Abstract:
A fiber optic transceiver incorporating a lens array with an integrated mirror and method of creating the same is disclosed. The transceiver includes the lens array and transceiver housing used to convert optical signals to electrical signals. The lens array includes a fiber side that can be connected to a fiber optic connector. The lens array also has a device side that can be connected to a photodetector. The lens array also includes a mirror that is positioned to transmit an optical signal received from the fiber side to the device side. Both the fiber side and the device include lenses used to provide focused transmission of optical signals. Accordingly, optical signals can be transmitted from a fiber optic connector to a photodetector in a compact and efficient manner at high bandwidths.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a fiber optic transceiver having efficient connection structure. More specifically, the present invention relates to a fiber optic transceiver assembly that receives and transmits at faster data rates while reducing signal loss by incorporating a compact lens array having an integrated folding mirror. 
   Modern fiber telecommunication and data communication systems use transmitter/receiver components, commonly known as transceivers. As is well known, fiber optic transceivers facilitate bi-directional signal transmissions between electronic devices and fiber optic system components. The transceivers include photodetectors, which convert received optical signals to electric signals which can then be used by many electronic devices. Photodetectors are typically positioned at the receiving end of the fiber optic data, video, or audio link. The most common photodetector is the semiconductor photodiode, which produces current in response to incident light. In addition, the transceivers also include transmitter components which produce optical signals. The transmitter portion may include light emitting diodes, laser diodes, or similar components to produce optical signals in response to provided electrical signals. Coupling optical signals into and out of an optical fiber often requires the use of precise optical components to ensure efficient signal transfer. Unfortunately, these optical components are potential sources of signal loss due to contamination or imperfections. 
   Demand for bandwidth in fiber communication systems is limitless. From economic and practical perspectives, it is desirable to minimize the size of all fiber optic components in the system. In fact, certain systems, such as those used for data transmission networks, equipment used for national defense, and the like, require compact yet efficient fiber optic components. As such, it is beneficial to reduce the size of components, provide the most efficient system layout, and eliminate unnecessary parts. Simply stated, there exists a need for a compact fiber optic transceiver assembly that reliably performs at high data rates. 
   The efficient connection of fiber optic cables is important in maintaining efficient operation. To maintain this efficient operation, it is desirable to avoid unnecessary bending or twisting of optical fibers. Thus, the geometry of the fiber connections is also important. Because connections are made directly to the transceiver, this geometry also affects the length of electrical connections mentioned above. 
   It is commonly known that, both optical and electrical signal losses increase as the number of components and connections in a fiber optic system are increased. These signal losses are very critical given the high frequency at which these systems operate. Light sources, such as lasers, and/or optical detectors are often connected to an electric amplifier which has electrical leads. These connections can be a source of signal loss, and often result in reductions in performance because of the electrical lead lengths. Accordingly, it would be very beneficial to provide fiber optic transceiver assembly that does not require long electrical leads between the optoelectric components and related electronic amplifiers. 
   Despite efforts by fiber optic transceiver manufacturers to standardize and minimize fiber optic transceivers, there still exists a need for a compact fiber optic transceiver assembly that performs at high data rates. In addition, there exists a need for a fiber optic transceiver assembly that efficiently and compactly couples optical signals from a standard fiber array connector to a transceiver without bending fiber optic cables. There also exists a need for a fiber optic transceiver assembly that allows for reduced length of electrical leads between the laser or detector photodiode, and the related amplifiers. 
   BRIEF SUMMARY OF THE INVENTION 
   In light of the aforementioned problems, it is one object of the present invention to provide a lens array that permits the creation of a multi-channel fiber optic transceiver assembly that is substantially smaller than previous assemblies while allowing for performance at high data rates and optimum cable routing. A second object of the present invention is to eliminate long electrical leads between the lasers or detectors of the transceiver and the related amplifier chips thereby allowing data to be transmitted at higher data rates while reducing signal loss. A third object of the present invention is to provide better compatibility for standard pick and place automated assembly and manufacturing practices thus lowering costs. 
   The present invention provides the aforementioned advantages and more by incorporating a unique coupling technique between the fiber and the transceiver. More specifically, the present invention includes a lens array having a fiber side connected to a fiber optic connector, a device side attached to a transceiver and a coupling mirror that accommodates optical transmission between the fiber and device sides. The lens array also has a back side configured to appropriately position the mirror surface and achieve the desired redirection of optical signals. As described in further detail below, the fiber side and device of the lens array are oriented perpendicular to one another. As such, in the preferred embodiment, the mirror will be positioned at 45 degrees relative to those sides in order to accommodate signal transmission. 
   The fiber side of the lens array includes at least one fiber side lens used to receive or transmit an optical signal to/from the fiber optic cable. In the preferred embodiment, a ribbon cable is used, thus a plurality of lenses are necessary. As mentioned above, the mirror side includes a reflective surface positioned diagonally relative to both the fiber side and the device side, where the mirror surface is used to appropriately direct the optical signal to/from the fiber side lens. In a similar manner, the device side also includes a device side lens to receive/transmit the optical signal transmitted to/from the mirror. Again, a number of device side lenses are used in the preferred embodiment. The transceiver assembly, in accordance with the present invention, also includes a transceiver housing used to house the components necessary to achieve the desired optical/electrical conversion. For example, the housing will accommodate the optical elements (i.e., photodetectors, light sources) which are positioned immediately adjacent to the lens array. The transceiver housing also includes additional components (a microprocessor, amplifiers, capacitors, etc.) used in the conversion of the optical signal to an electrical signal, or visa versa. 
   Due to the positioning of components in the transceiver assembly, many of the above-mentioned advantages are obtained. Easy connection to the fiber optic cable is achieved due to the configuration of the lens array. Further, efficient coupling to the optoelectric components is achieved in a manner that avoids long lead/cable length. This is made possible due to the placement of these optoelectric components directly on the circuit board, and the positioning of the lens array directly there above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a fiber side of a lens array in accordance with the present invention; 
       FIG. 2  is a perspective view of a device side of the lens array; 
       FIG. 3  is a perspective view of a mirror side of the lens array; 
       FIG. 4  is a front view of the lens array shown in  FIG. 1 ; 
       FIG. 5  is a front view of the device side of  FIG. 2 ; 
       FIG. 6  is a back view of the lens array of  FIG. 3 ; 
       FIG. 7  is a top view of the lens array of  FIG. 3 ; 
       FIG. 8  is a cross sectional view of the lens array; 
       FIG. 9  is a detailed view of a device side lens in accordance with the present invention; 
       FIG. 10  is a detailed view of a fiber side lens in accordance with the present invention; 
       FIG. 11  is a side perspective view of the lens array in accordance with the present invention as it is mounted on an interposer and die; 
       FIG. 12  is a side perspective view of a fiber optic transceiver incorporating the lens array in accordance with the present invention; 
       FIG. 13  is side perspective view of the fiber optic transceiver of  FIG. 12  connect to a fiber optic cable with an MT ferrule; and 
       FIG. 14  is a cross section of a single transmission path within the lens array. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIGS. 1-3  there is shown a lens array  10  in accordance with the present invention. Lens array  10  is depicted as a substantially rectangular component, which includes a fiber side  12 , a device side  14  and a back side  16 . In addition, lens array  10  includes a top side  15  (as more specifically shown in  FIG. 7 ). Those skilled in the art can appreciate that the size and shape of lens array  10  can be varied depending on the type of fiber optic connector and/or device to which it is coupled. In one embodiment of the present invention all non-critical surfaces of lens array  10  have a frosted or otherwise textured surface to facilitate adhesion of lens array  10  to other components in a fiber optic transceiver assembly. 
   Fiber side  12  is shown in greater detail in  FIG. 4 . Fiber side  12  has a connector receptacle  17  with a plurality of fiber side optical openings  18 .  FIG. 4  depicts a total of twelve fiber side optical openings  18 ; however those skilled in the art can appreciate that the size/shape of connector receptacle  17  and the number of fiber side optical openings  18  can vary in different fiber optic systems depending on type of fiber optic cable or the type of connector used. Many different types of connectors are presently used for fiber-to-fiber and fiber-to-component connections, including FC, fiber distributed data interface (FDDI), LC, MT Array, subscription channel (SC), SC Duplex and straight tip (ST) connectors. These different types of connectors are used in varying applications based upon their unique performance and overall characteristics. Structures on fiber side  12  will be specifically configured to cooperate with the type of connector being used. As shown in  FIG. 4 , fiber side  12  further has connecting pins  20  used to attach a fiber optic connector  62  more completely (shown in  FIG. 14 ) to lens array  10 . 
     FIG. 5  shows a front view of lens array  10  in greater detail. Device side  14  has a device receptacle  21  with a plurality of device side optical openings  22 . Again, those skilled in the art can appreciate that the shape and size of device receptacle  21  and the number of device side optical openings  22  can vary in different fiber optic systems depending on type of fiber optic cable, type of connector, type of device and the like. Those skilled in the art can also recognize that there are several different types of electro-optic components, including but not limited to, PIN photodiodes, avalanche photodiodes, LEDs, lasers, vertical cavity surface emitting lasers (VCSEL), and the like. The selection of particular components will depend on spectral characteristics of both the fiber optic system and the optical elements. Device side  14  also includes alignment fiducials  24  used to secure lens array  10  to the related optical components of a transceiver assembly (shown in  FIG. 11 ). 
     FIG. 6  shows mirror side  16  in greater detail, while  FIG. 7  shows top side  15  in greater detail. As will be discussed in further detail below, a mirror surface  26  is created at this location which will provide an internal reflective surface for the optical signals being transmitted through lens array  10 . The material/air interface at mirror surface  26  provides sufficient internal reflectance to cause optical signals to be appropriately redirected. Top side  15  also includes alignment sites  30  provided for viewing alignment features when coupling lens array  10  with a photodetector  52  and a fiber optic connector  62 . Alignment sites  30  are constructed of any optically clear substance that permits light transmission. 
   Referring now to  FIG. 8  there is shown a cross sectional illustration of lens array  10  in accordance with the present invention. Fiber side  12  has a fiber side lens  32  positioned in opening  18  of lens array  10 . Similarly, device side  14  has a device side lens  34  which is positioned in opening  22  of the lens array  10 . As can be appreciated, both fiber side lens  32  and device side lens  34  are formed during the molding of lens array  10 . Alternatively, these could be separately formed components. Fiber side lens  32  and device side lens  34  are constructed from any heat-resistant amorphous polymeric material available for injection molding, including but not limited to amorphous polyetherimides, polyimides, polycarbonates, polymethyl methacrylate (PMMA), and the like. Mirror surface  26  is positioned at a particular angle of reflection  40  with respect to the fiber side optical path or optical axis  42 . A reflective area  38  on reflective surface  26  provides 100% reflection for all optical signals in this area.  FIG. 8  shows an angle of reflection  40 , or the angle between fiber side optical signal axis  42  and reflective surface  26  (and the mounting surface  39  of lens array  10 ), is a 45° angle to achieve a 90° redirection of the optical signal. Those skilled in the art can appreciate that the angle of reflection  40  can change depending on the position of fiber side  12  with respect to device side  14  in order to provide proper transmission of an optical signal along device side optical axis  44 , and subsequently to device side lens  34 . 
     FIG. 9  depicts detailed dimensions of device side lens  34  as used in one embodiment. A signal area  46  for signals transmitted between mirror surface  26  and device side lens  34  is preferably within a 250 μm diameter around a middle of device side lens  34 . Referring to  FIG. 10 , a similar illustration of fiber side lens  32  is shown. A signal area  48  of optical signals transmitted between fiber side lens  32  and mirror surface  26  is also preferably within a 250 μm diameter around a middle of fiber side lens  32 . While  FIGS. 9 and 10  shows particular curvatures for device side lens  34  and fiber side lens  32 , respectively, those skilled in the art will recognize that various lens curvatures can be used depending on the specific characteristics of the fiber optic system. 
   Now that each component of the present invention has been discussed, following is a discussion of the assembly and operation of a fiber optic transceiver  50  incorporating lens array  10  in accordance with the present invention. Referring to  FIG. 11 , in one embodiment of the present invention, lens array  10  in accordance with the present invention is incorporated into transceiver  50  by attaching device side  14  of lens array  10  to an operative transceiver surface  52  via device receptacle  21 , where operative transceiver surface  52  can be an interposer (not shown) and a die (not shown), such as a vertical cavity surface emitting laser (VSCEL) and a photodiode array die as commonly known in the art. While the figures depict the operative transceiver surface  52  as a photodiode, those skilled in the art recognize that many configurations are possible including combinations of surface illuminated or substrate illuminated photodiodes, phototransistors, and surface or substrate emitting, LEDs, VSCELs, edge emitting laser diodes, and the like. 
   Referring now to  FIG. 12 , lens array  10  and a circuit board attached to transceiver surface components  52  are inserted into a transceiver housing  58  which also includes a microcontroller  54  capacitors  56  and amplifiers (not shown). Transceiver housing  58  includes mounting openings  60  whereby transceiver  50  can be mounted within a fiber optic system. As will be easily appreciated, the above mentioned components within housing  58  help to provide efficient operation of transceiver  50  by providing additional functions, such as filtering, signal conditioning, amplifying, gain adjusting, etc. 
     FIG. 13  illustrates a fiber optic connector  62  which is inserted into transceiver casing  58  via connector receptacle  17  in order to secure fiber optic connector  62  to lens array  10 . In this manner, a fiber optic cable  64  carrying optical signals is coupled to lens array  10 . As can be seen, this connection does not require bending or twisting of fiber optic cable  64 . Again, this helps to maintain efficient operation. In addition, a “compact package” results after the connection is made, meaning that optical signals do not have to travel great distances to reach the sensitive surfaces of transceiver  50 . Further, all electrical components are close to one another, thus eliminating long lead lengths. 
   An example of one transmission path within lens array  10  is shown in  FIG. 14 . Here, an optical signal is carried by fiber optic cable  64  to fiber side lens  32 . Preferably, optical signal  42  is received at and emitted from within a 25 μm radius and collected by the fiber side lens  32  as previously discussed in relation to  FIGS. 8-10 . Optical signal  42  then travels to reflective surface  26 , and is redirected. Upon reflection off reflective surface  26 , the optical signal travels to device side lens  34 . Again, referring to  FIGS. 8-10 , it is preferable for optical signal  46  to be directed to within a 10 μm radius at the point of focus of device side lens  34 . While the above discussion involves transmission from the fiber to the transceiver, in actual use signals will be transmitted in both directions. Thus, the transmit mode will cause optical signals to travel in the opposite direction. As also shown in  FIG. 14 , this particular embodiment transmits the optical beam through the transparent substrate  66  of the transceiver chip, in this case is made of sapphire but could be silicon or other material substantially transparent to the signal beam  44 . Other embodiments could focus the optical beam  44  directly on the emitting/detecting surface  52 . 
   The aforementioned components of fiber optic transceiver  50  in accordance with the present invention can be attached to one another with techniques commonly known in the art, including but not limited to mechanical fastening, soldering, thermo-compression bonding, adhesives and epoxies, and the like. 
   As discussed above, the lens array  10  of the present invention utilizes a reflective surface  26  to accomplish the desired redirection of optical signals. This type of “mirror” is known by those skilled in the art as a totally internal reflecting (TIR) mirror. In this structure, light transmitted inside a material which is incident to a smooth outer surface, will be totally reflected off that surface, rather than transmitted through the air on the opposite side of the surface. This characteristic is created by designing an appropriate angle of reflection, and appropriately selecting materials. Specifically, the angle of reflection must be shallow enough, and the material index of refraction large enough for this internal reflection to occur. Thus, utilizing the angled reflective surface  26  of the present invention, and appropriate materials making up lens array  10 , this TIR mirror structure is achieved. Naturally, different structures could be utilized. For example, if the refractive index of the various materials was not appropriate, a more classical mirror could be attached to reflective surface  26 , to achieve the desired reflection of optical signals. Naturally, polished or further processed surfaces could also be utilized to cause reflection at reflective surface  26 . While the preferred embodiment includes the TIR mirror, each of these other options are considered to be within the scope of the present invention. 
   In addition to the variations discussed above, it is not necessary for reflective surface  26  to be entirely flat. As will also be anticipated by those skilled in the art, reflective surfaces having various curves or contours may be utilized to appropriately redirect optical signals in a desired manner. As such, the present invention is not intended to be limited to flat mirrors and/or reflective surfaces, but also includes contoured or curved surfaces. 
   As mentioned above, a TIR mirror is contemplated in the preferred embodiment. One potential concern for such a mirror is the contamination or interference caused by moisture build-up. To alleviate this concern, the lens array  10  of the present invention may include a protective cover on reflective surface  26 . The protective cover may exist immediately on the back of reflective surface  26 , or may create an air gap behind this surface. In this way, the possibility of moisture developing on reflective surface  26  is eliminated, and the reflective characteristics can be maintained. This same concept could also easily be utilized at the input/output interfaces. (i.e., device side lens  34  and fiber side lens  32 ). Specifically, a gap or window could be created adjacent to fiber side lens  32  to create isolation and avoid the possibility of condensation building up upon these surfaces as well. In this case, the fibers themselves would be placed in direct contact with these windows, thus avoiding any possibility of condensation being created at that interface. Similar structures could easily be created adjacent device side lens  34 . 
   To further clarify the nature of the preferred embodiment, it should be made clear that the lens array  10  of the present invention is contemplated to be a single molded part. In the molding process, appropriate lenses and surfaces are created to accommodate the receipt and transmission of optical signals using material with appropriate optical transmission characteristics. More specifically, the material is optically transmissive in order to accommodate the functions outlined above. Within the body of lens array  10 , free space transmission of signals is utilized. Stated alternatively, each of the signals received at the various lens are not contained or otherwise isolated within lens array  10 . Rather, the signals are appropriately directed and reflected by the lens and reflective surfaces themselves in order to achieve desired operation. As contemplated, this requires appropriate alignment and positioning of the various lenses and reflective surface  26 , in order to achieve this function. Naturally, the material chosen is also preferably moldable, to achieve appropriate molding and formation of the desired lens product. In the preferred embodiment, this material is also tolerant to very high temperatures. By being appropriately temperature tolerant, the lens array will be able to withstand subsequent manufacturing operations such as a reflow soldering processes, etc., once attached to a circuit board. 
   The invention has herein been described in its preferred embodiments to provide those skilled in the art with the information needed to apply the novel principles and to construct and use the embodiments. However, it is to be understood that the invention can be carried out by specifically different devices and that various modifications can be accomplished without departing from the scope of the invention itself, which is set out in the following claims: