Abstract:
Techniques for multiple channel optical transceivers for use in network devices are provided. In general, a row of optical emitters are disposed adjacent to a row of optical detectors in order to provide increased bandwidth and reduced optical crosstalk. Each row can be electrically coupled to an associated transmitting electronic board or detecting electronic board to reduce electronic crosstalk. The configuration of the optical emitters and detectors allow enhanced flexibility in dressing out the optical fibers and routing them to other network devices.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to optical transceiver modules. More specifically, the invention relates to optical transceiver modules with multiple channels including a dual row pattern of optical emitters/detectors and separate transmit and detect electronics. 
   As fiber optics developed, many new technologies emerged to enhance their use. For example, fairly recently, a specification for a new generation of optical modular transceivers was developed named “small form-factor pluggable” (SFP). SFP transceivers are designed to be high bandwidth, small physical size and easily changeable (including being hot-swappable) on the line card of the network device. 
   Unfortunately, integrated circuit (e.g., application specific integrated circuit or ASIC) densities have increased to the point that line cards are now optical port density limited, rather than switch or processor limited. Thus, the electronics on the motherboards of the line card have the capacity to process more optical information than is being transmitted and received from the optical ports of the line card. This extra capacity is potential bandwidth that is not being realized. As a result, many line cards that use conventional SFP optics strand bandwidth. 
   There have been many attempts to achieve higher optical port densities. For example, parallel ferrule connectors have been utilized to solve the problem of optical port density on the line card faceplate. However, this typically requires fanout cables that are bulky, expensive and may be unreliable. 
   Single-mode parallel solutions are available, but they have typically been very large, expensive and difficult to manufacture. Additionally, they may require permanently attached fiber pigtails due to alignment requirements. 
   As a solution to solve the high cost of these early parallel offerings, the parallel vertical cavity self emitting laser (VCSEL) technology was developed. However, VCSEL technology blossomed at shorter wavelengths (e.g., 850 nm) and enabled only very short multi-mode applications. Also, the majority of VCSEL based parallel optics are designed for parallel data transfer, where all channels of data are synchronous or plesiochronous. These products, therefore, typically do not allow multiple channels that are totally independent (e.g., four independent, serial data channels). Lastly, the reliability of this solution is still questionable. 
   It would be beneficial to have innovative techniques for providing optical transceiver modules that provides multiple channel optics without the disadvantages normally associated with this capability. Additionally, it would be beneficial if the optical and electrical crosstalk is reduced or eliminated. 
   SUMMARY OF THE INVENTION 
   The present invention provides innovative techniques for multiple channel optical transceiver modules for use in network devices. In general, a row of optical emitters (e.g., laser diodes or light emitting diodes (LEDs)) are disposed next to a row of optical detectors (e.g., laser detectors). Each row can be electrically coupled to an associated transmitting electronic board or detecting electronic board within the module. 
   Advantages include that the fiber cables from the optical transceiver module can be dressed out as multiple pairs or duplexes. Reduced optical crosstalk can be achieved as a result of the separate optical emitter/detector rows. Reduced electrical crosstalk can be achieved through the separate transmitting and detecting electronic boards. As the optical emitters and detectors are in separate rows, fabrication of the bars can made more efficient and with higher yields than hybrid bars. Thus, multiple channel optical transceiver modules can be provided with one or more of these features with the added flexibility. Some specific embodiments of the invention are described below. 
   In one embodiment, the invention provides an optical transceiver module. The module comprises a row of multiple optical emitters and a row of multiple optical detectors, wherein the row of optical emitters is parallel to the row of optical detectors. In some embodiments, there are four optical emitters and four optical detectors. 
   In another embodiment, the invention provides an optical transceiver module. The module comprises a transmitting electronic board electrically coupled to an optical emitter for controlling the optical emitter and a receiving electronic board electrically coupled to an optical detector for receiving electrical signals from the optical detectors. The transmitting and receiving electronic boards can be retained in the module in parallel. 
   In another embodiment, the invention provides an optical transceiver module. The module comprises a row of four optical emitters; a transmitting electronic board electrically coupled to the row of optical emitters for controlling the optical emitters; a row of four optical detectors, wherein the row of optical emitters is parallel to the row of optical detectors; and a receiving electronic board electrically coupled to the row of optical detectors for receiving electrical signals from the optical detectors 
   Other features and advantages of the invention will become readily apparent upon review of the following description in association with the accompanying drawings, where the same or similar structures are designated with the same reference numerals. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an example of a parallel optical transceiver that is pluggable into a line card. 
       FIGS. 2A and 2B  show conventional ferrule patterns that include transmitting and receiving optical fibers. 
       FIG. 2C  shows a ferrule pattern of one embodiment of the invention for interfacing with a row of four optical emitters and a row of four optical detectors. 
       FIG. 2D  shows how the optical fibers from the ferrule pattern in  FIG. 2C  can be dressed out as one or more fiber pairs. 
       FIG. 3  illustrates an embodiment of the invention including transmit and receive bars and separate electronic boards for transmitting and receiving. 
       FIG. 4  shows the dual row oritentation taking advantage of an angled surface on the ferrule to reduce optical crosstalk in the transceiver. 
       FIGS. 5A and 4B  show an example of a cable that can be connected to a parallel optical transceiver of the invention. 
       FIG. 6  illustrates another example of a cable that can be utilized with embodiments of the invention. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
   In the description that follows, the present invention will be described in reference to embodiments that are used in association with multiple channel optical transceivers for use with line cards of network devices. However, embodiments of the invention are not limited to any particular version, protocol, environment, application, or implementation. For example, although embodiments of the invention will be described in reference to specific embodiments, the invention can be advantageously applied to many embodiments. Therefore, the description of the embodiments that follows is for purposes of illustration and not limitation. 
     FIG. 1  shows an example of a multiple channel optical transceiver that is pluggable into a line card. A line card  1  is inserted into a network device such as a switch, router, crossconnect, and the like. Line card  1  includes a motherboard  3  including electrical components/connections (not shown) and a bezel  5 . A connector  7  is mounted on motherboard  3  in order to electrically couple an optical transceiver module  9  to electrical components on the motherboard. 
   Optical transceiver module  9  is pluggable into connector  7 . A cage assembly  11  is mounted on motherboard  3  to protect and retain optical transceiver module  9  once it is inserted into connector  7 . As shown, connector  7  has two slots and associated rows of pins for accepting parallel electronic boards that are housed with the optical transceiver module. Connector  7  can be a single two-row connector or two single-row connectors on above the other. An internal configuration of optical transceiver module  9  will be discussed in more detail in reference to  FIG. 3 . 
   A plug  13  can be inserted into optical transceiver module  9 . For example, the plug can be an MTP or MPO plug. Plug  13  includes a ferrule  15  that retains and aligns the multiple optical fibers in the cable. As shown, optical transceiver module  9  can include a latch  17  to assist in retaining plug  13  in transceiver module  9  when inserted therein. Other types of plugs and retention mechanisms can be utilized with other embodiments. 
   The ferrules retain optical fibers so they can interface with corresponding optical emitters and optical detectors.  FIGS. 2A and 2B  show conventional ferrule patterns that include transmitting and receiving optical fibers. 
   In  FIG. 2A , a ferrule  101  retains eight optical fibers. Typically, the spacing of the optical fibers in this arrangement is every 125 microns. Four of the optical fibers  103  transmit to the optical transceiver module and four of the optical fibers  105  receive optical transmissions from the optical transceiver. In this configuration, optical fibers that are similar are grouped together. 
     FIG. 2B  shows a different ferrule pattern. A ferrule  111  includes four optical fibers  113  that transmit to the optical transceiver module alternating with four optical fibers  115  that receive optical transmissions from the optical transceiver. In this configuration, transmitting and receiving optical fibers are alternated. 
   Optical emitters and detectors are disposed within the optical transceiver module to align with the optical fibers in the ferrule. For example, a bar that includes both laser diodes and detectors may need to be manufactured for the ferrule patterns of  FIGS. 2A and 2B . 
   A problem results in that laser diodes and detectors are generally incompatible, which makes hybrid bars difficult to manufacture and resulting low yields. Additionally, the spacing between transmitting and receiving optical fibers can be fairly close (e.g., 125 microns), which can increase optical crosstalk.  FIG. 2C  shows a ferrule pattern of one embodiment of the invention for interfacing with a row of four optical emitters and a row of four optical detectors. 
   A dual row ferrule  121  retains eight optical fibers. A row of four optical fibers  123  that transmit to the optical transceiver module are disposed parallel to a row of four optical fibers  125  that receive optical transmissions from the optical transceiver. As indicated by a dashed line  127 , a bar of laser diodes can be manufactured for one half and a bar of laser detectors can be manufactured for the other half. Thus, manufacturing a hybrid bar is not required. 
   Furthermore, the additional spacing between the laser diodes and detectors results in reduced optical crosstalk. For example, because the fabrication of every other laser diode or detector  129  can be skipped, the spacing can be 250 microns between adjacent laser diodes and detectors (i.e., both within a row and row-to-row). Additionally, this configuration creates multiple transmit/receive pairs, which makes transitions to duplex fiber cable much easier. 
   Conventional equipment and settings can be utilized to manufacture these bars. As an example, the equipment for manufacturing bars for  FIGS. 2A and 2B  can be utilized to make the separate bars. When done in this manner, the fabrication of laser diodes and detectors  129  can be skipped to save costs. Alternatively, laser diodes and detectors  129  can be manufactured on the bars, but not utilized. 
     FIG. 2D  shows how the optical fibers from the ferrule pattern in  FIG. 2C  can be dressed out as one or more fiber pairs. As shown, a pair  141  includes a transmitting optical fiber and a receiving optical fiber. In some embodiments, four pairs are supported. Each pair can be a line cord pair (e.g., similar to speaker wire) where a user can separate the individual lines as the desired. By allowing the transmit and receive optical fibers to go to different locations, daisy-chained connections can be easily supported. Parallel ribbon fiber optic cables require all ports to go to a same port and requires receiving and transmitting optical fibers to go to the same transceiver, which prevents daisy-chaining. Conventional techniques such as the use of two breakout cables, couplers and cables also do not provide the flexibility provided by embodiments of the invention. 
   In other embodiments, the optical fibers are dressed out in single lines (e.g., eight single lines). In still other embodiments, mixed pairs and single lines can be present. Thus, the optical fibers can be dressed out in different configurations depending on the application (see also  FIG. 6 ). 
   Now the description will turn to further specifics of the optical transceiver module.  FIG. 3  illustrates a optical transceiver module including transmit and receive bars and separate electronic boards for transmitting and receiving. A motherboard  201  has a connector  203  mounted thereon. Connector  203  has two slots and associated rows of pins for accepting parallel electronic boards that are housed within an optical transceiver module  205  (the dashed lines represent the outline of the module so that internal components can be seen). 
   Within optical transceiver module  205  is a transmitting electronic board  207  and a receiving electronic board  209 . Each board has the electrical circuitry and components to perform the associated tasks. The boards have edge connectors that provide the electrical connection to the motherboard via connector  203  when inserted in the twin slots of the connector. 
   Flexible electrical connections couple transmitting electronic board  207  to a transmitting bar  211 , which can have a row of laser diodes or LEDs (see, e.g.,  FIG. 2C ). Similarly, flexible electrical connections couple receiving electronic board  209  to a receiving bar  213 , which can have a row of laser detectors. A ferrule (e.g., MTP ferrule)  215  is a part of the cable plug and retains optical fibers so they can optically couple to transmitting bar  211  and receiving bar  213 . 
   Electrical crosstalk within optical transceiver module  205  is reduced or eliminated because the transmitting and receiving electronics are on separate, parallel boards as shown. Conventional optical transceivers modules include an electronic board with both transmitting and receiving circuitry/components, which facilitates electrical crosstalk. 
     FIG. 4  shows how the dual row orientation in some embodiments can take advantage of an angled surface on the ferrule to reduce optical crosstalk in the transceiver. A receiving optical fiber  251  delivers light to receiving bar  253 . Similarly, light from transmitting bar  255  is delivered to transmitting optical fiber  257 . As shown receiving bar  253  and transmitting bar  255  are on a substrate  259  that communicates to the electronic boards through flexible electrical connections. 
   A ferrule  261  retains the optical fibers and is angled at the end proximal to receiving and transmitting bars  253  and  255 , respectively. The orientation of the receiving and transmitting bars to the angle of the ferrule is designed so that light reflected at the aperture of transmitting optical fiber  257  is directed away from the aperture of receiving optical fiber  251 . Thus, optical crosstalk can be reduced by the specific orientation of the optical emitters and detectors relative to the angled end on ferrule  261 . 
     FIGS. 5A and 5B  show an example of a cable that can be connected to a parallel optical transceiver of the invention. With regard to  FIG. 5A , an optical transceiver module  301  includes an adapter  303  at one end for receiving the end of a cable housing  305 . Cable housing  305  includes a dense face mountable interconnect  307  for connecting to adaptor  303 . 
   A ferrule  309  retains the optical fibers for optical coupling to optical emitters and detectors in optical transceiver module  301 . As shown, cable housing  305  has a 90 degree bend, which may be desirable for routing the cables. Eight cables  311  are shown extending out of furcation block  313 . These cables can be dressed out as four independent duplex cables for connection to line cards in other network devices. In other embodiments, there can be fewer or more cables, the cables can be dressed out as pairs or as single cables, or any combination depending on the application. 
     FIG. 5B  shows dense face mountable interconnect  307  of cable housing  305  inserted into optical transceiver module  301 . These figures illustrate one way of connecting the optical transceiver module to the optical fibers in the cables, but other techniques may be advantageously utilized with the invention. 
   For example, in one embodiment, a MTO or MTP plug is utilized that fans out into four duplex cables.  FIG. 6  illustrates an example of this cable. A plug  401  houses a ferrule  403  that retains the optical fibers. The parallel cable of optical fibers are separated out into individual optical fibers by a furcation block  404 . The furcation block can provide buffering and strain-relief in addition to routing the optical fibers into standard “yellow jacket” cabling. There are eight optical fibers that are dressed out into four duplex cables  405  as shown. As mentioned previously, the optical fibers may be dressed out as eight single cables or many other configurations. 
   While the above is a complete description of preferred embodiments of the invention, various alternatives, modifications, and equivalents can be used. It should be evident that the invention is equally applicable by making appropriate modifications to the embodiments described above. For example, although the invention has been described in relation to specific embodiments, the invention can be advantageously applied to other embodiments. Therefore, the above description should not be taken as limiting the scope of the invention as defined by the metes and bounds of the appended claims along with their full scope of equivalents