Patent Publication Number: US-2002012504-A1

Title: Angled fiber optic connector

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/187,186, filed Mar. 6, 2000, the entire disclosure of which is incorporated herein by reference. 
    
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002] N/A  
       BACKGROUND OF THE INVENTION  
       [0003] This invention relates to fiber optic connectors and in particular to an optical fiber connector having an angled portion.  
       [0004] It is well known that optical fibers have a larger signal bandwidth than copper conductors. As such, optical fibers are increasingly being used in present day communications systems to facilitate higher bandwidth communications and/or a larger number of users per system.  
       [0005] Optical fibers however, have the physical disadvantage of being more fragile than metallic copper wire and therefore the handling and routing of optical fibers and cables requires extra precautions. For example, there is a limit to the amount that an optical fiber may be bent or curved before degradation in the light transmission through the fiber occurs. The fiber begins to leak light from the core of the fiber due to the bend in the optical fiber. This loss of light from the optical fiber thereby increases the attenuation of the optical signals within the optical fiber. In addition, internal micromechancial stresses in the optical fiber caused by the tight bending can also physically degrade the optical fiber by reducing the amount of mechanical stress the fiber may endure prior to breaking.  
       [0006] To avoid light loss and maintain a useful longevity in a bent optical fiber, the turn typically requires a bend radius of 2 cm or more. This radius may be substantially reduced to as little as 50μ using a miniature bend. To form a miniature bend, the diameter along a length of bare fiber is reduced to as little as 1μ or less, by, for example, drawing, etching, or a combination thereof. In the reduced diameter region, the fiber conducts light by internal reflection at least partially due to the difference in index of refraction at the interface between the fiber and the surrounding environment, generally air. Thus, in this region, the fiber may be bent with no substantial light loss from the bend. See U.S. Pat. Nos. 5,138,676 and 5,452,383, the disclosures of which are incorporated by reference herein.  
       [0007] Small diameter fiber optic cables are typically terminated at each end in a connector, in a process referred to as connectorization. A connectorized cable is particularly susceptible to being damaged by being excessively bent at the point where optical fiber enters the connector beyond the bend radius of the cable where damage occurs.  
       [0008] One prior art solution to allowing connectorized cables to be used has been to include a flexible strain relief boot extending from the connector and encasing a section of the fiber optic cable. These strain relief boots are permanently attached to the fiber optic connector and are flexible enough to allow some bending of the optical fiber that is necessary for the proper routing and connection of the cable. However, the flexible strain relief boots are designed to prevent the cable from being damaged by limiting the amount of bend a cable is subjected to.  
       [0009] Even with flexible strain relief boots the installation of fiber optic cables in a junction box or to a connector panel may damage the fibers by over bending them. In many installations there may be tens or hundreds of fiber optic cables that are to be routed through junction boxes or connected to connector panels. These junction boxes and connector panels often have a limited volume of space available for the cabling process. The connectors of such fiber optic cables are commonly inserted horizontally into the junction boxes within which the connector panels are vertically oriented. The cables are often routed in a direction perpendicular to their connectors in the space between the connector panel and the external door. The door of the junction box or connector panel is also vertical and typically closes in a plane parallel to the connector panel. Typically, it is desirable for the space between the closed door and the connector panel to be as small as possible to minimize the space taken up by the junction box or connector panel. However, minimizing the space between the door and the connector panel may excessively bend the strain relief boot that encases a portion of the optical fiber thus forcing the fiber optic cable to bend excessively.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010] The present invention provides a connector that allows an optical fiber to be bent beyond the typical minimum bend radius close to the ferrule and while not increasing signal degradation due to the bend. More particularly, an angled fiber optic connector is disclosed in which a curved body portion includes an is interior passageway extending through the curved body portion and an optical fiber having a treated portion, wherein the treated portion is disposed within the interior passageway. In one aspect of the invention, the optical fiber has been treated with an annealing process to reduce the micromechanical stresses associated with bending or tightly curving an optical fiber. In another aspect of the invention, the optical fiber is treated by fusion tapering. In a further aspect of the invention, the optical fiber is treated by etching. The optical fiber can also be suspended within the internal passageway to prevent physical contact between the optical fiber and any of the interior surfaces of the passageway to prevent other optical losses.  
       [0011] The curved body portion is rigidly attached to a main body portion that includes a ferrule. The main body portion attaches to a connector adapter portion to allow mating with a complimentary connector adapter. In addition, a flexible strain relief boot may be attached to the curved body portion to provide an increased amount of strain relief. In another aspect of the angled fiber optic connector, a back body portion may be rigidly attached to the curved body portion. The back body portion may be used to facilitate attaching a flexible strain relief boot thereto using standard mating connectors.  
       [0012] Additional aspects, features and advantages of the present invention are also described in the following Detailed Description. 
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
     [0013] The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:  
     [0014] Fig. 1  is a side cross sectional view of the angled fiber optic connector;  
     [0015]FIG. 2 is a side cross sectional view of another embodiment of the angled fiber optic connector;  
     [0016]FIG. 3 is a plan view of the side surface of the bent body portion of the angled fiber optic connector in FIGS. 1 and 2; and  
     [0017]FIG. 4 is a plan view of another embodiment of the bottom surface of the bent body portion of the angled fiber optic connector in FIGS. 1 and 2 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0018] Referring to FIG. 1 an angled fiber optic connector  100  is illustrated. A fiber optic cable  112  enters a flexible boot  110  that is attached to a curved body portion  108 . Typically, the flexible boot  110  and the curved body  108  are attached using some mechanical means such as a standard jack/clip system (not shown) and/or an epoxy. The flexible boot  110  may be made of any suitably flexible material that is able to flex and bend at arbitrary angles in response to externally applied forces. The fiber optic cable  112  passes through the flexible boot  110  and is rigidly attached to the curved body portion  108  in any suitable manner, for example by using a strength member  115  and a crimp ring  116 . The outer cable layers and the jacketing material  114  of the fiber optic cable  112  are stripped free from the cable  112  leaving the optical fiber  104  free.  
     [0019] The optical fiber  104  is disposed with an interior passageway  126  of the curved body portion  108 . The optical fiber  104  is secured within the passageway  126  using an epoxy or piece of plastic at one or both ends of the interior passageway  126 .  
     [0020] A main body portion  106  is rigidly attached to the curved body portion  108 , typically using a mechanical means (not shown) and/or an epoxy. The free end  122  of the optical fiber  104  is disposed within a ferrule  102  to ensure that an accurate mating connection with a second fiber (not shown) occurs. The ferrule  102  that is rigidly attached to the main body portion  106  fits within an alignment sleeve  124  that is contained within the connector adapter  120 . The connector adapter  120  is rigidly attached to the main body  106 . Typically the main body  106  and the connector adapter  120  have some mechanical means (not shown) to rigidly secure the main body portion  106  and the connector adapter  120  together. The connector adapter  120  may be configured to mate with a panel connector, another optical fiber connector, or may be an inline component.  
     [0021] The connector adapter portion  120  may be a standard fiber optic connector design to ensure that the interface between the ferrule from the angled fiber optic connector  100  and the ferrule of a mating connector (not shown) occurs in a precise and well understood manner. This helps to ensure that the necessary optical and environmental performance of the optical connection created by the two connectors meets the applicable optical and physical standards. The connector adapter  120  may be a standard commercial optical fiber connector, which may include, but should not be limited to, a FC, SC, LC, Biconic, ST, and D 4  type optical fiber connectors. These standard fiber optic connectors also may include standard mechanical interface portions that can be used to rigidly secure the connector adapter  120  to the main body portion  106 .  
     [0022] In some connector designs, such as an LC connector, a rear body portion is attached to the front body of the connector which holds the ferrule. In an alternative of the angled fiber optic connector illustrated in FIG. 2, the curved body portion  108  is rigidly connected to a back body portion  132 , typically using a mechanical means (not shown) and/or an epoxy. Furthermore the back body portion  132  can be adapted to receive a standard jack/clip system used on a standard strain relief boot  110 .  
     [0023] The curved body portion  108  can bend or curve the optical fiber  104  beyond the radius at which internal micromechanical stresses occur in the optical fiber  104 . As discussed above, these micromechanical stresses can cause a degradation in the optical and physical performance of the optical fiber. This degradation can include increased attenuation of the optical signal, creation of other optical modes, and a reduction in the useable lifetime of the optical fiber. To prevent the optical fiber from degrading due to the bending, the fiber must be suitably treated by reducing the diameter to cause the fiber to conduct light by internal reflection as discussed above. However, the optical fiber can be further treated to reduce the amount of micromechanical stresses formed by the bending. By reducing the internal micromechanical stresses within the optical fiber, a bent optical fiber can have an optical performance and a useful lifetime that is comparable to the prior art fiber optic connectors.  
     [0024] The optical fibers  104  can be further treated using an annealing process to reduce the internal micromechanical stresses that occur within the bent or curved portion of the optical fiber. Preferably, the optical fiber annealing process includes heating the optical fiber  104  to a temperature of 1500 degrees F for a sufficient time to ensure that the necessary internal micromechanical stresses have been relieved. Typically, a few seconds at this temperature suffices to relieve the micromechanical stresses. Alternatively, the annealing process may also be carried out at a lower temperature but over a longer time period, or at a higher temperature for a shorter period of time.  
     [0025] The optical fiber  104  may be inserted and secured within the passageway  126  prior to the annealing process taking place. The heating process is typically performed prior to the curved body portion  108  being attached to the main body portion  106  and/or the flexible strain relief boot  110  or other rear body portion. Because of the high temperatures that are used, the curved body portion  108  should be fabricated from a high temperature material that is able to withstand the temperatures during processing without physically degrading. In a preferred embodiment, the curved body portion  108  can be constructed out of a ceramic material; however, other materials such as metals, filled epoxies, glass, and high temperature plastics may also be used.  
     [0026] Other methods that may be used to relieve the micromechanical stresses may be used as well. Other suitable treatments of the optical fiber  104  include fusion tapering of the curved portion of the optical fiber, etching the curved portion of the optical fiber, or a combination of fusion tapering and etching. These processes may be followed by subsequent annealing of the curved portion of the optical fiber, if necessary.  
     [0027] In addition to the micromechanical stresses causing an increase in attenuation of the optical signal, other optical losses may be caused by any physical contact between the optical fiber  104  and the interior surfaces of the passageway  126 . Any contact between the optical fiber  104  and a material having an index of refraction greater than that of air can result in light leaking from the optical fiber. This leaking light results in the degradation of the optical signal carried by the optical fiber. Light is able to leak from the optical fiber when the critical angle, which defines the angle at which total internal reflection occurs, is changed by a material physically contacting the optical fiber that has an index of refraction greater than air.  
     [0028] These other optical losses may be avoided by preventing the optical fiber  104  from physically contacting the interior surface of the passageway  126 . In one embodiment, the treated portion of the optical fiber  104  is suspended within the passageway  110  such that the optical fiber  104  does not physically contact the interior surfaces of passageway  126 . The optical fiber  104  may be suspended within the passageway  126  with sufficient tension to avoid the optical fiber drooping and coming into contact with a surface of passageway  126 . This suspension can be accomplished by securing the optical fiber  104  with a piece of plastic or epoxy on each end of the passageway  126  as the optical fiber  104  is held with sufficient tension to prevent the optical fiber from drooping. Alternatively, the optical fiber  104  may be secured at one or both ends of the passageway  126  but with less tension allowing the optical fiber  104  to droop within the passageway  126 . To allow for the optical fiber  104  to droop within the passageway, the passageway is further hollowed out in some areas in which the optical fiber  104  droops the maximum amount, to prevent the optical fiber  104  from physically contacting the interior surfaces of the passageway  126 . In one embodiment using an optical fiber  104  having a radius of 15-20 microns, the radius of the passageway  110  may be 0.75-1.0 millimeters.  
     [0029] Alternatively, an “optical signal loss penalty” may be incurred by allowing the optical fiber  104  to physically contact a portion of the interior surface in passageway  126 . The optical signal loss penalty can be determined by calculation or measurement, and the resulting degradation of the signal is included in the system optical link calculations and design. Based on the system optical link characteristics, one skilled in the art would be able to determine the loss penalty that could be incurred before system performance is degraded beyond a predetermined threshold.  
     [0030] Some existing fiber optic connectors may utilize a “floating ferrule” design in which the optical fiber  104  is rigidly attached to the ferrule  102  and the ferrule  102  spring loaded and biased with an outward force from the front end portion. In order to accommodate a floating ferrule, the jacket and strength member of the optical fiber are rigidly attached only at the interface between the curved body portion and the back body portion or the flexible strain relief boot. In this way, as the connectors contact one other, the respective ferrules are biased back within the respective main body portions  106  creating slack within the optical fiber  104 . The slack in the optical fiber  104  must be absorbed within the rigid curved connector portion  108 .  
     [0031] Therefore, in the angled fiber optic connector  100  using a floating ferrule design, the optical fiber  104  is rigidly attached both to the ferrule tip and to the curved body portion  108 . This allows the slack in the optical fiber  104  that is created by the retracting ferrule to be taken up within the passageway  126  within the curved body portion  108 . The passageway  126  can be further hollowed out to allow the slack created by the retracting optic fiber to be taken up within the passageway  126  without the optical fiber  104  physically contacting the interior surface of passageway  110 .  
     [0032] In an alternative embodiment illustrated in FIGS. 3 and 4, the passageway  126  of the curved body portion  108  can be a slot sized and dimensioned to allow the optical fiber to be contained therewithin. In the embodiment illustrated in FIG. 3, the slot or channel  304  may be on the side  302  or top  306  of the curved body portion  108 . The optical fiber  104  can be placed in the slot  304  either before or after being annealed as described above.  
     [0033] In the embodiment illustrated in FIG. 4 the slot or channel  402  may be on the bottom  308  of the curved body portion  108 . The optical fiber  104  can be placed in the slot or channel  402  and a filler material  404  such as an epoxy may be used to prevent the optical fiber from falling out of the slot or channel  402 . The filler material  404  may include a plurality of filler material  404  spaced apart from one another, leaving spaces  406 . If a slot is used, a cover such as a piece of heat shrinkable tubing (not shown) may be employed to prevent dust and debris from contacting the optical fiber  104  and causing a degradation in performance.  
     [0034] Having described the embodiments consistent with the present invention, other embodiments and variations consistent with the present invention will be apparent to those skilled in the art. Therefore, the invention should not be viewed as limited to the disclosed embodiments but rather should be viewed as limited only by the spirit and scope of the appended claims.