Abstract:
A COB (Chip On Board) package type bi-directional transceiver module is disclosed to include a photosensitive member bonded to a printed circuit board by COB (Chip On Board) package and adapted for receiving a first optical signal, and a light source installed by TO-can package and adapted for transmitting a second optical signal.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a bidirectional transceiver module and more particularly, to a COB package type bi-directional transceiver module, which has the photo diode bonded to the printed circuit board by COB (chip on board) package and the laser diode installed by means of TO package. 
   2. Description of the Related Art 
   A bi-directional WDM (wavelength division multiplexer) transceiver module is capable of transmitting and receiving two light sources of different wavelengths (1550/1330 nm) through a SMF (Single Mode Fiber), achieving bi-directional transmission operation. This bi-directional transmission design increases the use of the bandwidth of a fiber. In comparison to the design of conventional bi-directional fiber optic transmission modules, this bi-directional transmission design saves one fiber optic, minimizes module size, and increases the use of bandwidth in high density main distribution facility room. 
     FIG. 1  is a schematic drawing of a bi-directional WDM transceiver module according to the prior art. According to this design, the bi-directional WDM transceiver module comprises a laser diode  11 , a photo diode  12 , a WDM (wavelength division multiplexer)  13 , a filter  14 , and a module housing  17  houses the members. The bi-directional WDM transceiver module is connectable to a SMF (Single Mode Fiber)  16  through a fiber optic connector  15  (for example, a receptacle, pigtail, or the like) for bi-directional transmission of signal. The bi-directional WDM transceiver module uses the laser diode  11  as light source that receives electric signal from driver and converts the signal into optical signal of wavelength λ 1  (for example, 1550 nm) for transmission. The bi-directional WDM transceiver module uses the photo diode  12  as photosensitive means to receive optical signal of wavelength λ 2  (for example, 1310 nm) and to convert the signal into an electric signal, for enabling the electric signal to be amplified by a TIA (Transimpedance Amplifier) for output. The WDM  13  is adapted to separate the light sources of wavelength λ 1  and wavelength λ 2 , for enabling optical signal of λ 1  from laser diode  11  to pass through WDM  13  to the SMF  16  for output. Optical signal of λ 2  from SMF  16  is reflected onto the filter  14  by the WDM  13  and then sent received by the photo diode  12 . Therefore, the bi-directional WDM transceiver module achieves bi-directional transmission operation. 
   The manufacturing of the aforesaid prior art bi-directional WDM transceiver module is started from the laser diode  11  which is housed in a TO package, and then the ferrule of the fiber optic connector  15  is aligned to the laser diode  11  and welded on the module housing  17 , and then the photo diode  12 , which is also housed in a TO package, and the other components are mounted in the module housing  17 , completing OSA (Optical Sub-assembly) manufacturing process, forming a structure of bi-directional transceiver as shown in  FIG. 2 . During the manufacturing process of the bi-directional transceiver, the LD adopts TO packaging, and the photo diode can also adopts TO packaging. 
   In order to satisfy heavy bandwidth requirement for telecommunication and network, optical communication networks will become more and more popular in city areas. However, due to limited land space and heavy rent for office in city areas, there is a limitation to the expansion of trucking space. Therefore, it is important to provide more number of transmission ports with same size of telecommunication and network facility. The most effective and direct way to solve the problem is to reduce the size of the bi-directional transceiver so that more transmission ports can be provided in a limited space. 
   SUMMARY OF THE INVENTION 
   The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a COB (Chip On Board) package type bi-directional transceiver module, which has the photo diode directly bonded to the signal receiving and amplifying printed circuit board of bi-directional transceiver at the same side that optical signal comes in by means of COB (Chip On Board) package to effectively save the module size, eliminating the use of conventional TO package and lead wires. 
   According to one embodiment of the present invention, the COB (Chip On Board) package type bi-directional transceiver module comprises a photosensitive member bonded to a signal receiving and amplifying printed circuit board of bi-directional transceiver at the same side that optical signal comes in by COB (Chip On Board) package and adapted for receiving a first optical signal, and a light source installed by TO-can package and adapted for transmitting a second optical signal. The photosensitive member can be a photo diode, preferably, a PIN photo diode. The light source can be a laser diode. The wavelength of the first optical signal is 1550 nm, and the wavelength of the second optical signal is 1310 nm. Alternatively, the COB (Chip On Board) package type bi-directional transceiver module can be so made that the first optical signal has the wavelength of 1310 nm, and the second optical signal has the wavelength of 1550 nm. The COB (Chip On Board) package type bi-directional transceiver module further comprises a WDM (Wavelength Division Multiplexer) adapted to separate the first optical signal and the second optical signal. 
   According to a second embodiment of the present invention, the COB (Chip On Board) package type bi-directional transceiver module comprises a photosensitive member adapted for bonding to a signal receiving and amplifying circuit board at the same side that optical signal comes in by COB (Chip On Board) package for receiving a first optical signal, and a light source adapted for bonding to a laser driving circuit board thereof at the same side that optical signal emits out by COB (Chip On Board) package for transmitting a second optical signal. According to this embodiment, the photosensitive member can be a photo diode, preferably a PIN photo diode, and the light source can be a laser diode. The photosensitive member and the light source can be bonded to a common printed circuit board. Alternatively, the photosensitive member and the light source can respectively be bonded to a respective printed circuit board. The wavelength of the first optical signal is 1550 nm, and the wavelength of the second optical signal is 1310 nm. Alternatively, the COB (Chip On Board) package type bi-directional transceiver module can be so made that the first optical signal has the wavelength of 1310 nm, and the second optical signal has the wavelength of 1550 nm. The COB (Chip On Board) package type bi-directional transceiver module further comprises a WDM (Wavelength Division Multiplexer) adapted to separate said first optical signal and said second optical signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic drawing showing the arrangement of a bi-directional transceiver module according to the prior art. 
       FIG. 2  is a schematic structural view of the prior art bi-directional transceiver module. 
       FIG. 3  is a schematic plain view of a COB (Chip On Board) package type bi-directional transceiver module according to the present invention. 
       FIG. 4  is an elevational view of the COB (Chip On Board) package type bi-directional transceiver module according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 3 , a bi-directional transceiver module is shown comprising a chip photo diode  31  directly bonded to a circuit board  32  at the same side that optical signal comes in by means of COB (Chip On Board) package and electrically connected to a signal receiving and amplifying circuit by wire bonding, a protective shield  33  with a lens therein covered over the chip photo diode  31  for condensing the focus, a laser diode  11  installed by TO package, a WDM (wavelength division multiplexer)  13 , a filter  14 , a fiber optic connector  15 , and a module housing  17 . The WDM  13  is adapted to separate optical signals of different wavelengths (the first optical signal and the second optical signal) from the laser diode  11  and the chip photo diode  31 . The laser diode  11  and the fiber optic connector  15  are engrafted on the module housing  17  by laser welding and prior art alignment technique so that the light emits from the laser diode  11 , passes through the WDM  13 , enters the fiber optic connector  15 , and goes out from the transceiver. The module housing  17  is made of metal and equipped with two pins  34 . Pin  34  intersects the PCB and locates the module housing  17  at a specific position on PCB so that the light coming from outside and entering the fiber optic connector  15  is reflected by the WDM  13 , passes through the filter  14  and protective shield  33 , and directs to the chip photo diode  31 . 
   Referring to  FIG. 4 , the chip photo diode is installed by means of COB package, and the laser diode is installed by means of TO package. Alternatively, the chip photo diode and the laser diode both can be installed by COB package to minimize the size of the bi-directional transceiver module. 
   As indicated above, the invention uses COB (Chip On Board) package to directly bond the photo diode to the printed circuit board at the same side that optical signal comes in to reduce the module size, while having the laser diode installed by means of TO package. Using COB package to bond the photo diode to the printed circuit board instead of TO package greatly reduce the module size. Therefore, the invention enables an optical communication facility to provide more number of communication ports without increasing the size. Because of reduced size, signal transmission distance is relatively reduced, resulting in low noise and high reliability. 
   A prototype of COB (Chip On Board) package type bi-directional transceiver module has been constructed with the features of the annexed drawings of  FIGS. 3 and 4 . The COB (Chip On Board) package type bi-directional transceiver module functions smoothly to provide all of the features discussed earlier. 
   Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.