Abstract:
Improved apparatus and method allow rapid and precise alignment of a fiber optic array on a substrate, in which the offset between the end faces of the array and the edge of the substrate must be precisely known. The arrangement is adaptable for the construction of microlens assemblies and other optical elements that must be precisely placed proximate the end faces of the optical fibers.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to alignment of optical devices. More particularly this invention relates to a technique for the axial alignment of the end face of an array of optical fibers with an edge of a support block. 
     2. Description of the Related Art 
     In the past, the assembly and manufacture of optical assemblies having a linear array of optical elements has been time consuming and prone to quality control problems. The latest developments in optical cross-connect assemblies have only magnified these problems. Precisely engineered optical receiver arrays are required in these devices. A general demand for more precisely constructed assemblies having greater reliability has translated into a demand for better manufacturing apparatuses and processes. 
     Optical devices of the type addressed by the present invention currently in use involve an array of optical fibers having light transmitted therethrough. In typical devices the light exiting the end faces of the fibers is transmitted through a plurality of waveguides, which produce a diffraction pattern. The diffracted light is collimated by focusing optics, and then falls on a detector array. 
     In current devices, it is required to precisely position an assembly of micro-lenses close to the end faces of an optical fiber array. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary object of some aspects of the present invention to provide an improved technique for attaching the end of an optical fiber array to a glass block, such that the end faces of the block and the array are in precise alignment. 
     It is another object of some aspects of the present invention to attach an array of microlenses in precise alignment with corresponding members of an optical fiber array. 
     The invention provides a method for aligning two blocks, including the steps of placing an end face of a first block in a first face-to-face contacting position against a planar wall, laterally stabilizing the first block in the first face-to-face contacting position, and disposing the bottom surface of a second block in a second face-to-face contacting position with the top surface of the first block, wherein an end face of the second block is in a third face-to-face contacting position with the wall. The method further includes applying pressure against the top surface of the second block while maintaining the second face-to-face contacting position, wherein the pressure is distributed substantially over the top surface of the second block. The method further includes, while applying the pressure, adhering the bottom surface of the second block to the top surface of the first block. 
     According to an aspect of the method, the pressure is applied by disposing a third block on the top surface of the second block, and applying the pressure to the third block. The third block can be a Delarin block. 
     Another aspect of the method includes applying an adhesive to the bottom surface of the second block prior to disposing the bottom surface of the second block on the top surface of the first block, and curing the adhesive. The adhesive can be UV glue or an epoxy glue. 
     According to an additional aspect of the method, the wall has a lower segment and an upper segment that is offset from the lower segment, wherein in the first face-to-face contacting position the end face of the first block contacts the lower segment, and in the second face-to-face contacting position the end face of the second block contacts the upper segment. 
     According to one aspect of the method, the second block includes an array of optical fibers. 
     Another aspect of the method includes disposing an array of microlenses on the second block proximate an outlet of the array of optical fibers. 
     According to a further aspect of the method, the wall includes a first pin and a second pin that is spaced apart from the first pin. 
     The invention provides a method for aligning an array of optical elements on a block, including the steps of placing an end face of a first block in a first face-to-face contacting position against a planar wall, laterally stabilizing the first block in the first face-to-face contacting position, disposing the bottom surface of a fiberoptic array in a second face-to-face contacting position with a top surface of the first block, wherein an end face of the fiberoptic array is in a third face-to-face contacting position with the wall. The method includes applying pressure against the top surface of the fiberoptic array, while maintaining the second face-to-face contacting position, wherein the pressure is distributed substantially over the top surface of the fiberoptic array, and while applying the pressure, adhering the bottom surface of the fiberoptic array to the top surface of the first block. 
     According to an aspect of the method, the pressure is applied by disposing a third block on the top surface of the fiberoptic array, and applying the pressure to the third block. The third block may be a Delarin block. 
     Another aspect of the method includes applying an adhesive to the bottom surface of the fiberoptic array prior to disposing the bottom surface of the fiberoptic array and curing the adhesive. The adhesive may be UV glue or epoxy glue. 
     According to still another aspect of the method, the wall includes a lower segment and an upper segment that is offset from the lower segment, wherein in the first face-to-face contacting position the end face of the first block contacts the lower segment, and in the second face-to-face contacting position the end face of the fiberoptic array contacts the upper segment. 
     An additional aspect of the method includes disposing an array of microlenses on the fiberoptic array proximate the end face of the fiberoptic array. 
     According to one aspect of the method, the wall includes a first pin and a second pin that is spaced apart from the first pin. 
     The invention provides an apparatus for aligning an optical array, including a receiving section that accepts a first block and an array of optical elements, wherein the array of optical elements includes a second block. The apparatus further includes a retaining section adjacent the receiving section for stabilizing the first block in an operating position, wherein the retaining section includes a platform that carries the first block thereon. The apparatus further includes an upright frame, which has an extension that overhangs the platform, and has a wall that abuts the first block and the second block during alignment thereof. The apparatus further includes a plurality of horizontally directed stabilizers mounted on the retaining section that urge the first block into a first face-to-face contacting position with a lower segment of the wall, and a vertically directed stabilizer mounted on the extension that holds a bottom surface of the second block in face-to-face contact with a top surface of the first block and holds an end face of the second block in a second face-to-face contacting position with an upper segment of the wall. 
     According to an aspect of the apparatus, the horizontally directed stabilizers each comprise an upright stub having a hole bored therethrough, and a pin inserted through the hole. The pin may be a bolt threaded through the hole. 
     According to yet another aspect of the apparatus, the vertically directed stabilizer includes a pin inserted through a bore that is formed in the extension. The pin can be a bolt threaded through the bore. 
     According to still another aspect of the apparatus, the wall includes two upright posts and a gap therebetween. 
     According to an additional aspect of the apparatus, the lower segment of the wall includes a niche, the end face of which is offset from the upper segment of the wall. 
     One aspect of the apparatus the lower segment of the wall includes an outstanding step that is offset from the upper segment of the wall. 
     According to a further aspect of the apparatus, a width dimension of the extension is less than a width dimension of the platform. 
     The invention provides an apparatus for aligning an optical array, including a receiving section that accepts a first block, and an array of optical elements, wherein the array of optical elements includes a second block. The apparatus further includes a retaining section adjacent the receiving section for stabilizing the first block in an operating position, wherein the retaining section includes a platform for carrying the first block thereon. The apparatus further includes an upright frame having an extension that overhangs the platform, wherein the width dimension of the extension is less than the width dimension of the platform. The apparatus further includes a wall that abuts the first block and the second block during alignment thereof, a plurality of horizontally directed stabilizers mounted on the retaining section that urge the first block into a first face-to-face contacting position with a lower segment of the wall. The horizontally directed stabilizers each comprise an upright stub that has a hole bored therethrough and a first bolt threaded through the hole, and a vertically directed stabilizer mounted on the extension that holds a bottom surface of the second block in face-to-face contact with a top surface of the first block, and holds an end face of the second block in a second face-to-face contacting position with an upper segment of the wall, wherein the vertically directed stabilizer includes a second bolt threaded through a bore that is formed in the extension. 
     According to an aspect of the apparatus, the wall includes two upright posts an a gap therebetween. 
     According to an additional aspect of the apparatus, the lower segment of the wall includes a niche that is offset from the upper segment of the wall. 
     One aspect of the apparatus the lower segment of the wall includes an outstanding step that is offset from the upper segment of the wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of these and other objects of the present invention, reference is made to the detailed description of the invention, by way of example, which is to be read in conjunction with the following drawings, wherein: 
     FIG. 1 is a partial top view of an array of optical fibers, which can be aligned in accordance with a preferred embodiment of the invention; 
     FIG. 2 is a perspective view of an alignment apparatus in accordance with a preferred embodiment of the invention; 
     FIG. 3 is a sectional view of the alignment apparatus shown in FIG. 2 with the bolts removed; 
     FIG. 4 is a sectional view of an alignment apparatus according to an alternate embodiment of the invention; 
     FIG. 5 is a sectional view of an alignment apparatus according to an alternate embodiment of the invention; 
     FIG. 6 is a perspective view of an alignment apparatus according an alternate embodiment of the invention; 
     FIG. 7 is an enlarged view of a portion of the alignment apparatus shown in FIG. 6; 
     FIG. 8, is a perspective view of the alignment apparatus shown in FIG. 2 with a glass block in a working position; 
     FIG. 9, is a perspective view of the alignment apparatus similar to FIG. 8; 
     FIG. 10 is a perspective view of the alignment apparatus shown in FIG. 2 with a fiberoptic assembly ready for placement therein for alignment; 
     FIG. 11 is a perspective view of the alignment apparatus shown in FIG. 2 with a fiberoptic assembly in place; and 
     FIG. 12 illustrates a fiberoptic assembly, which has been completed according to a preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent however, to one skilled in the art that the present invention may be practiced without these specific details. 
     In describing the embodiments herein, the following conventions are used. The Z-axis is nominally horizontal, and has the same direction as the optical axes of an array of optical fibers that is being held and manipulated. The X-axis refers to the horizontal axis that is orthogonal to the Z-axis. The Y-axis is the vertical axis, and is orthogonal to both the X-axis and the Z-axis. Rotation about the X-axis, Y-axis, and Z-axis is referred to as theta-X, theta-Y and theta-Z motion respectively. Of course, it is possible to operate the apparatus disclosed herein in many positions and orientations, in which case the X-axis, Y-axis, and Z-axis are appropriately translated. 
     Alignment Issue 
     Turning now to the drawings, reference is made to FIG. 1, which illustrates a top view of an array of optical fibers, which can be aligned in accordance with a preferred embodiment of the invention. The array  10  includes a plurality of optical fibers  12 ,  14 ,  16 ,  18 , the terminal segments of which are embedded in a substrate  20 . The substrate  20  can be a glass block. The array  10  is constructed such that the edge  22  of the substrate  20  and the end faces of the optical fibers  12 ,  14 ,  16 ,  18  are aligned within a tolerance in the Z-axis that is given by the dimension “A”. In some manufacturing applications, an assembly of microlenses (not shown) may be positioned near the outlet of the array  10 . In order for the assembly of microlenses to function properly with the array  10 , the dimension “A” is required to be less than 1 micron. If the tolerance were not met, then the focal points of the microlenses would vary unacceptably in the Z-axis. A supporting block  24  is needed for additional physical support, because the optical fibers  12 ,  14 ,  16 ,  18  of the array  10  are too delicate to support an assembly of microlenses. It is necessary to position the array  10  atop the block  24 , and to align the edge  22  of the array  10  in parallel with the edge  26  of underlying block  24 , and at a known distance “D” from the edge  26 . In some embodiments the distance “D” can be zero. 
     First Embodiment 
     Reference is now made to FIG. 2, which illustrates an alignment apparatus for a fiberoptic array that is constructed and operative in accordance with a preferred embodiment of the invention. An alignment apparatus  28  has a receiving section  30  that receives a fiberoptic array to be aligned, and a retaining section  32 , which stabilizes the fiberoptic array during its alignment. 
     The retaining section  32  has a platform  34 , which supports the fiberoptic array during alignment. A frame  36  is disposed adjacent the platform  34 , The frame  36  has an extension  38  that overhangs the platform  34  and is provided with a retaining bolt  40  threaded therethrough. The purpose of the retaining bolt  40  is to urge the fiber-optic array that is to be aligned against the platform  34 , and thereby vertically stabilize it. The extension  38  is narrower than the platform  34 . It is thus possible to view the platform  34  from above through two open corners  42 ,  44  that are formed by the base of the extension  38  and the frame  36 . In applications requiring more exacting visual control, it is possible to fabricate the extension  38  from a transparent material. 
     The retaining section  32  is provided with two laterally disposed stubs  46  that project upward, each supporting a stabilizing bolt  48  threaded therethrough. The stabilizing bolts  48  are substantially horizontally disposed, and are angled inward toward the central axis of the alignment apparatus  28 . The stabilizing bolts  48  are used to further stabilize the fiberoptic array that is to be aligned, as will be disclosed in further detail hereinbelow. A staging area  50  disposed intermediate the stabilizing bolts  48  admits the fiberoptic array that is to be aligned into an operational position in the receiving section  30 . A hole  52  is threaded through the retaining section  32 . It can optionally receive a mounting bolt or screw (not shown), if it is desired to secure the alignment apparatus  28  to an optical stage (not shown) or other working platform. Anodized aluminum is a suitable material for the construction of the alignment apparatus  28 . 
     Reference is now made to FIG. 3, which illustrates a sectional view of the alignment apparatus  28 . The platform  34  is bounded by a flat wall  54 , which abuts the fiberoptic array that is to be aligned. It is desirable that the wall  54  be precisely planar. 
     Second Embodiment 
     Reference is now made to FIG. 4, which illustrates a sectional view of an alignment apparatus that is constructed and operative in accordance with an alternate embodiment of the invention. An alignment apparatus  56  is similar to the alignment apparatus  28  (FIGS. 2,  3 ), except that a platform  58  is continuous with the floor of a niche  60  that is formed in the lower portion of a wall  62 . The niche terminates in a short vertical segment  64 . With this embodiment, a lower block can be attached beneath a fiber optic array, and aligned so as to project forward a known distance beyond the end face of the array. 
     Third Embodiment 
     Reference is now made to FIG. 5, which illustrates a sectional view of an alignment apparatus that is constructed and operative in accordance with an another alternate embodiment of the invention. An alignment apparatus  66  is similar to the alignment apparatus  28  (FIGS. 2,  3 ), except that the lower segment of a wall  68  has an outward step or extension  70 . A platform  72  terminates at a short vertical segment  74  that forms the free end of the extension  70 . With this embodiment, an underlying block can be attached beneath a fiber optic array or another block, and aligned such that the end face of the overlying fiber optic array or other block projects forward a known distance beyond the end face of the underlying block. 
     Fourth Embodiment 
     Reference is now made to FIG. 6, which is a perspective view of an alignment apparatus that is constructed and operative in accordance with another alternate embodiment of the invention. An alignment apparatus  76  is similar to the alignment apparatus  28  (FIGS. 2,  3 ), except that that two upright pins  78 ,  80  are disposed at the end of a platform  82 . 
     Reference is now made to FIG. 7, which is an enlarged schematic view of a portion of an alignment apparatus similar to that shown in FIG. 6. A fiber-optic array is shown in alignment position. The fiber-optic array has a top block  86  mounted on a bottom block  88 . During alignment, the block  86  and the block  88  are both in held in firm contact with the pins  78 ,  80  by pressure exerted by the stabilizing bolts  48  (FIG.  6 ). The difference between the embodiment illustrated in FIG.  2  and FIG. 3, and the embodiment of FIG.  6  and FIG. 7 is that the function of the wall  54  (FIG. 3) is carried out by the pins  78 ,  80 . The embodiment of FIG. 7 can be successfully operated even if the blocks  86 ,  88  have an imperfect planar end face. 
     Operation 
     Operation of the alignment apparatus will now be disclosed with reference to the first embodiment. Reference is now made to FIG. 8, which is a perspective view of the alignment apparatus  28  (FIG.  2 ). It is convenient to orient the alignment apparatus  28  diagonally on the optical table (not shown), such that the wall  54  faces a corner of the optical table. Preferably, a stereo microscope (not shown) is positioned above the alignment apparatus  28  in order to view the alignment operation from above. The procedure can be viewed from the side using direct vision. A video camera (not shown) may optionally be positioned to view the alignment apparatus  28  from the side. 
     A glass block  90  is in a working position on the platform  34 . A mounting screw  92  secures the alignment apparatus  28  to an optical table (not shown). Prior to mounting the glass block  90 , the surfaces of the alignment apparatus  28  that come into contact with the surfaces of the fiberoptic array that is to be aligned are cleaned with a suitable cleaning substance. It is desirable to meticulously clean the surfaces of the fibers of the fiberoptic array that is to be aligned, and the surfaces of the glass block  90 . 
     A Delarin block  94  which is preferably less than 5 millimeters in thickness is set atop the glass block  90 , and the retaining bolt  40  is gently tightened against the Delarin block  94 . A glass block can be used instead of the Delarin block  94 , provided that its face is accurately planar. Interposition of the Delarin block  94  between the retaining bolt  40  and the glass block  90  uniformly distributes the pressure produced by the retaining bolt  40  over the glass block  90 . The stabilizing bolts  48  are then tightened to urge the glass block  90  against the wall  54 . The alignment apparatus  28  is constantly viewed from the side, and from above through the stereo microscope (not shown) as the retaining bolt  40  and the stabilizing bolts  48  are tightened, in order to assure that the end face of the glass block  90  is accurately positioned in face-to-face contact with the wall  54 . 
     Reference is now made to FIG. 9, which is a perspective view of the alignment apparatus  28  (FIG.  2 ). The description of FIG. 9 is to be read in conjunction with the disclosure of the next stage in the alignment operation and with FIG.  8 . The retaining bolt  40  is released, and the Delarin block  94  is removed. The glass block  90  continues to be stabilized by the stabilizing bolts  48 . 
     Reference is now made to FIG. 10, which is a perspective view of the alignment apparatus  28  (FIG.  2 ), and illustrates a fiberoptic array that is to be aligned. The description of FIG. 10 is to be read in conjunction with the disclosure of the next stage in the alignment operation and with FIG. 9. A fiberoptic array  96  comprises a glass plate  98  that encloses the terminal segments  100  of a plurality of optical fibers  102 . A thin layer of UV-glue is spread over the glass plate  98 , taking care that the glue does not extend closer than 2 mm. to the end faces  104  of the optical fibers  102 . Restricting the placement of the glue in this manner is desirable in order to prevent the glue from obscuring the end faces  104 . A glue such as UV-81, available from Norland Co., is suitable. It is important that the UV-glue be applied to the glass plate  98 , and not to the glass block  90 . Other glues, such as epoxy, can be substituted for the UV-glue. 
     Reference is now made to FIG. 11, which is a perspective view of the alignment apparatus  28  (FIG.  2 ), and illustrates a fiberoptic array during a further stage of its alignment. The description of FIG. 11 is to be read in conjunction with the disclosure of the next stage in the alignment operation and with FIG.  10 . The fiberoptic array  96  is passed into the alignment apparatus  28  over the staging area  50 , until the end faces  104  of the optical fibers  102  are near the wall  54 . The top surface of the glass block  90  and the bottom surface of the glass plate  98  are then in face-to-face contact. While viewing the procedure from above through the corners  42 ,  44 , using the stereo microscope (not shown), the end faces  104  are urged against the wall  54  until they are in firm contact with the wall  54 . The fiberoptic array  96  is manually held in position, while a Delarin block  106  is placed atop the glass plate  98 . The Delarin block  106  is preferably less than 5 mm. In thickness, and slightly smaller than the glass plate  98  in order to continue to view the glass plate  98  from above. Then the retaining bolt  40  is gently tightened against the Delarin block  106 . Interposition of the Delarin block  106  between the retaining bolt  40  and the glass plate  98  uniformly distributes the pressure produced by the retaining bolt  40  over the glass plate  98  and the glass block  90 . 
     A UV gun  108  is then directed horizontally toward the side of the glass and the glass block  90 , which are then exposed to ultraviolet light for about a minute. After loosening the stabilizing bolts  48 , the fiberoptic array is then removed from the alignment apparatus  28  and the entire glue-containing area exposed to the UV gun for an additional four minutes, in order for the glue to harden. 
     Reference is now made to FIG. 12, which illustrates a completed assembly  110 , comprising the fiberoptic array  96 , now mounted on and properly aligned with the glass block  90 .