Abstract:
A mesh ( 36 ) is placed around a bundle ( 32 ) of fused glass fibers. The bundle is then immersed in a leaching bath ( 44 ). The ends of the bundle are protected from the bath fluid by furrules ( 34 ). Some of the glass of the bundle is leached out, so as to provide a flexible fiber bundle.

Description:
BACKGROUND  
         [0001]    The present invention relates to leached fiber bundles (LFBs) which are used in endoscopes and for optical signal communications, and more particularly, to improved methods of producing such LFBs with higher quality and reliability.  
           [0002]    It has been previously known to produce image conductors or guides for endoscopes or for transmitting optical signals in the form of LFBs. Such LFBs include a large number of optical fibers, which may be arranged in an ordered array, with each fiber having a small diameter, for example 10-100 microns. The LFBs may be formed by drawing a fiber bundle preform having a number of pre-arranged optic fiber preforms, in the form of glass rods and/or tubes, together with at least some leachable glass spacers located between or encapsulating each of the desired optic fiber preforms. The fiber bundle preform is drawn down to the desired size for the optical fibers, which are fused together with the leachable glass spacers as they are drawn, with the leachable glass spacers maintaining a space between the individual optic fibers. In order to form a flexible image guide, the ends of the fused optical fiber bundle are protected with a soft, etch resistant coating, and the leachable glass from the spacers is leached from the fused optical fiber bundle, typically using an acid etch bath. Once the leaching process is complete, the individual optical fibers in the middle portion of the leached optical fiber bundle are free and allow the LFB to be flexed, while the ends are still held together. Ferrules are then installed on the ends to protect the ends from damage and maintain the fibers in position. The flexible middle portion may be placed within a flexible outer sheath to prevent the individual optical fibers from being damaged.  
           [0003]    There are several problems with this prior known process. Due to the small size of the optic fibers, the individual fibers in the LFB are extremely sensitive to outside surface damage and breakage during handling, such as during removal from the etch bath and further processing, such as the installation of the end ferrules. This creates an additional expense due to the special handling required for such further operations. The optic fibers of the LFB can also suffer from damage or breakage during use in the final product or application, for example in a flexible endoscope, due to friction and abrasion between adjacent fibers as the middle, flexible portion of the LFB is flexed. This results in a loss of image definition and degradation of transmission capability. It would be advantageous to reduce the possibility of such optical fiber damage during the formation of the LFB and in the subsequent handling and production of the final product in which the LFB is utilized. It would also be advantageous to reduce production cost and provide a longer useful life for LFBs.  
         SUMMARY  
         [0004]    Briefly stated, in one aspect the present invention provides a method of manufacturing a leached fiber bundle, which includes: (a) arranging a plurality of optic fiber preforms and leachable spacers to form a fiber bundle preform; (b) heating and drawing the fiber bundle preform to obtain a drawn fiber bundle having a desired size of optic fibers within the bundle; (c) polishing the optical ends of the drawn fiber bundle; (d) coating the ends of the drawn fiber bundle with a leaching agent resistant material; (e) leaching material from the spacers from a middle portion of the drawn fiber bundle so that individual optic fibers are free in the middle portion to form a flexible leached fiber bundle; (f) applying an anti-friction powder to the free middle portion of the optic fibers in the leached fiber bundle to reduce abrasion and friction between the optic fibers during flexing of the leached fiber bundle; and (g) applying a sheath over at least the middle portion of the leached fiber bundle.  
           [0005]    In another aspect, the invention provides a method of manufacturing a leached fiber bundle with reduced damage during production by: (a) arranging a plurality of optic fiber preforms and leachable spacers to form a fiber bundle preform; (b) heating and drawing the fiber bundle preform to obtain a drawn fiber bundle having a desired size of optic fibers within the bundle; (c) installing a ferrule on each of the ends of the drawn fiber bundle; (d) polishing the optical ends of the drawn fiber bundle; (e) coating the ends of the drawn fiber bundle with a leaching agent resistant material; (f) leaching material from the spacers from a middle portion of the drawn fiber bundle so that the optic fibers are free in the middle portion to form a flexible leached fiber bundle, and preferably (g) applying an anti-friction powder to the free middle portion of the optic fibers in the leached fiber bundle to reduce abrasion and friction between the optic fibers during flexing of the leached fiber bundle; and (h) applying a sheath over at least the middle portion of the leached fiber bundle. This reduces the increased cost involved with installing a ferrule on the ends of a LFB after it has been etched, and reduces the possibility of fiber damage.  
           [0006]    In another aspect, the invention provides a method of manufacturing a leached fiber bundle with reduced potential for fiber damage by: (a) arranging a plurality of optic fiber preforms and leachable spacers to form a fiber bundle preform; (b) heating and drawing the fiber bundle preform to obtain a drawn fiber bundle having a desired size of optic fibers within the bundle; (c) polishing the optical ends of the drawn fiber bundle; (d) coating the ends of the drawn fiber bundle with a leaching agent resistant material; (e) enclosing the drawn fiber bundle with a leaching agent resistant mesh; (f) leaching material from the spacers from a middle portion of the drawn fiber bundle so that the optic fibers are free in the middle portion to form a flexible leached fiber bundle; and preferably (g) applying an anti-friction powder to the free middle portion of the optic fibers in the leached fiber bundle to reduce abrasion and friction between the optic fibers during flexing of the leached fiber bundle; and (h) applying a sheath over at least the middle portion of the leached fiber bundle.  
           [0007]    One or more of the above methods can be utilized individually or in combination in order to produce LFBs with lower cost and less damage during manufacture, as well as higher reliability in the final end product. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The foregoing summary, as well as the following detailed description of the preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements shown.  
         [0009]    [0009]FIG. 1 is a cross-sectional view of an optical fiber bundle preform used to produce the fiber bundle in accordance with the present invention.  
         [0010]    [0010]FIG. 2 is a schematic elevational view illustrating the drawing of the optical fiber bundle preform in order to form a fused optical fiber bundle.  
         [0011]    [0011]FIG. 3 is an elevational view of the fused optical fiber bundle in accordance with the present invention hasting ferrules installed on each end.  
         [0012]    [0012]FIG. 4 is an elevational view similar to FIG. 3 showing the fused optical fiber bundle of FIG. 3 wrapped in an etching material resistant mesh.  
         [0013]    [0013]FIG. 5 is an elevational view illustrating the leaching of the fused optical fiber bundle to remove the spacer material between the optic fibers to form a flexible leached fiber bundle.  
         [0014]    [0014]FIG. 6 is an elevational view, partially broken away, of the flexible leached fiber bundle with the end ferrule after the leaching process.  
         [0015]    [0015]FIG. 7 is a cross-sectional view of the flexible area of the leached fiber bundle showing an optional sheathing in accordance with the present invention taken along line  7 - 7  in FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    Certain terminology is used in the following description for convenience only and is not considered limiting. The terms “a” and “one” are defined as including one or more of the referenced item unless specifically noted. The term “array” as used herein is intended to include any type of ordered, two-dimensional arrangement of fiber ends, such as for a flexible image bundle.  
         [0017]    The invention relates to a method of manufacturing a leached fiber bundle  10 , a shown in FIG. 6, which is adapted for use as, for example, an image conductor or guide for endoscopes or for transmission of optical signals. The leached fiber bundle  10  includes a plurality of optic fibers  12  which may be as small as ten microns in diameter or smaller. As shown in FIG. 7, the leached fiber bundle  10  may be enclosed in a sheathing of protective material  14 , which is preferably a flexible polymeric material. However, the sheathing  14  is not necessary.  
         [0018]    In order to manufacture the leached fiber bundle  10 , a plurality of optic fiber preforms  20  are preferably arranged in an ordered array and spaced apart using leachable spacers  22  to form a fiber bundle preform  24 , as shown in FIG. 1. The optical fiber preforms  20  are preferably formed from high index glass cores surrounded by a lower index cladding material. The optic fiber preforms  20  are preferably arranged in rectilinear pattern with the leachable spacers  22  being used to keep the optical fiber preforms  20  spaced apart from one another. The spacers  22  are preferably tubular as shown, with the optic fiber preforms  20  being located within the spacers  22 . While the optical fiber preforms  20  and spacers  22  are shown as circular, those skilled in the art will recognize that other shapes could be utilized for the optic fiber preforms  20  and/or the spacers  22 . For example, the optic fiber preforms  20  and the spacers  22  could be rectilinear in order to hold the optical fiber preforms  20  in a predetermined spacial relation. Alternatively, the spacers  22  could be in the form of separate rods located in the spaces between the optic fiber preforms  20 .  
         [0019]    The spacers  22  are preferably formed of an acid-soluble material, such as an acid-soluble glass. However, other suitable materials can be utilized. The optic fibers preforms  20  are preferably made of an etch resistant material.  
         [0020]    As shown in FIG. 2, the fiber bundle preform  24  is preferably heated and drawn in the usual fashion by heating the fiber bundle preform  22  locally utilizing heaters  30  and pulling on the fiber bundle preform in the longitudinal direction to obtain a drawn fiber bundle  32  having a desired size and/or spacing of the optic fibers  12  within the bundle  32 . This is preferably done in a drawing tower. However, other drawing arrangements may be utilized depending upon the particular circumstances.  
         [0021]    The drawn fiber bundle  32  is preferably cut to a desired length for further processing. As shown in FIG. 3, end ferrules  34  are preferably placed over the ends and bonded and/or crimped in position. The end ferrules  34  and bonding agent are preferably made of an acid etch resistant material, or may be coated with an acid etch resistant material, if desired. Depending upon the particular application, the end ferrules  34  may be omitted or installed after leaching of the spacer material drawn fiber bundle  32 . However, this entails higher costs and has a greater probability of damaging the optic fibers  12 . An advantage of one embodiment of the present invention is to install the ferrules  34 , which could be required for a particular connector arrangement or merely as protection for the ends of the leached fiber bundle  10 , while the drawn fiber bundle  32  is still a single rigid structure in order to provide for easier handling and less damage to the optic fibers  12 .  
         [0022]    As shown in FIG. 4, it is preferred in accordance with another embodiment of the invention that a leaching resistant mesh  36  is installed over the drawn fiber bundle  32  prior to leaching the leachable material of the spacers  22  from the drawn fiber bundle  12 . The mesh  36  is preferably formed of an acid resistant polymeric material, such as polyolefine, and may be an open mesh woven tube, net or a mesh fabric material which can be held in place on the drawn fiber bundle  32  via acid etch resistant straps or bands. The specific size and shape of the mesh may be varied based upon the diameter of the optic fibers  12  and/or the glass material being utilized. The mesh  36  could be formed of a woven fabric having the-desired permeability. The mesh  36  must be open enough to allow free movement of leached material as well as the acid leaching agent therethrough.  
         [0023]    As shown in FIG. 5, the drawn fiber bundle  32  with the protected ends, which may be protected either through coating with an acid etch resistant material or via installation of the etch resistant ferrules  34 , is placed in a leaching tank  44 , which may contain, for example hydrochloric acid or any other suitable leachant, depending upon the composition of the leachable spacers  22 . The spacer rod material is leached from a middle portion of the drawn fiber bundle  32  so that individual optic fibers  12  are free in the middle portion to form the leached fiber bundle  10 .  
         [0024]    After sufficient neutralization and/or rinsing of the leached fiber bundle  10 , the leached fiber bundle  10  is ready for incorporation into an endoscope or for use as a optical signal transmission cable.  
         [0025]    In accordance with the invention, the mesh  36  helps to prevent damage to the small diameter optic fibers  12  in the middle portion of the leached fiber bundle  10 . In one aspect of the invention, a sheath, such as the sheath  14  as shown in FIG. 7, is applied over at least a portion of the leached fiber bundle  10  to provide protection for the optic fibers  12 . An anti-friction powder  40 , such as TOS-Pearls® which are available from GE Bayer Silicone or other suitable anti-friction or parting powders such as talcum powder or PTFE powder may be utilized. This anti-friction powder  40  reduces abrasion and friction between the individual fibers  12  during flexing of the leached fiber bundle  10 . This helps to prevent premature wear and breakage of the individual fibers in the leached fiber bundle  1 I which lead to degradation and loss of images or signals being transmitted through the leached fiber bundle  10 . Utilizing the anti-friction powder leads to increased product life as compared to the prior known bundles.  
         [0026]    Through the use of the methods in accordance with the present invention, it is possible to provide higher quality leached fiber bundles  12  with less damage to the individual optic fibers  12  during the manufacturing process. This produces higher yields and less scrapage due to manufacturing defects, leading to overall reduced production costs due to less rejects. Additionally, the reliability and life of the leached optic fiber bundle in use can be substantially increased.  
         [0027]    While the preferred embodiments of the invention have been described in detail, the invention is not limited to the specific embodiments described above, which should be considered as merely exemplary. Further modifications and extensions of the present invention may be developed, and all such modifications are deemed to be within the scope of the present invention as defined by the appended claims.