Abstract:
An assembly for housing optical components includes sides formed of an optically transmissive material, such as anti-reflective glass. Optical energy interacts with optical components retained within the assembly via the optically transmissive material. Collimated lens assemblies, which are attached to optical fibers, are adhesively attached to the optically transmissive sides. This assembly is especially amenable to an automated assembly process because it allows easy alignment of the collimated lens assembly with optical components retained within the assembly, and adherence of the collimated lens assembly to the optically transmissive side thereafter.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of fiber optics, and specifically to housings for optical components. 
     BACKGROUND 
     The increase in voice and data communications in recent years has contributed to a need to transmit and receive data at increasingly higher rates. Optical fiber communications systems are used to help meet this need. Advantages of optical fiber systems over, for example, electrical systems include increased bandwidth and smaller size. Packaging of fiber optic systems is an important factor to consider when attempting to achieve these smaller size systems. 
     Packaging optical components in a planar geometry (flat), rather than in a cylindrical geometry, is preferred to efficiently utilize space. FIG. 1 is a top view of a prior art planar package. Optical components such as isolators, taps, wavelength division multiplexers (WDMs), and lenses, are typically housed in area  2  (components not shown). Optical fiber pairs  4  and  6  are attached to collimated lens assemblies  10  and  12 , respectively. Multiple collimated lens assemblies may also be attached to each of the two sides to which collimated lens assemblies  10  and  12  are attached (multiple collimated lens assemblies not shown in FIG.  1 ). Energy is optically coupled to components within area  2  through openings  14  in the housing  8 . 
     Typically, collimated lens assemblies  10  and  12  are either laser welded or soldered to the housing  8 . Laser welding often results in positional shifts of optical components after attachment. This shifting of components is referred to as post-weld shift. Post-weld shift often results in a misalignment of components. Misalignment can result in degraded processing performance, increased insertion loss, and, at times, discarding the assembly. Laser welding requires access, by the laser welder, to the surfaces to be welded. The spacing required between lens assemblies can inhibit the welding process. Spacing the lens assemblies far enough apart such that access is available to a laser welder limits the number of lens assemblies per side. Laser welding also requires high amounts of energy to perform the welding process. 
     Soldering requires sustained heat for relatively long periods of time in order to flow the solder. This heat often detrimentally affects other components. Another disadvantage associated with soldering is positional shifts of optical components caused by cooling shrinkage. This positional shift of components can cause the same detrimental effects as post-weld shift (e.g., component misalignment, increased insertion loss, and decreased processing performance). Thus, a need exists for a planar packaging apparatus and method which does not inherently suffer the above disadvantages. 
     SUMMARY OF THE INVENTION 
     A planar fiber optic housing comprises a region for retaining optical components in a planar configuration. At least one side of the region comprises an optically transmissive material for coupling optical components thereto. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures: 
     FIG. 1 is a top view of a prior art planar package; 
     FIG. 2 is an isometric view of an exemplary embodiment of a structure for retaining optical components in a planar configuration having optically transmissive sides in accordance with the present invention; 
     FIG. 3 is an isometric view of an optical component assembly in accordance with the present invention optically coupled to optical fibers; 
     FIG. 4 is an exploded view of an optical component assembly, in a planar configuration, in accordance with the present invention; and 
     FIG. 5 is a flow diagram of an exemplary fabrication process of a planar optical component assembly in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of the present invention comprises an optical component planar housing having two opposing, optically transmissive sides. Energy is optically coupled between optical fibers and the optical components through anti-reflective (AR) glass windows, which form the opposing sides of the planar housing. The optical fibers are attached to collimated lens assemblies and the collimated lens assemblies are adhesively attached to the windows. Adhesively attaching the collimated lens assemblies to the windows facilitates an automated assembly process and eliminates problems associated with welding collimated lens assemblies to non-transparent housing sides. 
     Referring now to the drawings, wherein like reference numbers refer to like elements throughout, FIG. 2 is an isometric view of an exemplary embodiment of a structure for retaining optical components in a planar configuration having optically transmissive sides in accordance with the present invention. In FIG. 2, base structure  20  forms the bottom of region  24 . Region  24  may retain optical components such as wavelength division multiplexers (WDMs), lenses, prisms, taps, reflectors, and isolators (components not shown in FIG.  2 ). As depicted in FIG. 2, members  21  and  22  are integral with base structure  20 , and form opposing sides of region  24 . It is envisioned, however, that members  21  and  22  may be separate from base structure  20 , but rigidly attached by any appropriate means such as adhesively, snap fit, press fit, or bolted. Base structure  20  and/or members  21  and  22  may comprise any appropriate material, such as stainless steel. 
     Opposing sides  31  and  32  comprise openings  29  (not shown in FIG. 2) and  30 , respectively. Openings  29  and  30  each allow optical energy to enter and exit region  24 . Windows  26  and  28  are attached to sides  31  and  32 , respectively. Windows  26  and  28  comprise an optical transmissive material, such as glass or anti-reflective glass. Windows  26  and  28  may be attached to sides  31  and  32 , respectively, by any means, such as press fit coupling, snap fitting, welding, soldering, and/or adhesively. 
     FIG. 3 is an isometric view of an optical component assembly in accordance with the present invention optically coupled to optical fibers. Optical fibers  36  and  38  are attached to collimated lens assembly  50 . Collimated lens assemblies are used to optically couple energy between optical fibers and optical components. As shown in FIG. 3, collimated lens assemblies  50 ,  51 , and  53  optically couple energy between optical fibers and components positioned in region  24  (components not shown in FIG.  3 ), through windows  26  and  28 . 
     Collimated lens assemblies may comprise combinations of several components, such as lenses, filters, ferrules, and wavelength division multiplexers (WDMs). Exemplary collimated lens assembly  50  comprises a ferrule  44 , a lens  46 , and an optical filter  34 . Ferrule  44  is a cylindrical device having apertures sized to fit optical fibers  36  and  38 . Optical fibers  36  and  38  are mounted in ferrule  44 . Ferrule  44  centers and aligns optical fibers  36  and  38 . Optical fibers  36  and  38  are terminated within ferrule  44 . Typically, cylindrical ferrules are limited to housing no more than two optical fibers because of the strict tolerances associated with transferring optical energy between a pair of optical fibers. Lens  46  focuses optical energy. 
     Lens  46  may comprise any suitable lens, such as a gradient radial index (hereinafter GRIN) lens, a molded aspheric lens, or a ground spherical lens. In the exemplary embodiment shown in FIG. 3, lens  46  is a GRIN lens. Note that collimated lens assemblies  50  and  51  each comprise filter  34  attached to the lens of the collimated lens assembly. Filter  34  is optional. Note that collimated lens assembly  53  does not comprise a filter. Depending upon system requirements, other optical components (e.g., WDM) may be positioned between the lens of the collimated lens assembly and the window. 
     Collimated lens assembly  50  is attached to window  26  and collimated lens assemblies  51  and  53  are attached to window  28 . The attachment of collimated lens assembly  50  to window  26  and collimated lens assemblies  51  and  53  to window  28 , may be by any appropriate means, such as through the use of an adhesive (e.g., optical quality heat cured epoxy MH77A). Adhesively attaching the collimated lens assemblies to the windows does not require sustained localized heating, in contrast to soldering and laser welding. Therefore components are not as susceptible to heat damage. Also, because adhesively attaching the collimated lens assemblies to the window does not require access by a laser welder, more collimated lens assemblies can be adhered to the window. Furthermore, windows  26  and  28  may be adjusted in size to accommodate any number of collimated lens assemblies and therefore, more optical fibers. Additionally, the curing process associated with adhesively attaching the collimated lens assemblies to the windows does not misalign the components to the same degree as does post weld shift. 
     Thus the alignment procedure associated with adhesively attaching collimated lens assemblies to the windows is less time consuming and more easily accomplished than the alignment process associated with laser welding. 
     Optical fibers  36  and  38  are axially positioned within bend limiter tubing  40 . Bend limiter tubing  40  is a hollow, generally cylindrical sleeve through which optical fibers  36  and  38  are positioned to limit the bending of the optical fibers. In an exemplary embodiment of the invention, optical fibers  36  and  38  are attached to the inner surface of bend limiter tubing  40  with a filler material. The filler material may comprise, for example, a commercially available pliable adhesive (e.g., silicone). Attaching optical fibers  36  and  38  to the inner surface of bend limiter tubing  40  facilitates the automated assembly process by reducing the motion of optical fibers  36  and  38 . The filler material reduces axial motion of optical fibers  36  and  38  in the directions indicated by arrow  48 . Axial motion may be caused by mechanical strain applied to optical fibers  36  and  38  during the assembly process. Axial motion may also be caused by expansion and contraction of optical fibers  36  and  38 , and/or other components, due to thermal variation. Excessive axial motion may cause optical fibers  36  and  38  to bend and ultimately sustain damage. The filler material also reduces radial motion of optical fibers  36  and  38 , thus reducing the possibility of any damage due to radial motion. 
     Support member  42  provides support for bend limiter tubing  40  and optical fibers  36  and  38 . In an exemplary embodiment of the invention, optical fibers  36  and  38  are rigidly attached to collimated lens assembly  50 . This rigid attachment also contributes to the bending of optical fibers  36  and  38  when subjected to axial motion. The support provided by support member  42  reduces bending of optical fibers  36  and  38 , and reduces the possibility of optical fibers  36  and  38  becoming detached from collimated lens assembly  50 . In an exemplary embodiment of the invention, bend limiter tubing  40  is attached to support member  42 . Attachment of bend limiter tubing  40  to support member  42  may be achieved through the use of, for example, an adhesive such as epoxy. Attachment of bend limiter tubing  40  to support member  42  facilitates the automated assembly process by reducing movement of bend limiter tubing  40 , which in turn reduces movement of optical fibers  36  and  38 . 
     It is emphasized that the embodiment of the invention shown in FIG. 3 is exemplary. FIG. 3 shows two optical fibers,  36  and  38 . FIG. 3 shows support member  42  as an integral part of base structure  20 . It is envisioned that base structure  20  and support member  42  may be separate, but rigidly attached by any appropriate means such as adhesively, snap fit, press fit, or bolted. 
     FIG. 4 is an exploded view of an optical component assembly, in a planar configuration, in accordance with the present invention. Region  24  within the housing, may retain any combination of optical components. Optical components  54  and  56  represent exemplary optical components which may be retained in region  24 , examples of which include lenses, reflectors, isolators, taps, and WDMs. In the exemplary embodiment of the invention shown in FIG. 4, optical component  54  is an isolator and optical component  56  is a prism. In this embodiment, isolator  54  ensures that optical energy is directed toward optical component  56  with minimal reflection of optical energy back toward collimated lens assembly  50 . Optical energy which has interacted with isolator  54  is directed toward prism  56 . Prism  56 , apportions and routes the optical energy received from isolator  54  to collimated lens assemblies  51  and  53 . 
     Isolator  54  and prism  56  form a free air space optical network. Optical energy is coupled between window  26  and isolator  54 , between isolator  54  and prism  56 , and between prism  56  and window  28 , through air. A free air space optical network may not be appropriate in an environment with high ambient optical energy. In high ambient optical energy environments, it is advantageous to provide a cover, such as upper portion  52  over region  24 . Upper portion  52  also protects optical components within region  24  from damage (e.g., dust, collision, contamination) during storage, shipping, and use. Opening  70 , in upper portion  52  may remain open or be filled with material. An example of a filler material for hole  70  is a membrane comprising a wicking agent to withdraw moisture from region  24 . 
     Upper portion  52  is positioned opposite base structure  20  and support members  42 . Upper portion  52  is attached to base structure  20  and/or support member  42 . Attachment of upper portion  52  to base structure  20  and/or support member  42  may be accomplished by any means known in the art (e.g., adhesives, press fit, bolted, or snaps). Bend limiting tubing  40  is positioned between support member  42  and upper portion  52 . Positioning and attaching bend limiting tubing  40  between support member  42  and upper portion  52  facilitates the automated assembly process by limiting movement of bend limiting tubing  40  and optical fibers  36  and  38 . 
     Bend limiter tubing  40  is positioned around each group of optical fibers coupled to the optical component housing. Placing bend limiter tubing around all optical fibers facilitates the automated assembly process by reducing fiber motion. Support members  42  provide support for all bend limiter tubes  40 . Supporting all bend limiter tubes  40  with support member  42  facilitates the automated assembly process by reducing motion of the optical fibers and bend limiter tubing. In various embodiments of the invention, bend limiting tubing  40  is attached to support member  42  and/or upper portion  52 . Attachment of bend limiter tubing  40  to support member  42  and/or upper portion  52  may be achieved through the use of, for example, an adhesive such as epoxy, or a press fit. Attachment of bend limiter tubing  40  to support member  42  and/or upper portion  52  facilitates the automated assembly process by reducing movement of bend limiter tubing  40 , which in turn reduces movement of optical fibers  36  and  38 . 
     As described below, an optical component assembly in accordance with the present invention, and as depicted in FIG. 4 facilitates an automated assembly process by allowing the placement of optical components, such as exemplary optical components  54  and  56 , in region  24 , separate from the alignment, and coupling of collimated lens assemblies to windows  26  and  28 . FIG. 5 is a flow diagram of an exemplary fabrication process of a planar optical component assembly in accordance with the present invention. The description of the process depicted in FIG. 5 refers to elements in FIG.  4 . 
     Initially, in step  60 , alignment of collimated lens assemblies  50 ,  51 , and  53  with optical components  54  and  56  is performed to determine nominal placement coordinates to be used in the automated assembly process. Base structure  20 , support structures  42 , and windows  26  and  28  are provided preassembled (hereinafter “the housing assembly”). The nominal placement coordinates determine the location of optical components  54  and  56 , and collimated lens assemblies  50 ,  51 , and  53  on the housing assembly. Initial alignment is performed by positioning collimated lens assembly  50 , on window  26 . Optical components  54  and  56  are positioned in their approximate locations within the housing assembly. Photodetectors (photodetectors not shown in FIG. 4) are positioned on window  28  at the approximate expected locations of collimated lens assemblies  51  and  53 . A photodetector is an optoelectric device for receiving optical energy and providing an electrical signal. The voltage or current of the electrical signal is proportionate to the intensity of the received optical energy. Optical energy is provided through collimated lens assembly  50  and optical components  54  and  56 , to the photodetectors. The positions of optical components  54  and  56 , collimated lens assembly  50 , and the photodetectors are adjusted until the voltage or current of the electrical signals provided by the photodetectors is maximized; thus indicating proper optical alignment. Nominal placement coordinates are determined from these positions, and are programmed into an automated assembly placement mechanism. 
     Once the initial alignment is complete and nominal placement coordinates have been established, the automated assembly process begins. First, the housing assembly is placed on a conveyor belt. In step  62 , the housing assembly is then moved to an epoxy station where a pattern of epoxy is deposited in region  24  of the housing assembly. The pattern of epoxy corresponds to the placement coordinates and shapes of optical components  54  and  56 . 
     In step  64 , optical components  54  and  56  are positioned and attached to the housing assembly in accordance with the placement coordinates. The housing assembly is clamped by a clamping mechanism having a heater. The heater starts the curing process as the optical components are placed within the housing assembly and adhesively attached to the housing assembly by the pattern of epoxy. Optical components  54  and  56  are placed in the housing assembly by an automated placement mechanism, which places the optical components in the proper position and location within a small tolerance. 
     In step  66 , collimated lens assemblies  50 ,  51  and  53  are aligned with optical components  54  and  56 . Collimated lens assemblies, optical fibers, and bend limiters are provided preassembled. Each optical fiber is provided with a connector at the end opposite the collimated assembly. This connector allows for providing, receiving, and measuring optical signals. Alignment in step  66  is performed to compensate for the tolerances associated with the placement of optical components  54  and  56 . First, the collimated lens assemblies are positioned in accordance with the nominal placement coordinates. Optical energy is provided via the connector on the fibers attached to collimated lens assembly  50 . The optical energy received via the connectors on the fibers attached to collimated lens assemblies  51  and  52  is monitored while collimated lens assemblies  50 ,  51 , and  53  are positioned to ensure maximum throughput of optical energy. In step  68 , collimated lens assemblies  50 ,  51  and  53  are adhesively attached to the housing assembly in accordance with the most recent alignment positions. 
     Many of the automated assembly steps herein described are performed concurrently. Thus, the process depicted in FIG. 5 facilitates an automated assembly process of a plurality of packages by allowing separate and concurrent (1) assembly of the housing assemblies, (2) assembly of collimated lens assemblies and optical fibers, and (3) alignment, positioning, and attachment of optical components and collimated lens assemblies. 
     Although illustrated and described herein with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention.