Abstract:
Optical fibers are inserted and bonded in a two dimensional array of feedthroughs provided by an insert having a top plate, a bottom plate and a sandwiched spacer plate. Top and bottom plate feature funnel shaped hole sections that capture the approaching fiber end during its insertion. The funnel sections terminate in narrow hole sections that tightly hold the inserted fiber ends. Having top and bottom plate spaced apart provides for high angular precision of the bonded fiber ends with minimal fabrication effort of the insert. Optical fibers may be combined in linear arrays and simultaneously inserted significantly reducing assembly efforts. The insert is attached to a fiber housing and hermetically sealed within an external housing, which features a glass plate to provide beam propagation to and from the fiber ends. An optical gel fills the gap between the insert&#39;s output face and the glass plate.

Description:
CROSS REFERENCE  
       [0001]    The present application cross references the concurrently filed U.S. patent application for a “Method and Apparatus for Applying a Gel” of Janusz Liberkowski, and the U.S. patent application Ser. No. 09/866.063, filed May 21, 2002, both of which are hereby incorporated by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to devices for holding optical fibers, and in particular to devices for holding optical fibers organized in arrays.  
         BACKGROUND  
         [0003]    Many fields of technology have benefited from the ability to transmit signals via waveguides such as optical fibers. In particular, optical fibers have enabled the construction of various types of local and long-distance communications networks. The signals propagating through an optical network are typically launched and out-coupled from individual optical fibers through their end facets. For example, in optical network components such as optical fiber switches and optical fiber cross connects, signals are out-coupled from one fiber and in-coupled into another fiber.  
           [0004]    In accordance with well-known principles of optics, light emitted from the end facet of a fiber diverges in a cone-shaped pattern determined by the numerical aperture N.A.=n sinθ max  of the fiber. In this equation n is the refractive index into which the fiber emits the light and θ max  is the half angle of the cone shaped emission pattern.  
           [0005]    In most optical networks and/or components it is important to minimize loss when connecting an optical fiber to an optical system. To accomplish this, the diverging light beams emitted by the optical fibers in the array are typically collimated and/or refocused by lenses. To effectively couple the individual fibers of a fiber array with other optical components or systems, the individual fibers and all other optical elements along the emitting and/or received light paths need to be precisely positioned and aligned. Specifically, precise alignment means that 1) light is emitted from each optical fiber at a precisely known position within the array, 2) light is emitted from each optical fiber at substantially the same angle (i.e., the optical fibers are aligned substantially parallel to each other), 3) light is emitted from each optical fiber at substantially the same distance from the collimating and/or refocusing lenses, and 4) each optical fiber has substantially the same numerical aperture.  
           [0006]    The prior art teaches aligning optical fibers in an array of V-grooves. Such arrays typically include a small number of optical fibers (e.g., up to about 64) arranged in parallel in a single plane. For example, U.S. Pat. No. 6,027,253 to Ota et al. discloses an optical fiber array including a V-groove substrate having V-grooves on which optical fibers are arranged and a fiber fix substrate for fixing the optical fibers arranged on the V-grooves. Furthermore, V-groove arrays have also been adapted to requirements that fiber arrays be hermetically sealed to prevent ambient air from entering into the package holding the fiber array. A sealed fiber array and method for its manufacture using V-grooves is taught in U.S. Pat. No. 6,215,944 to Ota et al. Additional improvements to V-groove chips for fiber arrays having a wick stop trench to prevent adhesive moving via capillary action along the length of the V-groove are discussed in U.S. Patent Application Publication 2002/0003933 to Sherrer et al.  
           [0007]    Other approaches to providing hermetically sealed packages for fibers are also known. For example, U.S. Pat. No. 6,216,939 to Thackara teaches a method for making a hermetically sealed package comprising at least one optical fiber feedthrough. The package has at least one solder perform between a sealing surface of a lid and a sealing surface of a housing. Applying pressure and heat so as to press the fiber or fibers into the solder seals the assembly. More general teaching on how to achieve fiber optic-to-metal connection seals can be found in U.S. Patent No. 5,658,364 to DeVore et al.  
           [0008]    Fiber arrays disposed on substrates with V-grooves and lodged between substrates as taught by Thackara are mostly suitable for constructing single-plane arrays. As the number of fibers increases such arrays become unwieldy. Many applications like, for example, in telecommunications are expected to require optical fiber arrays including more than one hundred (and potentially more than one thousand) optical fibers. Unfortunately, single-plane arrays are impractical for such applications. Moreover, efficient coupling of light output by an optical fiber array into another optical system becomes more difficult when aligning very large quantities of optical fibers than when dealing with only a few optical fibers.  
           [0009]    Alternative approaches have been proposed in the prior art where high precision optical fiber arrays are more specifically adapted for dealing with larger numbers of fibers and two dimensional fiber arrays. For example, U.S. Pat. No. 5,907,650 to Sherman et al. teaches a high precision optical fiber array connector and method. In a most notable embodiment, the fibers are arrayed and positioned via openings of two masks spaced by a sandwiched layer. The openings are fabricated by laser cutting. A plurality of optical fibers include fiber ends having substantially truncated conical side surfaces that extend through the openings. When the conical surfaces engage the mask opening walls, a bonding material is applied to the mask forward face and exposed tips. After curing of the bonding material, the forward face is grinded and polished such that the exposed tips are made planar with the bonding material. The invention requires conical shaping of the fiber ends. Etching techniques are described as primary conical shaping techniques. The centering of a single fiber within an opening is accomplished as a line contact between the conically shaped cladding and an opening edge, which may result in damage of the cladding and an eventual loss in alignment precision. Also, all fibers have to be held with a certain force inside the openings to assure contact between the conical cladding and the corresponding opening edge during curing of the bonding material. In cases with a high number of fibers it may be difficult to hold each individual fiber with the required force during the curing process. The conical shape of the fiber ends is required for finding the openings and for centering the fiber ends in the assembly position. Damages of the fiber ends may occur as an eventual result of failed assembly attempts. Therefore, there exists a need for a method and apparatus that provides precise alignment of optical fibers without special treatment and/or fabrication effort of the fiber ends. The present invention addresses this need.  
           [0010]    U.S. Patent Application Publication 2001/0051028 to Gutierrez et al. aims at providing a high-density fiber terminator/connector.  
           [0011]    The terminator/connector and method of making it comprise using deep reactive ion etching to etch a plurality of holes in a silicon substrate and placing fibers in the holes. The holes can be cylindrical in shape or non-cylindrical. Micro-machined kinematical alignment mechanisms or locators may be provided to position the optical fibers at the centers of the holes. The alignment mechanism includes elastic flaps concentrically placed around the assembled fibers and are intended to snuggly hold the fibers in position. Since the flaps deflect angularly a snuggly contact is questionable. Also, the flexible nature of the alignment mechanism may render it sensitive to bending momentums induced by the fibers themselves. To keep such bending moments to a minimum, pre alignment of the fibers is provided by slim conical hole sections fabricated below the flaps. Unfortunately, such slim conical hole sections result in a relatively small entry diameter making an insertion of the fiber end difficult to accomplish. Therefore, there exists a need for a structure that provides for an independent dimensioning of an insertion cone. The present invention addresses this need.  
           [0012]    Although the teachings of Sherman and et al. and Gutierrez et al. address a number of the challenges in the way of a high precision array of optical fibers, their solutions are not sufficiently precise and robust for large arrays of optical fibers. What is needed is an optical fiber array that can accommodate a large number of fibers, achieve hermetic sealing and preserve excellent alignment of the fibers including planarity, parallel alignment, relative position between the fibers as well as absolute position of fibers in the array. Furthermore, it would be highly advantageous if such array would permit tuning of the orientation of the array in the holder.  
         OBJECTS AND ADVANTAGES  
         [0013]    In view of the shortcomings of the prior art, it is an object of the present invention to provide an apparatus for holding optical fibers in an array that satisfies the requirements of high alignment precision between fibers themselves and with respect to external devices. Specifically, the device of the invention is to provide excellent planarity, parallel alignment, relative position and absolute position of the optical fibers of the array.  
           [0014]    It is another object of the invention to ensure that the device be sufficiently robust such that the precisely aligned fibers preserve their alignment over time.  
           [0015]    It is yet another object of the invention to provide for a hermetic seal between the fibers, and especially the fiber ends and the external environment.  
           [0016]    It is another object of the invention to provide the fiber housing with hermetic sealing from the external environment of the apparatus while attached to the apparatus  
           [0017]    Still another object of the invention is to provide a mechanism for tuning the orientation of the array in the device.  
           [0018]    These and other objects and advantages will become apparent upon reading the following description.  
         SUMMARY  
         [0019]    The objects and advantages of the invention are achieved with the aid of an insert for holding at least one optical fiber, and typically a large array of optical fibers. The insert has a top plate, a bottom plate and a spacer plate in the middle. An array of feedthroughs is provided by the insert for easily receiving and precisely positioning optical fibers. Each feedthrough includes two narrow hole sections on both ends of a wide hole. The wide hole is formed into the spacer plate, the narrow hole sections are fabricated in the top plate and the bottom plate. Adjacent to each narrow hole section is an expanding hole section that operates as a funnel during insertion of a fiber in the feedthrough. A fiber end is easily inserted in a feedthrough since the expanding sections capture the fiber end and center it on the narrow hole sections while the fiber end is moved forward. Consequently, a large number of fibers may be easily inserted and tightly positioned within the insert without need to particularly shape the fiber ends. Also, there is no need to hold the fiber ends in a certain position along the feedthroughs&#39; axes during the bonding of the fibers in the insert. This additionally simplifies the assembly procedure.  
           [0020]    Spacing the two narrow hole sections apart provides for two defined positions for each fiber end. The orientation of the fiber end at the level of the output face remains substantially unaffected by eventual bending of the fiber in the proximity of the insert that might occur prior to bonding the fibers. As an advantageous result, the tilting of the fiber in the two narrow hole sections is so small that may be neglected.  
           [0021]    In a preferred embodiment, the insert is employed in an apparatus designed for holding an optical fiber or an array of optical fibers. The apparatus has a fiber housing for mounting the insert. In one embodiment, the fiber housing has a front portion and the insert is mounted on the front portion. The fiber housing provides hermetic sealing from the external environment of the apparatus while attached to the apparatus.  
           [0022]    The external housing has a glass plate disposed in a plane-parallel orientation relative to the insert. Thus, when the fiber housing is placed inside the external housing the glass plate is located parallel and next to the output face. Furthermore, in order to ensure proper optical out-coupling from the optical fibers, an optical gel is interposed between the glass plate and the insert.  
           [0023]    A lens plate is positioned on top of the glass plate. The lens plate has a number of lenses arrayed in correspondence to the feedthrough array. Precise positioning of the lens plate is provided by an adjustment device that holds the lens plate while optical tests are performed. Once the optimal position of the lens plate is set, the lens plate is soldered to the external housing.  
           [0024]    The details of the invention are presented in the below description with reference to the attached drawing figures. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0025]    [0025]FIG. 1 depicts an isometric view of an insert in accordance with the invention.  
         [0026]    [0026]FIGS. 2 a ,  2   b  illustrate a cross-sectional view of a feedthrough of the insert of FIG. 1. FIG. 2 a  shows an ideal assembly condition of the insert&#39;s individual plates and a fiber end. FIG. 2 b  shows an exemplary worst-case assembly condition.  
         [0027]    [0027]FIG. 3 shows a perspective view of the insert of FIG. 1 attached to a fiber housing.  
         [0028]    [0028]FIG. 4 depicts an external housing with a glass plate.  
         [0029]    [0029]FIG. 5 shows a schematic section view of the final apparatus.  
         [0030]    [0030]FIG. 6 illustrates a lens plate and the upper portion of the external housing of FIG. 4 with the glass plate attached to it. Through the glass plate is visible the insert of the assembled fiber housing. 
     
    
     DETAILED DESCRIPTION  
       [0031]    The invention will be best understood by initially referring to an insert  10  as show in FIG. 1. Insert  10  has a top plate  20  and a bottom plate  30 . A spacer plate  40  is sandwiched between plates  20 ,  30 . All plates  20 ,  30 ,  40  are preferably made of silicon wafers or other suitable material. In the present embodiment, plates  20 ,  30  have a height  20   h  and  30   h  of about 500 μm, and spacer plate  40  has a height  40   h  of about 1,000 μm Even though this heights  20   h ,  30   h , and  40   h  have proven advantageous for the purposes of the present invention, the scope of the invention is not limited by specific values of them.  
         [0032]    The insert  10  has a number of feedthroughs  11 , which are explained in more detail in FIGS. 2 a  and  2   b . The feedthroughs  11  hold the fiber ends  58 . The insert  10  is dimensioned to provide sufficient space for a predetermined number of fiber ends  58  fixedly held preferably in rows and columns. An exemplary insert  10  may have about 30 rows and 40 columns. Minimizing the spacing between the feedthroughs  11  is limited by a minimum amount of contact area between the plates  20 ,  30 ,  40  to assure proper bonding of them. In the preferred embodiment, the spacing between individual feedthroughs  11  is about 1000 μm. The insert  10  also provides a peripheral area without feedthroughs  11 . Along this peripheral area the insert  10  is bonded with its insertion face  32  to a fiber housing  60  (see FIGS. 3, 6).  
         [0033]    Top plate  20  has an output face  21  at which optical beams are emitted and/or received by the fiber ends  58 , which are shown in FIG. 1 as extending above the output face  21  as it may be the case during an intermediate assembly step as is described further below.  
         [0034]    The plates  20 ,  30 ,  40  are bonded together in a well-known fashion. The top plate  20  is bonded with its first attaching face  22  to the top of the spacer plate  40  and the bottom plate  30  is bonded with its second attaching face  31  to the bottom of the spacer plate  40 . At the bottom of the bottom plate  30  is an insertion face  32  where the fiber ends  58  are inserted during assembly. Alignment holes  27  are fabricated in each of the plates  20 ,  30 ,  40  to provide accurate alignment prior to the well-known bonding of them.  
         [0035]    Referring now to the cross-sectional views of FIGS. 2 a  and  2   b  the elements of a single feedthrough  11  are explained in detail. In order to precisely position the fiber end  58  at the level of the output face  21  , a sufficient length of the fiber end  58  needs to be fixedly held. This is particularly important in cases, where the feedthrough  11  has to have sufficiently wide cross section(s) to provide for an easy assembly.  
         [0036]    Unfortunately, the effort and cost for fabricating precise holes increase more than proportional with the hole depth. In the present invention, this problem is addressed by providing first and second narrow hole sections  24 ,  34  positioned along the upper and lower end of the feedthrough  11 . In that way, the narrow hole sections  24 ,  34  are fabricated only with their depths  24   h ,  34   h  while a positioning relevant feedthrough height  11   h  is provided. In an exemplary embodiment, the depths  24   h ,  34   h  may be in the range between 100 μm and 200 μm and the feedthrough height  11   h  in the range between 1600 μm and 1700 μm. As can be seen in FIG. 2 b , the feedthrough height  11   h  sums from top plate height  20   h , spacer plate height  40   h  and second narrow hole height  34   h.    
         [0037]    Postioning precision includes an angular offset  50   a , which is defined as the angle between the fiber end&#39;s  58  axis  50   x  and a normal of the output face  21 . In FIG. 2 b , the offset angle  50   a  is drawn between the fiber axis  50   x  and the first hole axis  24   x , which is also normal to output face  21 . For the purpose of the present invention it is desirable to keep the angular offset  50   a  to a minimum.  
         [0038]    Since the insert  10  is fabricated from individual plates  20 ,  30 ,  40 , positioning inaccuracies between the individual plates  20  and  30  may result in an offset  11   o  between the narrow hole axes  24   x  and  34   x . The offset  11   o  eventually contributes to the angular offset  50   a . The oversize of the narrow hole sections  24 ,  34  may also contribute to the angular offset  50   a . In that context, FIG. 2 b  depicts a worst-case assembly condition where misalignment between the plates  20 ,  30  and hole oversizes add up in the most unfavorable fashion. In such case, a maximum for the angular offset  50   a  may be defined by the following Equation [1] wherein FH stands for the feedthrough height  11   h , T equals the top hole diameter  24   d , B equals the bottom hole diameter  34   d , D equals the fiber end diameter  52   d , FO equals the feedthrough offset. 11   o , and α the angular offset  50   a.   
         α= arctg ( FO+T+B− 2 D/FH )  [1] 
         [0039]    A well-known result of the angular offset  50   a  is a degradation of the optical signal propagating in and/or out of the fiber end  58 , which may be called insertion loss. The following Table A lists exemplary values for the insertion loss in dependence of the contributing elements as presented in the Equation [1]. IL represents the insertion loss in Table A. As can be seen in Table A, the second narrow section  34  may have a slightly large diameter than the first narrow section  24 . During insertion of fiber ends  58  in the first narrow section  24  the fiber ends are already pre aligned by the second narrow section  34  providing for a tighter fit of the fiber end  58  at the output face  21  without inhibiting the insertion of it.  
                                       TABLE A                       T   B   FH   FO   D   α   IL       [μm]   [μm]   [μm]   [μm]   [μm]   [degrees]   [dB]                   127.9   129.9   1510.0   6.0   125.0   0.40   0.09       127.9   129.9   1610.1   6.0   125.0   0.37   0.08       127.9   129.9   1710.0   6.0   125.0   0.35   0.07       127.9   129.9   1810.0   6.0   125.0   0.33   0.06       127.9   129.9   1910.0   6.0   125.0   0.32   0.06       127.9   129.9   2010.0   6.0   125.0   0.30   0.05                  
 
         [0040]    Efficiency of the fiber end&#39;s  58  preparation and insertion in the feedthrough  11  is the key to large numbers of fiber ends  58  assembled in a single insert  10 . Costly conical shaping of the fiber ends  58  needs to be avoided. Also, the precision with which the fiber end  58  is approached for insertion needs to be kept as low as possible. To accommodate for these needs, a first expanding section  25  is fabricated into the attachment face  22  and a second expanding section  35  is fabricated into the insertion face  32 . Both expanding sections  25 ,  35  are substantially aligned with their adjacent narrow sections  24 ,  34  such that a first through hole  23  is provided in the top plate  20  and a second through hole  33  is provided in the bottom plate  30 .  
         [0041]    The expanding sections  25 ,  35  have a funnel angle  25   a ,  35   a , which is fabricated by a wet etch operation. As is well-known in the art, the angle created by the wet etch is dependent on the crystallographic orientation of the wafer. In the present invention, preferably a wafer with 1-0-0 crystallographic orientation is used, which produces funnel angles  25   a ,  35   a  of 115°. This angle provides sufficient funnel widths  25   d ,  35   d  for given section heights  25   h ,  35   h . At the same time, the expanding sections  25 ,  35  are sufficiently steep such that the tip of the fiber end  58  may slide along their walls towards the narrow sections  24 ,  34 . The fiber tip does not require special shaping and can be inserted when approached within the widths  25   d ,  35   d.    
         [0042]    In the preferred embodiment, the cladding  51  is removed from the fiber end  58  prior to assembly and only a bare fiber  52  is inserted in the feedthrough  11 . The scope of the invention includes embodiments where the narrow hole diameters  24   d ,  34   d  are dimensioned to capture the bare fiber  52 .  
         [0043]    The central portion of the feedthrough  11  is provided by the spacer hole  41  fabricated into the spacer plate  40  with a uniform diameter  41   d  that roughly corresponds to the width  25   d . Since the hole  41  does not contribute to the positioning of the fiber end  58  , it may be fabricated with reduced precision and consequently with reduced effort and cost. Whereas narrow hole sections  24 ,  34  are fabricated with highest precision using masks and a deep reactive ion etch. Now, referring to FIG. 3 it is described in detail how the feedthrough  11  is utilized to easily assemble large arrays of fiber ends  58  on the insert  10 . The teachings presented above for a single feedthrough  11  apply to an entire feedthrough array distributed in the insert  10  as is exemplarily shown in FIGS. 1, 3. To take advantage of the reduced assembly accuracies provided by the expanding sections  25 ,  35  a number of fiber ends  58  may be arrayed prior to insertion. A flexible sheet  57  may elastically hold a number of optical fibers  50  (see FIGS. 3, 6 ) fanning out from a fiber string  54  at one end such that a number of fiber ends  58  stick out at the opposing other end in a substantially parallel fashion and with a spacing that corresponds approximately to the spacing of a single row of feedthroughs  11 .  
         [0044]    The accuracy of the spacing between the fiber ends  58  arrayed on the sheet  57  has to be merely within the range of the second funnel width  25   d . A multitude of fiber ends  58  may be inserted simultaneously with an effort comparable to that for inserting a single fiber end  58 . In a case where forty fiber ends  58  are provided on a single sheet  57 , the insertion process may be substantially shortened also by a factor forty. This example is solely presented for demonstrating a main advantage of the present invention without any claim of accuracy thereof. Details about the sheet  57  and the associated parts are found in the US Patent Application, Ser. No. 09/866.063, filed May 21, 2002, which is hereby incorporated by reference.  
         [0045]    The insert  10  is a very thin and fragile structure. To integrate it in a larger assembly it is circumferentially attached in a well-known fashion on the top portion  61  of the fiber frame  60 . The expanding sections  35  remain freely accessibly at the inside of the fiber frame  60 . The fiber frame  60  has a lengthy shape extending in insertion direction away from the insertion face  32 . At the opposing end, the fiber frame  60  has a flange structure  62  with first assembly holes  67 . The fiber frame  60  features further a window  63  through which a number of sheets  57  may be accessed and held for insertion by a vacuum holding device (not shown). The window  63  is also placed and dimensioned to provide visual contact to the insertion face  32  as indicated by arrow VC.  
         [0046]    During an initial assembly step, the fiber frame  60  is fixedly held upside down. A sheet  57  is inserted in the fiber frame  60  and temporarily fixed to the vacuum holding device. The vacuum device is moved such that the arrayed fiber ends  58  are in approximate alignment with their predetermined expanding sections  25 . Visual monitoring through the window  63  assures proper alignment and insertion of the array of fiber ends  58 .  
         [0047]    Once the fiber ends  58  are inserted, gravity keeps them in place and the process may be repeated until the insert is populated with fiber ends  58  in a predetermined fashion. Some feedthroughs  11  may remain unpopulated.  
         [0048]    Once the insertion process is completed, a first resin may be poured onto the insertion face  32 , which is still pointing upwards. After a sufficient curing period, the fiber frame  60  may be turned around such that the output face  21  points upwards. At that assembly stage, the previously applied first resin is cured and fixedly holding the fiber ends  58  within their feedthroughs  11 .  
         [0049]    In a following step, a temporary barrier (not shown) is placed around the insert. The temporary barrier rises sufficiently above the level of the output face  21  such that a second resin poured onto the output face  21  is prevented from running off. Immediately following the pouring of the second resin, a vacuum is applied to the uncured second resin such that air eventually trapped in the feedthroughs  11  and beneath the second resin may travel to the top. The second resin may outgas and bubble during vacuum application. The vacuum is applied for a short period only such that the second resign may have sufficient time to settle down before the curing begins. Air bubbles and bubbles from outgasing have enough time to travel to the top of the resign away from the output face  21 .  
         [0050]    After the second resin has cured completely, the temporary barrier is removed. Then, the portions of the second resign and the fiber ends  58  that extend above the output face  21  are removed too. The output face  21  is finally polished whereby a planar and smooth surface is created between the output face  21  , the tips of the fiber ends  58  and the second resign filling the gap between the fiber ends  58  and the first narrow section  24 . Eventually unpopulated feedthroughs  11  are filled by the second resign as well. The final subassembly includes the fiber frame  60 , the insert  10  and a number of optical fibers  50  terminating in the fiber ends  58  on one end and well-known optical connectors on their other ends.  
         [0051]    The insertion loss is highly influenced by the surface quality of the fiber ends&#39;  58  tips. Only the slightest scratches, deposits and/or corrosion result in significant disturbance in the beam propagation. To provide optimum protection of the polished output face  21 , a glass plate  73  (see FIG. 4, 5,  6  ) is placed on top of the output face hermetically sealing it off. The process by which this is accomplished is best explained by referring now to FIG. 4.  
         [0052]    To successfully seal the output face  21 , an optical gel  66  (see FIG. 5) fills the gap between the glass plate  73  and the output face  21 . The optical gel  66  has preferably a refractive index that substantially matches the refractive index of the glass plate  73 . Entrapped air bubbles need to be avoided in order to assure undisturbed beam propagation through the gel  66  and the glass plate  73 . For that purpose and for providing additional sealing of the insert&#39;s  10  circumference, an external housing  70  is provided for receiving the pre assembled fiber frame  60  as described under FIG. 3.  
         [0053]    Prior to assembling the fiber frame  60 , the glass plate is bonded to a flange  75  in a fashion similar to that of the insert  10  bonded to the fiber frame  60 . The external housing  70  features also assembly holes  77  that correspond to the fiber frame&#39;s holes  67  and a flange structure  78  for integrating the final apparatus in another device like, for example, an optical relay station. Solder pins  74  are placed adjacent the flange  75 . Their function is explained below with FIG. 6.  
         [0054]    After the glass plate  73  has been bonded to the external housing  70 , the optical gel  66  may be applied to the polished output face  21 . An inventive procedure and apparatus for applying the gel  66  on the output face  21  are described in the concurrently filed U.S. patent application titled “Method and Apparatus for applying an optical gel” of Janusz Liberkowski, which is hereby incorporated by reference.  
         [0055]    After the optical gel  66  is applied, the fiber frame  60  is inserted in the external housing  70 , as shown in FIG. 5. To position the fiber frame  60  inside the external housing  70 , well-known alignment features like, for example, alignment pins  72  of the external housing  70  and corresponding alignment holes  65  (see FIG. 3) of the fiber frame  60  may be utilized. Attachment screws  79  screwed in the assembly holes  67 ,  77  force the output face  21  against the inside of the glass plate  73 . Elastic members  71  may be eventually used to gradually squeeze the optical gel  66  out of the gap into a cavity  68  surrounding the insert  10 . The surrounding cavity  68  is formed by the insert&#39;s  10  circumference, the fiber housing  60  and the external housing  70 .  
         [0056]    [0056]FIG. 5 shows also a lens plate  80  being assembled on top of the glass plate  73 . An air gap  76  remains between the glass plate  73  and the lens plate  80 . The lens plate is bonded to a frame.  81 , which is soldered to pins  74  of the external housing  70  after proper positioning of the lens plate  80 .  
         [0057]    Now referring to FIG. 6, the process of positioning and fixing the lens plate  80  is described. A number of individual lenses  83  are arrayed on the lens plate  80  in conjunction with the array of feedthroughs  11 . In an initial well-known step the lens plate  80  is aligned relative to the external housing  70  such that the lenses  83  are substantially aligned with the fiber axes  50   x . Precise positioning of the lens plate  80  is provided by, an adjustment device that holds the lens plate while optical tests are performed.  
         [0058]    Once the lenses  83  are aligned, the lens plate  83  is plan parallel moved in a direction substantially perpendicular to the output face  21  until the emitting light is properly focused by the lenses  83 . During this focusing step, a mirror is placed at a predetermined focal plane of the final assembly. The mirror reflects the emitted light back through the lenses  83 . As the lenses  83  approach their predetermined assembly position, the emitted light is increasingly focused, which results in a gain of the light mirrored back into the fiber end  58 . Once the reflected light reaches a maximum, the lens plate  80  is properly positioned.  
         [0059]    During the alignment procedure, the solder pins  74  extend into the solder holes  82  without touching them. After the alignment is completed the position of the lens plate  80  is fixed by soldering the pins  74  within the holes  82 .  
         [0060]    An additional important utility of the external housing  70  is its sealing function within an optical device like, for example, an optical switching fabric. For that purpose, a seal may be placed on the attachment flange  78  that assists in hermetically sealing the interior of the optical device while the optical connector of the present invention is attached to it.  
         [0061]    Accordingly, the scope of the invention described in the specification above is set forth by the following claims and their legal equivalent.