16.24 Hz, 1H), 6.66 (d, J=8.08 Hz, 2H), 1.55 (m, 6H), 1.34 (m, 6H), 1.05 (t, 6H), 0.89 (t, 9H).
[0129] To a sealed vial were added 10 (50 μl, 50 μg in 50 μL of ethanol), [I-125] sodium iodide, and 1 N HCl (100 μL). Subsequently, 100 μL of H2O2 (3%, in water) was added via a syringe at room temperature. After 10 min, the iodination reaction was terminated by an addition of saturated NaHSO3, and the resulting solution was neutralized to pH 7-8 by adding a saturated NaHCO3 solution. The mixture was extracted with ethyl acetate (3×1 ml). The combined organic layers were dried over Na2SO4, and the solvent was removed by a stream of dry nitrogen gas. The residue was purified by high performance liquid chromatography (HPLC; C-18 column, acetonitrile: DMGA (5 mM, pH 7.4): 60/40, flow rate: 1 mL/min; retention time: 21 min) to get 18.5 MBq of final pure product with radiochemical purity over 98% and a specific activity near the theoretical limit (80 TBq/mmol). The chemical identity was verified by co-injection of the "cold standard" (nonradioactive compound).
[0130] Partition coefficients (PC) were measured by mixing the radioligands with 3 g (3.65 mL) 1-octanol and 3 g (3.0 mL) buffer (pH 7.40, 0.1 M phosphate) in a test tube. The test tube was vortexed for 3 mM at room temperature and then centrifuged (3500 rpm, 5 mM) 1 ml of samples from the 1-octanol and buffer layers were assayed for radioactivity content in a well γcounter. The partition coefficient was determined by calculating the ratio of cpm/g of 1-octanol to that of the buffer. Samples from the 1-octanol layer were repartitioned until consistent partitions of coefficient values were obtained. The measurement was repeated at least three times. PC was 2.5±0.1 at pH 7.40.
[0131] While under anesthesia, 0.1mL of a saline solution (consisting of saline (2 mL, 9 mg/mL), propylene glycol (2 mL), ethanol (0.7 mL) and HCl (0.3 mL, 0.3 nM))25 containing 5 μCi of radioactive tracer, was injected into the tail veins of mice (Swiss-Webster, 2 month old, 2 mice per group). The mice were sacrificed by heart puncture at 2 mM, 30 mM, 60 min and 120 mM post injection under anesthesia. Brains were rapidly removed and weighed, and the brain uptake was expressed as percentage of injection dose per gram organ (% ID/g), which was calculated by a ratio of per gram tissue counts to counts of 1% of the initial dose (100 times diluted aliquots of the injected radioligand) measured at the same time.
[0132] Mouse brain sections were incubated in [125I]9 (20% Ethanol, 4,380,000 cpm/16 ml) for 1 hr. The slides were quickly washed with PBS buffer (10 mM, pH 7.0) 3 times, saturated Li2CO3 in 40% ethanol (2×3 mM), 40% ethanol (2 mM) and H2O (30 sec). After drying by air, the slides were put in a cassette and exposed to film for 44 hrs to obtain images.
[0133] Normal control mice were deeply anesthetized and perfused transcardially with saline (10 mL) followed by fixation with 4% PFA in PBS (10 mL, 4° C., pH 7.6). Brain tissues were then removed, postfixed by immersion in 4% PFA overnight, dehydrated in 30% sucrose solution, embedded in freezing compound (OCT, Fisher Scientific, Suwanee, Ga.), cryostat sectioned at 10 μm on a microtome and mounted on superfrost slides (Fisher Scientific). The brain sections were incubated with compound 3, 6 and 7 (10 μM, 1% DMSO in PBS (10 mM, pH 7.0)) for 20 minutes at room temperature in dark. Excess compounds were washed by briefly rinsing the slides in PBS (10 mM, pH 7.0) and coversliped with fluoromount-G mounting media (Vector Laboratories, Burlingame, Calif.). Sections were then examined under a Leica DRMB microscope equipped for fluorescence.
[0134] Under anesthesia, wild-type mice were injected with compounds 6 and 7 (20-80 mg/kg) via the tail vein, and the mice were then perfused transcardially with saline (10 ml) followed by 4% PFA in PBS (10 ml, 4° C., pH 7.6). Brain tissues were then removed, postfixed by immersion in 4% PFA overnight, dehydrated in 30% sucrose solution, cryostat sectioned at 16 μm on a microtome and mounted on superfrost slides (Fisher Scientific), and imaged directly under fluorescent microscopy without any further staining.
[0135] Sprague-Dawley (SD) rats were asphyxiated with CO2. When the rat had stopped breathing, the skin/fur over the neck was wetted with a spray of 70% ethanol. The brains were then taken out and put into 0.32 mol/L sucrose (1×Colman buffer) in the homogenizer, first with the loose pestle 5˜8 times and then with the tight pestle until the solution reached a uniform consistency. The solution was then transferred from the homogenizer to the corresponding tubes. The tubes were centrifuged at 1000 rpm (4° C.) for 10 minutes. The resulting supernatant was carefully removed and transferred into Beckmann tubes that were previously filled with 2.80 mol/L sucrose and mixed thoroughly. After carefully overlaying nearly to the top of the tube with 0.25 mol/L sucrose, the tube was spun in the Beckman ultracentrifuge for 2.5 hr at 35,000 rpm (4° C.). The 0.25 mol/L sucrose layer was drawn off and discarded. The myelin fraction was collected at 0.25 mol/L and 0.85 mol/L sucrose interface and the pellet was collected at 0.85 mol/L and /1.4 mol/L sucrose interface. Both myelin and pellet were washed with buffer (1×colman, 7˜8 mL) three times before suspended in buffer (1×colman, 5 mL) and kept in -80° C. freezer for future use. The concentration of myelin and pellet were determined by Bio-Rad Protein Assay.
[0136] In the spectrophotometry-based binding assays, a solution of 6 or 7 (800 μL, 12.5 μM) dissolved in 10% DMSO buffer solution containing 10 mM MgCl2 and 10 mM PBS (pH 7.4) was incubated with isolated myelin or pellets at different concentrations ranging from 0.06 to 14 μg/tube. Each tube contained 10 μM of 6 or 7, 10% DMSO buffer, and membrane fraction in a final volume of 1 mL. Following incubation at room temperature for 1 hr, the free and bound 6 or 7 was separated by centrifugation at 6000 rpm for 10 min The supernatant was then collected and the UV absorption of free 6 or 7 determined by UV spectrometer were at 350 nm or 363 nm. The concentration of free 6 or 7 was obtained by comparison to a standard curve. In parallel, non-specific binding was determined using pellets under the same condition. All assays were performed in triplicate.
[0137] The radioligand-based binding assays were carried out in 12×75 mm borosilicate glass tubes. For saturation studies, the reaction mixture contained 50 μL of myelin fraction (1˜2 μg, 1× PBS), 50 μL of [3H]BMB (diluted in 1× PBS, 0.25˜3.5 nM) in a final volume of 500 μL. Nonspecific binding was defined in the presence of cold BMB (1 μM, diluted in PBS (containing 1% DMSO) in the same assay tubes. For the competition binding, 10-5 to 10-10 M compounds and 1.87 nM [3H]BMB were used for the studies. The mixture was incubated at 37° C. for 2 hrs. The bound and free radioactivity were separated by rapid vacuum filtration through Whatman GF/B filters using a Brandel M-24R cell harvester followed by 3×2 mL washes of PBS at room temperature. Filters containing the bound radioligand were dissolved in 6 mL biodegradable counting cocktail overnight and the radioactivity was assayed next day in the scintillation counter (Beckman) with 42% counting efficiency. The results of saturation and inhibition experiments were subjected to nonlinear regression analysis using Graph Pad Prism 4 by which Kd and Ki values were calculated.
[0138] We screened a series of derivatives based on coumarin that possess the same pharmacophore as stilbene. Coumarin is a naturally occurring compound in plants with many important biological activities. We found that the Coumarin derivitive 3-(4-aminophenyl)-2H-chromen-2-one (CMC), is highly permeable across the BBB and selectively localizes in myelinated regions. Our studies in a hypermyelinated mouse model indicate that CMC is a sensitive probe that can be used for in situ staining of myelin.
[0139] 3-(4-aminophenyl)-2H-chromen-2-one (CMC) was obtained from Matrix Scientific (Columbia, S.C.). The rest of compounds screened were obtained from Sigma-Aldrich (Milwaukee, Wis.), TCI American, (Portland, Oreg.) and used without further purification. The Coumarin derivatives are soluble in DMSO and other commonly used organic solvents. The coumarin derivatives are fluorescent compounds and the excitation and emission spectra of CMC was recorded using Fluorescence Spectrophotometers (Varian. Inc., Palo Alto, Calif.) as shown in FIG. 9.
[0140] Swiss-Webster R/J mice were obtained from The Jackson Laboratory, Bar Harbor, Minn., and used as control. Transgenic mice expressing constitutively active Akt (HAAkt308D473D, Akt-DD; Ontario Cancer Institute, Toronto, Canada) driven by the Plp promoter (Wight P A, Duchala C S, Readhead C, Macklin W B (1993) A myelin proteolipid protein-LacZ fusion protein is developmentally regulated and targeted to the myelin membrane in transgenic mice. J Cell Biol 123:443-454) were prepared and used as an animal model of hypermyelination. In this model, the Akt cDNA was inserted into the AscI/PacI sites of the modified Plp promoter cassette, and the Plp promoter/Akt-DD insert was injected to generate transgenics in SJL/SWR FI mice to induce hypermyelination. Positive founders were identified by PCR amplification of tail DNA using IntronSV40F (5'-GCAGTGGACCACGGTCAT-3') (SEQ ID NO:1) and Akt lower (5'-CTGGCAACTAGAAGGCACAG-3') (SEQ ID NO:2) primer sequences. Analyses were done from littermatched mice in all developmental experiments, and where possible with older animals.
[0141] For immunohistochemistry, mice were deeply anesthetized and perfused with PBS followed by 4% paraformaldehyde in PBS via the ascending aorta. Brains were dissected out, incubated for 24 hrs in 4% paraformaldehyde at 4° C., cryoprotected and sectioned (30 μm) with a sliding microtome. Sections were immunostained overnight at 4° C. with rabbit anti-MBP antibody (Chemicon-Millipore, Bedford, Mass.) 1:2000 dilution in 3% normal goat serum in PBS, followed by one hour incubation at room temperature with IRDye 800CW Goat Anti-Rabbit (LI-COR Biosciences, Lincoln, Nebr.) 1:5000 dilution. Images of the stained mouse brain sections were acquired on the LI-COR Odyssey infrared imaging system (LI-COR Biosciences, Lincoln, Nebr.).
[0142] Free floating sections were incubated in 1% H2O2/Triton-100 for 10 min, then incubated in a solution of test compounds (100 μM) in 1% DMSO/PBS for 30 min at room temperature. The sections were washed three times with PBS before cover-slipping with fluorescence mounting medium (Vectashield, Vector laboratories).
[0143] Following tissue staining with each test compound, images of mouse brain sections were acquired on a Leica DMI6000 inverted microscope (1.25× and 5× objectives) with a Hamamatsu Orca-ER digital camera, and operated with Improvision's Volocity software. Image J software was used to quantify pixel intensities values. The corpus callosum between the midline and below the apex of the cingulum was defined as region of interest (ROI). The density of myelin in the corpus callosum of wildtype mice was given the arbitrary value of 100, and the density of myelin in Plp-Akt-DD mice was determined as a percentage of wild-type mice. The data were analyzed using the GraphPad Prism, GraphPad Software, La Jolla, Calif., with a nonpaired Student's t test. For correlation, MBP immunoreactivity of the adjacent sections was also determined and quantified on the LI-COR Odyssey infrared imaging system, using 21 μm resolution, 1.2 mm offset with highest quality, and 3.0 channel sensitivity. The integrated densities of the midline corpus callosum were obtained using the associated Odyssey software. Statistical analysis was performed using a nonpaired Student's t-test (GraphPad Prism).
[0144] In this experiment, 25 mg/kg of CMC was administered through i.v. injection in the tail vein of 2-month old wild-type mice and Plp-Akt-DD mice Animals were sacrificed at 1 hr after injection through heart puncture. The brains were removed and fixed in 4% PFA. The brains were then sectioned and fluorescent images were directly acquired on a Zeiss Axiovert 200M inverted microscope (2.5× objective) with a AxioCam digital camera (Carl Zeiss Microlmagibg, Inc, Thornwood, N.Y.).
[0145] To date, we have screened several coumarin derivatives that potentially bind to myelin membranes. The structures of these coumarin derivatives are shown in FIG. 8. All of these compounds are fluorescent and the emission and excitation spectra of CMC are recorded as shown in FIG. 9. The maximal excitation wavelengths were found at 407 nm and the maximal emission wavelengths were found at 551 nm for CMC (Log P 2.68).
[0146] The fluorescent nature of these coumarin derivatives allows for staining of mouse brain tissue sections in a way similar to other conventional myelin stains. The tissue staining represents a direct approach to evaluate the binding specificity of the test compounds for myelin sheaths. The myelinated corpus callosum region was then examined by fluorescent microscopy. As shown in FIG. 10, at 100 uM concentration, CMC selectively stained intact myelin tracks in the wild-type mouse brain. Among these coumarin derivaties, CMC shows the highest contrast (FIGS. 10A and B). For correlation, the MBP immunostaining was also conducted in adjacent sections (FIG. 10E).
[0147] The staining pattern was found consistent with immunohistochemical MBP staining and was proportional to the size of corpus callosum region as demonstrated in a hypermyelinated Plp-Akt-DD mouse model. Compared to the control sections, the hypermyelinated mouse brain showed that the corpus callosum region was significantly enlarged (FIGS. 10C and D). The enlargement was also confirmed by MBP antibody staining using adjacent brain sections (FIG. 11F). Quantitative analysis indicated that the fluorescent intensity is proportional to the level of myelination. As shown in FIG. 11, the MBP antibody staining showed a fluorescent intensity that is 1.31-fold higher in the Plp-Akt-DD model that that in the wild-type control brain. Similarly, CMC staining also exhibited a fluorescent intensity in proportion to the level of myelination. In the Plp-Akt-DD mouse brain, the fluorescent intensity of CMC was found 1.27-fold higher than that in the wild-type mouse brain, which was consistent with MBP immunostaining.
[0148] Following our in vitro studies, we investigated the ability of CMC to monitor myelin contents ex vivo in the mouse brain. A dose of 0.5 mg CMC (25 mg/kg) was injected via the tail vein into wild-type mice and Plp-Akt-DD mice. One hr postinjection, mice were perfused and brains were removed and sectioned as described above. CMC staining of myelin was then directly examined under fluorescent microscopy. As shown in FIG. 12, CMC entered the brain and selectively labeled myelin sheaths of the corpus callosum and cerebellum of the wild-type mice and Plp-Akt-DD mice.
[0149] From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims. All references, publications, and patents cited in the present application are herein incorporated by reference in their entirety.
2015-07-09 Thioflavin derivatives for use in the antemortem diagnosis of alzheimer's disease and in vivo imaging and prevention of amyloid deposition
According to various embodiments, the present teachings provide an intermediate transfer member including a layer having a phosphorous containing polyamideimide having dispersed therein a conductive additive. A method of manufacturing the intermediate transfer member is provided.
1. An intermediate transfer member comprising: a layer comprising a phosphorous containing polyamideimide represented by: ##STR00004## wherein R is aryl having from about 6 to about 24 carbon atoms and m is from about 5 to about 200, wherein the phosphorous containing polyamideimide has dispersed therein a conductive additive.
3. The intermediate transfer member of claim 1, wherein the conductive additive is from about 1 weight percent to about 60 weight percent of the layer.
4. The intermediate transfer member of claim 1, wherein the conductive additive comprises carbon black.
5. The intermediate transfer member of claim 1, wherein the layer has a surface resistivity of from about 10.sup.9 ohms/square to about 10.sup.13 ohms/square.
6. The intermediate transfer member of claim 1, wherein the phosphorous comprises from about 1 weight percent to about 20 weight percent of the phosphorous containing polyamideimide.
7. The intermediate transfer member of claim 1, wherein the layer has a thickness of from about 30 microns to about 400 microns.
8. The intermediate transfer member of claim 1, wherein the layer further comprises polymers selected from the group consisting of polyimides, non-phosphorous containing polyamideimides and polyetherimides.
9. An intermediate transfer member comprising: a substrate layer; and a surface layer comprising a phosphorous containing polyamideimide represented by: ##STR00005## wherein R is aryl having from about 6 to about 24 carbon atoms and m is from about 5 to about 200, wherein the phosphorous containing polyamideimide has dispersed therein a conductive additive, wherein the surface layer is disposed on the substrate layer.
11. The intermediate transfer member of claim 9, wherein the conductive additive is from about 1 weight percent to about 60 weight percent of the surface layer.
12. The intermediate transfer member of claim 9, wherein the conductive additive comprises carbon black.
13. The intermediate transfer member of claim 9, wherein the surface layer has a surface resistivity of from about 10.sup.9 ohms/square to about 10.sup.13 ohms/square.
14. The intermediate transfer member of claim 9, wherein the phosphorous comprises from about 1 weight percent to about 20 weight percent of the phosphorous containing polyamideimide.
16. The intermediate transfer member of claim 9, wherein the surface layer further comprises polymers selected from the group consisting of polyimides, non-phosphorous containing polyamideimides and polyetherimides.
17. A method of manufacturing an intermediate transfer member comprising: dissolving a phosphorous containing polyamideimide having a formula ##STR00006## wherein R is aryl having from about 6 to about 24 carbon atoms and m is from about 5 to about 200, in a solvent; milling the dissolved phosphorous containing polyamideimide with a conductive additive to form a dispersion; coating the dispersion on a substrate layer; and curing the dispersion to form the intermediate transfer member.
18. The method of claim 17, wherein the solvent is selected from the group consisting of tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, N,N'-dimethylformamide, N,N'-dimethylacetamide and N-methylpyrrolidone.
19. The method of claim 17, wherein the conductive additive comprises from about 1 to about 60 weight percent of the total solids of the dispersion.
[0002] This disclosure is directed to an image-forming apparatus and an intermediate transfer member.
[0004] Image-forming apparatuses in which a color or black and white image is formed by using an intermediate transfer member to electrostatically transfer toner are well known. When an image is formed on a sheet of paper in a color image-forming apparatus using such an intermediate transfer member, four color images in yellow, magenta, cyan and black respectively, are generally first transferred sequentially from an image carrier such as a photoreceptor and superimposed on the intermediate transfer member (the primary transfer). This full color image is then transferred to a sheet of paper in a single step (the secondary transfer). In a black and white image-forming apparatus, a black image is transferred from the photoreceptor, superimposed on an intermediate transfer member, and then transferred to a sheet of paper.
[0005] Polyamideimide (PAI) has been used as a material for an intermediate transfer member. It has been observed that PAI is very difficult to release from the coating substrate, for example, aluminum or stainless steel. In addition, PAI is intrinsically hydrophilic, which has negative impact on transfer efficiency especially in humid environments.
[0006] There is a need to develop new intermediate transfer member materials that possess comparable mechanical strength to PAI and easy to release from the coating substrate. It would also be desirable to have an ITB material that is more hydrophobic.
[0007] According to various embodiments, the present teachings provide an intermediate transfer member including a layer having a phosphorous containing polyamideimide having dispersed therein a conductive additive.
[0008] A further aspect disclosed herein is an intermediate transfer member having a substrate layer and a surface layer. The surface layer includes a phosphorous containing polyamideimide having dispersed therein a conductive additive disposed on the substrate layer.
[0009] A further aspect disclosed herein is a method of manufacturing an intermediate transfer member. The method includes dissolving a phosphorous containing polyamideimide having a formula
wherein R is aryl having from about 6 to about 24 carbon atoms and m is from about 5 to about 200, in a solvent. The dissolved phosphorous containing polyamideimide is milled with a conductive additive to form a dispersion. The dispersion is coated on a substrate layer and cured to form the intermediate transfer member.
[0010] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the present teachings and together with the description, serve to explain the principles of the present teachings.
[0014] It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding of the embodiments rather than to maintain strict structural accuracy, detail, and scale.
[0015] Reference will now be made in detail to embodiments of the present teachings, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
[0016] In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific exemplary embodiments in which the present teachings may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present teachings and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present teachings. The following description is, therefore, merely exemplary.
[0017] Referring to FIG. 1, an image-forming apparatus includes an intermediate transfer member as described in more detail below. The image-forming apparatus is an image-forming apparatus of an intermediate transfer system comprising a first transfer unit for transferring the toner image formed on the image carrier onto the intermediate transfer member by primary transfer, and a second transfer unit for transferring the toner image transferred on the intermediate transfer member onto the transfer material by secondary transfer. Also in the image-forming apparatus, the intermediate transfer member may be provided as a transfer-conveying member for conveying the transfer material in the transfer region for transferring the toner image onto the transfer material. Having the intermediate transfer member that transfers images of high quality and that remains stable for a long period is required.
[0018] The image-forming apparatus described herein is not particularly limited as far as it is an image-forming apparatus of intermediate transfer type, and examples include an ordinary monochromatic image-forming apparatus accommodating only a monochromatic color in the developing device, a color image-forming apparatus for repeating primary transfer of the toner image carried on the image carrier sequentially on the intermediate transfer member, and a tandem color image-forming apparatus having plural image carriers with developing units of each color disposed in series on the intermediate transfer member. More specifically, it may arbitrarily comprise an image carrier, a charging unit for uniformly charging the surface of the image carrier, an exposure unit for exposing the surface of the intermediate transfer member and forming an electrostatic latent image, a developing unit for developing the latent image formed on the surface of the image carrier by using a developing solution and forming a toner image, a fixing unit for fixing the toner unit on the transfer material, a cleaning unit for removing toner and foreign matter sticking to the image carrier, a destaticizing unit for removing the electrostatic latent image left over on the surface of the image carrier, and others by known methods as required.
[0019] As the image carrier, a known one may be used. As its photosensitive layer, an organic system, amorphous silicon, or other known material may be used. In the case of the image carrier of cylindrical type, it is obtained by a known method of molding aluminum or aluminum alloy by extrusion, and processing the surface. A belt form image carrier may also used.
[0020] The charging unit is not particularly limited, and known chargers may be used, such as a contact type charger using conductive or semiconductive roller, brush, film and rubber blade, scorotron charger or corotron charge making use of corona discharge, and others. Above all, the contact type charging unit is preferred from the viewpoint of excellent, charge compensation capability. The charging unit usually applies DC current to the electrophotographic photosensitive material, but AC current may be further superposed.
[0021] The exposure unit is not particularly limited, and, for example, an optical system device may be used, which exposes a desired image on the surface of the electrophotographic photosensitive material by using a light source such as semiconductor laser beam, LED beam, liquid crystal shutter beam or the like, or through a polygonal mirror from such light source.
[0022] The developing unit may be properly selected depending on the purpose, and, for example, a known developing unit for developing by using one-pack type developing solution or two-pack type developing solution, with or without contact, using brush and roller may be used.
[0023] The first transfer unit includes known transfer chargers such as a contact type transfer charger using member, roller, film and rubber blade, and scorotron transfer charger or corotron transfer charger making use of corona discharge. Above all, the contact type transfer charger provides excellent transfer charge compensation capability. Aside from the transfer charger, a peeling type charger may be also used together.
[0024] The second transfer unit may be same as the first transfer unit such as a contact type transfer charger using transfer roller and others, scorotron transfer charger and corotron transfer charger. By pressing firmly by the transfer roller of the contact type transfer charger, the image transfer stage can be maintained. Further, by pressing the transfer roller or the contact type transfer charger at the position of the roller for guiding the intermediate transfer member, the action of moving the toner image from the intermediate transfer member to the transfer material may be done.
[0025] As the photo destaticizing unit, for example, a tungsten lamp or LED may be used, and the light quality used in the photo destaticizing process may include white light of tungsten lamp and red light of LED. As the irradiation light intensity in the photo destaticizing process, usually the output is set to be about several times to 30 times of the quantity of light showing the half exposure sensitivity of the electrophotographic photosensitive material.
[0026] The fixing unit is not particularly limited, and any known fixing unit may be used, such as heat roller fixing unit and oven fixing unit.
[0028] A color image-forming apparatus for repeating primary transfer is shown schematically in FIG. 1. The image-forming apparatus shown in FIG. 1 includes a photosensitive drum 1 as image carrier, a transfer member 2 as an intermediate transfer member such as a transfer belt, a bias roller 3 as transfer electrode, a tray 4 for feeding paper as transfer material, a developing device 5 by BK (black) toner, a developing device 6 by Y (yellow) toner, a developing device 7 by M (magenta) toner, a developing device 8 by C (cyan) toner, a member cleaner 9, a peeling pawl 13, rollers 21, 23 and 24, a backup roller 22, a conductive roller 25, an electrode roller 26, a cleaning blade 31, a block of paper 41, a pickup roller 42, and a feed roller 43.
[0029] In the image-forming apparatus shown in FIG. 1, the photosensitive drum 1 rotates in the direction of arrow A, and the surface of the charging device (not shown) is uniformly charged. On the charged photosensitive drum 1, an electrostatic latent image of a first color (for example, BK) is formed by an image writing device such as a laser writing device. This electrostatic latent image is developed by toner by the developing device 5, and a visible toner image T is formed. The toner image T is brought to the primary transfer unit comprising the conductive roller 25 by rotation of the photosensitive drum 1, and an electric field of reverse polarity is applied to the toner image T from the conductive roller 25. The toner image T is electrostatically adsorbed on the transfer member 2, and the primary transfer is executed by rotation of the transfer member 2 in the direction of arrow B.
[0030] Similarly, a toner image of a second color, a toner image of a third color and a toner image of a fourth color are sequentially formed, and overlaid on the transfer member 2, and a multi-layer toner image is formed.
[0031] The multi-layer toner image transferred on the transfer member 2 is brought to the secondary transfer unit comprising the bias roller 3 by rotation of the transfer member 2. The secondary transfer unit comprises the bias roller 3 disposed at the surface side carrying the toner image of the transfer member 2, backup roller 22 disposed to face the bias roller 3 from the back side of the transfer member 2, and electrode roller 26 rotating in tight contact with the backup roller 22.
[0032] The paper 41 is taken out one by one from the paper block accommodated in the paper tray 4 by means of the pickup roller 42, and is fed into the space between the transfer member 2 and bias roller 3 of the secondary transfer unit by means of the feed roller 43 at a specified timing. The fed paper 41 is conveyed under pressure between the bias roller 3 and backup roller 22, and the toner image carried on the transfer belt 2 is transferred thereon by rotation of the transfer member 2.
[0033] The paper 41 on which the toner image is transferred, is peeled off from the transfer member 2 by operating the peeling pawl 13 at the retreat position until the end of primary transfer of the final toner image, and conveyed to the fixing device (not shown). The toner image is fixed by pressing and heating, and a permanent image is formed. After transfer of the multi-layer toner image onto the paper 41, the transfer member 2 is cleaned by the cleaner 9 disposed at the downstream side of the secondary transfer unit to remove the residual toner, and is ready for next transfer. The bias roller 3 is provided so that the cleaning blade 31 made of polyurethane or the like may be always in contact, and toner particles, paper dust and other foreign matter sticking by transfer are removed.
[0034] In the case of transfer of a monochromatic image, the toner image T after primary transfer is immediately sent to the secondary transfer process, and is conveyed to the fixing device, but in the case of transfer of multi-color image by combination of plural colors, the rotation of the transfer member 2 and photosensitive drum 1 is synchronized so that the toner images of plural colors may coincide exactly in the primary transfer unit, and deviation of toner images of colors is prevented. In the secondary transfer unit, by applying a voltage of the same polarity (transfer voltage) as the polarity of the toner to the electrode roller 26 tightly contacting with the backup roller 22 disposed oppositely through the bias roller 3 and transfer member 2, the toner image is transferred onto the paper 41 by electrostatic repulsion. Thus, the image is formed.
[0035] The intermediate transfer member 2 can be of any suitable configuration. Examples of suitable configurations include a sheet, a film, a web, a foil, a strip, a coil, a cylinder, a drum, an endless mobius strip, a circular disc, a belt including an endless belt, an endless seamed flexible belt, an endless seamless flexible belt, an endless belt having a puzzle cut seam, and the like. In FIG. 1, the transfer member 2 is depicted as a belt.
[0036] In an image on image transfer, the color toner images are first deposited on the photoreceptor and all the color toner images are then transferred simultaneously to the intermediate transfer member. In a tandem transfer, the toner image is transferred one color at a time from the photoreceptor to the same area of the intermediate transfer member. Both embodiments are included herein.
[0037] Transfer of the developed image from the photoconductive member to the intermediate transfer member and transfer of the image from the intermediate transfer member to the substrate can be by any suitable technique conventionally used in electrophotography, such as corona transfer, pressure transfer, bias transfer, and combinations of those transfer means, and the like.
[0038] The intermediate transfer member can be of any suitable configuration. Examples of suitable configurations include a sheet, a film, a web, a foil, a strip, a coil, a cylinder, a drum, an endless strip, a circular disc, a drelt (a cross between a drum and a belt), a belt including an endless belt, an endless seamed flexible belt, and an endless seamed flexible imaging belt.
[0039] In an embodiment shown in FIG. 2, the intermediate transfer member 54 is in the form of a film in a one layer configuration. The intermediate transfer member 54 includes a phosphorous containing polyamideimide substrate layer 52 having dispersed therein conductive filler particles 51.
[0040] For high speed machines, the industrial trend is to focus on multi layer members separating layer functions. In an embodiment shown in FIG. 3, the intermediate transfer member 54 is in the form of a film in a two layer configuration. The intermediate transfer member 54 includes a substrate layer 50. An outer layer of a phosphorous containing polyamideimide substrate layer 52 is disposed on the substrate layer 50. Both the substrate layer and outer layer contain conductive filler particles 51.
[0041] Suitable polyimides for the substrate layer 50 in FIG. 3 include those formed from various diamines and dianhydrides, such as poly(amide-imide), polyetherimide, siloxane polyetherimide block copolymer such as, for example, SILTEM STM-1300 available from General Electric, Pittsfield, Mass., and the like. For example, polyimides that include aromatic polyimides such as those formed by the reacting pyromellitic acid and diaminodiphenylether are sold under the tradename KAPTON®-type-HN, available from DuPont. Another suitable polyimide available from DuPont and sold as KAPTON®-Type-FPC-E, is produced by imidization of copolymeric acids such as biphenyltetracarboxylic acid and pyromellitic acid with two aromatic diamines such as p-phenylenediamine and diaminodiphenylether. Another suitable polyimide includes pyromellitic dianhydride and benzophenone tetracarboxylic dianhydride copolymeric acids reacted with 2,2-bis[4-(8-aminophenoxy)phenoxy]-hexafluoropropane available as EYMYD type L-20N from Ethyl Corporation, Baton Rouge, La. Other suitable aromatic polyimides include those containing 1,2,1',2'-biphenyltetracarboximide and para-phenylene groups such as UPILEX®-S available from Uniglobe Kisco, Inc., White Planes, N.Y., and those having biphenyltetracarboximide functionality with diphenylether end spacer characterizations such as UPILEX®-R also available from Uniglobe Kisco, Inc. Mixtures of polyimides can also be used.
[0042] Polyamideimde (PAI) as an intermediate transfer belt (ITB) material is very difficult to release from a coating substrate, for example, aluminum or stainless steel. PAI as an ITB is intrinsically hydrophilic, which has negative impact on transfer efficiency especially in humid environments. Disclosed herein is a modified PAI that overcomes the problems of release and transfer efficiency detailed above. A single layer ITB as shown in FIG. 2 or dual layer ITB as shown in FIG. 3 is described. The dual layer, as shown in FIG. 3, includes phosphorous containing PAI 52 as the surface layer disposed on a substrate 50. The dual layer ITB possessed a surface resistivity of about 109 ohm/sq, provided excellent color density with excellent print quality, toner transfer and cleaning efficiency. The single layer P-PAI ITB printed similarly.
[0044] The reaction above employs 9, 10-dihydro-oxa-10-phosphaphenanthrene-10-oxide (DOPO), 4-aminoacetophenone, and aniline mixed with an acid such as p-toluenesulfonic acid monohydrate and heated to 120° C. for under nitrogen gas while stirring. The reaction mixture is cooled to room temperature, 150 ml of methanol is added. The slight yellowish precipitate is collected by filtration, and washed with methanol. The collected dried powder is added into a mixture of 1,2,4-benzenetricarboxylic anhydride and hexamethylene diisocyanate in solvent, such as N,N'-dimethylformamide (DMF). After stirred at room temperature for about 4 hours, the brownish clear solution is heated to 90° C. for 2.5 hours. After cooling to room temperature, the phorphorous containing polyamide imide (P-PAI) is obtained.
wherein R is aryl having from about 6 to about 24 carbon atoms; m is from about 5 to about 200 or in embodiments m is from 10 to 180 or from about 20 to about 150. The amount of phosphorous in the P-PAI is from about 1 weight percent to about 20 weight percent of the phosphorous containing polyamide imide, or in embodiments from about 2 weight percent to about 18 weight percent of the phosphorous containing polyamide imide, or in embodiments from about 5 weight percent to about 15 weight percent of the phosphorous containing polyamide imide.
[0046] Due to the incorporation of phosphorous into the PAI a surface layer can be prepared that is hydrophobic in nature. It is theorized that since phosphorous has less affinity to water than to nitrogen, an increase in the hydrophobicity of the surface layer is obtained. Another attribute of the disclosed PAI intermediate transfer member is that a flame retardant ITB is also obtained.
[0047] Certain electrically conductive particles 51 dispersed in the phosphorous containing polyamideimide layer 52 (shown in FIG. 2 and FIG. 3), decrease the resistivity into the desired surface resistivity range of from about 109 ohms/square, to about 1013 ohms/square, or from about 1010 ohms/square, to about 1012 ohms/square. The volume resistivity is from about 108 ohm-cm to about 1012 ohm-cm, or from about 109 ohm-cm to about 1011 ohm-cm. The resistivity can be provided by varying the concentration of the conductive particles.
[0048] Examples of conductive fillers include carbon blacks such as carbon black, graphite, acetylene black, fluorinated carbon black, and the like; metal oxides and doped metal oxides, such as tin oxide, antimony dioxide, antimony-doped tin oxide, titanium dioxide, indium oxide, zinc oxide, indium oxide, indium-doped tin trioxide, and polymers such as polyaniline and polythiophene, and mixtures thereof. The conductive filler may be present in an amount of from about 1 to about 60 and or from about 3 to about 40, or from about 5 to about 20 parts by weight of total solids of the intermediate transfer member.
[0049] Carbon black surface groups can be formed by oxidation with an acid or with ozone, and where there is absorbed or chemisorbed oxygen groups from, for example, carboxylates, phenols, and the like. The carbon surface is essentially inert to most organic reaction chemistry except primarily for oxidative processes and free radical reactions.
[0050] The conductivity of carbon black is primarily dependent on surface area and its structure, generally, the higher the surface area and the higher the structure, the more conductive the carbon black. Surface area is measured by the B.E.T. nitrogen surface area per unit weight of carbon black, and is the measurement of the primary particle size. The surface area of the carbon black described herein is from about 460 m2/g to about 35 m2/g. Structure is a complex property that refers to the morphology of the primary aggregates of carbon black. It is a measure of both the number of primary particles comprising primary aggregates, and the manner in which they are "fused" together. High structure carbon blacks are characterized by aggregates comprised of many primary particles with considerable "branching" and "chaining", while low structure carbon blacks are characterized by compact aggregates comprised of fewer primary particles. Structure is measured by dibutyl phthalate (DBP) absorption by the voids within carbon blacks. The higher the structure, the more the voids, and the higher the DBP absorption.
[0052] Further examples of conductive fillers include doped metal oxides. Doped metal oxides include antimony doped tin oxide, aluminum doped zinc oxide, antimony doped titanium dioxide, similar doped metal oxides, and mixtures thereof.
[0053] Suitable antimony doped tin oxides include those antimony doped tin oxides coated on an inert core particle (e.g., ZELEC®ECP-S, M and T) and those antimony doped tin oxides without a core particle (e.g., ZELEC®ECP-3005-XC and ZELEC®ECP-3010-XC, ZELEC® is a trademark of DuPont Chemicals Jackson Laboratories, Deepwater, N.J.). The core particle may be mica, TiO2 or acicular particles having a hollow or a solid core.
[0054] In another embodiment, the electrically conductive particles include antimony doped tin oxide coated on an inert core particle (e.g., ZELEC® ECP-S, M and T). ZELEC® is a trademark of DuPont Chemicals Jackson Laboratories, Deepwater, N.J. The core particle may be mica, TiO2 or acicular particles having a hollow or a solid core.
[0055] In another embodiment, antimony doped tin oxide particles are prepared by densely layering a thin layer of antimony doped tin oxide onto the surface of a silica shell or silica-based particle, wherein the shell, in turn, has been deposited onto a core particle. The crystallites of the conductor are dispersed in such a fashion so as to form a dense conductive surface on the silica layer. This provides for excellent conductivity. Also, the particles are fine enough in size to provide adequate transparency. The silica may either be a hollow shell or layered on the surface of an inert core, forming a solid structure. Forms of antimony doped tin oxide are commercially available under the tradename ZELEC® ECP (electroconductive powders) from DuPont Chemicals Jackson Laboratories, Deepwater, N.J. Particularly preferred antimony doped tin oxides are ZELEC® ECP 1610-S, ZELEC® ECP 2610-S, ZELEC® ECP 3610-S, ZELEC® ECP 1703-S, ZELEC® ECP 2703-S, ZELEC® ECP 1410-M, ZELEC® ECP 3005-XC, ZELEC® ECP 3010-XC, ZELEC® ECP 1410-T, ZELEC® ECP 3410-T, ZELEC® ECP-S-X1, and the like. Three commercial grades of ZELEC® ECP powders are preferred and include an acicular, hollow shell product (ZELEC® ECP-S), an equiaxial titanium dioxide core product (ZELEC ECP-T), and a plate shaped mica core product (ZELEC® ECP-M).
[0056] The phosphorous containing PAI layer has a Young's modulus of from about 4,000 to about 10,000, or from 5,000 to about 9,000, or from about 6,000 to about 8,000 MPa; a break strength of from about 80 to about 300, or from about 100 to about 250, or from about 120 to about 200 MPa.
[0057] The thickness of the intermediate transfer member shown in FIG. 2 is from about 30 microns to about 400 microns, or from about 50 microns to about 200 microns, or from about 70 microns to about 150 microns.
[0058] In FIG. 3, the outer layer thickness is from about 1 micron to about 150 microns, or from about 10 microns to about 100 microns
[0059] A method of manufacturing the intermediate transfer member includes dissolving the P-PAI in a solvent. The solvent can be any solvent that dissolves the P-PAI. Examples include tetrahydrofuran (THF), methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), N,N'-dimethylformamide (DMF), N,N'-dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP) and the like and mixtures thereof. The solution of the dissolved P-PAI is milled with a conductive additive to form a dispersion. The dispersion is coated on a substrate such as polyethylene naphthalate (PEN), glass, aluminum, or stainless steel and cured for a single layer. The cured layer is separated from the substrate. In embodiments where a dual or multi-layer ITB is desired the dispersion of P-PAI and conductive filled is coated on a substrate such as polyimide or polyetherimide and cured.
[0060] The dispersion is coated on the substrate layer in any suitable known manner. Typical techniques for coating such materials on the substrate layer include flow coating, liquid spray coating, dip coating, wire wound rod coating, fluidized bed coating, powder coating, electrostatic spraying, sonic spraying, blade coating, molding, laminating, and the like.
[0061] In embodiments, the P-PAI may be mixed with other polymers such as polyimides, non-phosphorous containing polyamideimides and polyethereimides. Polyimide examples that can be used in the layer contacting P-PAI are inclusive of known low temperature, and rapidly cured polyimide polymers, such as VTEC® PI 1388, 080-051, 851, 302, 203, 201, and PETI-5, all available from Richard Blaine International, Incorporated, Reading, Pa. These thermosetting polyimides can be cured at temperatures of from about 180 to about 260° C. over a short period of time, such as from about 10 to about 120 minutes, or from about 20 to about 60 minutes; possess a number average molecular weight of from about 5,000 to about 500,000, or from about 10,000 to about 100,000, and a weight average molecular weight of from about 50,000 to about 5,000,000, or from about 100,000 to about 1,000,000. Also, other thermosetting polyimides that can be cured at temperatures of above 300° C. include PYRE M.L® RC-5019, RC 5057, RC-5069, RC-5097, RC-5053, and RK-692, all commercially available from Industrial Summit Technology Corporation, Parlin, N.J.; RP-46 and RP-50, both commercially available from Unitech LLC, Hampton, Va.; DURIMIDE® 100, commercially available from FUJIFILM Electronic Materials U.S.A., Inc., North Kingstown, R.I.; and KAPTON® HN, VN and FN, all commercially available from E.I. DuPont, Wilmington, Del.
[0064] Specific embodiments will now be described in detail. These examples are intended to be illustrative, and not limited to the materials, conditions, or process parameters set forth in these embodiments. All parts are percentages by solid weight unless otherwise indicated.
[0065] The P-PAI material was prepared via the reaction scheme described previously. Experimentally, 9, 10-dihydro-oxa-10-phosphaphenanthrene-10-oxide (DOPO) (108.1 g), 4-aminoacetophenone (67.6 g), p-toluenesulfonic acid monohydrate (2.56 g) and aniline (232.8 g) were mixed and heated to 120° C. for 18 hours under flowing nitrogen gas, with magnetic stirring. After the reaction mixture was cooled down to room temperature, 150 ml of methanol was added. The slight yellowish precipitate was collected by filtration, and washed by 3×250 ml of methanol. This dried powder (21.3 g) was added into a mixture of 1,2,4-benzenetricarboxylic anhydride (19.2 g) and 4,4'-methylenebis(phenyl isocyanate) (8.7 g) in solvent DMF (70 g). After being stirred at room temperature for about 4 hours, the brownish clear solution was heated to 90° C. for 2.5 hours. After being cooled down to room temperature, a viscous brownish liquid was obtained comprising the disclosed P-PAI.
[0066] An ITB coating dispersion was prepared using the disclosed P-PAI, and special black SB-4 (Evonik) in NMP/DMF, where the weight ratio of the P-PAI/special black SB-4=90/10. As a comparison, a controlled ITB dispersion containing the non-phosphorous containing PAI (VYLOMAX® HR-11N, Toyobo) and special black SB-4 (Evonik) in NMP was prepared, where the weight ratio of VYLOMAX® HR-11N/special black SB-4=90/10. Both dispersions were coated on a stainless steel substrate, and cured at 200° C. for 1 hour.
[0067] After cooling to room temperature, the P-PAI/carbon black released from the substrate resulting in a 100 μm thick ITB device. In contrast, the controlled PAI/carbon black ITB did not release from the substrate unless it was immersed into water for at least 48 hours before it released. The disclosed P-PAI ITB device exhibited improved release property from the coating substrate, which is important for ITB manufacturing.
[0068] The above ITBs were tested for surface resistivity and Young's modulus, and the results are shown in Table 1. The surface resistivity of each belt is comparable. The modulus of the disclosed P-PAI ITB is significantly higher than that of the conventional PAI ITB.
[0069] Besides improved release property from the coating substrate, the disclosed P-PAI ITB was more hydrophobic since phosphorous is much less affinity to water than nitrogen. Another attribute of the P-PAI ITB is that it is flame retardant due to the incorporation of phosphorous.
[0070] Other embodiments of the present teachings will be apparent to those skilled in the art from consideration of the specification and practice of the present teachings disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present teachings being indicated by the following claims.
The disclosed technology includes, among others, methods and devices for measuring distributed fiber bend or stress related characteristics along an optical path of fiber under test (FUT) uses both a light input unit and a light output unit connected to the FUT at one single end.
1. A polarization-sensitive optical frequency domain reflectometer device for measuring a distributed fiber bend or stress in a fiber under test based on optical polarization sensing, comprising: a light source that produces probe light that is at least partially coherent; an optical unit that couples the probe light into a fiber link under test in an input state of polarization (I-SOP) and receives reflected probe light from the fiber link under test in an output state of polarization (O-SOP) to produce first and second optical signals in two different optical polarizations from the reflected probe light; an optical coupler that couples a portion of the probe light as an optical local oscillator light; an optical detection unit coupled to receive the optical local oscillator light and the first and second optical signals and configured to mix the optical local oscillator light with the first and second optical signals to perform coherent detection of the first and second optical signals; and a signal processor that processes information from the coherent detection of the first and second optical signals to compute a difference in measurements of an optical parameter in reflected probe light from two different locations in the fiber under test and compute a polarization-dependent property of a fiber bend or stress from the computed difference at different positions along a fiber path in the fiber link under test to provide an assessment of the fiber bend or stress in the fiber link under test.
2. An optical time domain reflectometer (OTDR) device, comprising: a light source that produces probe light at different optical wavelengths; an optical unit that directs the probe light to a fiber link under test and receive reflected probe light from the fiber link under test; an optical detector coupled to receive the reflected probe light from the optical unit to produce a detector signal; and a signal processor that processes information from the detector signal to perform: computing a first optical power difference in reflected optical signals from two different locations in the fiber under test at each of two or more different optical wavelengths; computing a second optical power difference in reflected optical signals from each of the two different locations in the fiber under test at the two different optical wavelengths; using the information on the first and second optical power differences to obtain optical loss caused by a fiber bend or stress present in the fiber link under test; and using the optical loss caused by a fiber bend or stress present in the fiber link under test to determine a parameter of the fiber bend or stress.
3. The device as in claim 2, wherein the light source includes different light sources at different wavelengths.
6. The device as in claim 2, wherein the light source includes a tunable light source that tunes to the different optical wavelengths.
7. The device as in claim 2, further comprising a sampling and averaging unit that processes the detector signal to produce an output to be processed by the signal processor.
8. The device as in claim 2, further comprising a control unit that is coupled to the light source to control generation of the probe light at the different optical wavelengths and is further coupled to the signal processor.
12. A method for using optical time domain reflectometer (OTDR) to measure a fiber link under test, comprising: operating a light source to produce probe light at different optical wavelengths; directing the probe light into a fiber link under test; directing reflected probe light from the fiber link under test into an optical detector to produce a detector signal; processing information from the detector signal to determine a fiber bend or stress present in the fiber link under test, wherein the processing includes: computing a first optical power difference in reflected optical signals from two different locations in the fiber under test at each of two or more different optical wavelengths; computing a second optical power difference in reflected optical signals from each of the two different locations in the fiber under test at the two different optical wavelengths; using the information on the first and second optical power differences to obtain optical loss caused by a fiber bend or stress present in the fiber link under test; and using the optical loss caused by a fiber bend or stress present in the fiber link under test to determine a parameter of the fiber bend or stress.
[0003] The entire content of the before-mentioned patent applications is incorporated by reference as part of the disclosure of this document.
[0004] This patent document relates to fibers and characterization of fibers in various fiber systems and fiber devices.
[0005] An optical fiber tends to be subject to bending, forces or stresses in applications. For example, fibers used for an optical network or fiber communication link, such as International Telecommunication Union recommended ITU-T G.652 single-mode optical fiber and cable, would suffer a fiber bend or stress loss which may adversely affect the performance or reliability of the fiber. Such fiber bending or stress could be measured by a commercial multiple-wavelength optical time domain reflectometer (OTDR), e.g. at 1310 nm or 1550 nm, to distinguish a bend loss from other types of losses, e.g. broken, connection loss, etc., uses measured different bend losses information at different wavelengths where usually a bend loss is higher at a short wavelength than that of at a long wavelength.
[0006] This patent document discloses technology for characterization of fibers in various fiber systems and fiber devices, including, among others, methods and apparatus for distributed measuring at least one fiber bend or stress related characteristics along an optical path of fiber under test (FUT) uses both a light input unit and a light output unit connected to the FUT at one single end.
[0007] The disclosed technology relates to measuring distributed bend- or stress-dependent characteristics of light paths and can be applicable to the distributed measurement of fiber birefringence induced from a fiber bend or stress, for example, bend or stress radius, bend or stress length, bend or stress strength, fiber reliability, fiber lifetime, etc., at a particular fiber distance (position), at or over a specified wavelength range, of an optical path which comprises mostly optical waveguide, such as an optical fiber link, for example, for an optical fiber used for the fiber to the home (FTTH) or any access optical networks (FTTx) or multi-dwelling unit (MDU).
[0008] One aspect of the disclosed technology is the light input unit injects into the FUT at least partially coherent and polarized light having a controlled input state of polarization (I-SOP) by an input polarization controller (I-PC), the output light unit extracts corresponding light from the FUT, analyzes and detects the extracted output light corresponding to at least one transmission axis of an output polarization controller (O-PC) or an output polarization analyzer by an analyzed output state of polarization (O-SOP), and processes the corresponding electrical signal to obtain transmitted coherent optical power for at each group consisting of at least two distances of the FUT, wherein the short-distance (zS) and long-distance (zL) said distances in each said group of distances being closely-spaced and the each said group having at least one pair of detected signals, having two or more pairs of detected signals, a processing unit then computes at least one difference in a measured optical parameter corresponding to each distance in each group of distance pair, the measured optical parameter being proportional to the power of the said analyzed and subsequently detected light, thereby defining a set of at least one measured optical parameter differences; computes the root mean-square or absolute mean value of said set of differences; and calculating the at least one polarization and or fiber birefringence and or bend or stress related FUT characteristics, for example fiber birefringence, bend or stress radius, bend or stress strength, bend or stress length, as at least one predetermined function of said root mean-square or absolute mean value, the predetermined function being dependent upon the small fiber distance difference between the distances corresponding to the said each at least said two pairs of closely-spaced distances, and a processing unit further computes at least one bend or stress related fiber characteristics, for example, a fiber mechanical reliability and or an expect lifetime and or a failure rate statistics and or a bend or stress induced loss of bended or stressed fiber for the optical fiber cable being used for a access optical network, for example fiber to the home (FTTH) or multi-dwelling unit (MDU) scenarios, as at least one predetermined function of said the at least one polarization and or fiber birefringence and or bend or stress related FUT characteristics along an optical fiber path.
[0009] Another aspect includes a polarization-sensitive optical frequency domain reflectometer device for measuring a distributed fiber bend or stress in a fiber under test based on optical polarization sensing. This device includes a light source that produces probe light that is at least partially coherent; an optical unit that couples the probe light into a fiber link under test in an input state of polarization (I-SOP) and receives reflected probe light from the fiber link under test in an output state of polarization (O-SOP) to produce first and second optical signals in two different optical polarizations from the reflected probe light; an optical coupler that couples a portion of the probe light as an optical local oscillator light; an optical detection unit coupled to receive the optical local oscillator light and the first and second optical signals and configured to mix the optical local oscillator light with the first and second optical signals to perform coherent detection of the first and second optical signals; and a signal processor that processes information from the coherent detection of the first and second optical signals to compute a difference in measurements of an optical parameter in reflected probe light from two different locations in the fiber under test and compute a polarization-dependent property of a fiber bend or stress from the computed difference at different positions along a fiber path in the fiber link under test to provide an assessment of the fiber bend or stress in the fiber link under test.
[0010] In yet another aspect, a method is provided for using optical time domain reflectometer (OTDR) to measure a fiber link under test and includes operating a light source to produce probe light at different optical wavelengths; directing the probe light into a fiber link under test; directing reflected probe light from the fiber link under test into an optical detector to produce a detector signal; and processing information from the detector signal to determine a fiber bend or stress present in the fiber link under test. The processing includes computing a first optical power difference in reflected optical signals from two different locations in the fiber under test at each of two or more different optical wavelengths; computing a second optical power difference in reflected optical signals from each of the two different locations in the fiber under test at the two different optical wavelengths; using the information on the first and second optical power differences to obtain optical loss caused by a fiber bend or stress present in the fiber link under test; and using the optical loss caused by a fiber bend or stress present in the fiber link under test to determine a parameter of the fiber bend or stress.
[0011] Those and other aspects and their implementations are described in greater detail in the drawings, the description and the claims.
[0013] FIG. 2A is a schematic diagram of an aspect of an optical frequency encoder embodying in the disclosed technology for the POFDR or OFDR;
[0014] FIG. 2B is a schematic diagram of another aspect of an optical frequency encoder embodying in the disclosed technology for the POFDR or OFDR;
[0015] FIG. 2C is a schematic diagram of an aspect of a clock generation embodying in the disclosed technology for the POFDR or OFDR;
[0016] FIG. 2D is a schematic diagram of an aspect of an optical frequency encoder for the clock generation embodying in the disclosed technology for the POFDR or OFDR;
[0017] FIG. 2E is a schematic diagram of another aspect of an optical frequency encoder for the clock generation embodying in the disclosed technology for the POFDR or OFDR;
[0018] FIG. 3 is a schematic diagram of an aspect of a reference and calibration means for the instrument embodying in the disclosed technology for the POFDR or OFDR;
[0019] FIG. 4A is a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POFDR or OFDR where a single-mode fiber (SMF) may be used;
[0020] FIG. 4B is a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POFDR or OFDR where a PMF may be used for some places;
[0021] FIG. 4C is a schematic diagram of another aspect of a polarization controller and optical router means embodying in the disclosed technology for the POFDR or OFDR where a SMF may be used;
[0022] FIG. 4D is a schematic diagram of another aspect of a polarization controller and optical router means embodying in the disclosed technology for the POFDR or OFDR where a PMF may be used for same places;
[0023] FIG. 4E is a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POFDR or OFDR;
[0024] FIG. 4F is a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POFDR or OFDR;
[0025] FIG. 4G is a schematic diagram of another aspect of a polarization controller and optical router means embodying in the disclosed technology for the POFDR or OFDR;
[0026] FIG. 4H is a schematic diagram of another aspect of a polarization controller and optical router means embodying in the disclosed technology for the POFDR or OFDR;
[0027] FIG. 4I is a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POFDR or OFDR;
[0028] FIG. 4J is also a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POFDR or OFDR;
[0029] FIG. 5A is a schematic diagram of an aspect of a polarization analyzer and coherent detection means embodying in the disclosed technology for the POFDR or OFDR;
[0030] FIG. 5B is a schematic diagram of an aspect of a polarization analyzer and coherent detection means embodying in the disclosed technology for the POFDR or OFDR;
[0031] FIG. 5C is a schematic diagram of another aspect of a polarization analyzer and coherent detection means embodying in the disclosed technology for the POFDR or OFDR;
[0032] FIG. 5D is a schematic diagram of another aspect of a polarization analyzer and coherent detection means embodying in the disclosed technology for the POFDR or OFDR;
[0033] FIG. 5E is a schematic diagram of an aspect of a polarization analyzer and coherent detection means embodying in the disclosed technology for the POFDR or OFDR;
[0034] FIG. 5F is a schematic diagram of an aspect of a polarization analyzer and coherent detection means embodying in the disclosed technology for the POFDR or OFDR where an optical switch is used for the local oscillation (LO) lights;
[0035] FIG. 5G is a schematic diagram of another aspect of a polarization analyzer and coherent detection means embodying in the disclosed technology for the POFDR or OFDR where another optical switch is used to add an additional fiber length for the local oscillation (LO) lights;
[0036] FIG. 5H is a schematic diagram as FIG. 5C but using conventional detectors (i.e. not balanced detectors) in the disclosed technology for the POFDR or OFDR;
[0038] FIG. 7 is a schematic diagram of an aspect of a reference and calibration means embodying in the disclosed technology for the POTDR where the coherent noise may also be estimated from an additional fiber that is related to the laser linewidth, etc.;
[0039] FIG. 8A is a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POTDR;
[0040] FIG. 8B is a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POTDR where the PMF used for some places for connections between components or modules;
[0041] FIG. 8C is a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POTDR;
[0042] FIG. 8D is a schematic diagram of another aspect of a polarization controller and optical router means embodying in the disclosed technology for the POTDR;
[0043] FIG. 8E is a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POTDR;
[0044] FIG. 8F is a schematic diagram of another aspect of a polarization controller and optical router means embodying in the disclosed technology for the POTDR;
[0045] FIG. 8G is a schematic diagram of another aspect of a polarization controller and optical router means embodying in the disclosed technology for the POTDR;
[0046] FIG. 8H is a schematic diagram of an aspect of a polarization controller and optical router means embodying in the disclosed technology for the POTDR;
[0047] FIG. 8I is a schematic diagram of another aspect of a polarization controller and optical router means embodying in the disclosed technology for the POTDR;
[0048] FIG. 9A is a schematic diagram of an aspect of a polarization analyzer and detection means embodying in the disclosed technology for the POTDR;
[0049] FIG. 9B is a schematic diagram of an aspect of a polarization analyzer and detection means embodying in the disclosed technology for the POTDR;
[0050] FIG. 9C is a schematic diagram of another aspect of a polarization analyzer and detection means embodying in the disclosed technology for the POTDR;
[0051] FIG. 9D is a schematic diagram of an aspect of a polarization analyzer and detection means embodying in the disclosed technology for the POTDR;
[0052] FIG. 9E is a schematic diagram of another aspect of a polarization analyzer and detection means embodying in the disclosed technology for the POTDR;
[0053] FIG. 10A is a flowchart illustrating operation of the POFDR measurement of FIGS. 1, 2, 3, 4, and 5;
[0054] FIG. 10B is a flowchart illustrating operation of the POTDR measurement of FIGS. 6, 7, 8 and 9.
[0055] FIG. 11 is an example of a schematic diagram of a high spatial resolution multi-wavelength OTDR embodying an aspect of the disclosed technology.
[0056] FIG. 12 is an example of a high spatial resolution multi-wavelength OTDR embodying an aspect of the disclosed technology.
[0057] FIG. 13 is an example of a high spatial resolution multi-wavelength photon counting OTDR embodying an aspect of the disclosed technology.
[0058] FIG. 14 is an example of a high spatial resolution multi-wavelength OFDR embodying an aspect of the disclosed technology.
[0060] Some commercial fibers used for access optical networks (FTTx) or multi-dwelling unit (MDU), e.g., recently developed new bend insensitive optical fiber such as the International Telecommunication Union's recommendation G.657 (Characteristics of a bending-loss insensitive single-mode optical fibre and cable for the access network), can be subject to significantly bending without exhibiting any noticeable optical loss due to fiber bending or under stress. In such fibers, it would be difficult for using currently commercial available OTDR to measure this type of fiber bend or stress using a conventional technique mentioned above, but it is still important even more critical to measure a fiber bend or stress characteristics for an estimation of a fiber reliability or a fiber lifetime or a fiber failure statistics for a fiber network, e.g., for the FTTx, FTTH, MDU, etc., quality analysis and lifetime estimation.
[0061] Thus, there is a need for a new method for characterizing such bend- or stress-related fiber characteristics as a function of distance along a fiber link, for example, from a single-end of the FUT, that can be used for the field test and measurement and monitoring for the optical networks, for example, FTTH, FTTx, MDU, etc.
[0062] One potential test method to measure fiber bend or stress is to measure a bend induced birefringence. The birefringence is defined as the local absolute value of the difference between the propagation constants of two orthogonal polarization modes in optical fibers used for optical communications systems that can be expressed as
where c is the speed of the light in vacuum, Δn is the refractive index difference, and ν is the light frequency. The birefringence in the fiber can be generated by many factors, for example from environment or fiber installation situation, for example, from bend, twist, anisotropic stress on an optical fiber, and such factors may also be varied with ambient conditions such as temperature. For example, the birefringence Δβ can be induced by the fiber bend or stress during the fiber installation and is proportional to 1/R2, where R is the bend radius [R. Ulrich, S. C. Rashleish, W. Eickhott, "Bending-induced birefringence in single-mode fibers", Optics Letters, Vol. 5(6), pp. 273-275 (1980)]. Highly bent or stressed fiber can induce significantly fiber birefringence that may also reduce the fiber lifetime or even to cause a fiber broken later. This is particularly problematical for the highly bent installed optical fiber at home for the FTTH application, for example, the fiber could be "clappered" or "bended" by a cover of fiber distribution box during installation. Thus, it is desirable to be able to obtain the local birefringence values or local bend or stress properties to know fiber bend or stress characteristics, for example, bend or stress radius, bend or stress strength and their length, etc., along the optical fiber so as to reduce or remove the bended or stressed fibers at an early stage. If the actual local birefringence values or local bend or stress characteristics of a communications optical fiber link (e.g. G.652, G.657) can be determined, it is possible to accurately estimate the installed fiber reliability or quality or even fiber lifetime.
[0063] Depending on the application, it is desirable to measure the birefringence for estimating the bend-related properties [A. M. Simith, "Birefringence induced by bends and twists in single-mode optical fiber", Applied Optics, Vol. 19(15), pp. 2606-2611 (1980)] at a given distance. However, in many practical cases, it is not possible to measure the fiber birefringence at a given precision position by a commercial available OTDR. This is because such bend or stress often occurs in a very short distance, for example of 1 to 50 mm, and a commercial OTDR has a limited spatial resolution as such as large as 500 mm for commonly designed test wavelengths, for example 1310 nm and 1550 nm. However, the fiber birefringence may be induced by a small bend radius, such as of 1-50 mm as mentioned above, or there may be no or negligible loss from the bended or stressed fiber, especially for these recently new developed bend insensitive fiber, and hence it is not possible to obtain a reliable determination of the bend or stress properties of an installed optical fiber.
[0064] There is a number of approaches are known in the art for the measurement of the local birefringence along a fiber length.
[0065] Kim, et al, described the local distributed measurement of the birefringence in a very low birefringence single mode fiber by analyzing the backscattered light, where bending-induced birefringence measurements for various bending radii were reported in good agreement with those calculated (Electronics Letters, 5 Mar. 1981, Vol. 17, No. 5, pp. 193-194). However such method has several disadvantages as of a very poor spatial resolution of 1 meter when using a 10 ns OTDR pulse, unreliable results because there is no any polarization controller for the launched light and the analysis light and as well it would be very sensitive to the environment, e.g. fiber moving. Galtarossa, et al, reported spatially-resolved distributed measurements of fiber birefringence for single-mode fibers (Galtarossa et al, "Statistical characterization of fiber random birefringence", Optics Letters, Vol. 25, No. 18 pp. 1322-1324 (2000)) but its spatial resolution is limited to 0.5 m due to a 5 ns OTDR pulse being used. Palmieri, et al, reported spatially-resolved distributed measurements of bending-induced birefringence for single-mode spun fibers by using a polarization-sensitive optical frequency domain reflectometer (POFDR) (OFC/NFOEC, 21-25 Mar. 2010, Page OWS2), where the combined effect of spin rotation and bending birefringence is presented. However, such measurement cannot provide reliable measurement for the fiber birefringence or bend proprieties, such as bend radius, bend length, and bend strength, due to sensitive to the environment, e.g. fiber moving, thus it may not be practical to be developed for the field test and measurement application.
[0066] In using OTDR to measure the local birefringence along an optical fiber, a linear polarizer can be inserted at the light in and output port for measurements such as in a polarization sensitive OTDR (POTDR). Such POTDR basically measures local birefringence (1/beat-length) as a function of distance z along the fiber, or, in other words, distributed birefringence. Referring to the simple example of a retardation waveplate, the birefringence is the retardation (phase difference) per unit length between the "slow" and "fast" axes. Therefore, the retardation can be determined by the product of the birefringence and the thickness of the waveplate. Indeed it is suitable for measuring major commercial optical fibers, e.g. SMF-28, that typically have a beating length of ˜5 m up to ˜100 m. However, it is not possible or rather difficult to measure small bend length in mm scale, for example, for the FTTH application, because of its limited spatial resolution, e.g. a smallest spatial resolution of 500-1000 mm. Also although it is possible to use very narrow light pulse for an OTDR to obtain a high spatial resolved OTDR trace, it would require an expensive laser and a high bandwidth electronics. For example, in known techniques require the use of short pulses; "short" meaning shorter than the beat length of any interested event length of the FUT, e.g. a few to tens mm scale for a potential "human" induced bending. In order for them to measure birefringence in fibers properly, without being limited to fibers of short beat length, one must use very short OTDR optical pulse width, e.g. typically of ˜10 to 100 ps, and such OTDR also requires a very wide electronic bandwidth, e.g. of over several GHz. On the other hand, if a long light pulse is used, only fibers having long beat lengths can be measured. Hence, although it might be possible, using known techniques and meeting the above-mentioned requirements, to make a reasonably successful and reliable field measurements of mm to cm scale birefringence from a bend during the fiber installation, e.g. FTTH, at present their scope of application and performance would be insufficient for a commercially-viable, stand-alone instrument.
[0067] It should be noted that a conventional polarization sensitive OTDR with a linear polarizer inserted before the output and input port could measure the fiber birefringence via beating length measurement for the standard optical fiber, however, such method is difficult to measure the local birefringence for a small distance of few mm to few cm that is not only limited by a conventional OTDR spatial resolution, e.g. of 50 to 100 cm, but also such measurement would not be reliable because of only a single input SOP is used.
[0068] It is also known that to use a polarimeter could measure the local birefringence along the test fiber path. However, again it would also provide a problematic measurement result due to fiber moving or vibration, etc. to induce an instability of the light SOP that is travelled inside the FUT during the measurement period or an instrument may be designed very expensively.
[0069] It should be noted distributed PMD can be measured by the fixed analyzer or equivalently wavelength scanning method, as described by H. Sunnerud, et at (H. Sunnerud, B.-E. Olsson, M. Karlsson, P. A. Andrekson, "Measurement of Polarization Mode Dispersion Accumulation Along Installed Optical Fibers", IEEE Photonics Technology Letters, Vol. 11 No. 7, July 1999, pp. 860-862) that was suffered significantly long measurement with reliability problem of fiber polarization fluctuation during the testing. A first successful commercial test and measurement instrument (FTB-5600, EXFO Inc.) for the field distributed PMD measurement was using random-scrambling technique, where many uncorrelated measurements are performed for many "closely-spaced optical frequency pairs" over a large wavelength to estimate a distributed cumulative PMD along the fiber so as to significantly reduce the measurement sensitivity to moving of the test fiber (N. Cyr, H. Chen, U.S. Pat. No. 7,920,253, "Polarization optical time domain reflectometer and method of determining PMD"; N. Cyr, H. Chen, G. W. Schinn, "Random-Scrambling Tunable POTDR for Distributed Measurement of Cumulative PMD", Journal of Lightwave Technology, vol. 27(18), pp. 4164-4174 (2009)). However, such measurement technique could not provide high spatial-resolved distributed birefringence measurement neither fiber bend information, especially this instrument is limited to have a best spatial resolution of 5-10 m.
[0070] In summary, there is a need for a new method for characterizing such high spatial resolved polarization-dependent and or birefringence-dependent and or bend- or stress-dependent characteristics as a function of distance along a fiber link from a single-end of the FUT that is inherently robust to fiber movements and perturbations found in field conditions with high spatial resolution and does not require expensive laser, polarization optics, and electronics.
[0071] The disclosed technology in this patent document can be implemented in certain ways to eliminate, or at least mitigate, the disadvantages or limitations discussed above. The disclosed methods or devices can be used to provide more effective or alternative fiber characterization.
[0072] According to a first aspect of the disclosed technology, there is provided a method of measuring at least one polarization-dependent and or or birefringence-dependent bend- or stress-related characteristics of an optical path using light input means and light output means connected to the optical path at adjacent end, the light input means comprising light source means for supplying at least partially polarized light and means for controlling the input of the state of polarization (I-SOP) by an input polarization controller (I-PC) or an input polarization generator (I-PSG) of the at least partially polarized light and injecting the light into the FUT, and the output light means comprising means for extracting corresponding light from the FUT, detection and analyzing means for analyzing the output state of polarization (O-SOP) of extracted light from an output polarization controller (O-PC) or an output analyzer corresponding to the at least one transmission axis of the analyzer means to provide transmitted coherent optical power at each distance of an optical path in each of at least one group of a pair of distances, wherein the short-distance (zS) and long-distance (zL) said distances in each said group of distances being closely-spaced; and wherein the source and detection means are at the same end of the FUT and the light source comprises either CW lights or temporal pulses; and wherein the said group comprises a distance pair, said pair in each group corresponding to a small fiber distance (i.e. length) difference, and wherein the I-SOP and O-SOP are substantially constant for each said distance in each said group, and wherein at least one of the I-SOP and O-SOP is different between the respective said groups, the method including the steps of:
[0073] i. Computing the at least one difference in a measured optical parameter corresponding to each distance in said distance pair for each of the said at least one group, said measured optical parameter being proportional to the intensity of the said analyzed and subsequently detected light, thereby defining a set of at least one measured optical parameter difference;
[0074] ii. Computing the mean-square (or root-mean-square) or absolute value of said set of difference(s) as a function of the fiber distance;
[0075] iii. Calculating the at least one polarization-dependent or birefringence-dependent bend- or stress-related FUT characteristics as at least one predetermined function of said mean-square or absolute value, the predetermined function being dependent upon the small fiber distance or length difference between the distances corresponding to the each at least said one pair of closely-spaced fiber positions or locations;
[0076] iv. Computing the value of the at least one polarization and or fiber birefringence dependent bend- or stress-related FUT characteristics along an optical fiber path; and
[0077] v. Outputting the value of said at least one bend or stress related fiber characteristics, for example, a mechanical reliability or an expected lifetime or a failure rate statistics for bended or stressed fiber for the access optical networks, for example fiber to the home (FTTH) or multi-dwelling unit (MDU) scenarios, etc. (not limited), as at least one predetermined function of said at least one polarization-dependent or birefringence-dependent bend- or stress-related FUT characteristics along an optical fiber path.
[0078] In implementations, for measurement of birefringence, Δβ, at a specified distance z for each group includes distance pair having substantially said prescribed center distance, and the the at least one polarization-related FUT characteristics is the root-mean-square (RMS) or absolute mean value at the said center distance.
[0079] The measured optical parameter may be the computed normalized power, T(z,ω), and said predetermined function can be expressed for two uncorrelated the I-SOP and O-SOP, i.e. to use two uncorrelated polarization controllers, for a small fiber distance/length differences (Δz), according to the following differential formula,
where the SOP is averaged over at least one or more, or all I-SOPs and O-SOPs, the constant αs=3 {square root over (2)}, ω=2πν (ν is the optical frequency), and z is the optical fiber distance corresponding to the said center distance. Alternatively the said measured optical parameter may be the computed normalized power T(z,ω), and said predetermined function can be expressed for correlated the I-SOP and O-SOP, i.e. if a common (same) state of polarization controller is used as both the I-SOP and O-SOP, for small distance differences (Δz), according to the said above differential formula with the constant αs= {square root over (15)}.
[0080] The measured optical parameter may also be the computed normalized power, T (z,ω), and the predetermined function can be expressed for two uncorrelated the I-SOP and O-SOP, i.e. to use two uncorrelated polarization controller, for small fiber distance/length differences (δz), according to the following differential formula,
where the αs=3 {square root over (2)}, the SOP,ω is averaged over both I/O-SOPs, and optical frequency range. Alternatively the said measured optical parameter may be the computed normalized power, T(z,ω), and said predetermined function can be expressed for correlated the I-SOP and O-SOP, i.e. if a common (same) state of polarization controller is used as both the I-SOP and O-SOP, for small distance differences (δz), according to the differential formula with the constant αs= {square root over (15)} and z is the optical fiber distance corresponding to the center distance.
[0081] It should be noted that the measured birefringence at a specified distance z, Δβ(z,ω)), is the roundtrip birefringence value, and the forward fiber birefringence value (instead of the roundtrip birefringence value) may be calculated so as to estimate the fiber quality or lifetime or pass/fail situation, thus the forward distributed local birefringence may be computed from the measured roundtrip birefringence value by multiplying by a roundtrip factor as,
where η=0.5 or η≈0.61. It should be noted that a linear component of a forward (one way) local birefringence could be calculated by using η=0.5 for applying two independent I-PC and O-PC. An overall forward (one way) local birefringence could be calculated by using η≈0.61 or η= {square root over (3/8)}.
where the R is the bend or stress radius or bend or stress strength and the C is the constant that depends on the optical frequency and fiber properties, e.g. fiber cladding, refraction index, etc.
[0083] The second bend or stress parameter may be a bend length that is calculated from the said measured bend induced birefringence length. The bend induced birefringence length may be extracted from measured OFDR or OTDR trace that may be obtained after one or averaging over part of or all I/O-SOPs and center wavelengths.
[0084] In some implementations, for measurement of at least one the bend or stress related fiber characteristics, for example, a mechanical reliability and or an expect lifetime and or a failure rate statistics for bending of fiber, is calculated as one predetermined function of said the at least one bend related FUT characteristics along an optical fiber path.
[0085] Advantageously a high spatial resolution optical reflectometry may be applied for the said bend or stress related fiber characteristics measurement, for example OFDR, photo-counting OTDR, or high spatial resolved OTDR.
[0086] A polarization sensitive OFDR (POFDR) may be used to achieve a high spatial resolution for the said at least one birefringence-dependent bend or stress related fiber characterization, where an optical frequency encoder may be used by detecting these "zero-crossings" from a "sine" or "cosine" type interference signals from a reference or clock interferometer for the clock trigger signal generation for the data sampling.
[0087] Alternatively a POFDR may be used to achieve a high spatial resolution for the said at least one birefringence-dependent bend or stress related fiber characterization, where an optical frequency encoder may be used by detecting these "zero-crossings" from the "sine/cosine type" interference signals with a 90 degree phase difference from a reference or clock interferometer and or or their squared sine (or squared cosine) for the clock trigger signal generation for the data sampling, and such 90 degree phase different "sine/cosine type" (two) interference signals may be obtained by using two interferometers, either dependently or independently, with the approximately the same or similar interferometer characteristics but with a phase difference of about 90 degree, for example achieved by a phase shifter.
[0088] Alternatively a POFDR may be used to achieve a high spatial resolution for the said at least one birefringence-dependent bend or stress related fiber characterization, where an optical frequency encoder may be used by detecting these "zero-crossings" from three correlated interference signals with 120 degree phase difference from a reference or clock interferometer, for example by using an approximately symmetric 3×3 coupler, for the clock trigger signal generation for the data sampling.
[0089] A sampling clock signal may be generated from each "zero-crossing" of the said interference signal at a same or approximately closed time of "zero-crossing" by a revenant electronic circuit.
[0090] A POFDR may be used to achieve a high spatial resolution for the said at least one birefringence-dependent bend or stress related fiber characterization, where the said optical parameter may be measured by at least one coherent detection for measuring at least one polarization component with or without polarization analyzer, for example a linear polarizer or a polarization beam splitter.
[0091] In some implementations, a POFDR for measuring the said at least one birefringence-dependent bend or stress related fiber characteristics uses at least one balanced detector.
[0092] Alternatively a POFDR for measuring the said at least one birefringence-dependent bend or stress related fiber characteristics uses at least one conventional detector, i.e. non balanced detector.
[0093] Advantageously for the POFDR a reference reflector and a reference length may be used to provide these references for the light reflectivity and intensity. Also by performing at least two measurements for with and without an added additional fibre length on the FUT and or or with and without local oscillation lights would provide additional measurement information to remove those "ghost" events in the measurement.
[0094] Alternatively a high spatial resolved polarization sensitive OTDR (POTDR) may be used to measure the said at least one birefringence-dependent bend or stress related fiber characteristics.
[0095] Alternatively a high spatial resolved polarization sensitive photon counting OTDR may be used to measure the said at least one birefringence-dependent bend or stress related fiber characteristics.
[0096] In some implementations, the POFDR or POTDR may use a coherent noise detection to obtain a coherent noise level so that a coherent noise super-positioned on the FUT optical parameter measurement could be estimated and thereby it could be subtracted from the said measured optical parameter.
[0097] Advantageously the said POFDR or POTDR may use an internal reflectivity detection so that reflectivities from a FUT could be estimated accurately.
[0098] In some implementations, the POFDR may use an internal length reference to calibrate a FUT distance after the FTT for an acquired OFDR data.
[0099] In some implementations, the POFDR may use an additional fiber length to do at least two data acquisitions, at least one acquisition without any additional fiber length and at least one with an additional fiber length, to probe and remove these "ghost events". Such the said additional fiber length may be inserted at any position that could extend or short a test fiber length, for example between an instrument and a FUT, or at any location that could extend or short a local oscillation light length, for example via a 2×2 optical switch.
[0102] The measured optical parameter may be measured repeatedly for at least two times with the same I/O-SOP controller by the said I/O-PCs.
[0103] The mean-square (or root-mean-square) value may be computed by using said repeated measured optical parameters so as to reduce the noises, for example electronic noise, laser intensity or variation noise, laser phase noise, etc.
[0104] Alternatively the said mean-square (or root-mean-square) value may be calculated from one single (non-repeated) measured optical parameter "trace", wherein at least two "noise-uncorrelated"but "signal-correlated" data may be extracted from a small distance (or time) shifted the said measured optical parameter "trace".
[0105] The said at least one I-SOP and or at least one O-SOP may be controlled by at least one I-SOP or at least one O-SOP randomly or uniformly regarding the Poincare sphere.
[0106] According to a second aspect of the disclosed technology, there is provided measurement instrumentation, for measuring at least one polarization-dependent and or or birefringence-dependent bend- or stress related characteristics of an optical path (FUT), comprising: input light means and output light means for connection to the optical path at one end of the FUT for launching incident light, extracting, detecting, and analyzing light that has traveled at least part of the FUT and providing corresponding electrical signals, and processing means for processing the electrical signals from the output light means to determine said at least one polarization-dependent bend- or stress-related characteristics;
[0107] i. Computing the at least one difference in a measured optical parameter corresponding to each distance in said distance pair for each of the said at least one group, said measured power parameter being proportional to the power of the said analyzed and subsequently detected light, thereby defining a set of at least one measured power parameter difference;
[0108] ii. Computing the mean-square or absolute value of said set of differences as a function of fiber distance; and
[0109] iii. Calculating the at least one polarization-dependent and or or birefringence-dependent bend- or stress-related FUT characteristics as at least one predetermined function of said mean-square or absolute value, said predetermined function being dependent upon the said small fiber distance or length difference between the distance corresponding to the said each at least said one pair of closely-spaced fiber positions or locations;
[0110] iv. Computing the value of said at least one polarization-dependent and or or birefringence-dependent bend- or stress-related FUT characteristics along an optical fiber path; and
[0111] v. Outputting the value of said at least one bend or stress related fiber characteristics, for example, a mechanical reliability and or or an expect lifetime and or or a failure rate statistics for bended or stressed fiber for the fiber to the home (FTTH) or multi-dwelling unit (MDU) scenarios, as at least one predetermined function of said at least one polarization or fiber birefringence dependent bend- or stress-related FUT characteristics along an optical fiber path.
[0114] The various aspects of the disclosed technology, and their respective implementations, are predicated upon the same or similar underlying theory for measuring the same birefringence-dependent bend- or stress-related proprieties of the installed optical fiber link. Embodiments of these aspects can be advantageously used for a single-ended measurement for an optical fiber access network, for example for the FTTx test, measurement and monitoring applications.
[0115] In each of the examples of POFDR, there will usually be six main parts as shown in FIG. 1, namely an optical source 103, an optical frequency encoder unit 106, a reference and calibration unit 140, polarization controller and optical router 33, polarization analyzer and coherent detection unit 61, a control and data acquisition, analogue and digital signal processing unit 501, and together with a display unit 109, where all of the components of the measuring instrument are at the same end of the FUT.
[0116] Although each instrument in the described examples will have the above-described parts or sections, there will be many detailed differences in configurations for these six units according to the different birefringence-dependent fiber bend or stress measurement methods, namely fiber birefringence measurement based fiber bend or stress determination method.
[0117] Thus, for the fiber birefringence measurement based fiber bend determination method it comprises the input optical source controller 103 that will have an at least partially polarized light source, for example a tunable narrow linewidth laser with a linewidth of 1-1000 kHz for a POFDR, see FIG. 1, an input SOP (I-SOP) polarization controller (I-PC) 36 for controlling the SOP of lights from the light source 103 before it is injected into the FUT 100 (FIGS. 4A, 4B, 4C, 4D and 4E), a polarization determination means, either a polarization beam splitter (FIGS. 4A and 4B) or a linear polarizer (FIGS. 4C, 4D and 4E), and an optical router means (i.e. backreflection extractor) (FIGS. 4A, 4B, 4C, 4D and 4E) that could be either an optic circulator or a fiber coupler (or a beam splitter). The fiber pigtails could be either a single-mode fiber (SMF) or a polarization-maintaining fiber (PMF). The polarization controller and optical router means 33 described in FIGS. 4A, 4B, 4C, 4D and 4E uses a common polarization controller for the I/O-SOP polarization controller (I/O-PC), but such I/O-PC could be separated such as in FIG. 4J, where no any polarization determination means, either a polarization beam splitter or a linear polarizer, may be used in the polarization controller and optical router means 33 but it might be used in the polarization analyzer and coherent detection means 63 (FIGS. 5A and 5B). Alternatively different embodiments for the I-SOP and O-SOP controller may be as these configurations shown in FIGS. 4F, 4G, 4H and 4I, where a I/O-SOP could be controlled as either randomly or uniformly regarding to the Poincare sphere, e.g. by a polarization scrambler, or as several know uniform polarization states, e.g. by a polarization state generator (PSG) or input PSG (I-PSG). For the embodiments in FIGS. 4A, 4B, 4C, 4D and 4E with a polarization determination means, either a polarization beam splitter (FIGS. 4A and 4B) or a linear polarizer (FIGS. 4C, 4D and 4E), the polarization analyzer and coherent detection means 63 may use the embodiments in FIGS. 5C, 5D, 5F, 5G and 5H. It should be noted that an O-PC in a POFDR configuration could also be applied to adjust polarization of a LO light as shown in FIG. 5E to analyze the O-SOP.
[0118] The polarization analyzer and coherent detection unit 63 (FIGS. 5C, 5F, and 5G) may comprise local oscillation (LO) lights to measure the both signal inputs 1 and 2 by the coherent detections, e.g. each using two detectors A1 and A2 and detectors B1 and B2 (FIGS. 5F and 5G) to have two detection outputs A and B.
[0120] It should be noted that the coherent detection as shown in FIGS. 5A-5G could use only one detector, for example either a detector 62A1, or 62A2, 62B1, or 62B2.
[0121] An optical frequency encoder unit 106 (also called as a frequency clock or reference means) that is used to provide a clock trigger for sampling may comprise these optical components for an interferometer that may include a beam splitter 56, a delay line 70, optical reflectors 52 and 53 (FIGS. 2A, 2B) that could be Faraday rotator mirrors or fiber pigtailed fiber mirrors or any type mirror as long as they could reflect or rout the input light returning back to coupler 56 to produce an interference detection on the detector C 66. In order to produce more clock trigger signals, a frequency doubling technique (e.g. for N times, N≧1) may be used (FIG. 2C). The clock signal may be generated from a clock signal generation unit 71 by detecting those "zero-crossings" from the measured interference signals for the interferometer. To further increase the number of sampling clock triggers a sine/cosine method is used (FIG. 2D) to double the clock triggers where the interference signals from the "sine/cosine" method to have a 90 degree phase difference. Another method is to use an approximately symmetric 3×3 coupler to produce three interference signals each with a phase difference of 120 degree (FIG. 2E) so as to provide three time more clock triggers, e.g. from "zero-crossing" detection.
[0122] The input light source is a tunable narrow linewidth source. The analogue and digital signal processing unit may comprise a control, a data acquisition unit, a sampling and averaging unit and a data processor unit, analog-to-digital conversion being carried out in the sampling and averaging unit.
[0123] A reference and calibration means 140 includes the fiber length reference, for example 1 to over 10 meter for a short range POFDR with a measurable length of 100-2000 m and 10 to over 100 meter for a middle or long range POFDR with a measurable length of 2 to 100 km, and coherent noise detection 131, light reflectivity reference 129, as well to probe these "ghost" events by using an added additional length 123 on the FUT 100 by using a 2×2 optical switch 127 (FIG. 3). A similar purpose could be achieved by an 1×1 optical switch 125 to result an OFDR measurement with and without local oscillation lights (FIG. 5F), or to add an additional fiber length 123 with a 2×2 optical switch 127 (FIG. 5G).
[0124] In each of the examples of POTDR described herein, there will usually be five main parts as shown in FIG. 6, namely a pulse optical source 23, a reference and calibration unit 140, polarization controller and optical router 33, polarization analyzer and detection unit 61, and a control and data acquisition, analogue and digital signal processing unit 501, and together with a display unit 109, where all of the components of the measuring instrument are at the same end of the FUT. Thus, for the fiber birefringence measurement based fiber bend determination method the input optical source controller will comprise an at least partially polarized pulsed laser source 23, an input SOP (I-SOP) polarization controller (I-PC) 36 for controlling the SOP of light from the pulsed light source 23 before it is injected into the FUT 100 (FIGS. 8A, 8B, 8C, 8D, and 8E). The polarization analyzer an detection unit 61A is either having two photo-detectors A and B, 62A and 64A, respectively (FIGS. 9A and 9C), or having one photo-detector 62A (FIGS. 9B and 9D), o even having three or four or more detectors as such for a polarimeter design (FIG. 9E). If there may be no any no any polarization determination means used for the polarization controller and optical router means 33 (FIG. 6) described in FIGS. 8F, 8G, 8H and 8I), a polarization analyzer an detection unit 61A should have such polarization determination means, either a polarization beam splitter 34B or a linear polarizer 34A, as FIGS. 9C, 9D and 9E.
[0125] It is worthy to be noted that either a SMF or a PMF may be used for above described different embodiments, however, a PMF may be used where the light polarizations for both or either a light input from an optical source 103 or pulsed optical source 23 or signal input 1 or signal inputs 1 and 2 for the polarization analyzer and coherent detection 61 or polarization analyzer and detection 61A can be arranged to the PMF axis, e.g. usually in its slow axis.
[0129] It is worthy to be noted that above described different units or main parts may be combined differently according to embodiments in FIGS. 1 and 6 for the POFDR and POTDR, respectively. Also note that when a photon-counting OTDR may be used, all these POTDR embodiments should be applied.
[0130] For the single-end fiber bend or stress measurement method a distributed fiber birefringence can be extracted by analyzing backreflected light from Rayleigh backscattering or from the localized reflection so that the fiber bend or stress characteristics can be extracted and predicated. Note that fiber bend induced local birefringence is typical with a small length, for example 1 mm to 50 mm, and is typical higher that of inherently from a standard single-mode optical fiber, e.g. SMF-28. Thus a bend or stress induced local birefringence on a standard single-mode fiber could be measured by a high spatial resolved reflectometry, such as an OFDR, thus local bend or stress on the fiber could be estimated. For the birefringence based fiber bend or stress measurement method described, averaging over a certain wavelength range may be used to remove the wavelength related fluctuation, for example coherent noise. To use the single-end measurement method to measure distributed local fiber bend or stress, polarization sensitive OFDR (POFDR) or polarization sensitive OTDR (POTDR) traces as a function of fiber length must be analyzed and its SOP characterization at each fiber location or distance should be accurately measured or approximately estimated in a high spatial resolution, so it may be use a widely tunable narrow linewidth laser (CW) to obtain high spatial-resolved POFDR traces, for example having a tunable range 0.01 nm to 100 nm and a linewidth of 300 Hz to 10 MHz, or to use a very short pulse, for example 0.01 ns to 100 ns, in order to obtain a highly spatial resolved POTDR traces that does not suffer a problem of poor spatial resolution.
[0131] Some examples of the main fiber bend or stress measurement instrument configurations for a single-end distributed fiber bend or stress measurement according to the disclosed technology, and modifications, alternatives and substitutions thereto, will now be described with reference to FIGS. 1 to 9.
[0132] In the high spatial-resolved polarization-sensitive optical frequency domain reflectometer (POFDR) illustrated in FIG. 1 a unable CW narrow light source means 103 is coupled to a polarization maintaining fiber (PMF) for producing light source for launching into a fiber-under-test (FUT) 100 from connector port, which also receives corresponding backreflected light from the FUT 100 via connector 40, and an optical frequency encoder unit 106 consisting of fiber based Michelson interferometer having light beam splitter and combiner 56 (coupler 2), delay 70, reflectors means of mirrors 52 and 54 and detection means detector C 66 (FIG. 2B).
[0133] The input light, polarization controller and optical router means 33, and polarization analyzer and coherent detection means 63 may comprise a polarization-maintaining circulator or coupler 32 in FIGS. 4B and 5C or polarization-maintaining coupler, a polarization beam splitter (PBS) 34, and a input and output polarization controller (polarization controller or scrambler) 36. The circulator 32 is coupled to the input of PBS 34 by a second PM fiber (polarization-maintaining fiber) so that the optical path from the tunable light source 103 to the PBS 34 is polarization-maintaining A single-mode fiber can be used to couple the PBS 34 to the I/O-PC controller 36. However, a SM fiber may still be used (FIG. 4A).
[0134] The alignment of PMF is fixed in the factory in such a manner that substantially all of the optical power from the tunable CW narrow linewidth optical light source 103 is maintained in one of the two axes of the fiber 29, conventionally at the "slow" axis. Since the circulator 32 is polarization-maintaining, this alignment is maintained until the point between PBS 34 and I/O-PC 36. During attachment of each end of the PMFs to the components concerned, the azimuthal orientation of the PMF is adjusted to ensure maximum transmission of the optical lights towards the FUT 100.
[0135] In the polarization analyzer and coherent detection means 63 such as PMF may be used for the LO input that should be arranged to have 45 degree regarding to the PBS 84A and 82A axis so as to equally divide the light power in to two output ports for the coherent detections. The SM fiber may still be used, then a polarizer whose axis has a 45 degree regarding to the PBS axis may be used before the LO light incident into beam splitter 58A, in such case the LO light polarization may be arranged to have sufficiently lights, e.g. >0.01%, for the coherent detection. Otherwise a fiber based coherent detection configuration (FIGS. 5C-5G) may be used for the polarization controller and optical router 33 shown in FIGS. 4A-4J.
[0136] Backreflected light caused by Rayleigh scattering and, in some cases, discrete (Fresnel) reflections, from the FUT 100 enters the I/O-PC 36 in the reverse direction. Its SOP is transformed by the SOP controller or scrambler 36, following which the light is decomposed by the PBS 34 into two components having orthogonal SOPs, typically linear SOPs at 0 and 90 degree relative orientations. The first detector 64A or 64B1 and 64B2 (FIGS. 5C-5G) is connected to one of the two outputs of the PBS 34 to receive one of these orthogonal components and the circulator 32 (or coupler) is connected to the other output (with respect to backreflected light from the FUT 100). The second detector 62A or 62B1 and 62B2 (FIGS. 5C-5G) is in turn connected to that output port of the circulator 32 (or coupler) that transmits light from the PBS 34, so as to receive the other orthogonal component.
[0137] It should be noted, for the POFDR it requires to a local oscillation lights for the detection. Thus, before the any orthogonal components from PBS 34 being sent to detectors, a light splitter (coupler) provides a small portion of lights from the tunable CW narrow linewidth light source 103 as local oscillation lights for the coherent detection, where two local oscillation lights are obtained by light splitter 58 (coupler 4) and then combined by coupler 5 82 and coupler 84, respectively, to coherently measure the two orthogonal light components from PBS 36 that is originated from FUT 100 (FIGS. 5C, 5F and 5G). It should be worthy to mention here that such detection schemes in fact is as an interferometer, i.e. a light is split by coupler 27 and then they are combined together again by coupler 5 or 6 to form an interferometer, where typically the light is delayed after its "round-trip" time through the FUT 100. Note that the suitable calibration may be carried out for any related two detections for their relative detection efficiencies, wavelength dependence, overall optical components loss, etc., as will be described hereinafter, the sum of the detected powers from detection output A and B is proportional to the total backreflected power from the FUT 100.
[0138] Under the control of control unit 501, which also controls the tunable laser source 103, the sampling and averaging circuit, in known manner, uses an internal analog-to-digital converter to sample the corresponding electrical signals from the detectors 62A and 64A (for a POTDR) or 62A1, 62A2, 64B1, and 64B2 (for a POFDR) as a function of time to obtain the corresponding electrical signals, then signal processing, for example by fast Fourier transform (FFT) for an OFDR, averages the processed electronic signals to produce an OFDR trace that has the measured fiber loss (or attenuation) as a function of the FUT 100 distance.
[0139] It is appreciated to be noted that such signal processing, e.g. FFT, averaging, filtering, etc., in 92 and 94 may be processed by either a low-level FPGA or a high-level software of any computer, for example a person PC computer, PC tablet, etc. The resulting OFDR traces for different I/O-SOPs are used by a data processor 501 to derive the distributed local birefringence curve so as to estimate fiber bend properties, for example bend or stress strength, bend radius, bend or stress length, fiber reliability/quality and or or lifetime, as a function of the distance z along the FUT 100 from a single the same end of the FUT 100. It will be appreciated that the usual conversions will be applied to convert time delay which is calculated from a beating frequency after the FFT, where the beating frequency is proportional to both round-trip time of the light and tunable laser frequency speed, to distance according to refractive index of the FUT 100.
[0140] In addition to controlling the sampling in unit 501, the control unit controls the wavelength of the tunable laser source 103 or 23 and the I-SOP and O-SOP adjusted by I/O-PC 36. More specifically, for each setting k of the I/O-PC 36, the control unit 90 causes the backreflected power to be measured for at least one pair of distances zS.sup.(k) and zL.sup.(k), respectively, that are closely-spaced relative to each other. The center distance of the pair is defined as the average of two actual distances, i.e., zk=(zS.sup.(k)+zL.sup.(k))/2. (The labels S and L refer, for convenience and ease of understanding, to "short" and "long" with respect to the center distance zk).
[0141] It should be appreciated for the embodiments with the OFDR as in FIG. 1 that measures the beating frequency signals between the local oscillation (LO) light, e.g. from the beam splitter 27 (coupler B), and the reflected light signals from the FUT 100 in the time domain and then the measured signals are transferred into the frequency by the FFT, the first step of the data processing is to perform the FFT for the acquired the data from the detectors A and B, 62A1-62A2 and 64B1-B2, respectively, and then it may require a calibration or reference procedure to obtain an OFDR trace that is as a function of the distance.
[0142] If for the OTDR the above described procedure is not required, i.e. directly to obtain the OTDR curve as a function of the time and then of the distance after considering the light speed at the given FUT.
[0143] Since an OFDR tunable coherent optical source may be sensitive to the back-reflected lights, an optical isolator 23 may be sued as shown in FIG. 1.
[0144] It should also be appreciated for the embodiments with the OFDR as in FIG. 1 an optical frequency encoder unit 106, for example an interferometer either in fiber or free space, may be used, as shown in FIGS. 2A and 2B. In FIG. 2A, a free-space interferometer is used to obtain frequency reference signal, where the clock signal generation 71 may be as to produce the clock trigger signals from the cross-zeroing detection of the interference signal of the interferometer that is detected by the detector C. The FIG. 2B is similar as FIG. 2A but fiber components are used. In order to increase the clock trigger signals data sampling or to reduce the length of the delay line 70, further improved techniques may be required, for example to use the interference signal frequency mixing 73 after removing the DC level (FIG. 2C) so as to increase the cross-zeroing number. This interference signal frequency mixing 73 may be performed N times (N≧1) to obtain 2.sup.(N+1) zero-crossing so as to produce clock trigger signals 2.sup.(N+1) for the sampling, e.g. by ADC. The other method to increase the clock signals may be using sine and cosine encoder as shown in FIG. 2D where the clock signal could be extracted by calculating the "phase" in the phase diagram, for example evenly divided, or comparing their levels and "sign" to obtain even trigger signals. Moreover, simply the number of "zero-crossing" is simply doubled from the sine/cosine interference signals, and further these "zero-crossing" from the squared sine or squared cosine could be also be used for the clock trigger signal generation for the sampling. Such method may also be applied in the symmetric 3×3 coupler (FIG. 2E) where three sine function interference signals with different phase of 0 and +/-120 degree could be measured by detector C, detector D and detector E so as to increase the number of "zero-crossing" for three times if comparing a single interference (sine function) signal, for example for an interferometer.
[0145] It should be appreciated that, where the group may comprise more than one closely-spaced pair of distances, the center distance as defined above in fact differs for each pair in the group. The I/O-PC polarization controller 36 sets the different I-SOP and O-SOP in a well-defined known uniform or a random manner, such that the points conventionally representing SOPs corresponding to each member are uniformly distributed over the surface of the Poincare sphere, whether the distribution is in the uniform grid or random of points.
[0146] For the OFDR in order to remove or reduce the laser frequency sweeping nonlinearity, there may be an optical frequency encoder unit 106 that consists of a fiber based Michelson interferometer with delay 70, Faraday rotation mirrors 52 and 54, and detector C 66 as shown in FIG. 2B. The frequency clock or reference means 106 may provide signals from the interferometer for sampling the measurement signals by sampling and averaging unit 501 or alternatively providing signal for re-sampling of the measurement signals from the FUT 100.
[0147] Note the lights used for the said optical frequency encoder 106 may be obtained by a beam splitter or fiber coupler A 25 (FIG. 1), where an optical isolator 23 should be used to protect any lights returning back to the optical laser source 103.
[0148] Advantageously the balanced detection may be applied for the POFDR measurement, however a detection using one detector is also practical. The balanced detection may be constructed by the free-space optics as FIG. 5A or 5B or using fiber optic components as shown in FIGS. 5C-5G. It should be noted such balanced detection could be used for the examples of POFDR described in this document.
[0149] For the high spatial-resolved polarization-sensitive optical time domain reflectometer (POTDR) as illustrated in FIG. 6 comprises pulsed light source means 23, bidirectional polarization controller means 36 (conveniently referred to as an I/O PC controller means, sampling and averaging unit and data processor means 501, all controlled by a control unit 501, and detection means comprising first and second detectors A and B, 62A and 64A, respectively. The pulsed light source means 23 is coupled to a polarization maintaining fiber (PMF) 26 for producing light source for launching into a fiber-under-test (FUT) 100 from connector 40 via the I/O state of polarization (I/O-SOP) polarization controller (I/O-PC) means 36, which also receives corresponding backreflected light from the FUT 100, for example via an input and out port or connector. For the embodiments using the POTDR as illustrated in FIG. 6, etc. it may necessary to use a narrow light pulse width, for example 0.1 ns to 100 ns and a high detection bandwidth, e.g. up 10 MHz to 10 GHz, for the detectors A and B, 62A and 64A, respectively and a high sampling rate for the ADC. It is appreciated to be understood that the relative low sampling rate ADC may be used if the time shifting sampling technique, for example for the 1 ns light pulse the ADC may have sampling rate of 100 MSPS under sampling an operation of 10 shifted time with a step of 1 ns, may be applied in the embodiments for the sake of the low-cost instrument design.
[0150] The disclosed technology encompasses various modifications to the embodiments shown in FIGS. 1-9. For example, the PMF may be replaced by a polarization controller connected by non-polarization-maintaining fiber.
[0151] If the optical path between the output of tunable light source means 103 or 23 and the input of the polarization beam splitter 34 is polarization-maintaining, the polarization-maintaining circulator 32 could be replaced by a polarization-maintaining coupler (e.g., a 50/50 coupler). The circulator can be used and it gives about 3 dB more dynamic range than a 50/50 coupler.
[0153] Although these modifications may be applied separately, the embodiment of the disclosed technology illustrated in FIGS. 1 and 6 includes several such modifications.
[0154] Instead of PBS 34 in the FIGS. 4A, 4B and 8A, 8B, the polarization beam splitter 34 may comprise a polarizer 34A, at the expense of another polarization component of the test light. The detector is connected to one of the arms of the backreflection extractor 32, i.e. signal output 2, for example at an optic circulator or a coupler so as to detect a fraction of the backreflected light for processing to deduce the total backreflected power of the lights. Indeed when a polarization beam splitter 34 may be used as shown in FIGS. 4A, 4B and 8A, 8B the two signal outputs 1 and 2 are obtained for the coherent (POFDR) or non coherent detection (POTDR).
[0155] Alternatively for the embodiment of FIG. 4D, the polarizer 34A is removed, as shown in FIG. 1E. In such configuration, the detector 62 is still connected to one of the arms of the backreflection extractor 32, for example at an optic circulator or a coupler so as to detect a fraction of the backreflected light for processing to deduce the total backreflected power of the lights. Indeed in the embodiment of FIG. 1E only one of the two orthogonal light polarization components is detected due to the polarization sensitive coherent detection by detectors 62.
[0156] In the POFDR of FIG. 1 and the POTDR of FIG. 6 could then be carried out, although not required as stated above, to calibrate the relative sensitivities of the detectors including the losses induced by the intervening circulator or coupler, etc.
[0157] Alternatively for the embodiment, for example of FIGS. 4G, 4H and 8G, 8I, two separate and uncorrelated I-PC controller 36A or I-PSG 36C and O-PC controller 36B may be used. In the such embodiments, e.g. of FIGS. 4G, 4H and 8G, 8I, the same basic theory may be applied as such for the FIGS. 4A, 4B, 4C, 4D, 4E, 8A, 8B, 8C, 8D and 8E but having different theoretical constant as such described herein. The FIG. 4F or 8F is a simple configuration where the O-PC 36B is removed from FIG. 4G or 8G.
[0158] It should be appreciated that, in the embodiments involved with at least two detectors, calibration of the mean relative gain is not required; the measured total power is independent of SOP, and there is no need for an "absolute" calibration to directly measure absolute transmission values; they can be obtained to within an unknown constant factor. The subsequent normalization over the mean traces averaged over part or all SOPs, as described hereinbefore, eliminates the unknown factor.
[0159] It is envisaged that the detection means might comprise a single detector and normalized OFDR or OTDR traces be obtained by computing an average of all of the OFDR or OTDR traces, and dividing each of the OFDR or OTDR traces by the said average OFDR or OTDR trace, point by point, to obtain normalized OFDR or OTDR traces, as described in detail hereinbefore.
[0161] In the above-described embodiments, the operation of the I/O-PC polarization controller 36 is such that, for a given SOP of the light (which can be any SOP on the Poincare Sphere) received at its input, the SOP of the light leaving its output will be any one of a number of substantially uniformly distributed SOPs on the Poincare Sphere, whether the distribution is of deterministic or random nature. Typically, the number of I-SOPs and O-SOPs is each about 3-100 for normal acquisition mode while for 100-1000 for high quality acquisition mode, but it could be any practical number. It is noted that for the I/O-SOP random controlling mode the distribution of each of the I-SOPs and O-SOPs need not, and generally will not, be truly random; so pseudo-random might be a more appropriate term in the case where a random distribution is indeed used for convenience because it is easier and less expensive to implement than a uniform grid of I-SOPs and O-SOPs.
[0162] Although two detectors or two balanced detectors may be used to obtain two orthogonal polarization components simultaneously and advantageously a total power can be acquired for an accurate normalization for each I/O-SOP, it is envisaged that the two detectors or two balanced detectors descried in these embodiments could be replaced by one detector plus one optical switch.
[0163] A normalized OFDR trace would be obtained by dividing at least one of the OFDR or OTDR traces corresponding to the two detected different polarization components by the sum of the OFDR or OTDR traces corresponding to the two detected different polarization components. This alternative may be used regardless of whether the analyzer and detector unit comprises a PBS or a coupler. Any modification to the normalization and processing is expected to be minor and within the common general knowledge of a person skilled in this art.
[0164] It is also envisaged that a rotating polarization adjuster, whether it is with a polarizer or a PBS, may be used to sequentially acquire two orthogonal components for example via rotating the polarization by 90° to switch from detecting Px to detecting Py, or from detecting Py to detecting Px. The detector means 62, whether a single detector or two detectors, and the sampling and averaging unit 92, may be as used in standard commercial OTDRs that are known to a person skilled in this art.
[0165] It is also envisaged that an I/O-PC polarization controller or two separated I-PC controller and O-PC controller as illustrated in the embodiments as illustrated in FIGS. 1 and 6 may be used to sequentially acquire several "uniform" polarization states regarding Poincare sphere, for example linear vertical polarization state (LVP), linear +45 degree polarization state (L+45), right circular polarization state (RCP), and as well with their orthogonal polarizations as linear horizontal polarization state (LHP), linear -45 degree polarization state (L-45), left circular polarization state (LCP).
[0166] In the embodiment FIGS. 4F, 4H, 4G, 8F, 8G, and 8H, a input polarization state generator I-PSG 36C is employed to produce several "uniform" polarization states regarding Poincare sphere.
[0167] It should be noted that the polarization analyzer and detection means 61 could be designed as the light polarization analyzer, for example such polarization analyzer could be a polarimeter (FIG. 9E), a polarization scrambler with a linear polarizer or a polarization beam splitter.
[0168] The control unit 501 may advantageously be a separate computer. However, it is noted that a single computer could perform the functions of the signal processing, for example the FFT, averaging, filtering, etc. as for the sampling, signal processing and averaging unit 501, as well for the data processor and the control.
[0169] Various other modifications to the above-described embodiments may be made in implementations. For instance the tunable laser source 103 or 23 and I/O-SOP controller 36 could be replaced by some other means of providing the different polarization states of the laser lights entering the FUT 100 and analyzing the resulting backreflected signal caused by Rayleigh scattering and/or discrete reflections leaving the FUT 100.
[0170] Thus, a polarimeter may be used (splitters with three or more analyzers and photodetectors in parallel), which measures more than one polarization component of the backreflected signal simultaneously, or some other configuration, for example one after another, so that the power that reaches the photodetectors is dependent on the state of polarization (SOP) of the backreflected light.
[0171] It should be noted that each group is not limited to one pair of fiber distance. Indeed it may be advantageous to acquire an entire POFDR or POTDR trace for the FUT 100 with sufficiently spatial and sampling resolutions, and then to select the different distance steps for the signal (data) processing regarding to the bend radius, bend or stress strength, bend or stress length, etc.
[0172] It should also be noted that the above-described embodiment may have the change of the center wavelength for each I/O-SOP and the fiber bend or stress induced birefringence and bend or stress characteristics may be computed by averaging over an entire wavelength range.
[0173] It should be noted that the optical frequency encoder unit 106 may further consists of a oscillation signal (e.g. sine waveform) frequency doubling 73 to generate 2, 4, . . . , 2N times oscillation frequency to provide an accurately laser frequency determination by using a short delay 70 as illustrated in FIG. 3A. The optical frequency encoder unit 106 may have a further step to produce a clock signal from a clock signal generation 71 to trigger a AD converter to sample the measurement signals from detectors A and B, 62A and 64A, respectively.
[0174] In order to measure the FUT length beyond the laser coherent length, a frequency shifter and several different delay line may be used. Advantageously such arrangement could significantly increase an OFDR measurement distance for the FUT 100 without losing a spatial resolution of the instrument and its measurable distance is dependent on the number of delay lines.
[0178] To set I/O-SOP selected by the I/O-PC polarization controller 36 for each POFDR or each pair of POTDR traces.
[0182] With the group number register initialized to i=0, decision step 10.7 determines whether the total number of groups of traces have been acquired; if not, the program proceeds to step 10.8 to acquire the group i of OFDR or OTDR traces.
[0184] Once the ith OFDR or OTDR traces have been acquired as described above, in step 10.9 (see FIGS. 10A and 10B) the group is saved into the data file. It should be noted that for the OFDR step 10.9b is a FFT processing and length calibration to calculate the OFDR trace, i.e. to obtain loss as a function of FUT distance, but for the OTDR step 10.9b may be an optional step that may simple repeat the data acquisition of step 10.9a so as to remove those un-correlated noises in the mean square (MS) or root-mean square (RMS) computation, for example, to average away the electronic noise, polarization noise, in the MS or RMS optical signal (transmission) computation.
[0186] For the OFDR acquisition as for the embodiment in FIG. 1, after step 10.8, steps 10.9a and 10.9b will be repeated for K different center-wavelengths but the same I/O-SOP, selected by the I/O-PC controller 36 and until 2MK OFDR traces have been acquired after for M different I/O-SOPs and the acquired data are stored in the data file. Alternatively for the OFDR acquisition as for the embodiment in FIG. 10A, steps 10.9a and 10.9a' will be repeated for the same center-wavelengths and the same I/O-SOP, selected by the I/O-PC 36 for at least twice where a pair of OFDR traces has been acquired after step 10.9b and then stored in the data file, and then such steps of 10.9a and 10.9a' are repeated for M different I/O-SOPs. For the OTDR acquisition as for the embodiment in FIG. 10B, steps 10.9a and 10.9b will also be repeated for the same center-wavelengths and the same I/O-SOP, selected by the I/O-PC 36 for at least twice where a pair of OTDR traces has been acquired and stored in the data file, and then such steps of 10.9a and 10.9b are repeated for M different I/O-SOPs.
[0187] At this stage, the measurement parameters and all groups of OFDR or OTDR traces have been saved in the same data file.
[0188] If processing is initiated, step 10.14 allows the user to select the data file to be processed in a conventional "open file" dialog box, whereupon, in step 10.16, the data processor accesses the pre-saved acquisition data and associated measurement parameters from the data file, and uses the data to compute fiber bend or stress induced birefringence or bend or stress characteristics as a function of distance (z) along the FUT.
[0189] The manner in which the data processing step 10.19 in FIGS. 10A and 10B is processed following the below section (D) of "Theory and Signal Processing of Uniformly or Randomly Scrambled Input/Output SOP Analysis Method for Distributed Birefringence Measurement" and as well other procedures described herein.
[0191] Each group OFDR traces obtained for K center wavelength for one set input and output state-of-polarization (I/O-SOP) for the single-end POFDR based distributed fiber birefringence and bend analysis constitutes the elementary data points. Each OFDR acquisition consists of two OFDR traces and each such trace has N power values corresponding to N values tn of the time t, with n=0 . . . (N-1).
[0192] The data unit consists of two OFDR traces as such for FIGS. 4A and 4B where two OFDR traces are obtained simultaneously from photodetectors with their coherent detections (or alternatively sequentially in the case where an optical switch is used with one detector), all obtained with a given I/O-SOP as set by I/O-PC 36 and a swept wavelength range for a set central wavelength. Note it may be necessary to repeat such data acquisition for several different set central wavelengths, e.g. K, with the same I/O-SOP, especially for a `narrow` swept wavelength range may be used, for example of 2.5-125 GHz in C or L bands. Otherwise there is no required for many such `repeated` measurements for the central wavelengths if a wide swept wavelength may be used, for example >125 GHz in C or L bands or any telecom wavelength. (It is also necessary to be understood that too wide wavelength range, e.g. 20 nm in C-band, may not be necessary to bring significantly advantages but it may disadvantageously provide un-reliable measurement results in some case if there may be significantly depolarization from fiber PMD.) The two traces forming group k have been obtained in the following sequence (time flowing from left to right), where the labels x and y refer to the traces obtained simultaneously from photodetectors PDx and PDy corresponding to the detection output A and detection output B, respectively, for example as shown in FIG. 5C, Δλ=λL.sup.(k)-λS.sup.(k) (L, S mean Long and Short, respectively) equals to the tunable laser source swept wavelength range, the central wavelength is defined as λk=(λS.sup.(k)+λL.sup.(k))/2.
[0193] The overall data for the data processing (or stored in the data file after acquisition) is depicted as a below matrix (A) below, to which we will refer in all that follows. The matrix comprises K groups pair of OFDR traces (x and y) as a function of time (t), each consisting of N points corresponding to N values of time tn for K different laser central wavelengths that has a wavelength tuning range of Δλ, where n=0 . . . (N-1), for totally M different I/O-SOPs:
[0194] As shown in the data structure (D1), the data is the OFDR power as a function of time (t) (instead of power as a function of distance (z) as discussed in next section).
[0195] Also the data groups in the bold squares are considered these basic OFDR group traces, where the group traces from different I/O-SOPs must be processed independently, i.e. they can be considered un-correlated, but the group traces from the same I/O-SOP should be processed together before to extract the fiber birefringence and bend or stress information in order to achieve a best instrument performance.
[0196] It should emphasis again that if a wide wavelength range is used, for example >125 GHz along 1550 nm, then K can be set 1, i.e. only one single central wavelength is used. Otherwise, K may be set as 2 to 20 or any practical number if a wavelength range may be small, for example of 5-10 GHz, where it is important to require that every central wavelength must be different from each other.
[0197] Next step is the FFT computation for each acquired time domain OFDR RAW data in the Data matrix (A). The frequency domain data group can be obtained as described in following section.
[0198] After the FFT a new matrix data structure (B) is obtained that comprises K groups pair of OFDR traces (x and y) as a function of frequency (ν)--beating frequency between local oscillation lights and backreflected lights, each consisting of N' points corresponding to N' values of frequency νn' for K different laser central wavelengths that has the wavelength tuning range of Δλ, where n'=0 . . . (N-1), for totally M different I/O-SOPs:
[0199] As shown in the data structure (B), the data after the FFT is the OFDR power as a function of frequency or beating frequency (ν).
[0200] The measured light beating frequencies correspond the round-trip times of lights travelling for different locations/distances of the FUT and a laser frequency tuning speed so that it is also dependent on the fiber index, laser frequency tuning speed, etc. Here we propose an automatic fiber length calibration procedure by using a known length of the internal reference fiber to automatically calibrate the instrument so as to provide a fair accurate (but simple and robust) absolute FUT length if knowing the fiber type of the FUT is the same or similar as the internal reference fiber. Otherwise, if the fiber type is very different, then different ROIs (reflective of index) would provide a highly uncertainty for the measured fiber length. However, such uncertainty can be reduced to allow user to input a known ROI for the FUT. Indeed it is true for the most of fibers in the field, especially for the access network for the FTTH application, the standard optical fibers are used, e.g. G.652, G.657, with very similar ROIs.
[0201] The fiber length automatically calibration is to use an internal reference reflector that has a well known factory calibrated length and then every measurements in the field will compute the FUT length according to the reference length by simply to calculate the ratio between the measured FUT lengths and internal reference length. Although such length reference may not have a very high degree absolutely length accuracy, it can still provide fairly reliable and robust length measurement accuracy, e.g. with an uncertainty of <1 mm, especially helpful for the field T&M application. After the fiber length automatically calibration procedure, the spatial domain OFDR traces are ready for further computation and display (e.g. display of the distributed fiber loss, events, and optical return loss).
[0202] It is appreciated to be noted that above such length calibration procedure may not be necessary and such fiber length or distance could be obtained from other manner, such as a theoretical computation based on a laser frequency speed, a fiber ROI, etc. or any other method.
[0203] After above several steps, i.e. the FFT, length calibration procedures, etc., a new matrix data structure (C) is obtained that comprises K groups pair of OFDR traces (x and y) as a function of distance (z), each consisting of N'' points corresponding to N'' values of distance zn'' for K different laser central wavelengths that has the wavelength tuning range of AX, where n''=0 . . . (N''-1), for totally M different I/O-SOPs:
[0204] As shown in the data structure (C), the data after the FFT and internal reference length calibration or other method the OFDR power as a function of FUT distance (z) is ready for further bend analysis data processing, where the OFDR traces are similar as standard OTDR traces that is obtained in time domain acquisition using a pulsed light source.
[0205] It should be noted that for the POTDR configurations as described in embodiments FIGS. 6, 8A, 8B and 9A, the data structure (C) could be directly acquired after many averaging and above other steps are not required. However, the data structure for the POTDR should be as no repeated center wavelength required but require to do repeated measurements for at least twice for each Px and Py acquisition with the same I/O-SOP, etc. but acquired only from different time. Indeed such acquisition could advantageously reduce the noise after overall averaging of acquired data for many different I/O-SOPs, where a mean square calculation may be performed by using acquired POTDR data from different times.
[0206] Note in the instrument design for the distances between PBS 34 and two photodetectors (PDx and PDy) 62A and 64A must be set the same or very close.
[0207] As shown in the embodiment FIG. 1A where two photo-detectors are used for the OFDR acquisitions, thus it is necessary to perform the below described calibration procedure of the relative gain (including optical loss) for the two detectors PDx and PDy, respectively, before proceeding with any further computation. It should be noted the below described auto calibration includes for both electronic detection gain and optical insertion loss. Also this calibration is `relatively`, however, as we will describe in below data processing for the fiber birefringence and bend computation, there does not require for an absolute power measurement because of the normalization and equalization procedures could work with relative signal power or intensity although an absolute power calibration providing absolute light power value can also work for the signal processing, e.g. for the normalization and equalization procedures, etc.
[0208] The calibration principle is predicated upon the fact that, when an I/O-SOP polarization controller or scrambler is used to generate a sufficiently large number of SOPs so as to substantially cover the Poincare Sphere, in uniformly or random manner, the average power of the backreflected lights, high backreflections, e.g. from connection, etc., and Rayleigh backscattering (RBS) over any segments along the FUT will exit from the two ports of the PBS 34 with a 2:1 ratio, the higher power corresponding to the port to which detector A PDx is connected and the lower power corresponding to the port to which detector B PDy is connected. Hence, any observed deviation from this 2:1 ratio for the observed detector powers can be quantified and taken into account, as follows.
[0209] After the data acquisition, FTT and length calibration procedures are completed, 2KM groups of pair (two) OFDR traces obtained from both photodetectors (PDx detection output A and PDy detection output B, respectively) have been obtained and may be further stored, i.e., a total number of J=2KM traces from detector PDx and also J=2KM traces from detector PDy, as depicted in data matrix (c). The jth traces (j=0, 1 . . . (J-1)) from PDx and PDy are referred to below as Pkx,m(z)j and Pky,m(z)j, respectively, where k=0, 1 . . . (K-1) and m=0, 1 . . . (M-1).
[0210] If the overall losses in the two arms from the PBS 34 two detectors A and B, i.e. two optical paths from PBS 34 to detector A and detector B, respectively, were identical and the gains of both photodetectors and associated electronics were also equal, the ratio of the traces Px and Py after averaging over all J and over all the N values of z, for example using a known internal reference fiber length inside instrument or other fiber or device connected to instrument, would be
[0211] In practice, the ratio obtained from the average of the measured traces does not equal 2 because of different optical losses from the two arms of the PBS and different `effective` gains of the photodetectors, which includes the photodiode responsivity as well as the overall gains of the following electronics, amplifiers, and sampling circuit, etc. Note that it is not necessary to determine the individual gains or loss separately although it may still be an approach if a calibration procedure may be performed in such way. Therefore, before proceeding with the rest of the computations below, all the J traces obtained from photodetector PDy, i.e. all the Py(z)j, are multiplied as follows:
[0212] In practice, for the central wavelengths that are relatively closed to a narrow wavelength range, e.g. <5-20 nm, as the case for our fiber bend analyzer instrument, the relative wavelength dependence of the components, detectors, etc., may be negligible and this calibration process need only be carried out once per POFDR measurement sequence. Otherwise, this calibration may need to be carried out at every central wavelength, thereby increasing the overall calibration time, however this is still feasible because this calibration may not be required very often, for example at factory before the instrument being shipped out to costumers. However, if the instrument calibration is invalid due to environment changes then the user could still perform a calibration procedure according to his own environment situation. In another side for a case if an environment condition may be varied but it could be known, for example for a temperature issue that could be measured by using an internal temperature sensor, then a factory calibration data could still be used if such calibration data obtained in the factory are stored.
[0213] As a result of the calibration, i.e. after all Py traces have been multiplied by the measured relative gain as described above, the data processor now can compute the normalized OFDR traces. More precisely, the normalized traces in the case for the PBS embodiments are obtained by dividing either the sampled signal Px from detector PDx and signal Py from detector PDy by their sum (Px+Py) of the sampled signals from both of the detectors PDx and PDy which represents the total backreflected power before incident on the PBS, i.e., without selection of a particular polarization component.
[0214] It should be appreciated to be noted that this gain/loss calibration procedure can also be done by other different calibration method, for example by incident scrambled lights in the instrument via connector 40.
[0216] If a tunable laser and a polarization controller are used to launch and control the input light incident at an one end of FUT and a polarization state analyzer and power detectors (PDx and PDy) are used to measure the powers from the FUT from the same end of FUT 100, at two closely spaced fiber distances, zS and zL, around a given center distance, zc, for a large number M of input/output state of polarizations, i.e., I/O-SOPm, where m=1, 2, . . . , M, each referring to both the input-SOP (I-SOP) and the output-SOP (O-SOP) that sees the analyzer axis by the received light. Both the I-SOP and the O-SOP should be chosen in a well uniformly or random distributed manner, such that the points conventionally representing SOPs on the Poincare sphere are uniformly-distributed over the surface of sphere, whether the distribution is uniform or random grid of points. It has been observed that, on average over a sufficiently large, uniformly distributed number K (≧3-100) of I/O-SOPs, the mean-square difference between normalized powers measured at a distance pair of zS and zL is related to the local birefringence, Δβ(z,ω), at a given center distance, zc, where zc=(zS+zL)/2, by a simple known relationship, valid in all cases for any type of practical FUTs,
where < >SOP represents an average over the M I/O-SOPs, Δz=zL-zS is the distance step, ω=2πc/λ. The equation (4) can be valid for the correlated I/O-SOP setting as the set-up embodiment in FIG. 1A where one polarization controller or scrambler 36 is used, and in such POFDR configuration αs= {square root over (15)}. ΔT(z,ω) is a transmission difference between the two analyzed transmissions (i.e. normalized powers) measured at zS and zL, respectively, and its mean-square transmission difference is,
[0217] The equation (4) could be valid for the uncorrelated I-SOP and O-SOP, for example by two uncorrelated polarization controllers or scramblers, and then αs=3 {square root over (2)} is a theoretical constant. For the set-up configuration where one polarization or scrambler is used, then αs= {square root over (15)}. ΔT(z,ω) is a transmission difference between the two analyzed transmissions (i.e. normalized powers) measured at zS and zL, respectively, and its mean-square transmission difference ΔT(z,ω)2 for the transmission difference ΔT(z,ω) between the two analyzed transmissions (i.e. normalized powers) measured at zS and zL, respectively, can be computed as a function of distance z, where z=(zS+zL)/2 and Δz=(zL-zS),
and, for a short wavelength range, the mean-square difference may be averaged over both SOP and wavelengths as,
where the reference mean-value βo is a theoretical constant that is dependent on measurement input and output polarization set-up configurations, i.e. either two uncorrelated polarization controllers or scramblers or one correlated polarization controller or scrambler.
[0219] For the set-up configuration using two uncorrelated polarization controllers or scramblers, for example as FIG. 1D,
and for the set-up configuration using only uncorrelated polarization controllers or scramblers, for example as FIGS. 1B and 1C, where x polarization component is detected,
[0222] Its mean-square transmission difference <ΔT(z,ω)2> for the transmission difference ΔT(z,ω) between the two analyzed transmissions (i.e. normalized powers) measured at zS and zL, respectively, can be computed as a function of distance z, where z=(zS+zL)/2 and Δz=(zL-zS),
and, for a short wavelength range, the average of many different central wavelengths can be used, the mean-square difference may be averaged over both SOP and wavelengths as,
[0223] Furthermore, for the rms local birefringence measurement, the average of many different central wavelengths, especially for a short wavelength range can be used for each individual acquisition, i.e., in equation (1) averaging could also be carried out over both many I/O-SOPs and wavelengths to obtain the rms local birefringence, Δ(z), over the prescribed wavelength range as,
[0224] where < >SOP,ω as in equations (12') and (13) represents the average over the K I/O-SOPs for M different central wavelengths each with a predefined wavelength range. For the set-up configuration when a common (same) state of polarization controller or scrambler is used as both input and output light SOPs' controlling, the theoretical constant αs in equations (4) and (13) αs can be expressed as,
[0226] It should be noted that equations (4) and (13) are the simple differential formula which are valid for a sufficiently small distance step Δz (Δz=zL-zS) between the closely-spaced distances. However, for a large distance step other differential formula may be used, for example, arcsin formula as,
[0228] The local birefringence value or averaged local birefringence (RMS or mean) value over an wavelength range that is extracted from above equations (4), (13), (15) and (16) is valid for the single-end measurement for both configurations when a common (same) state of polarization controller (scrambler), and when two uncorrelated (different) state of polarization controllers (scramblers), then a different theoretical constant αs must be applied.
[0229] It should also be noted that the local birefringence value or averaged local birefringence value over a wavelength range that is extracted from above equations (4), (13), (15) and (16) is not the one-way (forward) birefringence value from the FUT, for example, for the single-end measurement configuration it is a roundtrip value for the FUT. Thus, a roundtrip factor (e.g. η≈0.61) is required to multiply on a measured roundtrip local birefringence for equations (4), (13), (15) and (16) in order to provide one-way (forward) distributed local birefringence of the test fiber.
[0230] It should be noted that equations (4) and (15) produce a fiber birefringence value at a given (fixed) wavelength or a given laser spectral wavelength range, e.g. for OFDR it has a swept wavelength range Δλ at a center wavelength λc or for OTDR it is referred as a pulsed laser spectral width with a center wavelength λc, or defined as the average wavelength for a particular prescribed wavelength range that is used in the measurement and equations (13) and (16) gives an averaged fiber birefringence over an optical prescribed wavelength/frequency range, where the fiber birefringence may be varied with the optical wavelength/frequency.
[0231] For the typical fiber with the weak bend or stress induced birefringence the weak mode coupling may be expected for the birefringence in the single short bend length/distance, for example, a half or quarter turn bend, e.g. with a radius of 5-20 mm, that presents a bend fiber length of few cm.
[0232] Above equations described for the single-end distributed fiber birefringence measurement can apply for measuring single-end fiber local birefringence as a function of distance z by analyzing the Rayleigh backscattering lights for each location (z) along FUT length--a distributed bend or stress measurement. Thus, it is necessary to use a high spatial resolved reflectometery, for example to apply a wide tunable frequency range for the OFDR, e.g. 1-10 nm. It should also be noted in order properly to measure the distributed bend or stress induced fiber birefringence a high spatial resolved polarization sensitive reflectometery, for example POFDR, etc., is recommended, especially for accurately measuring the bend radius, bend or stress length and especially for measuring fiber bend events one after another within a short distance. However, other type high spatial-resolved OTDR may be also possible, such as photon-counting OTDR or an improved high spatial resolved commercial available OTDR instrument.
[0233] For the typically FTTH fiber installation situation it may be expected that the fiber bend or stress events may be separated by over few to thousands mm although some events may be located very closely, for example few mm, thus a well designed commercial available OTDR with a short OTDR pulse, for example ˜0.1 ns to 10 ns, may also be used for the above fiber bend induced birefringence analysis although a poor performance may be expected.
[0234] The different ΔT(z,ω) values obtained with different I/O-SOPs may be different between whole OFDR traces as a function of z, instead of just one single number. Also note T(ν,z) is a normalized and equalized trace as a function of fiber length z.
[0235] It should be noted that a very narrow tunable laser frequency range of the OFDR would give a poor spatial resolution. A wide tunable and high coherence laser sources can be used, e.g. tunable external cavity laser, tunable narrow linewidth fiber laser, tunable narrow linewidth semiconductor laser, etc., for the OFDR or a very short pulse for the OTDR so as to have a sufficient spatial resolution in the field. However, when a very wide wavelength light source may be used, a "depolarization" effect may be occurred because of possible fiber PMD. Indeed for a very short fiber, such effect may be negligible, however, a "depolarization" may also come from if a FUT length is long or even from other sources, for example the light polarization fluctuation due to fiber moving, et al. It should be noted that such "depolarization" effect may be only related to the light polarization, but it may also be related to any "noises" and such "noises" could/might degrade the signal's polarization, and such "noise" could be from any sources, for example, the laser phase noises mixed with these beating signals at their same beating frequencies for an POFDR. Here we take account of the finding that when the tested light "polarization" may be varied due to any such "depolarization" effect the mean-square differences <ΔT(z,ω)2>SOP or <ΔT(z,ω)2>SOP,ω are "scaled down" by a factor that can be computed independently from the same raw data and such factor could be a relative variance of the traces and as a function of z.
[0236] It is worthy to be noted that in order to further reduce the `variation` or `fluctuation` or any `noises`, e.g. from a laser phase, on the measured optical parameter, the relative variance of the OFDR or OTDR traces may be calculated by an average over both the I/O-SOP and wavelengths.
[0237] Furthermore the averages indicated in equation (16) can be carried out over both I/O-SOPs and wavelengths and for the averages over many central wavelengths is particular important for the randomly birefringence mode coupling. However, no wavelength averages may be required for the weak birefringence mode coupling (as equations (4) and (15)) and indeed this could be some situations for the field FTTH fiber bend or stress induced weak birefringence cases where the local fiber birefringence may be induced from only a quarter or a half turn bend. But averaging over an enough wavelength range is critical to reduce the coherence noise as well to have an enough spatial resolution. It was observed that a 1 to 2 nm continuously tunable wavelength range to have a spatial resolution of 1 mm is sufficiently for the instrument design requirement regarding its cost, performance, etc. for the field test and measurement application, while other design parameters may also be possible, for example to use several discrete central wavelengths with a continuous narrow tunable wavelength range, as shown for the data matrix (A), (B) and (C) where K>1. Note if K could be set 1 if a swept wavelength range is wide.
[0238] Moreover, when the forward fiber birefringence value is to be displayed instead of the roundtrip birefringence value so as to estimate the fiber quality or lifetime or pass/fail situation, the result is multiplied by the above-specified roundtrip factor which for the both weak birefringence mode coupling case and randomly birefringence mode coupling case can be written as,
[0239] It is worthy to be noted that a linear component of the forward (one way) local birefringence could be calculated by using η=0.5 for two independent I-PC and O-PC. An overall local birefringence could be calculated by using η≈0.61 or η= {square root over (3/8)} for applying either two independent or dependent I-PC and O-PC.
[0241] As mentioned above for the most practical fiber bend or stress induced birefringence situations in the field, for example FTTH, the weak birefringence mode coupling in a short fiber bend distance/length may be possible so the equation (15) can be written as,
[0242] It is worthy to be understood that above MS or RMS computation has significantly advantages over the mean value computation. This is because the MS or RMS computation could reduce the detection noises to the second order because the mean-square transmission difference ΔT (z,ω)2 computation will remove the linear term of transmission difference multiplying noise after averaging many I/O-SOPs. Indeed such MS or RMS computation could significantly improve the instrument performance because it may be much tolerate the noises, e.g. detection electronic noise, polarization noise from fiber moving, et al.
[0243] It should also be noted and emphasise here that above said MS or RMS computation for the POTDR measurements may use repeated data measurements, as shown steps 10.9a and 10.9b (FIG. 10B) for the OTDR data acquisition or steps 10.9a and 10.9a' (FIG. 10A), and in such repeated data signal processing these noises, e.g. from detection, polarization, laser phase, et al, could be significantly reduced. It should be noted that such repeated data computation could be applied for any MS or RMS calculation so that the noise term could be no longer squared in the MS or RMS computation to remove or significantly reduce those randomly uncorrelated noises, especially for the mean-square transmission difference computations as for Equations (5), (5') and (8').
[0245] An optical fiber tends to be subject to bending, forces or stresses in applications. For example, fibers used for an optical network or fiber communication link, such as International Telecommunication Union recommended ITU-T G.652 single-mode optical fiber and cable, would suffer a fiber bend or stress loss which may adversely affect the performance or reliability of the fiber. Such fiber bending or stress could be measured by a commercial multiple-wavelength optical time domain reflectometer (OTDR), e.g. at 1310 nm or 1550 nm, to distinguish a bend loss from other losses, e.g. broken or connection loss, by use of the measured bend or stress induced loss difference information at different wavelengths. Such measurement is based on a bigger mode field diameter at a longer wavelength, thus for the most installed telecom optical fiber a bend or stress induced loss is higher at a longer wavelength, for example a bend loss at 1550 nm is bigger than that at 1310 nm
[0246] The disclosed technology below includes, among others, methods apparatus for distributed measuring at least one fiber bend or stress related characteristics along an optical path of fiber under test (FUT) uses both a light input unit and a light output unit connected to the FUT at one single end. The disclosed technology provides, for example, methods and devices for measuring distributed bend- or stress-dependent characteristics of optical paths and can be applicable to the distributed measurement of bend parameters, for example, bend or stress radius, bend or stress length, bend or stress strength, fiber reliability and or quality, etc., and or fiber loss or attenuation difference between at least two wavelengths at a particular fiber distance, i.e. position or length, of an optical path which comprises mostly optical waveguide, such as an optical fiber or cable link, for example, for an optical fiber used for the optical network such as fiber to the home (FTTH) or any access optical network (FTTx) or multi-dwelling unit (MDU).
[0247] One aspect of the disclosed technology is the light input unit injects at least two different wavelengths, the short-wavelength (λS) and long-wavelength (λL), into the FUT. The input light at different wavelengths may be injected into the FUT in different ways, for example, sequential injection of one wavelength at a time by one after another or simultaneously injecting the different wavelengths. The output light unit extracts corresponding light from the FUT, analyzes and detects the extracted output light power, and processes the corresponding electrical signal to obtain transmitted optical power at each distance along the length of the FUT. A processing unit is provided to process the signals from the output light unit and computes at least one power difference in a measured power parameter corresponding to each of two distances from at least two different wavelengths, for example short-wavelength (λS) and long-wavelength (λL), respectively, the measured power difference parameter at a pair of distances being proportional to local fiber loss or attenuation parameter. The processing unit calculates the at least one bend or stress related FUT characteristics, for example, bend or stress radius, bend or stress strength, etc., as at least one predetermined function of the fiber loss (or loss difference) parameter value, and determines the measurement of the at least one bend or stress related FUT parameter, for example, a fiber bend or stress length. The processing unit further computes at least one bend or stress related fiber characteristics, for example, a mechanical reliability and or or an expected lifetime and or a failure rate statistics from macro-bend or stressed for the optical networks, for example, optical fiber or cable for the home (FTTH) or multi-dwelling unit (MDU) scenarios, as at least one predetermined function of the at least one bend or stress related FUT parameter, for example, macro-bend or stress radius or bend or stress strength along an optical fiber or cable path. The disclosed technology also provides methods for an instrument calibration or reference procedure of the fiber bend or stress information, for example, fiber bend or stress coefficient, for unknown fiber type by adding at least one known bend information, for example, the fiber bend or stress radius or strength, on an optical fiber or cable under test. Such a instrument calibration or reference procedure for the FUT can be used to acutely measure and characterize any fiber macro-bend or stress related bend characteristics on the FUT.
[0248] Another aspect of the disclosed technology includes an identification of fiber type along an optical FUT path from measured at least one macro-bend related information, for example, bend induced fiber loss, bend induced fiber birefringence, and others, by adding additional known macro-bend, for example, bend radius, on a FUT by using both a light input unit and a light output unit connected to the FUT at one single end.
[0249] Some commercial fibers used for access optical networks (FTTx) or multi-dwelling unit (MDU), e.g., recently developed new bend insensitive optical fiber such as the International Telecommunication Union's recommendation G.657 (Characteristics of a bending-loss insensitive single-mode optical fibre and cable for the access network) can be subject to significantly macro-bend without exhibiting any noticable bend loss, and, therefore, it would be difficult for various currently commercial available OTDR systems to measure this type of fiber bend using various existing techniques. This is in part because there is nearly no or negligible macro-bend induced loss, for example, in the optical spectrum at 1310 nm or 1550 nm, but the fiber may still be subject a macro-bending or stress or significantly macro-bending or stress from a poor fiber installation that may result a poor fiber reliability so as to short a fiber lifetime or even failure for networks. In practical fiber deployment, strongly macro-banded or stressed fiber could adversely affect the installed fiber quality and reliability, or could reduce a lifetime for the fiber. In various applications, it is desirable to measure such fiber macro-bend characteristics to estimate the fiber properties to provide an assessment on the fiber reliability or estimate on a fiber lifetime or a fiber failure statistics for a fiber network, e.g. for FTTH, FTTx, MDU, etc., and or for a quality analysis and a lifetime estimation. The disclosed technology can be used to advantageously identify a bend-caused loss and a bend characteristics and thus provides the capability beyond some existing OTDR methods.
[0250] In properly characterizing fiber macro-bands or stresses, it is important to estimate the fiber local bend or stress prosperities, e.g. bend radius, bend or stress length, bend or stress strength, etc., for a communications optical fiber cable link, e.g. using G.652 or G.657 fiber, so that it could be possible to accurately estimate an installed fiber reliability or quality or lifetime. In particular, due to r widely deployment of bend insensitive optical fiber for the optical network, for example, the FTTH access network, such bend insensitive optical fiber tends to exhibit no or negligible bend loss at the common used communication wavelengths (e.g., 1310 nm and 1550 nm). In such deployment, the deployed fiber may still be highly bended and such macro-bend may cause a problem for the fiber quality or even shorting the fiber life time. Therefore, testing and measuring the fiber bend properties can be important for current optical networks such as the FTTH access network when the bend insensitive optical fiber, for example G.657, is installed.
[0251] The disclosed technology in this document can be implemented to meet those and other needs for characterizing bend- or stress-related fiber characteristics as a function of distance along a fiber link, e.g., a link from a single-end of the FUT, that can be used for the field test and measurement for the optical networks, for example, FTTH, FTTx, MDU, etc.
[0252] For example, one test method to measure fiber bend or stress is to measure a bend induced birefringence, where the birefringence can be induced by the fiber bend or stress during the installation and is proportional to 1/R2, where R is the bend radius, so that it is possible to determine bend properties. Highly bent fiber would reduce the fiber lifetime or even to cause a fiber broken. This issue is particularly problematic for the highly bent installed optical fiber at home for the FTTH application. Thus, it is desirable to be able to obtain the local bend or stress characteristics or it is best to find local bend or stress properties at each fiber distances, for example, bend radius, bend or stress length, bend or stress strength, etc., along the optical fiber or cable.
[0253] Depending on the application, it is often desirable to measure the bend or stress induced fiber loss at specified wavelengths for an estimation of bend- or stress-related properties at a given distance. However, in many practical cases, it is not possible to measure the fiber loss at a given precision position by commercial available OTDR. This is because there may be no or negligible loss for the bend insensitive fiber, for example, for wavelengths at 1310 nm and 1550 nm, or due to a poor spatial resolution from an OTDR, for example a commercial OTDR has a limited spatial resolution of as large as 50 cm for designed wavelengths but a typically bend or stress length may be of a few mm to few cm, and hence it is not possible to obtain a reliable determination of the bend properties. The fiber loss or attenuation is varied as a function of the wavelength and the macro-bend loss should be higher at the longer wavelength. Hence, measurements at different wavelengths provide useful information.
[0254] It should also be noted distributed PMD can be measured by the fixed analyzer or equivalently wavelength scanning method which tends to take long measurement times and suffer reliability problem of fiber polarization fluctuation during the testing. An early successful commercial test and measurement instrument (FTB-5600, EXFO Inc.) for the field distributed PMD measurement was using random-scrambling technique, where many uncorrelated measurements are performed for many "closely-spaced optical frequency pairs" over a large wavelength to estimate a distributed cumulative PMD along the fiber so as to significantly reduce the measurement sensitivity to moving of the test fiber. However, it can be difficult for such a measurement technique to provide distributed bend or stress or bend or stress induced birefringence information, and as well such method is limited to have a long spatial resolution of greater than 5 m.
[0255] The disclosed technology can be used for, in some implementations, characterizing high spatial resolved wavelength-dependent loss and or bend- or stress-dependent characteristics as a function of distance along a fiber link from a single-end of the FUT that could also distinguish fiber type between a traditional optical fiber, e.g. a SMF-28, a bend insensitive optical fiber, etc.
[0256] The disclosed technology can be implemented in ways that can eliminate, or at least mitigate, the disadvantages or limitations discussed above. The disclosed methods or devices can be used to provide more effective or alternative fiber characterization.
[0257] In one aspect of the disclosed technology, there is provided a method of estimating at least one bend- or stress-related characteristics of an optical path by measuring wavelength-dependent-losses at at least two different wavelengths using light input means and light output means connected to the optical path at adjacent end, the light input means comprising light source means for supplying at least partially coherent light and light incident means for injecting said light into the FUT, and output light means comprising means for extracting corresponding light from the FUT, detection means for detecting the output power of extracted light corresponding to the at least two wavelengths to provide transmitted optical power difference at each distance of an optical path in each pair of distances, wherein the short-distance (zS) and long-distance (zL) said distances in each said group of distances being closely-spaced and analyzing means for analyzing said each optical power differences at each distances of an optical path in said each distance pair for each said at least two different wavelengths; and wherein the source, detection and analyzing means are at the same end of the FUT and the light source comprises either temporal pulses (or tunable CW narrow linewidth coherent lights); and wherein the said optical power difference parameter for said each at least two different wavelengths is different between the respective said at least two wavelengths, the method including the steps of:
[0258] i. Computing an optical power difference in a measured power parameter corresponding to each distance in said each pair of distances for each of the said at least two wavelengths at least one wavelength is a long wavelength, for example beyond 1600 nm, said measured power parameter being proportional to the power of the said analyzed and subsequently detected light, and wherein the said optical power difference is a fiber loss or fiber attenuation;
[0259] ii. Computing at least one different optical power difference (loss) between said at least two different wavelengths as a function of fiber distance, and distinguishing the macro-bend induced fiber loss from other losses;
[0260] iii. Calculating the value of bend- or stress-related FUT characteristic, for example bend radius, bend or stress strength, as at least one predetermined function of a said fiber loss or attenuation value at at least one corresponding optical wavelength at a longer wavelength or a fiber bend loss or attenuation difference between two different wavelengths, said predetermined function being dependent upon the small fiber distance or length difference between the distances corresponding to the closely-spaced fiber positions or locations;
[0261] iv. Computing the bend or stress parameter may also include a bend or stress length that is measured from the said different optical power difference (loss) according to the bend induced wavelength-dependent loss parameter at the at least one wavelength, from the longest wavelength, from the measured fiber loss or attenuation parameter, for example by using a high spatial resolved OTDR; and
[0262] v. Computing and outputting the value of the at least one bend or stress related fiber characteristic, for example, a mechanical reliability or an expect lifetime or a failure rate statistics for bended or stressed fiber to the home (FTTH) or multi-dwelling unit (MDU) scenarios, as at least one predetermined function of the one bend- or stress-related FUT characteristic along an optical fiber path.
[0263] In implementations, for measurements of wavelength-dependent fiber loss at a specified distance z for each said group comprises distance pairs having substantially said prescribed central distance, and the said bend-related FUT characteristic is computed from a wavelength dependent loss value, ΔL.sub.λj.sub.-dB(z,λ) at the at least one wavelength that may be measured at L or UL band of the telecommunication bands or even beyond, i.e. longer than L or U band wavelength or even greater than 1675 nm, for a bend distance Δz.
where the R(z) is the bend radius, the Rth is defined as a "threshold" bend radius where for this "threshold" bend radius there is no any or negligible bend or stress induced attenuation or loss on the optical fiber, and the η(λ) is the fiber type related bend or stress coefficient or simple as a fitting coefficient. Note that Rth and η(λ) could either from theoretical numerical simulations or from experimental calibrations, for example for a given optical fiber the Rth and η(λ) can be obtained from at least two bend induced loss measurements for two different bend radius. The ΔL.sub.λj.sub.-dB(z,λ) is a bend or stress induced loss without any non bend- or stress-related losses and depends on the optical wavelength, λ, and fiber properties, e.g. fiber cladding radius, refraction index, etc., Δz is the bend distance or a portion of bend or stress length.
[0265] The bend radius or bend or stress strength may be computed from the bend induced loss parameter, ΔL.sub.λj.sub.-dB(z,λ), from the longest wavelength according to the predetermined function.
[0266] The bend radius or bend or stress strength may be computed from the bend induced loss parameters, ΔL.sub.λj.sub.-dB(z,λ), from at least one or advantageously more wavelengths according to the predetermined function so that an improved instrument performance may be achieved.
[0267] The measurement can be performed by a high resolution OTDR, for example using a very short light pulse and a wide bandwidth detection OTDR, or photon-counting OTDR, or tunable CW narrow linewidth coherent lights based optical frequency domain reflectometer (OFDR).
[0268] In implementations, for measurement of at least one bend or stress related fiber characteristics, for example, a mechanical reliability or an expect lifetime or a failure rate statistics for bending of fiber, is calculated as one predetermined function of the at least one bend or stress related FUT characteristics along an optical fiber path.
[0269] The bend radius or bend or stress strength may also be computed from the bend or stress induced loss parameter, ΔL.sub.λj.sub.-dB(z,λ), from only one wavelength loss measurement according to the predetermined function assuming the loss parameter measured from the said one wavelength may be bend or stress induced fiber loss or attenuation or may mainly or major come from the fiber macro-bend or stress. Accordingly, a low-cost simple instrument can be realized by only using one wavelength laser to measure the bend or stress induced loss and such wavelength could be at any wavelength within telecom bands but advantageously in some implementations the wavelength can be a long wavelength, for example >1625 nm or even >1675 nm OFDR or OTDR instrument. Indeed it could be a test and measurement situation if the loss induced from bend or stress could be identified without using the second wavelength loss information, for example it is known there is no any other loss except for the bend or stress induced loss.
[0270] In implementations, measurements based on one optical wavelength or at least two optical wavelengths may be used. For example, in one implementation of measurements using two wavelengths, the measurements at the first wavelength can be used to obtain the main measurements for the loss measurement according to the predetermined function while the measured loss parameter from the second wavelength may be mainly used to identify the loss type, for example bend or stress induced fiber loss or attenuation although two wavelength fiber loss or attenuation information could improve the measurement reliability so as to improve the instrument performance.
[0271] The bend or stress induced fiber loss or attenuation could be extracted from a fiber total loss subtracting the non-bend or non-stress related loss and such non-bend or non-stress related loss could be obtained from any means, for example a reference measurement for the FUT without any bend or stress, or a fiber loss from a location that is close to the bend or stress position or even far away from the bend or stress location as long as a relationship between the measured fiber loss and the non-bend or non-stress loss may be known. The bend or stress induced loss parameter(s), ΔL.sub.λj.sub.-dB(z,λ), from the said wavelength(s) is the measured total loss to subtract these non-bend or non-stress related loss(es).
[0273] It should be noted that a bend radius may not be a radius and may be any bend or stress related strength parameter.
[0274] The disclosed technology can be implemented to provide a method to obtain the Rth and η(λ) coefficients either from theoretical numerical simulations or from experimental testing, for example for a given optical fiber the Rth and η(λ) can be obtained from at least two bend induced loss measurements from at least one wavelength for at least two different bend radius and then the Rth and η(λ) could be extracted according to the said formula
or the Rth and η(λ) can be obtained from at least two bend induced loss measurements for two different wavelengths for at least one bend radius and then the Rth and η(λ) could be extracted according to the said formula
[0275] A second aspect of the method is to provide an identification of fiber type along an optical FUT path from measured at least one macro-bend or stress related information, for example bend induced wavelength-dependent fiber loss, and or or bend induced fiber birefringence, etc., by adding additional known macro-bend, for example a bend radius, on a FUT by using both a light input unit and a light output unit connected to the FUT at one single end.
[0276] In a third aspect of the disclosed technology, a measurement instrumentation is provided for measuring at least one wavelength-dependent-loss bend- or stress-related characteristics of an optical path to include input light means and output light means connected to the optical path at adjacent end, the light input means comprising light source means for supplying at least partially coherent light and light incident means for injecting said light into the FUT, and output light means comprising means for extracting corresponding light from the FUT, detection means for detecting the output power of extracted light corresponding to the at least two wavelengths to provide transmitted optical power difference at each distance of an optical path in each distance pair, analyzing means for analyzing said each optical power difference at each distance of an optical path in said each distance pair for each said at least two different wavelengths, and processing means for processing the electrical signals from the output light means to determine said at least one wavelength-dependent-loss bend- or stress-related characteristic. The processing means performs the following processing:
[0277] i. Computing an optical power difference in a measured power parameter corresponding to each distance in said each pair of distances for each of the said at least two wavelengths at least one wavelength is a long wavelength, for example beyond 1600 nm, said measured power parameter being proportional to the power of the said analyzed and subsequently detected light, and wherein the said optical power difference is a fiber loss or fiber attenuation;
[0278] ii. Computing at least one different optical power difference (loss) between said at least two different wavelengths as a function of fiber distance, and distinguishing the macro-bend induced fiber loss from other losses;
[0279] iii. Calculating the value of bend- or stress-related FUT characteristic, for example bend radius, bend or stress strength, as at least one predetermined function of a said fiber loss or attenuation value at at least one corresponding optical wavelength at a longer wavelength or a fiber bend loss or attenuation difference between two different wavelengths, said predetermined function being dependent upon the said small fiber distance or length difference between the distances corresponding to the said closely-spaced fiber positions or locations;
[0280] iv. Computing the said bend or stress parameter may also include a bend or stress length that is measured from the said different optical power difference (loss) according to the said bend induced wavelength-dependent loss parameter at said at least one wavelength, e.g., from the longest wavelength, from the said measured fiber loss or attenuation parameter, for example by using a high spatial resolved OTDR; and
[0281] v. Computing and outputting the value of said at least one bend (macro-bend) or stress related fiber characteristics, for example, a mechanical reliability and or or an expect lifetime and or or a failure rate statistics for bended or stressed fiber of fiber to the home (FTTH) or multi-dwelling unit (MDU) scenarios, as at least one predetermined function of said one bend-related FUT characteristic along an optical fiber path.
[0282] The measurement instrumentation also provides a method to obtain the said Rth and η(λ) coefficients either from experimental testing, for example for a given optical fiber the Rth and η(λ) can be obtained from at least two bend induced loss measurements from at least one wavelength for at least two different bend radius and then the Rth and η(λ) could be extracted according to the said formula
or the Rth and η(λ) can be obtained from at least two bend induced loss measurements for two different wavelengths for at least one bend radius and then the Rth and η(λ) could be extracted according to the formula below:
[0283] FIGS. 11-14 show examples of a high spatial resolution OTDR devices or systems based on the disclosed technology, which can be advantageously used for various measurements including, e.g., single-ended measurements of the optical fiber bend or stress for the FTTx test, measurement and monitoring applications.
[0284] The examples include, among other components, (i) an optical source controller, (ii) an analyzer and detection unit, (iii) an analogue and digital signal processing unit, together with one single control unit, where all of the components of the measuring instrument are at the single (same) end of the FUT. Different examples may be implemented with various differences in configurations according to the different fiber bend measurement methods such as a fiber long wavelength loss measurement based fiber bend determination method. For example to select a wavelength in L or U bands or even >1675 nm that can have a measurable fiber loss that is induced from a fiber macro-bend while probably there may be now any or have negligible loss at telecomm wavelengths, for example at 1310 nm, 1490 nm and 1550 nm.
[0285] For the multi-wavelength high spatial-resolved optical time domain reflectometer (OTDR) as illustrated in an embodiment of FIG. 1 includes different pulsed light sources at different wavelengths, e.g. 22-B1, 22-B2, . . . , 22-BN. Each light source may be a laser such as a DFB laser, a Fabry-Perot diode laser or other laser to enable selecting different central wavelength lasers for the OTDR acquisition, for example, 1550 nm, 1675 nm, or a wavelength longer than 1700 nm. A power splitter means or device 29 such as an optical coupler is provided to combine light of different wavelengths to the FUT 100. An optical circulator or coupler 32 is provided as a backreflection extractor between the optical splitter or coupler device 29 and the FUT 100 to direct the back reflection of the light from the FUT 100 to an optical detector 62A. A signal condition circuit (e.g., sampling and averaging unit) 92 is coupled to receive the optical detector output from the optical detector 62A, a data processor means or unit 94 is to receive the output from the sampling and averaging unit 92 and a display is coupled to the data processor 94 to display information to a user. Those components are controlled by a control unit 90. The sampling and averaging unit 92 performs signal sampling and averaging that is synchronized with the light pulsed source 22-B1, or 22B2, . . . , or 22-BN via control 90. The light pulsed source 22-B1, . . . , 22-BN is launched into a fiber-under-test (FUT) 100 from a connector 40, which also receives corresponding backreflected light from the FUT 100 that are caused by Rayleigh scattering and, in some cases, discrete (Fresnel) reflections via the connector 40 in the reverse direction.
[0286] In addition to controlling the sampling in unit 92, the control unit 90 controls or selects the wavelength of the laser sources 22-B1, . . . , 22-BN. More specifically, for each setting k of the laser central wavelengths, the control unit 90 causes the backreflected power to be measured at at least one pair of distances zS.sup.(k) and zL.sup.(k), respectively, that are closely-spaced relative to each other. The center distance of the distance pair is defined as the average of two actual distances, i.e., zC=(zS.sup.(k)+zL.sup.(k))/2. The labels S and L refer to "short" and "long" with respect to the center distance zC. A power difference in one pair of distances is a fiber loss (i.e. attenuation). The same computation may be performed for different OTDR trace at at least another one wavelength. A loss difference is then known at at least two different wavelengths, for example between 1550 nm and 1650 nm or 1675 nm (a wavelength beyond 1675 nm).
[0287] Other different embodiments as shown in FIGS. 2 and 3 are also possible, where in FIG. 2 a multi-wavelength pulsed laser source 22-B, for example from a widely tunable laser, could be used to select different wavelengths for the OTDR acquisition, while in FIG. 3 a multi-wavelength high spatial-resolved photon-counting OTDR would be used for achieving a high spatial resolution where a counter 92A is used.
[0288] Due to the single-mode fiber has different mode field diameter (MDF) for different wavelengths and a mode field diameter increases via wavelength increases, for example a MFD at 1550 nm is bigger that of 1310 nm and a MFD at 1650 nm is bigger than that of at 1550 nm and 1310 nm and also a macro-bend loss is proportional to 1/MFD, and then there is a difference for the bend induced losses between different wavelengths, i.e. loss at a longer is higher than that of at short wavelength. Generally the other loss, e.g. splice loss, connection loss, has less sensitive to the wavelength, thus the bend induced loss can distinguished from other losses after its loss can be measured at at least at two different wavelengths, e.g. at 1550 nm and 1650 nm or 1625 nm and 1675 nm, etc. Such losses can be measured by an OTDR as embodiments of FIGS. 1 and 2, photon-counting OTDR as embodiment of FIG. 3, or OFDR as shown in embodiment FIG. 14, etc.
[0289] After knowing the loss that is induced from macro-bending or stressing, a bend radius or a bend or stress strength can be estimated (see below section) and a bend or stress length may also be measured from an OTDR trace, in particular from a high spatial resolved OTDR or OFDR trace.
[0290] In some implementations, for an OTDR or OFDR design at least a one laser wavelength may be designed in the bend sensitive wavelength, e.g. a wavelength longer that 1625 nm or even beyond 1700 nm with properly photodetector. Such OTDR or OFDR design can have a sensitive detection for the bend induced loss although there may be no or negligible bend induced loss at a short wavelength, for example <1600 nm, so as to estimate the bend radius, or bend length, etc. This is particular important for testing the new developed and installed bend insensitive optical fiber which may have a negligible losses at short communication wavelengths at 1310 nm, 1490 nm and 1550 nm from fiber macro-bend, but it may be possible to have some measurable bend loss if its loss is measured at a long wavelength, e.g. beyond 1600 nm in the L band or UL band, or even >1650 nm or 1700 nm and such wavelength laser (e.g. DFB) and photodetector are commercially available.
[0291] For optical fiber loss (attenuation) based fiber macro-bend determination method in a long wavelength, e.g. > in the C, or L, or U bands, or >1675-1725 nm, the input light controller will comprise a such light source, for example a narrow linewidth or moderately broadband light source either pulses or CW lights, that is injected into the FUT. The input light source is narrow or moderately broadband, or tunable, either a pulsed for the OTDR based embodiments or a CW tunable narrow linewidth laser source for the OFDR based embodiments. Thus, for a fiber loss based fiber bend estimation method the input light controller will comprise at least two lasers with two different wavelengths, in which at least one wavelength laser can have a measurable macro-bend induced fiber loss or attenuation. In some implementations, a long wavelength laser, e.g. DFB at wavelength 1650 nm, could be used for the bend induced loss measurement. Indeed this is particularly important for the bend characteristics estimation for the bend insensitive optical fibers. The laser can be any laser source that are injected into the FUT 100. The analyzer and detection unit may comprise an photodetector, e.g. APD. The analogue and digital signal processing unit may comprise a control, a data acquisition unit, a sampling and averaging unit and a data processor unit, analog-to-digital conversion being carried out in the sampling and averaging unit.
[0292] For the single-end fiber bend or stress measurement method a distributed fiber loss (i.e. attenuation) can be extracted by analyzing backreflected light power from Rayleigh backscattering so that the fiber bend characteristic can be extracted and predicated. For the fiber loss based fiber bend measurement method it is important to resolve the wavelength dependent fiber loss (attenuation) difference the fiber loss measurement may be performed at the bend loss sensitive wavelengths, for example in L or U band or beyond 1675 nm. To use the single-end measurement method to measure distributed fiber bend properties, however, OFDR or OTDR traces as a function of fiber length must be analyzed, a widely tunable narrow linewidth laser (CW) may be used for the OFDR to obtain high spatial-resolved OFDR traces, for example having a tunable range 0.01 nm to 100 nm and a linewidth of 100 Hz to 1000 GHz, or to use a short OTDR pulse for the OTDR, for example 0.01 ns to 1000 ns, in order to obtain OTDR traces with a high spatial resolution.
[0293] Examples of the main the fiber bend measurement methods and instrument configurations for single-end distributed fiber bend measurement, and modifications, alternatives and substitutions thereto, will now be described with reference to FIGS. 11 to 14.
[0294] Examples of the fiber macro-bend measurement methods can use a wavelength resolved fiber loss or attenuation to estimate or predict the fiber bend radius or bend strength. In particularly losses at at least two different wavelengths are measured where there is a measurable loss at at least one wavelength.
[0295] In the designed embodiments a macro-bend or stress can be known and distinguished from other OTDR or OFDR events, e.g. losses from connection, broken, etc., after the loss measurement is performed at at least two different wavelengths, i.e. to use a wavelength resolved fiber loss or attenuation measurement where any fiber loss difference can be used to distinguish the bend loss from other losses, and a fiber loss or attenuation at a longer wavelength can be used for estimation or prediction of the fiber bend characteristics, such as radius or bend strength, etc. Advantageously it should be appreciated that such wavelength-dependent-loss based fiber bend analysis can be applied to use a long wavelength loss, e.g. at >1625 nm or even beyond 1675 nm, etc, to calculate the fiber bend radius or bend strength, in which a loss measurement in other wavelengths, e.g. at 1310 nm, 1550 nm, is negligible. Indeed it is true for the bend insensitive optical fiber that have nearly `zero` attenuation from a related small bend radius at 1310 nm or 1550 nm but it could have some measurable bend induced loss at wavelength ≧1650 nm.
[0296] From an estimation of the fiber bend properties, the bend strength, bend radius, bend length, fiber reliability/quality and or or fiber lifetime can be predicated as a function of the distance z along the FUT 100.
[0297] It will be appreciated that the usual conversions will be applied to convert time delay to distance according to refractive index of the FUT 100.
[0298] After knowing a loss from a fiber bend, for example at a long wavelength, it should be appreciated to be understood that a fiber bend characteristics, e.g. bend radius, bend strength, etc., can be estimated or computed by assuming to know the bend loss at a test wavelength and a fiber type, e.g. G.652 or G.657, etc. A bend length can be further estimated from a measured high spatial resolution OTDR or OFDR trace, for example to find a bend begin location, or a bend region, or bend length, etc. Indeed such bend measurement requires a high spatial resolution reflectometery, for example to use a very short OTDR pulse with a wide electronic bandwidth as illustrated in FIGS. 1 and 2, or a high spatial-resolved optical frequency domain reflectometer (OFDR) as illustrated in FIG. 4, or a photon-counting OTDR as illustrated in FIG. 3, etc.
[0299] The high spatial-resolved optical frequency domain reflectometer (OFDR) illustrated in FIG. 14 comprises a high coherent tunable CW narrow light source means 22 that has a very narrow linewidth, e.g. to have a coherent length of tens to thousands meters, and can also select different central wavelengths, for example 1550 nm, 1675 nm, or >1700 nm etc., power splitter means 24 (coupler 1), sampling and averaging unit 92 and data processor means 94, all controlled by a control unit 90, and detection means comprising first and second detectors A and B, 62 and 64, respectively, and a clock means 106 consisting of a fiber based Michelson interferometer having a light beam splitter and combiner 56 (coupler 2), a delay 70, reflectors means of mirrors 52 and 54 and a detection means detector C 66. A tunable CW narrow light source means 22 is coupled to a polarization maintaining fiber (PMF) 26 for producing light source for launching into a fiber-under-test (FUT) 100 from connector 40, which also receives corresponding backreflected light from the FUT 100 via a connector 40.
[0300] The input light controller means 102 and analyzer and detection means 104 comprise a backreflected light extractor, specifically a polarization-maintaining circulator 32 in FIG. 4 or polarization-maintaining coupler, a polarization beam splitter (PBS) 34. The circulator 32 is coupled to the input of PBS 34 by a second PM fiber (polarization-maintaining fiber) so that the optical path from the tunable light source 22 to the PBS 34 is polarization-maintaining A single-mode fiber may be used to couple the PBS 34 to the I/O-SOP controller 36.
[0301] The alignment of PMF 26 is fixed in the factory in such a manner that substantially all of the optical power from the tunable CW narrow linewidth light source 22 is maintained in one of the two axes of the fiber 29 and conventionally at the "slow" axis. Since the circulator 32 is polarization-maintaining, this alignment is maintained until the point between PBS 32. During attachment of each end of the PMFs to the components concerned, the azimuthal orientation of the PMF is adjusted to ensure maximum transmission of the optical lights towards the FUT 100.
[0302] Backreflected light caused by Rayleigh scattering and, in some cases, discrete (Fresnel) reflections, from the FUT 100 enters the instrument via the connection port 40 in the reverse direction.
[0303] In addition to controlling the sampling in unit 92, the control unit 90 controls or selects the wavelength of the laser sources 22. More specifically, for each setting k of the laser central wavelengths, the control unit 90 causes the backreflected power to be measured at at least one pair of distances zS.sup.(k) and zL.sup.(k), respectively, that are closely-spaced relative to each other. The center distance of the distance pair is defined as the average of two actual distances, i.e., zC=(zS.sup.(k)+zL.sup.(k))/2. The labels S and L refer to "short" and "long" with respect to the center distance zC. A power difference in one pair of distances is a fiber loss (i.e. attenuation). The same computation may be performed for different OTDR or OFDR traces at at least another one wavelength. A loss difference is then known at at least two different wavelengths, for example between 1550 nm and 1650 nm or 1675 nm (a wavelength beyond 1675 nm).
[0304] It should be appreciated for the embodiments with the OFDR as in FIG. 4 that measure the beating signals between the local oscillation light, e.g. from the beam splitter 28 (coupler 3), and the reflected light signals from the FUT 100 in the time domain and then the measured signals are transferred into the frequency by A fast Fourier transform (FFT), the first step of the data processing is to perform the FFT for the acquired data from the detector A and B, 62A and 64A, respectively, and then it may require a calibration or reference procedure to obtain an OFDR trace that is a function of the distance. However, if for the OTDR this described procedure is not required, i.e. directly to obtain the OTDR curve as a function of the time and then of the distance of the test fiber (FUT) after considering the light speed at the given FUT, i.e. ROI. For the OFDR in order to remove or reduce the laser frequency sweeping nonlinearity, there may be a clock or reference means 106 that consists of a fiber based Michelson interferometer with a delay 1 70, Faraday rotation mirrors 52 and 54, and detector C 66. The clock or reference means may provide signals from the interferometer for sampling the measurement signals by sampling and averaging unit 92 or alternatively providing signal for re-sampling of the measurement signals from the FUT 100 as illustrated in FIG. 14.
[0305] It should be appreciated that, where the group may comprise more than one closely-spaced pair of distances, the center distance as defined above in fact differs for each pair in the group.
[0306] Different from the high spatial-resolved optical time domain reflectometer (OTDR) as illustrated in FIGS. 1, 11, 12 and 13, the OTDR in FIG. 14 includes two optical detectors 62 and 64 to receive optical signals from the backreflection extractor 32 and a polarization beam splitter 34, respectively. The OTDRs as illustrated in FIGS. 11, 12 and 13 may use a narrow light pulse width, for example 0.1 ns to 100 ns and a high detection bandwidth for the detector 62 and a high sampling rate for the ADC. In implementations, the relative low sampling rate ADC may be used if the time shifting sampling technique, for example for the 1 ns OTDR light pulse the ADC may have a sampling rate of 100 MSPS (under sampling) with an operation of 10 time shifting with a step of 1 ns, may be applied in the embodiments for the sake of the low-cost instrument design.
[0307] Before the operation of the multi-wavelength OTDR or OFDR based wavelength-dependent-loss measurement for the bend analysis is described in more detail, and with a view to facilitating an understanding of such operation.
[0308] Various other modifications to the above-described embodiments may be made. For instance the tunable laser source 22 could be replaced by some other means, for example widely tunable laser, discrete wavelength lasers, etc.
[0309] Measurements can be performed to one pair of fiber distances or additional distances. In some implementations, it may be advantageous to acquire an entire OFDR or OTDR trace for the FUT 100 with sufficiently spatial and sampling resolutions, and then to select the different distance steps for the signal (data) processing regarding to the bend radius, bend length, and other parameters.
[0310] The following describes one example of a method of operation of the OTDR based wavelength-dependent-loss measurement for the distributed measurement of fiber bend or stress prosperities as a function of FUT length.
[0311] The user first causes the system to initialize the OTDR, specifically initializing the pulsed light source 22, the OTDR detection and processing section, acquisition for the N (N≧2) high spatial-resolved OTDR traces at N different wavelengths where at least one wavelength OTDR trace would be sensitive to the bend induced fiber loss or attenuation. In particular such wavelength is set at a long wavelength region, for example from 1600 nm or beyond 1675 nm. It should be appreciated to be understood that the longer wavelength is, the more sensitive it is to the fiber bend induced loss so as to obtain a more sensitive bend measurement. Otherwise, if there is no any bend induced loss at any wavelength, it is impossible to characterize the bend properties, such as bend radius, bend strength, bend length, etc. For most commercial OTDR, an InGaAs APD may be used. However, advantageously a Ge photodetector may be used and it is more sensitive to detect the light beyond 1650 nm. Other laser and detector may also be possible to be used, for example to use a laser wavelength >1700 nm pulsed DFB and a relevant photodetector that can detect the light beyond wavelength 1700 nm. Indeed such laser and photodetector are commercially available.
[0312] The instrument then calculates the fiber loss or attenuation at the same fiber location for different wavelengths, where at least one loss must be extracted from one wavelength, and then further compute their differences or at least one such said difference. If there may be a loss difference between any two OTDR measurements, then a bend on the FUT may be determined and any loss from any wavelength can be used to estimate the bend properties, but a higher loss at a longer wavelength may be used to determine these macro-bend characteristics. If there is only one measured loss at a longest or longer wavelength but there is no any other losses at other wavelengths, one could also determine a bend characteristics of the test fiber.
[0313] The instrument will further perform a computation of the fiber bend radius or strength according to the measured fiber loss or attenuation and the fiber wavelength dependent bend coefficient, for example by using a factory calibrated wavelength dependent bend coefficient for a known fiber type. Note it is an advantage to have more than one measured fiber losses so as to have an accurately bend characterization.
[0314] Therefore the bend radius or bend strength as well a bend length will be estimated, respectively.
[0315] The last step will compute fiber bend characteristics as a function of distance (z) along the FUT, for example fiber quality, fiber reliability, lifetime and failure statistics.
[0316] It should be appreciated to be understood that above steps might also be used for the photon counting OTDR operation after an OTDR trace is acquired.
[0317] It should also be noted that for an OFDR operation the acquisition is firstly obtaining an time domain signal and then to obtain a spatial domain OFDR trace (similar as OTDR trace) after a FFT operation, and then above steps could be used.
[0319] Spatial Domain Data Structure--After the OTDR data acquisition or after a FFT operation of the OFDR data acquisition for at least two lasers with different wavelengths, a new matrix data structure (D1) is obtained that comprises K groups OTDR traces as a function of distance (z), each consisting of N points corresponding to N values of distance zn for K different laser central wavelengths, where n=1 . . . N, for totally K different wavelength lasers:
[0320] Fiber Coefficient Measurement/Calibration for Known Fibers--For the currently optical network fiber link installation, mostly the fiber types might be known, for example for the FTTH access network standard optical fiber of G.652, G.657(.A, B, etc.). It is necessary to measure the "threshold" bend radius or a fitting coefficient Rth and the fiber type related bend or stress coefficient or a fitting coefficient η(λ) and then users can select a properly fiber "threshold" bend radius Rth and the fiber type related bend or stress coefficient η(λ) or even to input the fitting coefficients for them regarding the FUT fiber type so that the fiber bend characteristics could be accurately calculated. This fiber bend coefficient measurement or calibration could be done/calibrated at the factory or by user.
[0321] In the field if user may not know the fiber type, it may also be possible to identify the fiber type by performing a fiber bend induced loss measurement for at least one wavelength, for example to bend the fiber to have at least one and, in some cases, two known radius, e.g. of 10 mm, and then such fiber bend fitting coefficients can be measured and calibrated.
[0322] Signal Processing of Distributed Bend or Stress Measurement Based on Wavelength-Dependent-Loss Analysis Method--As described above that the single-mode fiber, e.g. G.652, G.657, has different mode field diameter (MDF) for different wavelengths and a mode field diameter increases via wavelength increases so as to have an increased bend induced loss, for example a MFD at 1550 nm is bigger that of 1310 nm and a MFD at 1650 nm is bigger than that of at 1550 nm and 1310 nm, therefore a macro-bend loss is larger in the longer wavelength than that of a short wavelength because a bend loss is proportional to the MFD. Thus there is a difference for the band losses between different wavelengths. Also the bend induced loss can distinguished from other losses if bend losses can be measured at at least for two different wavelengths, e.g. at 1550 nm and 1650 nm or 1625 nm and 1675 nm (even beyond 1700 nm for an improved bend sensitive test and measurement), etc. This is because other losses have less or negligible wavelength dependence. Such losses can be measured by an OTDR or PC-OTDR or OFDR, as shown in embodiments FIGS. 11-14. Since most bend radius and length is small in the FTTH fiber installation, e.g. several mm and sew cm, a high spatial resolved reflectometery, for example a modified short pulse and wide detection bandwidth commercial OTDR, or a high spatial-resolved OFDR and PC-OTDR, should be used. Based on knowing the loss from macro-bending at a given wavelength for the measurement, a bend radius or bend strength can be estimated (see below section) by knowing a fiber type and using a factory (or user) calibrated wavelength dependent bend coefficient η(λ) that is a constant dependent on the optical wavelength, λ, and fiber properties, e.g. fiber cladding radius, refraction index, etc., and also a bend length can be measured from a measured OTDR or OFDR trace.
[0323] After the measurement of backreflected light power (e.g. Rayleigh Back Scattering) or fiber macro-bend loss (attenuation) at different wavelengths by an OTDR or OFDR, a loss between two different fiber distance zS and zL can be obtained. If there may be a fiber bend then such losses may come fiber bend and can be distinguished from other losses as described above, i.e. bend losses are different at different wavelengths. The fiber bend loss can be expressed as,
where P(z,λ) is the measured backreflected light power at a distance z and at a wavelength λ, and i (i=1 . . . I, I>1) is an index for the laser wavelength number.
[0324] In some implementations, for the measurement of the wavelength-dependent loss at a specified distance z for each said group comprises distance pairs having substantially said prescribed center distance, and the said bend- or stress-related FUT characteristic is the wavelength-dependent loss values, ΔL.sub.λj.sub.-dB(z,λ), at at least two different wavelengths, at the said at least one wavelength-dependent loss value is measured at L or UL band of the telecommunication bands or even at the further longer wavelengths.
where the R(z) is the bend radius, the Rth is defined as a "threshold" bend radius where for this "threshold" bend radius there is no any or negligible bend or stress induced attenuation or loss on the optical fiber, and the η(λ) is the fiber type related bend or stress coefficient or simple as a fitting coefficient. Note that Rth and η(λ) could either from theoretical numerical simulations or from experimental calibrations, for example for a given optical fiber the Rth and η(λ) can be obtained from at least two bend induced loss measurements for two different bend radius. The ΔL.sub.λj.sub.-dB(z,λ) is a bend or stress induced loss without any non bend- or stress-related losses and depends on the optical wavelength, λ, and fiber properties, e.g. fiber cladding radius, refraction index, etc., Δz is the bend distance or a portion of bend or stress length. ΔL.sub.λj.sub.-dB(z,λ) is a bend or stress induced loss at a given wavelength for a bend distance Δz. The bend or stress parameter may be a bend or stress radius R(z) or a bend or stress strength that is computed from the bend or stress induced wavelength-dependent loss parameter, ΔL.sub.λj.sub.-dB(z,λ), at a said given wavelength, λ, e.g., from a long wavelength, for example a bend or stress radius R(z) could be computed from said predetermined function according to the equation (2).
[0326] It should be noted that the ΔL.sub.λj.sub.-dB(z,λ) does not include the non-bend or -stress related loss that may usually be dependent on the wavelength, for example dependent on the 1/λ4.
[0327] It is appreciated that equation (2) is not the only formula but it could other formulas that may come from theoretical analysis, simulations and experiments.
[0328] It should also be noted that the η(λ) could be obtained from a factory calibration from known fiber type, or a user field reference measurement in the field by introducing a known bend radius (diameter) on the test fiber (i.e. FUT) or other source or method, for example by knowing fiber characteristics, e.g. standard fibers G.652, G.655, G.657, etc.
[0329] The bend radius may be computed from the said bend induced wavelength-dependent loss parameter, ΔL.sub.Δj.sub.-dB(z,ω), from the longest wavelength according to the said predetermined function.
[0330] The said Rth and η(λ) coefficients could be extracted from either experimental testing or theoretical analysis or simulations, for example for a given optical fiber the Rth and η(λ) can be obtained from at least two bend induced loss measurements from at least one wavelength for at least two different bend radius and then the Rth and η(λ) could be extracted according to the equation (2); or the said Rth and η(λ) can be obtained from at least two bend induced loss measurements for two different wavelengths for at least one bend radius and then the Rth and η(λ) could be extracted according to according to the equation (2).
[0331] The bend parameter may be a bend length that is measured from the different optical power difference (i.e. fiber loss) according to the said bend induced wavelength-dependent loss parameter, ΔL.sub.λj.sub.-dB(z,λ), at at least one wavelength, e.g., from the longest wavelength.
[0332] In some cases, at least one bend or stress related fiber characteristics, for example a mechanical reliability and or an expect lifetime or a failure rate statistics for bending of a fiber, is calculated as one predetermined function of said the at least one bend related FUT characteristics along an optical fiber path.
[0333] While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
[0334] Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document.
2016-04-07 1-dimensional and 2-dimensional distributed fiber-optic strain and stress sensors based on polarization maintaining fiber using distributed polarization crosstalk analyzer as an interrogator
2014-12-11 Distributed fiber bend and stress measurement for determining optical fiber reliability by multi-wavelength optical reflectometry