Abstract:
The invention is a method and apparatus for transmitting the light from one or more transmitting arrays of optical devices to one or more receiving arrays of optical devices where each optical device in a transmitting array transmits an initially diverging light beam to a single optical device in a receiving array. Each optical device in a receiving array receives a converging light beam from a single optical device in a transmitting array. The method consists of imaging the optical devices in one or more transmitting arrays on the optical devices in one or more receiving arrays. The light rays from each optical device in a transmitting array are superimposed on the light rays from the other optical devices in the transmitting array while traversing a common volume.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     (Not applicable) 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     (Not applicable) 
     BACKGROUND OF THE INVENTION 
     This invention relates generally to methods and apparatus for directing the light produced by a plurality of light sources to a plurality of light sinks and more specifically to methods and apparatus for connecting arrays of light sources to arrays of light sinks. 
     The tremendous information-carrying capacity of light beams is stimulating the development of the hardware building blocks for communication systems of a variety of types. A variety of devices are presently available for the generation and detection of light for communication purposes. Moreover, these devices tend to be small, and the available manufacturing technology permits these devices to be fabricated precisely and economically into large-scale arrays. 
     What is not so readily available are the means for economically interconnecting arrays of these devices. The interconnection means of choice at the present time, particularly for long distances, is the fiber-optic cable consisting of a plurality of optical fibers held together by a flexible matrix. After decades of development, the connection of fiber-optic cables to optical devices remains a costly labor-intensive exercise. 
     It is becoming increasingly desirable to connect optical devices to other optical devices on the same printed-circuit board. For this purpose, guiding light beams from one array of optical devices to another array using waveguides have been explored during the past decade. The idea is to provide a waveguide between each pair of devices to be connected. Short-length fiber-optic cables are one possible way in which arrays of optical devices can be connected together. 
     Rather than using ready-made short-length fiber-optic cables to connect optical devices on a printed-circuit board, one might use custom-fabricated arrays of optical waveguides on suitable substrates. The manufacturing process for optical waveguide arrays is similar, at least in some respects, to the manufacturing process for integrated circuits. However, even though the integrated-circuit manufacturing process is complex, it is also cost-effective when amortized over millions of integrated circuits. Optical connectors based on arrays of optical waveguides are unlikely to have the market potential of commodity-type integrated circuits and will, for this reason, be significantly less cost-effective than the typical integrated circuit. 
     There is a continuing need for optical connectors that are as cost-effective as printed-circuit boards are for connecting arrays of electronic devices. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is a method and apparatus for transmitting the light from one or more transmitting arrays of optical devices to one or more receiving arrays of optical devices where each optical device in a transmitting array transmits an initially diverging light beam to a single optical device in a receiving array. Each optical device in a receiving array receives a converging light beam from a single optical device in a transmitting array. The method consists of imaging the optical devices in one or more transmitting arrays on the optical devices in one or more receiving arrays. The light rays from each optical device in a transmitting array are superimposed on the light rays from the other optical devices in the transmitting array while traversing a common volume. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of an optical system that illustrates the conceptual basis of the invention. 
     FIG. 2 shows a variation of the optical system shown in FIG.  1 . 
     FIG. 3 shows an embodiment of the invention. 
     FIG. 4 shows two members that can be assembled into the embodiment of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The basic function of the optical connector claimed herein is to funnel light from one or more transmitting arrays of optical devices to one or more receiving arrays of optical devices. A requirement that accompanies this basic function is (1) that each optical device in a transmitting array transmits light to a single optical device in a receiving array and (2) that each optical device in a receiving array receives light from a single optical device in a transmitting array. 
     The optical connector is basically an imaging system that for each optical device in a transmitting array images the exit aperture of the optical device (e.g. the aperture through which a VCSEL emits light) on the entry aperture of a receiving-array optical device (e.g. the aperture that defines the light-sensitive region of a photodiode) or on the end of an optical fiber. 
     The imaging process that is the subject of this invention is one where the diverging light rays from the optical devices in a transmitting array enter and then travel through a common volume together until they are subjected to a focusing process which brings about the separation of the light rays so that the light rays originating from a particular optical device in the transmitting array are focused on a particular optical device in the receiving array. The light-ray bundles from the transmitting-array optical devices travel together in a superimposed fashion through the common volume until they approach the receiving-array optical devices whereupon the light-ray bundles are once again separated into individual beams and imaged on individual receiving-array optical devices. 
     One might accomplish a similar result using a bundle of optical fibers with each fiber in the bundle connecting a particular optical device in the transmitting array to a particular optical device in the receiving array. Note that the light rays from a transmitting-array optical device is channeled to a receiving-array optical device through an optical fiber that services only one transmitting-array optical device. The light-ray bundles from the transmitting-array optical devices remain isolated from one another by being constrained to propagate through individual optical fibers. The light-ray bundles from the transmitting-array optical devices do not enter and then travel through a common volume together until they are finally separated and focused on the individual receiving-array optical devices, as is the case of the present invention. 
     The conceptual basis for the present invention is illustrated in FIG. 1 by an optical system  1  that funnels light from an array of vertical-cavity surface-emitting lasers (VCSELs)  3  to an array of photodiodes  5  and to the ends of the optical fibers in a fiber-optic cable held in a fiber-optic cable connector  7 . 
     The diverging light rays from the VCSEL array  3  of FIG. 1 propagate in a generally vertical direction to reflecting surface  11  and then continue after reflection from reflecting surface  11  in a generally horizontal direction to lenses  13  and  15  which collimate the light rays from the individual VCSELs. 
     In many situations, because of the locations and orientations of the transmitting and receiving arrays of optical devices, it is necessary to change the directions of propagation of the light rays one or more times as they pass through a common volume. These changes in direction can conveniently be accomplished through the use of reflecting surfaces or mirrors. 
     Still another way of bringing about a change in propagation direction is by using refraction whereby the light rays passing through a planar surface between two mediums having different indices of refraction experience a change in direction of propagation. The classic refraction-based device for accomplishing a change in direction of propagation is the prism. 
     An on-axis VCSEL is the one that emits a light ray that ends up collinear with the optical axis of lenses  13  and  15 . The bundle of diverging light rays from an on-axis VCSEL device is collimated by lenses  13  and  15  so that all of the rays are parallel to the optical axis of the lenses. 
     The bundle of diverging light rays from an off-axis VCSEL device is collimated by lenses  13  and  15  so that so that all of the rays are parallel but make an angle with respect to the optical axis that is proportional to the distance between the off-axis and the on-axis VCSEL devices. 
     The collimated light from the VCSELs passes through the hole  16  in aperture plate  17  which blocks scattered light and light from the peripheries of lenses  13  and  15 . 
     The VCSEL bundles of light rays that pass through the hole  16  in aperture plate  17  are split into two sets of bundles by beam splitter  19 . One set of bundles is reflected by beam splitter  19 , focused by lenses  21  and  23 , and directed toward the photodiode array  5  as a result of being reflected from reflecting surface  25 . The design of lenses  21  and  23  causes the light rays originating from a particular VCSEL to be focused on a particular photodiode. 
     The set of bundles that pass through beam splitter  19  are focussed by lenses  27  and  29  on the ends of a fiber-optic cable being held in the fiber-optic cable connector  7  and as a result, enter the optical fibers and are propagated to whatever devices are connected to the other ends of the optical fibers in the fiber-optic cable. 
     Another embodiment of the invention is illustrated in FIG. 2 wherein the light-ray bundles from two VCSEL arrays  31  and  33  are combined by means of combiner  35  and focused on the ends of a fiber-optic cable being held in the fiber-optic cable connector  37 . All of the un-numbered components in FIG. 2 play roles similar to those of corresponding components in FIG.  1 . The focusing function of lenses  21  and  23  in FIG. 1 becomes a collimating function in FIG. 2 where the bundles of light originate in VCSEL array  33 . 
     An embodiment of an optical connector  51  based on the optical system  1  of FIG. 1 is shown in FIG.  3 . The optical-connector housing  53  provides the structure for supporting the optical-system components and may also collaborate in other ways with the individual optical components in performing the functions required of the optical system. 
     The optical-connector housing  53  is made of a material such as an epoxy, plastic, or polyimide and in the preferred embodiment is optically transparent. In other embodiments, the housing  53  may be opaque. In the preferred embodiment, the optical-connector housing  53  is a solid body except for certain cavities visible in FIG.  3 . In other embodiments, the housing  53  may simply be an open structure that provides support for the optical-system components. 
     The function of reflecting surface  11  in FIG. 1 is accomplished by total internal reflection from surface  55  of the optical-connector housing  53  in FIG.  3 . Lens  57  (not visible in FIG. 3) and lens  59  correspond to the planar-convex lenses  13  and  15  of FIG.  1  and are attached on opposite sides of cavity  61 , planar surface to planar surface. 
     The aperture plate  17  and the beam splitter  19  of FIG. 1 slide respectively into slot  63  and slot  65  of optical-connector housing  53  of FIG.  3  and fastened with either a snap-fit or an adhesive. 
     Lens  67  and lens  69  (not visible in FIG. 3) correspond to the planar-convex lenses  21  and  23  of FIG.  1  and are attached on opposite sides of cavity  71 , planar surface of lens to planar surface of cavity. The function of reflecting surface  25  in FIG. 1 is accomplished by total internal reflection from surface  73  of the optical-connector housing  53  in FIG.  3 . 
     Lens  75  (not visible in FIG. 3) and lens  77  correspond to the planar-convex lenses  27  and  29  of FIG.  1  and are attached on opposite sides of cavity  79 , planar surface of lens to planar surface of cavity. 
     The optical-connector housing  53  is fabricated by an injection molding process. To ease the installation of the lenses into the optical-connector housing, the housing is molded in two members  81  and  83  as shown in FIG.  4 . Each member contains one-half of lens cavities  61 ,  71 , and  79  so that each of the lenses  57 ,  59 ,  67 ,  69 ,  75 , and  77 , can be easily positioned and adhesively attached to the sides of the cavities prior to assembling the two members  81  and  83 . 
     Member  81  is provided with resilient protuberances  85 ,  87 ,  89  (not visible in FIG.  4 ), and  91  (not visible in FIG. 4) that mate with recesses  93  (not visible in FIG.  4 ),  95  (not visible in FIG.  4 ),  97 , and  99  (not visible in FIG. 4) in part  83  when members  81  and  83  are pushed together thereby assuring the precise alignment of members  81  and  83  with respect to each other. 
     The VCSEL array and the photodiode array are typically in the form of integrated circuits that must be precisely mounted on a printed circuit board in accordance with the mating requirements of the optical connector. The optical connector is then mounted on the printed circuit board over and in precise alignment with the VCSEL array and the photodiode array. Techniques for accomplishing these tasks are well-known and may involve the use of templates, special jigs, and automation. Attachment will typically be accomplished using adhesives. 
     The fiber-optic cable must also be precisely aligned and attached to the optical connector. Typically, a fiber-optic cable connector is attached to the end of the fiber-optic cable and holds the optical fibers in precise alignment. The fiber-optic cable connector is then precisely aligned with and attached to the optical connector, typically by a mechanical latching means.