Patent Description:
The abstract of <CIT> reads: 'An MCF of the present embodiment has eight or more cores. A diameter of a common cladding is not more than <NUM>. Optical characteristics of each core are as follows: a TL at a predetermined wavelength of <NUM> is not more than <NUM> dB/km; an MFD at the predetermined wavelength is from <NUM> to <NUM>; a BL in a BR of not less than <NUM> or in the BR of not less than <NUM> and, less than <NUM> is not more than <NUM> dB/turn at the predetermined wavelength; λ0 is from <NUM> to <NUM>; λcc is not more than <NUM>; an XT or XTs at the predetermined wavelength is not more than <NUM>/km.

In accordance with one example, a multicore optical fiber is provided. The multicore optical fiber includes an inner glass region having a plurality of core regions surrounded by a common outer cladding, the inner glass region further having at least one marker and an outer diameter in the range of <NUM> microns and <NUM> microns, wherein each core region is comprised of a germania-doped silica core and a fluorine-doped silica trench, wherein a trench volume of the fluorine-doped silica trench is greater than, or equal to, <NUM>% Δ microns<NUM>, and an outer coating layer surrounding the inner glass region, wherein the outer coating layer comprises a primary coating layer and a secondary coating layer surrounding the primary coating layer, and wherein a ratio of a secondary coating layer thickness to a primary coating layer thickness is in a range of <NUM> to <NUM>, the outer coating layer having a diameter equal to or less than <NUM> microns, wherein each core region has a mode field diameter of <NUM> microns, or more, at <NUM>, a cable cutoff wavelength of <NUM>, or less, and a zero dispersion wavelength of <NUM>, or less.

In accordance with another example, a multicore optical fiber is provided. The multicore optical fiber includes an inner glass region having a plurality of core regions surrounded by a common outer cladding, the inner glass region further having at least one marker and an outer diameter in the range of <NUM> microns and <NUM> microns, wherein each core region has an outer radius of <NUM> microns, or more, and is comprised of a germania-doped silica core region, an inner cladding and a fluorine-doped silica trench, wherein a trench volume of the fluorine-doped silica trench is <NUM>% Δ microns<NUM>, or more, and an outer coating layer surrounding the inner glass region, wherein the outer coating layer comprises a primary coating layer and a secondary coating layer surrounding the primary coating layer, and wherein a ratio of a secondary coating layer thickness to a primary coating layer thickness is in a range of <NUM> to <NUM>, the outer coating layer having a diameter equal to or less than <NUM> microns, wherein each core region has a mode field diameter of <NUM> microns, or more, at <NUM>, a cable cutoff wavelength of <NUM>, or less, and a zero dispersion wavelength of <NUM>, or less.

Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the examples as described herein, including the detailed description which follows, the claims, as well as the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more examples, and together with the description serve to explain principles and operation of the various examples.

Reference will now be made in detail to the present preferred examples, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

The following detailed description represents examples that are intended to provide an overview or framework for understanding the nature and character of the claims. The accompanied drawings are included to provide a further understanding of the claims and constitute a part of the specification. The drawings illustrate various examples, and together with the descriptions serve to explain the principles and operations of these embodiments as claimed.

"Refractive index" refers to the refractive index at a wavelength of <NUM>.

The "refractive index profile" is the relationship between refractive index or relative refractive index and waveguide fiber radius. The radius for each region of the refractive index profile is given by the abbreviations r<NUM>, r<NUM>, r<NUM>, r<NUM>, etc. and lower and upper case are used interchangeably herein (e.g., r<NUM> is equivalent to R<NUM>).

The "relative refractive index percent" is defined as Δ%=100x(n<NUM><NUM>-nc<NUM>)/2ni<NUM>, and as used herein ni is the refractive index of region i of the optical fiber and nc is the refractive index of undoped silica. As used herein, the relative refractive index is represented by Δ and its values are given in units of "%", unless otherwise specified. The terms: delta, Δ, Δ %, % Δ, delta %, % delta and percent delta may be used interchangeably herein. In cases where the refractive index of a region is less than the average refractive index of undoped silica, the relative index percent is negative and is referred to as having a depressed region or depressed index. In cases where the refractive index of a region is greater than the average refractive index of the cladding region, the relative index percent is positive. An "updopant" is herein considered to be a dopant which has a propensity to raise the refractive index relative to pure undoped SiO<NUM>. A "downdopant" is herein considered to be a dopant which has a propensity to lower the refractive index relative to pure undoped SiO<NUM>. Examples of updopants include GeO<NUM> (germania), Al<NUM>O<NUM>, P<NUM>O<NUM>, TiO<NUM>, Cl, Br. Examples of down dopants include fluorine and boron.

"Chromatic dispersion", herein referred to as "dispersion" unless otherwise noted, of a waveguide fiber is the sum of the material dispersion, the waveguide dispersion, and the inter-modal dispersion. In the case of single mode waveguide fibers, the inter-modal dispersion is zero. Zero dispersion wavelength is a wavelength at which the dispersion has a value of zero. Dispersion slope is the rate of change of dispersion with respect to wavelength.

"Effective area" is defined as: <MAT> where f(r) is the transverse component of the electric field associated with light propagated in the waveguide. As used herein, "effective area" or "Aeff" refers to optical effective area at a wavelength of <NUM> unless otherwise noted.

The trench volume V<NUM> is defined for a depressed index region <MAT> where rTrench,inner is the inner radius of the trench cladding region, rTrench,outer is the outer radius of the trench cladding region, ΔTrenh(r) is the relative refractive index of the trench cladding region, and Δc is the average relative refractive index of the common outer cladding region of the glass fiber. In examples in which a trench is directly adjacent to the core, rTrench,inner is r<NUM> = r<NUM> (outer radius of the core), rTrench,outer is r<NUM>, and ΔTrench is Δ<NUM>(r). In examples in which a trench is directly adjacent to an inner cladding region, rTrench,inner is r<NUM> > r<NUM>, rTrench,outer is r<NUM>, and ΔTrench is Δ<NUM>(r). Trench volume is defined as an absolute value and has a positive value. Trench volume is expressed herein in units of %Δ-micron<NUM>, %Δ-µm<NUM>, or %-micron<NUM>, %-µm<NUM>, whereby these units can be used interchangeably.

The term "α-profile" refers to a relative refractive index profile, expressed in terms of Δ(r) which is in units of "%", where r is radius, which follows the equation, <MAT> where ro is the point at which Δ(r) is maximum, r<NUM> is the point at which Δ(r) % is zero, and r is in the range ri ≤ r ≤ rf, where Δ is defined above, ri is the initial point of the α-profile, rf is the final point of the α-profile, and α is an exponent which is a real number. The mode field diameter (MFD) is measured using the Peterman II method wherein, <MAT> <MAT> Mode field diameter depends on the wavelength of the optical signal in the optical fiber. Specific indication of the wavelength will be made when referring to mode field diameter herein. Unless otherwise specified, mode field diameter refers to the LP<NUM> mode at the specified wavelength.

The theoretical fiber cutoff wavelength, or "theoretical fiber cutoff", or "theoretical cutoff", for a given mode, is the wavelength above which guided light cannot propagate in that mode. A mathematical definition can be found in<NPL> wherein the theoretical fiber cutoff is described as the wavelength at which the mode propagation constant becomes equal to the plane wave propagation constant in the outer cladding. This theoretical wavelength is appropriate for an infinitely long, perfectly straight fiber that has no diameter variations.

Fiber cutoff is measured by the standard <NUM> (<NUM> meter) fiber cutoff test, FOTP-<NUM> (EIA-TIA-<NUM>-<NUM>), to yield the "fiber cutoff wavelength", also known as the "<NUM> fiber cutoff" or "measured cutoff". The FOTP-<NUM> standard test is performed to either strip out the higher order modes using a controlled amount of bending, or to normalize the spectral response of the fiber to that of a multimode fiber.

By cabled cutoff wavelength, or "cabled cutoff" as used herein, we mean the <NUM> (<NUM> meter) cabled cutoff test described in the EIA-<NUM> Fiber Optic Test Procedures, which are part of the EIA-TIA Fiber Optics Standards, that is, the Electronics Industry Alliance-Telecommunications Industry Association Fiber Optics Standards.

Unless otherwise noted herein, optical properties (such as dispersion, dispersion slope, etc.) are reported for the LP01 mode.

Referring to <FIG>, the terminal end of multicore optical fibers <NUM> having an inner glass region <NUM> containing a plurality of core regions <NUM> surrounded by a common outer cladding <NUM> and an outer coating layer <NUM> are illustrated, according to various examples. The plurality of core regions <NUM> each define a core-portion of inner glass region <NUM> and may be glass core regions each having a circular shape in cross-section and spaced apart from one another. Each core region <NUM> includes a core, an inner cladding surrounding the core and a trench. This allows the trench to be offset from the core and allows for a large trench volume. In some examples, the inner cladding may be omitted such that the trench is adjacent to the core. The common outer cladding <NUM> is shown having a generally circular end shape or cross-sectional shape in the examples illustrated. The plurality of core regions <NUM> each extend in a cylindrical shape through the length of the multicore optical fiber <NUM> and are illustrated spaced apart from one another and are surrounded and separated by the common outer cladding <NUM>. The multicore optical fiber <NUM> contains at least two core regions <NUM>, preferably at least three core regions <NUM>, and more particularly at least four core regions <NUM>, and therefore has a plurality of core regions <NUM>. It should be appreciated that two or more core regions <NUM> may be included in the multicore optical fiber <NUM> in various numbers of core regions and various fiber arrangements.

The multicore optical fiber <NUM> employs a plurality of glass core regions <NUM> spaced from one another and surrounded by the common outer cladding <NUM>. The core regions <NUM> and common outer cladding <NUM> may be made of glass or other optical fiber material and may be doped suitable for optical fiber. In one example, each core region <NUM> is comprised of germania-doped silica core, an inner cladding and a fluorine-doped silica trench. In one example, the shape of the multicore optical fiber <NUM> may be a circular end shape or circular cross-sectional shape as shown in <FIG>. According to other examples, end and cross-sectional shapes and sizes may be employed including elliptical, hexagonal and various polygonal forms. The multicore optical fiber <NUM> includes a plurality of core regions <NUM>, each capable of communicating light signals between transceivers including transmitters and receivers which may allow for parallel processing of multiple signals. The multicore optical fiber <NUM> may be used for wavelength division multiplexing (WDM) or multi-level logic or for other parallel optics of spatial division multiplexing. The multicore optical fiber <NUM> may advantageously be aligned with and connected to various devices in a manner that allows for easy and reliable connection so that the plurality of core regions <NUM> are aligned accurately at opposite terminal ends with like communication paths in connecting devices.

The multicore optical fiber <NUM> illustrated in <FIG> has an inner glass region <NUM> having four (<NUM>) circular-shaped core regions <NUM> arranged in a <NUM> x <NUM> array and surrounded by a common outer cladding <NUM>. Each of the circular-shaped core regions <NUM> has an outer radius R greater than, or equal to, <NUM> microns, and the outer radius R may be greater than, or equal to, <NUM> microns, where the outer radius R of each core region <NUM> is measured with respect to its center as shown in <FIG>. The outer radius R may have an upper limit of <NUM> microns. Adjacent core regions <NUM> are spaced apart from each other by a separation distance S, which is defined as a distance between the centers of adjacent core regions <NUM>. Separation distance S between centers of adjacent core regions <NUM> may be greater than, or equal to, <NUM> microns and may be greater than, or equal to, <NUM> microns. Separation distance S may be less than, or equal to, <NUM> microns which may correspond to a core center to fiber edge distance of <NUM> microns, or may be less than, or equal to, <NUM> microns which may correspond to a core center to fiber edge distance of <NUM> microns. The common outer cladding <NUM> is also shown having an outer circular shape defining the shape of the inner glass region <NUM> with a glass diameter Dg. The glass diameter Dg can be between <NUM> microns and <NUM> microns.

In the examples shown in <FIG>, the multicore optical fiber <NUM> has an inner glass region <NUM> having the core regions <NUM> arranged in a <NUM> x <NUM> array and centered within and about the center of inner glass region <NUM>. As such, the core regions <NUM> are spaced apart and centered within the inner glass region <NUM> such that they are symmetric about and evenly spaced from a center <NUM> of inner glass region <NUM>. In <FIG>, the inner glass region <NUM> includes a marker <NUM>. It should be appreciated that one or more markers may be employed to assist with identifying the alignment of the core regions <NUM>. The marker <NUM> is shown located at a symmetric position with respect to a pair of the core regions <NUM> in <FIG>, and is shown located adjacent to or closer to one core region <NUM> in <FIG> to mark that particular core region. The marker <NUM> may be employed to determine the alignment of the core regions <NUM> for interconnection with other fibers or connection devices. The marker <NUM> may be made of a fluorine-doped glass having a refractive index that is lower than that of silica.

The multicore optical fiber <NUM> includes an outer coating layer <NUM> which surrounds and encapsulates the inner glass region <NUM>. The outer coating layer <NUM> is shown in <FIG> as having a primary or inner coating layer <NUM> that immediately surrounds the inner glass region <NUM> and a secondary or outer coating layer <NUM> that immediately surrounds the primary coating layer <NUM>. The coating layer <NUM> may further include a tertiary layer <NUM> (e.g., ink layer) optionally surrounding or directly adjacent to the secondary coating layer <NUM>.

The coating layer <NUM> has a ratio of the thickness of the secondary coating layer <NUM> to the thickness of the primary coating layer in the range of <NUM> to <NUM>, according to one example. According to other examples, the ratio of the secondary coating layer thickness to the primary coating layer thickness may be in the range of <NUM> to <NUM>, more particularly in the range of <NUM> to <NUM>, and more particularly in the range of <NUM> to <NUM>. The ratio of the secondary coating layer thickness to the primary coating layer thickness within the range of <NUM> to <NUM> and the reduced thickness coating layer <NUM> advantageously aids in a desirable goal in reducing signal cross-talk between core regions <NUM> in the multicore optical fiber <NUM> and leakage of signal from the fiber cores to the outside of the multicore optical fiber <NUM>.

The primary coating layer <NUM> may be made of a known primary coating composition. For example, the primary coating composition may have a formulation listed below in Table <NUM> which is typical of commercially available primary coating composition.

where the oligomeric material may be prepared from H12MDI, HEA, and PPG4000 using a molar ratio n:m:p=<NUM>:<NUM>:<NUM>, H12MDI is <NUM>,<NUM>'-methylenebis(cyclohexyl isocyanate) (available from Millipore Sigma), HEA is <NUM>-hydroxyethylacrylate (available from Millipore Sigma), PPG4000 is polypropylene glycol with a number average molecular weight of about <NUM>/mol (available from Covestro), SR504 is ethoxylated(<NUM>)nonylphenol acrylate (available from Sartomer), NVC is N-vinylcaprolactam (available from Aldrich), TPO (a photoinitiator) is (<NUM>,<NUM>,<NUM>-trimethylbenzoyl)-diphenyl phosphine oxide (available from BASF), Irganox® <NUM> (an antioxidant) is benzenepropanoic acid, <NUM>,<NUM>-bis(<NUM>,<NUM>-dimethylethyl)-<NUM>-hydroxythiodi-<NUM>,<NUM>-ethanediyl ester (available from BASF), <NUM>-acryloxypropyl trimethoxysilane is an adhesion promoter (available from Gelest), and pentaerythritol tetrakis(<NUM>-mercaptopropionate) (also known as tetrathiol, available from Aldrich) is a chain transfer agent. The concentration unit "pph" refers to an amount relative to a base composition that includes all monomers, oligomers, and photoinitiators. For example, a concentration of <NUM> pph for Irganox® <NUM> corresponds to <NUM> Irganox <NUM> per <NUM> combined of oligomeric material, SR504, NVC, and TPO.

The secondary coating layer <NUM> may be made of a known secondary coating composition. The secondary coating may be prepared from a composition that exhibits high Young's modulus. Higher values of Young's modulus may represent improvements that make the secondary coating prepared for the coating composition better suited for small diameter optical fibers. More specifically, the higher values of Young's modulus enable use of thinner secondary coatings on optical fibers without sacrificing performance. Thinner secondary coatings reduce the overall diameter of the optical fiber and provide higher fiber counts in cables of a given cross-sectional area. The Young's modulus of secondary coatings prepared as the secondary coating composition may be equal to or greater than <NUM> MPa, more particularly about <NUM> MPa or greater, or about <NUM> MPa or greater and about <NUM> MPa or less or about <NUM> MPa or less. The results of tensile property measurements prepared from various curable secondary compositions are listed below in Table <NUM>.

Secondary Coating Compositions. Representative in curable secondary coating compositions are listed below in Table <NUM>.

SR601 is ethoxylated (<NUM>) bisphenol A diacrylate (a monomer). SR602 is ethoxylated (<NUM>) bisphenol A diacrylate (a monomer). SR349 is ethoxylated (<NUM>) bisphenol A diacrylate (a monomer). Irgacure® <NUM> is bis(<NUM>,<NUM>-dimethoxybenzoyl)-<NUM>,<NUM>,<NUM>-trimethylpentylphosphine oxide (a photoinitiator).

A comparative curable secondary coating composition (A) and a representative curable secondary coating composition SB within the scope of the disclosure are listed in Table <NUM>.

PE210 is bisphenol-A epoxy diacrylate (available from Miwon Specialty Chemical, Korea), M240 is ethoxylated (<NUM>) bisphenol-A diacrylate (available from Miwon Specialty Chemical, Korea), M2300 is ethoxylated (<NUM>) bisphenol-A diacrylate (available from Miwon Specialty Chemical, Korea), M3130 is ethoxylated (<NUM>) trimethylolpropane triacrylate (available from Miwon Specialty Chemical, Korea), TPO (a photoinitiator) is (<NUM>,<NUM>,<NUM>-trimethylbenzoyl)diphenyl phosphine oxide (available from BASF), Irgacure® <NUM> (a photoinitiator) is <NUM>-hydroxycyclohexyl-phenyl ketone (available from BASF), Irganox® <NUM> (an antioxidant) is benzenepropanoic acid, <NUM>,<NUM>-bis(<NUM>,<NUM>-dimethylethyl)-<NUM>-hydroxythiodi-<NUM>,<NUM>-ethanediyl ester (available from BASF). DC190 (a slip agent) is silicone-ethylene oxide/propylene oxide copolymer (available from Dow Chemical). The concentration unit "pph" refers to an amount relative to a base composition that includes all monomers and photoinitiators. For example, for secondary coating composition A, a concentration of <NUM> pph for DC-<NUM> corresponds to <NUM> DC-<NUM> per <NUM> combined of PE210, M240, M2300, TPO, and Irgacure® <NUM>.

Secondary Coating-Properties. The Young's modulus, tensile strength at break, and elongation at break of secondary coatings made from secondary compositions A, KB and SB were measured.

Secondary Coating-Properties-Measurement Techniques. Properties of secondary coatings were determined using the measurement techniques described below.

Tensile Properties. The curable secondary coating compositions were cured and configured in the form of cured rod samples for measurement of Young's modulus, tensile strength at yield, yield strength, and elongation at yield. The cured rods were prepared by injecting the curable secondary composition into Teflon® tubing having an inner diameter of about <NUM> (<NUM>"). The rod samples were cured using a Fusion D bulb at a dose of about <NUM> J/cm2 (measured over a wavelength range of <NUM>-<NUM> by a Light Bug model IL390 from International Light). After curing, the Teflon® tubing was stripped away to provide a cured rod sample of the secondary coating composition. The cured rods were allowed to condition for <NUM>-<NUM> hours at <NUM>° C and <NUM>% relative humidity before testing. Young's modulus, tensile strength at break, yield strength, and elongation at yield were measured using a Sintech MTS Tensile Tester on defect-free rod samples with a gauge length of <NUM>, and a test speed of <NUM>/min. Tensile properties were measured according to ASTM Standard D882-<NUM>. The properties were determined as an average of at least five samples, with defective samples being excluded from the average.

The results show that secondary coatings prepared from compositions SB, SC, and SD exhibited higher Young's modulus than the secondary coating prepared from comparative composition A. Secondary coatings with high Young's modulus as disclosed herein may be better suited for small diameter optical fibers. More specifically, a higher Young's modulus enables use of thinner secondary coatings on optical fibers, thereby enabling smaller fiber diameters without sacrificing performance. Thinner secondary coatings reduce the overall diameter of the optical fiber and provide higher fiber counts in cables of a given cross-sectional area.

The primary coating layer <NUM> may have a Young's modulus of less than, or equal to, <NUM> MPa and a Tg (glass transition temperature) of less than, or equal to, -<NUM>, and the secondary coating layer <NUM> may have a Young's modulus of <NUM> MPa, or more, and a Tg of <NUM>, or more.

The inner glass region <NUM> has an overall cross-sectional diameter Dg which may be in the range of <NUM>-<NUM> microns. The outer coating layer <NUM> may have a thickness in the range of <NUM>-<NUM> microns, or in the range of <NUM>-<NUM> microns, or in the range from <NUM>-<NUM> microns. The primary coating layer <NUM> may have a thickness in the range of <NUM>-<NUM> microns, or in the range from <NUM>-<NUM> microns, or in the range from <NUM>-<NUM> microns. The secondary coating layer <NUM> may have a thickness in the range of <NUM>-<NUM> microns, or in the range from <NUM>-<NUM> microns, or in the range from <NUM>-<NUM> microns. The optional tertiary coating layer <NUM> may have a thickness equal to or less than <NUM> microns, more particularly equal to or less than <NUM> microns, and more particularly in the range of <NUM>-<NUM> microns. The coated multicore optical fiber <NUM> has an overall fiber diameter Df equal to or less than <NUM> microns. More specifically, the overall diameter Df may be in the range of <NUM>-<NUM> microns, or in the range of <NUM>-<NUM> microns, or in the range of <NUM>-<NUM> microns.

Each core region <NUM> may be formed of germania-doped silica or other suitable glass and may have a fluorine-doped silica trench, wherein the trench volume of the fluorine-doped silica trench is greater than, or equal to, <NUM>% Δ microns<NUM>. The common outer cladding <NUM> may be made of silica or fluorine-doped silica or other suitable glass. It should be appreciated that the inner glass region <NUM> may be formed from a preform drawn at an elevated temperature (e.g., temperature of about <NUM>) in a furnace. The outer coating layer <NUM>, including one or more of the primary coating layer <NUM>, secondary coating layer <NUM> and tertiary coating layer <NUM>, may be applied after the uncoated optical fiber exits the furnace and is cooled.

The multicore optical fiber <NUM> shown in <FIG> includes seven (<NUM>) core regions <NUM> including a central core region <NUM> at the center of the multicore optical fiber <NUM> and six (<NUM>) evenly spaced core regions <NUM> generally circularly-spaced an equal distance from the central core region <NUM>. A marker <NUM> is shown located in a symmetric position between two core regions <NUM>. The marker <NUM> may have a diameter in the range of <NUM> to <NUM> microns, move particularly in the range of <NUM> to <NUM> microns, and more particularly in the range of <NUM> to <NUM> microns. In this example, the core regions <NUM> may each have a radius R in the range of <NUM>-<NUM> microns, for example, which may be smaller than the radius of the four core region having a radius R of about <NUM> microns in the examples shown in <FIG>. The multicore optical fiber <NUM> is thereby able to include a larger number of core regions <NUM> within a multicore optical fiber <NUM> having an overall diameter Df equal to or less than <NUM> microns. It should be appreciated that the multicore optical fiber <NUM> may include more or less core regions <NUM> according to other examples. In one example, the number of core regions <NUM> may be in the range of <NUM>-<NUM>. By employing a thin outer coating layer <NUM>, a greater number of core regions <NUM> may be employed. By employing a trench within each of the core regions <NUM>, signal cross-talk and signal interference between core regions <NUM> advantageously may be sufficiently prevented.

Each core region <NUM> has a trench-assisted refractive index design profile having a mode field diameter of <NUM> microns, or more, at a wavelength of <NUM>, a cable or fiber cut-off wavelength of <NUM> or less and zero dispersion wavelength of <NUM> or less. The trench volume of the trench in each core region <NUM> is <NUM>% Δ microns<NUM> or more, and <NUM>% Δ microns<NUM> or less. The signal cross-talk at <NUM> per <NUM> is -30dB or less and more preferably -40dB or less, and even more preferably -50dB or less.

The outer cladding OCi can have a trench volume of about <NUM>%Δ-square micrometers, or more. The outer cladding OCi can have a trench volume of about <NUM>%Δ-square micrometers, or more, about <NUM>%Δ-square micrometers, or more, or about <NUM>%Δ-square micrometers, or more. The outer cladding OCi can have a trench volume of about <NUM>%Δ-square micrometers or less, about <NUM>%Δ-square micrometers or less, about <NUM>%Δ-square micrometers or less, or about <NUM>%Δ-square micrometers or less. The outer cladding OCi can have a trench volume of from about <NUM>%Δ-square micrometers to about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers to about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers to about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers to about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers to about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers to about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers to about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers to about <NUM>%Δ-square micrometers, or about <NUM>%Δ-square micrometers to about <NUM>%Δ-square micrometers. For example, the outer cladding OCi can have a trench volume of about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>% A-square micrometers, about <NUM>%Δ-square micrometers, about <NUM>%Δ-square micrometers, or any trench volume between these values. Each outer cladding OCi can have the same or different trench volume. The trench volume of the outer cladding OCi can be determined as described above.

The multicore optical fiber <NUM> can be characterized by crosstalk between adjacent cores Ci of equal to or less than -<NUM> dB, as measured for a <NUM> length of the multicore optical fiber <NUM> operating at <NUM>. In some aspects, the multicore optical fiber <NUM> can be characterized by crosstalk between adjacent cores Ci of equal to or less than -<NUM> dB, as measured for a <NUM> length of the multicore optical fiber <NUM>. In some aspects, crosstalk between adjacent cores Ci is ≤ - <NUM> dB, ≤ -<NUM> dB, ≤ -<NUM> dB, ≤ -<NUM> dB, or ≤ -<NUM> dB, as measured for a <NUM> length of the multicore optical fiber <NUM> operating at <NUM>. The crosstalk can be determined based on the coupling coefficient, which depends on the design of the core and a distance between two adjacent cores, and Δβ, which depends on a difference in β values between the two adjacent cores. For two cores placed next to each other, assuming the power launched into the first core is P<NUM>, using coupled mode theory and considering the perturbations along the fiber, the power coupled to the second core, P<NUM>, can be determined using the following equation: <MAT>.

The crosstalk between the two cores grows linearly in the linear scale, but does not grow linearly in the dB scale. As used herein, crosstalk performance is reported for a <NUM> length of optical fiber. However, crosstalk performance can also be represented with respect to alternative optical fiber lengths, with appropriate scaling. For optical fiber lengths other than <NUM>, the crosstalk between cores can be determined using the following equation: <MAT> For example, for a <NUM> length of optical fiber, the crosstalk can be determined by adding "-<NUM> dB" to the crosstalk value for a <NUM> length optical fiber. For a <NUM> length of optical fiber, the crosstalk can be determined by adding "-<NUM> dB" to the crosstalk value for a <NUM> length of optical fiber.

In some examples, the core-to-core separation distance S is greater than, or equal to, <NUM> microns. In other examples, the core-to-core separation distance S is greater than, or equal to, <NUM> microns. In still further examples, the core-to-core separation distance S is greater than, or equal to, <NUM> microns.

In some examples, the minimum core region edge to fiber edge distance E (<FIG>) is greater than, or equal to, <NUM> microns, where the distance E is measured from the center of the core region <NUM> to the closest point on the outside edge of the inner glass region <NUM>. In other examples, the minimum core region edge to fiber edge distance E is greater than, or equal to, <NUM> microns.

In some examples, the outer trench radius is between <NUM> microns and <NUM> microns. In other examples, the outer trench radius is between <NUM> microns and <NUM> microns. The fiber <NUM> has an overall diameter Df measured across the fiber coating of less than, or equal to, <NUM> microns. In some examples, the coating layer outer diameter Df is less than, or equal to, <NUM> microns. In yet other examples, the coating layer outer diameter Df is less than, or equal to, <NUM> microns.

The coating layer <NUM> which is comprised of the primary coating layer <NUM>, secondary coating layer <NUM> and an optional tertiary layer <NUM> provides a puncture resistant coating for the multicore optical fiber <NUM>. The primary coating layer <NUM> may have an elastic modulus of less than, or equal to, <NUM> MPa and Tg (glass transition temperature) of less than, or equal to, -<NUM>. The secondary coating layer <NUM> may have a Young's modulus of <NUM> MPa, or more, and Tg of <NUM>, or more. In some examples, the puncture resistance of the fiber <NUM> is <NUM>, or more, and in other examples, the puncture resistance of the fiber <NUM><NUM>, or more.

The puncture resistance of secondary coatings suitable for the multicore optical fiber <NUM> for different combinations of secondary coating cross-section area and elastic modulus is shown in <FIG>. The cross-sectional area of the secondary coating layer corresponds to the area defined by the thickness of the secondary coating layer; that is, the area between an inner radius of the secondary coating layer and an outer radius of the secondary coating layer. Considering ratio of secondary coating layer thickness to primary coating layer thickness to be <NUM>, one gets secondary coating layer area of <NUM> micron<NUM> for a fiber coating diameter of <NUM> microns and <NUM> microns<NUM> for a fiber coating diameter of <NUM> microns. As seen, the secondary coating layer for use with multicore optical fiber <NUM> exhibits enhanced puncture resistance with increasing modulus of the secondary coating layer. The puncture resistance of the secondary coating layer is expressed herein in terms of a puncture load. The puncture load can be determined by a compressive test where the material is compressed by a probe or other type of device until the material ruptures. The puncture load of the secondary coating layer of multicore optical fiber <NUM> may be <NUM>, or more, <NUM> or more, <NUM>, or more, <NUM> or more, or <NUM> or more, for the thicknesses of the secondary coating layer disclosed herein.

Puncture Resistance of Secondary Coating. Puncture resistance measurements were made on samples that included a glass fiber, a primary coating, and a secondary coating. The glass fiber had a diameter of <NUM>. The primary coating was formed from the reference primary coating composition listed in Table <NUM> below. Samples with various secondary coatings were prepared as described below. The thicknesses of the primary coating and secondary coating were adjusted to vary the cross-sectional area of the secondary coating as described below. The ratio of the thickness of the secondary coating to the thickness of the primary coating was maintained at about <NUM> for all samples.

The puncture resistance was measured using the technique described in the article entitled "<NPL>). A summary of the method is provided here. The method is an indentation method. A <NUM>-centimeter length of optical fiber was placed on a <NUM>-thick glass slide. One end of the optical fiber was attached to a device that permitted rotation of the optical fiber in a controlled fashion. The optical fiber was examined in transmission under 100x magnification and rotated until the secondary coating thickness was equivalent on both sides of the glass fiber in a direction parallel to the glass slide. In this position, the thickness of the secondary coating was equal on both sides of the optical fiber in a direction parallel to the glass slide. The thickness of the secondary coating in the directions normal to the glass slide and above or below the glass fiber differed from the thickness of the secondary coating in the direction parallel to the glass slide. One of the thicknesses in the direction normal to the glass slide was greater and the other of the thicknesses in the direction normal to the glass slide was less than the thickness in the direction parallel to the glass slide. This position of the optical fiber was fixed by taping the optical fiber to the glass slide at both ends and is the position of the optical fiber used for the indentation test.

Indentation was carried out using a universal testing machine (Instron model 5500R or equivalent). An inverted microscope was placed beneath the crosshead of the testing machine. The objective of the microscope was positioned directly beneath a <NUM>° diamond wedge indenter that was installed in the testing machine. The glass slide with taped fiber was placed on the microscope stage and positioned directly beneath the indenter such that the width of the indenter wedge was orthogonal to the direction of the optical fiber. With the optical fiber in place, the diamond wedge was lowered until it contacted the surface of the secondary coating. The diamond wedge was then driven into the secondary coating at a rate of <NUM>/min and the load on the secondary coating was measured. The load on the secondary coating increased as the diamond wedge was driven deeper into the secondary coating until puncture occurred, at which point a precipitous decrease in load was observed. The indentation load at which puncture was observed was recorded and is reported herein as grams of force. The experiment was repeated with the optical fiber in the same orientation to obtain ten measurement points, which were averaged to determine a puncture resistance for the orientation. A second set of ten measurement points was taken by rotating the orientation of the optical fiber by <NUM>°.

Several fiber samples with each of the three secondary coating layers are shown. Each fiber sample included a glass fiber with a diameter of <NUM>, a primary coating layer formed from the example primary coating composition disclosed herein, and one of three secondary coating layers with different cross-section areas and elastic modulus. The thicknesses of the primary coating layer and secondary coating layer were adjusted to vary the cross-sectional area of the secondary coating layer as shown in <FIG>. The ratio of the thickness of the secondary coating layer to the thickness of the primary coating layer was maintained at about <NUM> for all samples.

Fiber samples with a range of thicknesses were prepared for each of the secondary coating layers to determine the dependence of puncture load on the thickness of the secondary coating. One strategy for achieving higher fiber count in cables is to reduce the thickness of the secondary coating layer. As the thickness of the secondary coating layer is decreased, however, its performance diminishes and its protective function is compromised. Puncture resistance is a measure of the protective function of a secondary coating layer. A secondary coating layer with a high puncture resistance withstands greater impact without failing and provides better protection for the inner glass region <NUM> of the multicore optical fiber <NUM>.

The puncture load as a function of cross-sectional area for the three coatings is shown in <FIG>. Cross-sectional area is selected as a parameter for reporting puncture load because an approximately linear correlation of puncture load with cross-sectional area of the secondary coating was observed. The three traces show the approximate linear dependence of puncture load on cross-sectional area for the secondary coating.

The higher modulus traces show an improvement in puncture load for high cross-sectional areas. The improvement, however, diminishes as the cross-sectional area decreases. At a cross-sectional area of <NUM><NUM>, for example, the puncture load of the secondary coating layer obtained from secondary coating layer having a modulus of <NUM> MPa becomes approximately equal to the puncture load of the secondary coating layer having a modulus of <NUM> MPa and the increase in puncture load of the secondary coating layer with a modulus of <NUM> MPa relative to the secondary coating layers having moduli of <NUM> MPa and <NUM> MPa becomes smaller than the increase observed at higher cross-sectional areas.

The puncture load of a secondary coating layer having a Young's modulus of at least <NUM> MPa at a cross-sectional area of about <NUM><NUM> is greater than, or equal to, <NUM>. The puncture load of a secondary coating layer having a Young's modulus of at least <NUM> MPa at a cross-sectional area of about <NUM><NUM> is greater than, or equal to, <NUM>. The puncture load of a secondary coating layer having a Young's modulus of at least <NUM> MPa at a cross-sectional area of <NUM><NUM> is greater than, or equal to, <NUM>. The puncture load of a secondary coating layer having a Young's modulus of at least <NUM> MPa at a cross-sectional area of <NUM><NUM> is greater than, or equal to, <NUM>. The puncture load of a secondary coating layer having a Young's modulus of <NUM> MPa is greater than, or equal to, <NUM> for a cross-sectional area of <NUM><NUM> and greater. Examples include secondary coatings having any combination of the foregoing puncture loads.

One example of a multicore optical fiber <NUM> having four core regions <NUM> arranged in a <NUM> x <NUM> array, as shown in <FIG>, is shown in <FIG> having a refractive index design profile as seen in <FIG>. In this example, each core region <NUM> is shown having a radius r<NUM> extending from <NUM> to about <NUM> microns and an outer cladding extending from about <NUM> microns to <NUM> microns embedded in a common cladding. For all examples disclosed herein, radial positions within a core region <NUM> are defined with respect to the centerline of the core region. That is, the zero of radial position corresponds to the centerline (or cross-sectional center) of each core region and radial position within each core region is defined with respect to its centerline. The core region <NUM> has a refractive index profile that includes a germania-doped silica core having a radius r<NUM> of about <NUM> microns, an inner cladding extending from a radius of about <NUM> microns to a radius r<NUM> of about <NUM> microns and a fluorine-doped silica trench extending from a radius of about <NUM> microns to a radius r<NUM> of about <NUM> microns. The trench shown in this example is a generally square-trench having a rectangular trench profile. The trench volume of the trench in the core region is greater than <NUM>% Δ microns<NUM>. <FIG> shows two-dimensional measurement data of a particular cross-section at a wavelength of <NUM> for the multicore optical fiber <NUM> of this example. In this example, the marker is not shown and three samples of the multicore optical fiber <NUM> were measured at three different fiber lengths, labeled Samples <NUM>-<NUM>, shown in Table <NUM> below.

In Table <NUM>, the optical properties of the <NUM> x <NUM> (four) arrangement of core regions of an exemplary multicore optical fiber <NUM>, with each core region having the refractive index design profile as seen in <FIG>, are illustrated. Sample <NUM> has a length of <NUM> meters, Sample <NUM> has a length of <NUM> meters, and Sample <NUM> has a length of <NUM> meters. The cable cut-off wavelength for each of the four core regions, the mode field diameter (MFD) at <NUM> and the MFD at <NUM> were measured for each of the four individual core regions, labeled core <NUM>, core <NUM>, core <NUM> and core <NUM>. The spectral attenuation in dB/km at a wavelength of <NUM>, optical time domain reflectometer (OTDR) and polarization mode dispersion (PMD) (ps/nm/km) were measured at various wavelengths including <NUM> and <NUM>. The zero dispersion wavelength referred to as Lambda Zero (nm) and the polarization mode dispersion (PMD) slope (ps/nm/km) at a wavelength of <NUM> for each of the four core regions were also measured. Cross-talk measurements on the four core regions of the multicore optical fiber <NUM> at wavelengths of <NUM> and <NUM> with each core region having a refractive index design profile as seen in <FIG> were measured and are shown below in Table <NUM>.

As seen in Table <NUM>, the cross-talk measurements on the four core regions at <NUM> and <NUM> for the multicore optical fiber with each core-portion having the refractive index design profile shown in sample <NUM> in Table <NUM> and <FIG> are listed. The cross-talk measurements for each of the cores <NUM>-<NUM> demonstrate low cross-talk performance. This is due in part to the core region spacing and the trench which confines the light and shields it from interference and from leaking into the cladding.

Relative refractive index design profiles of three examples <NUM>-<NUM> of the multicore optical fiber having exemplary trench assisted core regions, an MFD at a wavelength of <NUM> of greater than <NUM> microns and trench volumes greater than <NUM>% Δ microns<NUM> are shown in <FIG>. In each of examples <NUM>-<NUM>, the refractive index design profile reflects a generally rectangular trench formed in the core region. In example <NUM>, the trench is formed at a radius of about <NUM> microns to <NUM> microns. In example <NUM>, the trench is likewise formed at a radius of approximately <NUM> microns to <NUM> microns and extends deeper than in example <NUM>. In example <NUM>, the trench is formed at about <NUM> microns to <NUM> microns and is shallower than the trenches formed in examples <NUM> and <NUM>. Each fiber had a common outer cladding surrounding the core regions. Various parameters of the multicore optical fibers shown in examples <NUM>-<NUM> are listed in Table <NUM> below.

As can be seen in Table <NUM> above, the trench assisted core region designs of the multicore optical fibers having an MFD at <NUM> of greater than <NUM> microns and a trench volume greater than <NUM>% Δ microns<NUM> are illustrated.

Referring to <FIG>, the refractive index design profile for trench assisted core regions in multicore optical fibers having an MFD at <NUM> of greater than <NUM> microns, and trench volumes greater than <NUM>% Δ microns<NUM> are shown according to examples <NUM> and <NUM>. In example <NUM>, a generally rectangular trench is formed in the core region. In example <NUM>, the trench is shown by a depressed region dropping around a radius of about <NUM> microns to about <NUM> microns in a generally rectangular pattern. In example <NUM>, the trench is formed at a radius of about <NUM> microns to about <NUM> microns. The common outer cladding extends beyond the radius of about <NUM> microns. Various parameters were taken for the exemplary trench assisted core region designs in examples <NUM> and <NUM> and are shown in Table <NUM> below.

As can be seen in Table <NUM>, the examples <NUM> and <NUM> trench assisted core region designs and multicore optical fiber has an MFD at <NUM> greater than <NUM> microns and trench volumes greater than <NUM>% Δ microns<NUM> are shown.

Referring to <FIG>, a multicore optical fiber relative refractive index design profile is shown, according to example <NUM>, having a high alpha core region and rectangular trench design extending from a radius of about <NUM> microns to <NUM> microns. In <FIG>, the relative refractive index design profile for example <NUM> has a graded index alpha core region and a rectangular trench design extending from a radius of about <NUM> microns to about <NUM> microns. In <FIG>, the relative refractive index design profile for example <NUM> has a high alpha core region and a triangular trench design. The triangular trench design shows the trench formed along a ramped angle line that decreases from a radius of about <NUM> microns to about <NUM> microns. In <FIG>, a relative refractive index design profile is shown with a graded index alpha core region and a triangular trench design extending on a decreasing ramp from a radius of about <NUM> microns to about <NUM> microns in example <NUM>. Optical fiber design and optical properties of the fibers disclosed in each of examples <NUM>-<NUM> were calculated and are listed in Table <NUM> below.

The optical fiber design and optical properties of the multicore optical fiber disclosed in examples <NUM>-<NUM> are shown in Table <NUM>.

Claim 1:
A multicore optical fiber (<NUM>) comprising:
an inner glass region (<NUM>) having a plurality of core regions (<NUM>) surrounded by a common outer cladding (<NUM>), the inner glass region (<NUM>) further having at least one marker (<NUM>) and an outer diameter in the range of <NUM> microns and <NUM> microns, wherein each core region (<NUM>) is comprised of a germania-doped silica core and a fluorine-doped silica trench, wherein a trench volume of the fluorine-doped silica trench is greater than, or equal to, <NUM>% Δ micron<NUM>; and
an outer coating layer (<NUM>) surrounding the inner glass region (<NUM>), wherein the outer coating layer (<NUM>) comprises a primary coating layer (<NUM>) and a secondary coating layer (<NUM>) surrounding the primary coating layer (<NUM>), and wherein a ratio of a secondary coating layer (<NUM>) thickness to a primary coating layer (<NUM>) thickness is in a range of <NUM> to <NUM>, the outer coating layer (<NUM>) having a diameter equal to or less than <NUM> microns, wherein each core region (<NUM>) has a mode field diameter greater than, or equal to, <NUM> microns at <NUM>, a cable cutoff wavelength of <NUM>, or less, and a zero dispersion wavelength of <NUM>, or less.