Abstract:
A method is provided for attaching one or more optical fibers to a retaining device. The method includes: applying a fluid to a through hole in a retaining device; disposing an optical fiber proximate an end of the through hole; developing a differential pressure in the fluid across the through hole; drawing a portion of the optical fiber into the through hole using a force associated with said differential pressure.

Description:
BACKGROUND  
         [0001]    The present invention relates to optical fibers, and more particularly, to a method for attaching one or more optical fibers to a retaining device.  
           [0002]    In practical fiber optic systems, optical fibers may be secured within retaining devices such as capillary tubes or multi-fiber array substrates. The assembly of the optical fibers to these and other retaining devices typically requires manual insertion of the optical fiber within the retaining device. The standard processes for assembly of multi-fiber arrays and fiber capillaries can be described in further detail with reference to FIG. 1 and FIG. 2, respectively.  
           [0003]    Referring to FIG. 1, a cross-sectional, perspective view is provided for illustrating a typical multi-fiber array  100 . Two substrates, upper and lower substrates  102 ,  104  are stacked, and multiple optical fibers  106  are arranged in parallel between the two substrates  102 ,  104 . As shown in FIG. 1, the upper and lower substrates  102 ,  104  each have a surface on which V-shaped grooves  108  are formed. The grooves  108  on the bottom surface of the upper substrate  102  are respectively mated with the grooves  108  on the top surface of the lower substrate  104 . The optical fibers  106  are manually placed between the respective V-grooves  108  of the upper and lower substrates  102 ,  104  and fixed therein by adhesive  110 . Thus, proper alignment of the optical fibers  106  may be maintained by the V-grooves  108 .  
           [0004]    Referring to FIG. 2, the standard assembly process of a fiber capillary  200  can be described. First, a single fiber  202  is stripped of its plastic coating, revealing a portion of the optical fiber  202 . The stripped portion of the optical fiber  202  is cleaned and manually inserted into a hole  204  formed in the fiber capillary  200 .  
           [0005]    Because the standard methods for assembling optical fibers to retaining devices (e.g., multi-fiber array substrates and capillaries) require manual insertion of the fiber into the retaining device, these methods are slow and are subject to error and variation. Therefore, there remains a need for a method for assembling one or more optical fibers to a retaining device.  
         BRIEF SUMMARY  
         [0006]    In a first aspect of the present invention, there is provided a method for attaching one or more optical fibers to a retaining device. The method includes: applying a fluid to a through hole in a retaining device id; disposing an optical fiber proximate an end of the through hole; developing a differential pressure in the fluid across the through hole; drawing a portion of the optical fiber into the through hole using a force associated with said differential pressure. In one embodiment, the fluid is a compressible fluid, such as air. In an alternative embodiment, the fluid is an incompressible fluid, such as water. In another embodiment, the retaining device is a capillary tube.  
           [0007]    In a second aspect of the present invention, the method further includes: applying the fluid to a second through hole in the retaining device; disposing a second optical fiber proximate an end of the second through hole; developing the differential pressure in the fluid across the second through hole; and drawing a portion of the second optical fiber into the second through hole using a force associated with said differential pressure. In one embodiment, the retaining device is multi-fiber array substrate formed from an array of capillary tubes.  
           [0008]    In a third aspect of the present invention, a system for attaching one or more optical fibers to a retaining device includes: a fluid in communication with a through hole in the retaining device; and a means for developing in said fluid a differential pressure across said through hole, said differential pressure providing a force for drawing a fiber into said through hole.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    This disclosure will present in detail the following description of preferred embodiments with reference to the exemplary drawings wherein like elements are numbered alike in the several FIGURES:  
         [0010]    [0010]FIG. 1 is an exploded perspective view of a multi-fiber array of the prior art;  
         [0011]    [0011]FIG. 2 is a perspective view of a capillary tube and optical fiber of the prior art;  
         [0012]    [0012]FIG. 3 is a cross-sectional plan view of a system for inserting an optical fiber into a capillary tube;  
         [0013]    [0013]FIG. 4 is a cross-sectional plan view of the optical fiber inserted into the capillary tube;  
         [0014]    [0014]FIG. 5 is a cross-sectional plan view of a system for inserting a plurality of optical fibers into a multi-fiber array substrate; and  
         [0015]    [0015]FIG. 6 is a cross-sectional plan view of the plurality of optical fibers inserted into the multi-fiber array substrate. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    Some embodiments of the invention will now be described in detail in the following Examples. Referring to FIG. 3, a cross-sectional plan view of a system  300  for inserting an optical fiber  302  into a retaining device  304 . In the embodiment shown, retaining device  304  is a capillary tube.  
         [0017]    Optical fiber  302  includes a core  306 , with cladding  308  disposed around core  306 , and coating  310  disposed around cladding  308 . Coating  310  may be a plastic jacket, an acrylate coating or the like. A portion of coating  310  is removed to reveal cladding  308 . The stripped portion has a length “a” along the longitudinal axis of the optical fiber  302 . Optical fiber  302  may be any known fiber for use in fiber optic systems.  
         [0018]    An end  312  of fiber to be inserted in retaining device  304  may be flat cleaved or, preferably, the end  312  may be treated to increase the ease with which the fiber  302  slides into the retaining device  304 . For example, the fiber end  312  may be flat cleaved and then heated to melting so that a convex cross section is formed at the end  312 .  
         [0019]    Retaining device  304  may be a generally cylindrical structure including a through hole  314  extending along its longitudinal axis from one end surface  316  to the opposite end surface  318 . Through hole  314  has a fiber inlet end  320  positioned at end surface  316 , and an opposite end  322 , positioned at end surface  318 . Inlet end  320  and outlet end  322  may be of the same diameter; however, it is preferred that the inlet end  320  have a diameter larger than that of the outlet end  322  to ease insertion of the optical fiber  302  into the through hole  314 . In the embodiment shown, through hole  314  includes a conical portion  324  and a cylindrical portion  326 . The inside diameter of cylindrical portion  326  is selected such that it is greater than or equal to an outside diameter of the core  306  and cladding  308  of the optical fiber  302  but less than the outside diameter of the coating  310  (i.e., less than the outside diameter of the coated portion of fiber  302 ). Cylindrical portion  326  of through hole  314  has a predetermined length “b” along its centroidal axis.  
         [0020]    System  300  includes a fluid  306  in contact with the through hole  314  of retaining device  304  and at least a portion of optical fiber  302 . Fluid  306  may be a compressible fluid (e.g., air), or an incompressible fluid (e.g., water). System  300  also includes a means for developing a differential pressure in the fluid  306  across through hole  314  such that the pressure of fluid  306  proximate fiber inlet end  320  of through hole  314  is greater than the pressure of fluid  306  at the opposite end  322  of through hole  314 . In the embodiment of FIG. 3, the means for developing the differential pressure is shown as a vacuum pump  328  positioned one side of a seal  330 , which is attached to the retaining device  304 . The vacuum pump  328  evacuates fluid  306  at one side of the seal  330 , creating a pressure differential across the seal  330  and across the through hole  314 . It will be recognized that, rather than a vacuum pump located on the low pressure side of seal  330 , a positive pressure pump may be used on the high pressure side of seal  330 , or both types of pumps may be used together. Other pressurizing means may be used as well, such as diaphragms, plungers, and the like.  
         [0021]    In operation, a fluid pressure differential is created across through hole  314 , causing fluid  306  to pass through the through hole  314 . Optical fiber  302 , which is placed proximate to fiber inlet end  320  of through hole  314 , is acted on by the drag of fluid  306  passing through the through hole  314 . The force of the fluid  306  on the fiber  302  pulls the end  312  of fiber  302  into alignment with the through hole  314 . As the end  312  of the fiber  302  is drawn into the cylindrical portion  326  of the through hole  314 , the fiber  302  may plug the through hole  314 , preventing fluid  306  from passing through. With the through hole  314  plugged, the force applied by the fluid  306  on the fiber  302  in response to the differential pressure acts to draw the end  312  of fiber towards the end  322  of through hole  314 . Alternatively, if the diameter of the fiber  302  is such that fluid  306  continues to flow through the through hole  314  when end  312  of fiber  302  enters the cylindrical portion  326 , the drag of the fluid  306  on the fiber  302  will act to draw the end  312  of fiber  302  towards the end  322  of through hole  314  in response to the differential pressure. It will be appreciated that one or more of these forces may act on the fiber  302  to draw the fiber  302  into through hole  314  in response to the differential pressure. It will also be appreciated that such forces may be supplemented by forces on the fiber  302  that are not developed in response to the differential pressure.  
         [0022]    Referring to FIG. 4, the optical fiber  302  is shown inserted into the retaining device  304 . As shown in FIG. 4, the stripped portion of fiber  302  is fully inserted into the cylindrical portion  326  of the through hole  314 , and the coating  310  abuts a portion of the retaining device  304 , acting as a mechanical stop. The length “a” of the stripped portion (shown in FIG. 3) determines the amount of fiber  302  that is drawn into retaining device  304 .  
         [0023]    The method applied by system  300  for inserting an optical fiber  302  into a retaining device  304  allows optical fiber  302  to be inserted in an automated manner. Because the method can be automated, it allows the assembly to be made faster and subject to less error and variation than is possible with manual assembly methods.  
         [0024]    Referring to FIG. 5, system  300  is applied to insert a plurality of optical fibers  302  into a retaining device  500 . In the embodiment shown in FIG. 6, retaining device  500  is a multi-fiber array substrate comprising an array of capillary tubes. Retaining device  500  is a structure having a plurality of through holes  314  disposed therein and extending from a surface  502  to an opposing surface  504 . Each through hole  314  and optical fiber  302  are configured substantially as described above with reference to FIG. 3 and FIG. 4.  
         [0025]    In operation, each optical fiber  302  is placed proximate to a fiber inlet end  320  of a corresponding through hole  314 . A fluid pressure differential is created across seal  330 , thus creating a pressure differential across through hole  314 . Each fiber  302  is drawn into a corresponding through hole  314  under a force responsive to the differential pressure applied across the through hole  314 , as described with reference to FIG. 3 and FIG. 4 hereinabove.  
         [0026]    Referring to FIG. 6, the optical fibers  302  are shown inserted into the retaining device  500 . The stripped portion of each fiber  302  is fully inserted into the cylindrical portion  326  of the associated through hole  314 , and the coating  310  of each fiber  302  abuts a portion of the retaining device  500 , acting as a mechanical stop. The length “a” of the stripped portion (as indicated in FIG. 3) determines the amount of each fiber  302  that is drawn into retaining device  500 .  
         [0027]    The method applied by system  300  for inserting a plurality of optical fibers  302  into a retaining device  500  allows the optical fibers  302  to be inserted in an automated manner. Because the method can be automated, it allows the assembly to be made faster and subject to less error and variation than is possible with manual assembly methods.  
         [0028]    While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.