Patent Publication Number: US-2006013540-A1

Title: Single fiber optical transceiver module

Description:
CROSS-REFERENCES TO RELATED INVENTIONS  
      The present invention is related to commonly assigned U.S. patent application Ser. No. 10/741,805, filed on Dec. 19, 2003, titled “Bi-directional optical transceiver module having automatic-restoring unlocking mechanism”, commonly assigned U.S. patent application Ser. No. 10/815,326, filed on Apr. 1, 2004, titled “Small form factor pluggable optical transceiver module having automatic-restoring unlocking mechanism and mechanism for locating optical transceiver components”, commonly assigned U.S. patent application Ser. No. 10/850,216, filed on May 20, 2004, titled “Optical Transceiver module having improved printed circuit board”, and commonly assigned Chinese Patent Application No. 200420033019.8 filed on Feb. 27, 2004, titled “High performance single-fiber SFF optical transceiver module”. The disclosures of these related applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD  
      This disclosure relates to electro-optical devices, specifically, optical transceiver modules for telecommunication and data communication applications.  
     BACKGROUND  
      Computers are increasingly being connected to communication lines and other devices or networks with the computers performing as servers to the peripherally connected computers or devices. The data transfer throughput of computer servers can be increased significantly by using fiber optic lines.  
      Optical signals transmitted through optical fibers are typically converted to electronic signals by an optical transceiver before the optical signals are processed by a computer. Modern optical transceivers have been modularized with standard physical sizes under standard electrical interface agreements and standard optical interface agreements. One such standard agreement is the Small Form Factor (SFF) agreement, and another is the Small Form-factor Pluggable Multi-Source Agreement (SFP MSA).  
      An optical transceiver module typically includes one or more optical transceiver components, also known as optical sub-assemblies. One type of an optical transceiver component converts optical signals into electrical signals. Another type of optical transceiver component converts electrical signals into optical signals. A third type of optical transceiver component can handle both the optical-to-electrical conversions and the electrical-to-optical conversions. Such an optical transceiver component is sometime referred to as a bi-directional optical transceiver component.  
      When optical signals are carried on two optical fiber lines, one line for transmission and the other line for reception, two optical transceiver components are needed in each optical transceiver module. When both transmission and reception signals are carried on a single optical line, each optical transceiver module needs a bi-directional optical transceiver component. Such an optical transceiver module is called a single fiber optical transceiver module. If such an optical transceiver also complies with the SFF agreement, it is called a single fiber SFF optical transceiver module. If such an optical transceiver module complies with the SFP agreement, it is called a single fiber SFP optical transceiver module.  
      A single fiber SFF or SFP optical transceiver module includes a bi-directional optical transceiver component that comprises a photo diode, an optical multiplexer, and a laser unit. The photo diode in the optical transceiver component usually has limited optical signal sensitivity.  
     SUMMARY  
      In one aspect, an optical transceiver module is disclosed, comprising 
          an electrical interface adapted to receive or output an electrical signal;     an optical interface adapted to receive or output an optical signal; and     an optical transceiver component, comprising:     an Avalanche Photo Diode (APD) that converts an optical signal from the optical interface to an electrical signal; and     a laser unit that converts an electrical signal from the electrical interface to an optical signal.        

      In another aspect, an optical transceiver module is disclosed, comprising: 
          an electrical interface adapted to receive or output an electrical signal;     an optical interface adapted to receive or output an optical signal; and     an optical transceiver component, comprising: 
            an Avalanche Photo Diode (APD) that converts an optical signal from the optical interface to an electrical signal;     a laser unit that converts an electrical signal from the electrical interface to an optical signal; and     an optical multiplexer that receives an optical signal from the optical interface and sends the optical signal to the Avalanche Photo Diode and receives an optical signal from the laser unit and sends the optical signal to the optical interface.    
               

      In yet another aspect, an optical transceiver module is disclosed, comprising: 
          an electrical interface adapted to receive or output an electrical signal;     an optical interface adapted to receive or output an optical signal;     an optical transceiver component, comprising: 
            an Avalanche Photo Diode (APD) that converts an optical signal from the optical interface to an electrical current signal;     a laser unit that converts an electrical signal from the electrical interface to an optical signal; and    
            a step-up circuit that converts an electrical current signal from the Avalanche Photo Diode to an electrical voltage signal that is sent to the electrical interface.        

      Embodiments may include one or more of the following advantages. The present invention provides an Avalanche Photo Diode (APD) for optical-to-electrical conversion, which greatly enhances the optical receiving sensitivity. In addition, the present invention provides a step-up circuit in the Printed Circuit Board (PCB) of the optical transceiver module, which extends the functionality of the optical transceiver module.  
    
    
     DESCRIPTION OF DRAWINGS  
       FIG. 1  is a perspective view of an optical transceiver module in accordance with the present invention.  
       FIG. 2  is a partial perspective view of the optical transceiver module under its sheet metal cover.  
       FIG. 3  is a block diagram of the optical sub-assembly for the optical transceiver module of  FIG. 2 .  
       FIG. 4  is a circuit diagram of a step-up circuit. 
    
    
     DETAILED DESCRIPTION  
      Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.  
       FIG. 1  is a perspective view of a single fiber optical transceiver module  100 . The geometry and dimensions of the optical transceiver module  100  in  FIG. 1  are in consistence with a single fiber SFP optical transceiver module or a single fiber SFF optical transceiver module. In particular, the optical interface and the electrical interface are the same for an SFF optical transceiver module and an SFP optical transceiver.  FIG. 1  therefore illustrates both SFP and SFF optical transceiver modules within the scope of the present invention.  
      As shown in  FIG. 1 , the optical transceiver module  100  comprises a case body  110 , a sheet metal cover  120 , an electrical interface  130 , and an optical interface  140 .  
      Under the sheet metal cover  120 , shown as in  FIG. 2 , the optical transceiver module  100  further comprises a Printed Circuit Board (PCB)  220  and golden finger pin stripes  240  on the PCB  220 , a pair of optical connection supporting racks  230 , a bi-directional optical transceiver component  250  and its corresponding optical transceiver component container  260 . In  FIG. 2 , a majority portion of the optical transceiver component  250  is covered by the optical transceiver component container  260 .  
      The end of the optical transceiver component  250  shown in  FIG. 2  can be connected to the single optical fiber line to receive and transmit optical signals. The optical connection supporting racks  230  are used to lock the connector of the single optical fiber after a single optical fiber is inserted into optical interface  140 . On the opposite end of the optical transceiver component  250  (not shown in  FIG. 2 ) are several connection pins to be connected to the PCB  220 .  
      The optical transceiver component  250 , shown in  FIG. 3 , comprises an optical multiplexer  310 , an Avalanche Photo Diode (APD)  320 , and a laser unit  330 .  
      In the reception direction, the optical multiplexer  310  receives the optical input signals from the bi-directional single fiber optic line  340 , and transmits the optical signal to the input of the APD  320 . The APD  320  converts the optical signals into electrical current signals at the electrical output  360  and the electrical output  360  is sent to the PCB  220 . One the PCB, a special purpose IC chip processes the electrical signal from 360 and sends the processed electrical signal out of the optical transceiver module  100  through its electrical interface  130 .  
      In the transmission direction, when electric signals are to be converted to optical signals and sent out to the single fiber optical line, electrical transmission signals are received at the electrical interface  130  of the optical transceiver module  100 . The electrical transmission signals are then processed by a special purpose IC chip on the PCB  220 . The processed electrical signal from the IC chip feeds into the laser unit  330  as shown in  FIG. 3 . The laser unit  330  generates optical signals in response to the input electrical signals. The optical multiplexer  310  receives the optical signals generated by the laser unit  330  and in turn transmits the optical signals to the bi-directional single fiber optical line  340 .  
      On the reception path, a bias input  350  of the APD  320  is needed to insure the photo diode working properly. The bias voltage is supplied by the step-up circuit  400  shown in  FIG. 4 . The input point  470  to the step-up circuit  400  comes from the operation power supply of the optical transceiver module  100 . The output point  480  of the step-up circuit  400  drives the bias input point  350  of the APD  320 . The function of the step-up circuit  400  is to convert the operation power supply (usually around 3 V) to a high voltage power supply (usually around 60 V) at the bias input  350  of the APD  320  as the bias voltage.  
       FIG. 4  shows a detailed circuit diagram of the step-up circuit. The step-up circuit  400  comprises a direct current voltage converter  405 , a plurality of capacitors  410 ,  415 ,  420 , and  425 , a plurality of resistors  430  and  435 , an inductor  440 , and a plurality of diodes  445 ,  450 ,  455  and  460 . The step-up circuit  400  receives operation power supply as its input at point  470 , and the step-up circuit  400  outputs a high voltage power supply  480  that is connected to the bias input  350  of the APD  320 .  
      The present invention provides several advantages over similar prior art optical transceiver modules. First of all, an Avalanche Photo Diode (APD) is used instead of an ordinary photo diode in the present invention for the optical-to-electrical conversion. The APD greatly enhances the optical receiving sensitivity. Secondly, a step-up circuit is included on the Printed Circuit Board (PCB) of the optical transceiver module of the present invention. The step-up circuit generates a bias input for the APD from within the optical transceiver module, which eliminates a high voltage power supply from outside of the optical transceiver module.  
      Although specific embodiments of the present invention have been illustrated in the accompanying drawings and described in the foregoing detailed description, it will be understood that the invention is not limited to the particular embodiments described herein, but is capable of numerous rearrangements, modifications, and substitutions without departing from the scope of the invention. The following claims are intended to encompass all such modifications.  
     PART NUMBERS  
     
         
           100  optical transceiver module  
           110  body case of optical transceiver module  
           120  sheet metal cover of optical transceiver module  
           130  electrical interface  
           140  optical interface  
           220  printed Circuit Board  
           230  optical connection supporting racks  
           240  golden finger pins  
           250  optical transceiver component  
           260  optical transceiver component container  
           300  optical transceiver component block  
           310  optical multiplexer  
           320  Avalanche Photo Diode (APD)  
           330  laser unit  
           340  single fiber input/output  
           350  bias input  
           360  electric output  
           370  electrical transmission input  
           400  step-up circuit  
           405  direct current voltage converter  
           410  capacitor  
           415  capacitor  
           420  capacitor  
           425  capacitor  
           430  resistor  
           435  resister  
           440  inductor  
           445  diode  
           450  diode  
           455  diode  
           460  diode  
           470  step-up circuit input  
           480  step-up circuit output