Abstract:
Disclosed is a bi-directional optical link and method. The bi-directional optical link comprises a detector having an upper surface facing a predetermined direction and a beam turning device located over the surface. The bi-directional optical link also includes an emitter oriented to direct a beam of light toward the beam turning device, the beam turning device redirecting the beam of light toward the predetermined direction.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This document claims priority to and the benefit of the filing date of co-pending and commonly assigned provisional applications entitled “Bi-Directional Single Fiber Optical Link Using Lasers and Detectors”, assigned serial No. 60/097,981, filed Aug. 26, 1998, and “Bi-Directional Single Fiber Optical Link Using I-MSMS”, assigned serial No. 60/097,946, filed Aug. 26, 1998, both of which are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to the field of communications, and more particularly, to a system and method for optical bi-directional communication. 
     BACKGROUND OF THE INVENTION 
     Current communications systems and networks are becoming faster and more complex, using any one of number of mediums. Communication using these systems and networks is typically bi-directional in that signals are exchanged between two sources as they communicate for various purposes. More recently, fiber optic networks have been employed as the medium for communications. Typically, the optical fibers themselves may be very small and, consequently, coupling various devices to the optical fibers to create a communications link can be difficult and expensive. 
     An additional problem with current optical fiber communications systems is that optical fibers are often used for unidirectional communications. This is due in part to the difficulty of physically transmitting and receiving an optical signal on a single optical fiber that may be, for example, a single micron thick. Unfortunately, this results in the need for two optical fiber links to establish bi-directional communications. 
     SUMMARY OF THE INVENTION 
     The present invention provides a bidirectional optical link and method. In one possible embodiment, the bi-directional optical link comprises a detector having an upper surface facing a predetermined direction and a beam turning device located over the surface. The bidirectional optical link also includes an emitter oriented to direct a beam of light toward the beam turning device, the beam turning device redirecting the beam of light toward the predetermined direction. 
     The present invention may also be viewed as a method for conducting bi-directional optical communications, comprising the steps of positioning a detector having an upper surface to face a predetermined direction, placing a beam turning device over the upper surface, and, positioning an emitter so as to direct a beam of light toward the beam turning device so that the beam turning device redirects the beam of light toward the predetermined direction. 
     A significant advantage of the present invention is that it facilitates an increased positioning tolerance of the optical fiber with respect to the emitter/detector pair. Also, a single optical fiber can be used for bidirectional communication with significantly improved signal propagation. This is accomplished while reducing manufacturing costs of the optical link due to the increased positioning tolerance of the optical fiber. 
     Another advantage of the invention is that it is simple in design, user friendly, robust and reliable in operation, efficient in operation, and easily implemented for mass commercial production. 
     Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
     FIG. 1A is a drawing of a bi-directional communications link according to an embodiment of the present invention; 
     FIG. 1B is a top view of the bi-directional communications link of FIG. 1A; 
     FIG. 2A is a side view drawing of a detector used in the bi-directional communications link of FIGS. 1A and 1B; 
     FIG. 2B is a bottom view drawing of a detector used in the bi-directional communications link of FIGS. 1A and 1B. 
     FIG. 3A is a drawing of a bi-directional communications link according to another embodiment of the present invention; 
     FIG. 3B is a top view of the bi-directional communications link of FIG. 3A; 
     FIG. 4 is a drawing of a bi-directional communications link using an intermediate host according to another embodiment of the present invention; 
     FIG. 5 is a drawing of a yet bi-directional communications link using an intermediate host according to another embodiment of the present invention; and 
     FIG. 6 is a drawing of a third bi-directional communications link using an intermediate host according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1A, shown is a bi-directional optical link  100  according to an embodiment of the present invention. The bi-directional optical link  100  includes a thin film detector  103 , a thin film emitter  106 , and a beam turning device  109 . The detector  103  and the emitter  106  are disposed on a host substrate  113  as shown. The detector  103  is preferably flat in shape with a thickness that is, for example, relatively small. The detector  103  includes an upper surface  116  oriented to receive incident light  119  from a predetermined direction  123 , that is, for example, normal to the upper surface  116 . The incident light  119  propagates, for example, from an optical fiber  126  as shown where the optical fiber  126  has a core  129  and a cladding  133 . The emitter  106 , detector  103 , and the beam turning device  109  are thin film devices. 
     During operation of the bidirectional optical link  100 , the emitter  106  generates a beam of light  136  that is directed toward the turning device  109 . The turning device  109  redirects the beam of light  136  toward the predetermined direction  123  as shown. The optical fiber  126  is positioned so as to receive the beam of light  136  and to ensure that the incident light  119  propagates from the optical fiber  126  onto the upper surface  116  of the detector  103 . In other words, the optical fiber  126  is positioned so as to face the detector  103  and the turning device  109  from the predetermined direction  123 . Both the incident light  119  and the beam of light  136  are modulated accordingly. In this manner, the bi-directional optical link  100  advantageously allows a single optical fiber  126  to be used for bi-directional communications. 
     The emitter  106  may be, for example, an edge emitting laser or an edge emitting, light emitting diode (LED), or other suitable light source. The actual component chosen as the emitter depends in part on the capabilities and attributes of the component and the particular application. For example, edge-emitting lasers allow higher speed operation than LED&#39;s, but also include higher power consumption. The emitter  106  includes electrical contacts that are bonded to the host substrate  113  using suitable conductive bonding agents such as metals, conductive polymers, conductive epoxies, and other suitable materials known in the art. In particular, the electrical contacts are preferably bonded to counterpart electrical contacts on the host substrate  113 , where the circuit that drives the emitter  106  is also located on the host substrate  113 . The emitter  106  may be bonded to the host substrate  113  using non-conductive bonding agents as well. 
     Likewise, the detector  103  includes electrical contacts that are bonded to the counterpart contacts on the substrate  113  in a similar manner to the emitter  106 . The beam turning device  109  is then bonded to the upper surface  116  of the detector  103  using a nonconductive bonding agent as shown. The beam turning device  109  may be, for example, a reflective device such as a mirror. Also, optical gratings or other suitable devices may be used. 
     The host substrate  113  may comprise, for example, an actual circuit, glass, plastic, laminate, polymer, or other suitable material or device. The optical fiber  126  is held into place using suitable means. 
     Turning to FIG. 1B, shown is a top view of the bi-directional optical link  100 . The detector  103  is spherical in shape with a diameter d, for example, that is larger than the diameter c of the core  129 , and, given its general thickness, is in the shape of a disk. It is possible, however, that the diameter d may be any size relative to the diameter c of the core  129 , depending upon the performance sought by the ultimate design. The beam turning device  109  is generally located over the detector  103  at a position approximately near the center of the detector  103 . Interposed on the detector  103  and the beam turning device  109  are outlines of the core  129   a  and  129   b  of the optical fiber  126  (FIG. 1A) in first and second positions over the detector  103 . 
     The first and second positions of the cores  129   a  and  129   b  illustrate a positioning tolerance of the bi-directional optical link  100  that is a significant advantage of the present invention. The core  129   a  is shown substantially centered in the detector  103 , whereas the core  129   b  is off to the side. However, the beam turning device  109  is still positioned within the periphery of both cores  129   a  and  129   b.  It is a significant advantage that the optical fiber  126  need only be positioned relative to the detector  103  and the beam turning device  109  so as to capture the beam of light  136  redirected by the beam turning device  109 , while at the same time, illuminating enough of the detector  103  with the incident light  119  (FIG. 1A) so as to be detectable. This is due to, in part, to the relatively large diameter d of the detector  103  and the relatively small size of the beam turning device  109 . In terms of actual measurements, for example, given that the diameter c of the core  129  is approximately 1 micron, the size of the beam turning device  109  is much smaller. Although shown as a square, the beam turning device  109  may be any suitable shape, etc. As shown in FIG. 1B, the core  129  may be positioned over the detector  103  off center by the positioning tolerance X. 
     The size of the beam turning device  109  is optimized, keeping a couple of competing parameters in mind. On one hand, one wishes to maximize the size of the turning device  109  to ensure that a maximum amount of the beam of light  136  is coupled into the optical fiber  126 . On the other hand, one wishes to minimize the size of the beam turning device  109  to reduce the occlusion of the detector  103  by the beam turning device  109 . Thus, the actual sizes chosen for the beam turning device  109  should be specified with these competing interests in mind. Specifically, one should determine the size of the beam turning device  109  in light of the desired strength of the beam of light that is to be transmitted through the optical fiber  126  as well as a desired signal strength from the detector  103  in a worst case position of the optical fiber  126  over the detector  103 . 
     With reference to FIGS. 2A and 2B, shown are side (FIG. 2A) and bottom (FIG. 2B) views of an inverted metal-semiconductor-metal (MSM) photodetector  103   a  that is preferably employed as the detector  103  (FIGS.  1 A and  1 B). The MSM photodetector  103   a  is described in detail in Jokerst, N. M. et al.,  Thin Film Inverted MSM Photodetectors,  IEEE Photonics Technology Letters, Vol. 8, No. 2, (February 1996), that is incorporated herein by reference in its entirety. It is understood, however, that any detector that provides a suitable physical shape and electrical properties may be employed as the detector  103 . 
     To provide an overview, the MSM photodetector  103   a  includes a first portion  139  of semiconductor material that generates photogenerated excess carriers when exposed to the incident light  119 . The photodetector  103   a  also includes electrodes  143  and  146  with inter-digitated fingers  149 . When a bias voltage is applied to the inter-digitated fingers, an electric field is formed between the adjacent fingers  149  that causes the photogenerated excess carriers to be swept from the semiconductor material into the fingers, creating a photocurrent that is proportional to the power of the incident light  119 . 
     With reference to FIGS. 3A and 3B, shown is a bi-directional optical link  100   a  according to another embodiment of the present invention. The bi-directional optical link  100   a  is similar in most respects to the bi-directional optical link  100   a  except that a portion of the emitter  106   a  is located on the upper surface of the detector  103 . This embodiment provides a distinct advantage in that the distance that the beam of light  136  travels from the emitter  106   a  to the beam turning device  109  is reduced such that the beam of light  136  has greater spatial coherence. Consequently, more of the light  136  will strike the beam turning device  109  and, ultimately, be transmitted through the optical fiber  126 , resulting in greater transmission power. FIG. 3B shows a corresponding top view of the bi-directional optical link  100   a.  FIG. 3B particularly illustrates how the emitter  106   a  lies over a portion of the detector  103 , thereby occluding that portion. The emitter  106   a  is chosen preferably to reduce the amount of area of the detector  103  that is occluded. Although a portion of the detector  103  is lost due to the placement of the emitter  106   a  in this embodiment, the gain of transmission power into the optical fiber  126  may make this embodiment preferable for some applications. 
     With respect to FIG. 4, shown is a bi-directional optical link  100   b  according to another embodiment of the present invention. The bi-directional optical link  100   b  includes an intermediate host  153  on which the emitter  106   a  and the beam turning device  109  are disposed as shown. The intermediate host  153  is comprised of, for example, silicon or other suitable materials that are transparent to allow the beam of light  136  to pass therethrough. Attached to the intermediate host  153  are spacers  156  that allow the intermediate host  153  to be placed above the detector  103  on the host substrate  113 . Note that electrical connections to the emitter  106   a  may be made through the spacers  156  or via other conductive pathways. The detector  103  is bonded to the host substrate  113  as shown. The spacers may be attached to the intermediate host  153  using appropriate bonding materials. The intermediate host  153  along with the attached emitter  106   a  and beam turning device  109  are attached to the host substrate  113  by bonding the spacers to the host substrate  113 . Note that the emitter  106  (FIG. 1A) may also be employed in the place of the emitter  106   a  so as to prevent the occlusion of the detector  103  as discussed previously. 
     The operation of the bi-directional optical link  100   b  is similar to the bi-directional optical link  100  (FIG. 1A) and is not discussed herein. The bi-directional optical link  100   b  provides distinct advantages in that the emitter  106   a  and beam turning device  109  may be bonded to the intermediate host  153 . Then, assembly comprising the intermediate host  153 , the emitter  106   a,  the beam turning device  109 , and the spacers  156  is mounted on the host substrate  113 . 
     Turning to FIG. 5, shown is a bi-directional optical link  100   c  according to yet another embodiment of the present invention. The bi-directional optical link  100   c  is similar to the bi-directional optical link  100   b  of FIG. 4, except that the emitter  106   a  and the beam turning device  109  are located on top of the intermediate host  153 . 
     Finally, with reference to FIG. 6, shown is a bi-directional link  100   d  according to another embodiment of the present invention. The bi-directional link  100   d  includes an intermediate host  153  on which is mounted the emitter  106   a,  the beam turning device  109 , and a spacer  159  as shown. The detector  103  is then mounted to the emitter  106   a  and the spacer  159  to create a unified assembly. The assembly may then be mounted on an appropriate host substrate  113  (FIG.  1 A), etc. Note that the spacer  159  is preferably comprised of a transparent material to allow the incident light  119  to pass therethrough. 
     In addition to the forgoing, it is also possible to employ multiple stacked detectors  103  that are transparent to all but select frequencies as well as multiple emitters  106 / 106   a  to provide for multiple channel bi-directional transmission. Also, multiple detectors  103  may be arranged in an array in place of a single detector  103  in order to extend the exposure to incident light. 
     Many variations and modifications may be made to the above-described embodiment(s) of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of the present invention.