Abstract:
The disclosed invention relates to a bi-directional optical transceiver module and method of improving the efficiency and reliability of the same, where interference from optical crosstalk and electromagnetic waves are minimized and a wavelength division multiplexing filter can be easily mounted at a predetermined inclination angle, thereby improving the efficiency and reliability of the bi-directional optical transceiver module.

Description:
CLAIM OF PRIORITY 
   This application claims priority to an application entitled “BI-DIRECTIONAL OPTICAL TRANSCEIVER MODULE WITH DOUBLE CAPS,” filed in the Korean Intellectual Property Office on Oct. 10, 2002 and assigned Serial No. 02-61800, the contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a bi-directional optical transceiver module with double caps. More particularly, the present invention relates to a bi-directional optical transceiver module having double caps in which elements, such as a semiconductor laser and a photodiode, are integrated. 
   2. Description of the Related Art 
   Referring to  FIG. 1  showing the construction of a conventional bi-directional optical transceiver module, the conventional bi-directional optical transceiver module includes an optical waveguide element  132 , a sleeve  131 , a lens holder  120  serving as a body tube and having a cylindrical construction, a lens  140  converging each of input and output optical signals, a stem  114  supporting a lower end of the lens holder  120 , and a cap  110  disposed on the stem  114 . 
   The optical waveguide element  132  is packaged in the sleeve  131 . The optical waveguide element  132  serves as a medium through which an input optical signal  160  or an output optical signal  170  is transmitted when they are inputted into or outputted from the bi-directional optical transceiver module, respectively. 
   The lens holder  120  has a cylindrical construction, supports the lens  140 , and serves as a body tube forming a passage for the input optical signal  160  and the output optical signal  170 . The optical waveguide element  132  is inserted and fixed in an upper end of the lens holder  120 . 
   The lens  140  is an element for converging the input optical signal  160  inward of the cap  110  and the output optical signal  170  toward the inserted end of the optical waveguide element  132  and is packaged in an upper portion of the lens holder  120 . In general, the input optical signal  160  and the output optical signal  170  have different wavelengths than each other. 
   Referring to  FIG. 2 , the cap  110  is assembled with and covered on the upper surface of the stem  114 . The cap  110  has a hole formed through a central portion thereof, so that the input and output optical signals can be transmitted and received through the hole. Further, a view window  117  is disposed just under the hole. The view window  117  prevents foreign material from coming into the cap  110  while allowing the input and output optical signals to pass through the view window  117 . 
   The contents of the cap  110  include optical elements such as a photodiode  112 , a semiconductor laser  113 , and a wavelength division multiplexing filter  115 . The photodiode  112  receives the input optical signal  160  and converts it to a corresponding electrical signal. The semiconductor laser  113  modulates the electrical signal into the output optical signal  170 . The wavelength division multiplexing filter  115  separates the input optical signal  160  and the output optical signal  170  from each other and transmits them through their own respective paths. 
   The stem  114  is formed in a plurality of holes (not shown) passing through both faces, and a plurality of the metal lead wires  150  of the hole are arrayed to protrude its portion on the upper face of the stem  114 . The holes which the metal lead wires  150  are arrayed are filled with a sealing material (not shown) for fixing the metal lead wires  150 . The metal lead wires  150  comprises a direct current (DC bias lead), a high-frequency lead connected to a cathode of the semiconductor laser  113 , an anode lead connected to an anode of the photodiode  112  for monitoring an optical element outputted from the semiconductor laser  113 , and a common lead connected to a cathode of the semiconductor laser  113  and the photodiode  112 . 
   The photodiode  112  is created for monitoring the optical element outputted from the semiconductor laser  113  on the stem  114 , and each of the semiconductor laser  113  and the photodiode  112  is electrically connected to metal lead wires  180  by each of the leads  150  and a wire bonding method. 
   The stem  114  serves as a substrate for the optical elements housed in the cap  110  and supports the lower end of the lens holder  120 . 
   The advantage of a conventional bi-directional optical transceiver module is that it allows the packaging of a semiconductor laser and a photodiode together in a cap, thereby giving the conventional bi-directional optical transceiver module a relatively small volume where it may be employed in a relatively small optical system. 
   However, in the conventional bi-directional optical transceiver module, much time is required in assembling the wavelength division multiplexing filter, since the wavelength division multiplexing filter must be mounted at a predetermined angle in the optical path of the input and output optical signals. Further, when a portion of scattered or diffusion-reflected light generated in the wavelength division multiplexing filter, view window, or other elements in the path of the optical signals are introduced into the photodiode, they are superimposed on the normal input optical signal causing optical crosstalk. In addition, the electromagnetic waves generated by the lead wires of the semiconductor laser may also be introduced into the photodiode causing further interference with the electrical signal created in the photodiode. 
   SUMMARY OF THE INVENTION 
   Accordingly, there is a need to provide a bi-directional optical transceiver module where optical crosstalk or interference between the input and output optical signals are minimized to provide a bi-directional optical transceiver module with improved efficiency and reliability. 
   According to one aspect of the invention, a bi-directional optical transceiver module is provided with a wavelength division multiplexing filter that may be more easily mounted. 
   According to another aspect of the invention, further efficiency and reliability may be achieved by providing a bi-directional optical transceiver module where the electromagnetic Waves created by the metal lead wires connected to the semiconductor laser do not interfere with the operation of a photodiode converting an optical signal into an electrical signal. 
   Accordingly, there is provided a bi-directional optical transceiver module comprising: an optical waveguide element through which input and output optical signals pass; a lens holder in an upper end of which the optical waveguide element is inserted and fixed, the lens holder thereby serving as a body tube; a lens disposed at an upper portion in the lens holder, the lens converging each of the input and output optical signals; a stem supporting a lower end of the lens holder; an outer cap disposed on the stem, the outer cap enclosing a photodiode for receiving an input optical signal and converting it to a corresponding electrical signal; a semiconductor laser for modulating the electrical signal into a corresponding output optical signal; a wavelength division multiplexing filter placed at a location with a predetermined inclination angle where the input and output optical signals intersect one another; and an inner cap mounted within the outer cap isolating the photodiode preventing the electromagnetic waves generated by the metal lead wires of the semiconductor laser from interfering with the operation of the photodiode. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a sectional view showing a construction of a conventional bi-directional optical transceiver module; 
       FIG. 2  is a sectional view showing a construction of a cap employed in a conventional bi-directional optical transceiver module; 
       FIG. 3  is a sectional view showing a construction of a bi-directional optical transceiver module according to the present invention; 
       FIG. 4  is a sectional view showing a construction of double caps employed in the bi-directional optical transceiver module shown in  FIG. 3 ; 
       FIG. 5  is a sectional view showing the construction of the double caps shown in  FIG. 4 ; and 
       FIG. 6  is a construction of a bi-directional optical transceiver module having double caps according to a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In accordance with the present invention, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted as it may make the subject matter of the present invention unclear. 
   Referring to  FIG. 3  showing a construction of a bi-directional optical transceiver module having double caps according to a preferred embodiment of the present invention, the bi-directional optical transceiver module includes an optical waveguide element  332 , a sleeve  331 , a lens holder  320  having a cylindrical construction and serving as a body tube, a lens  340  disposed at an upper portion in the lens holder  320 , a stem  314  supporting a lower end of the lens holder  320 , an outer cap  310  disposed on the stem  314 , and an inner cap  311  mounted in the outer cap  310 . 
   The optical waveguide element  332  is packaged in the sleeve  331 . The optical waveguide element  332  serves as a medium through which an input optical signal  360  or an output optical signal  370  is transmitted when they are input into or output from the bi-directional optical transceiver module, respectively. In general, the input optical signal  360  and the output optical signal  370  have different wavelengths than each other. 
   The lens holder  320  has a cylindrical construction, it supports the lens  340 , and serves as a body tube forming a passage for the input optical signal  360  and the output optical signal  370 . The optical waveguide element  332  is inserted and fixed in an upper end of the lens holder  320 . 
   The lens  340  is an element for converging the input optical signal  360  inward of the cap  310  and the output optical signal  370  toward the inserted end of the optical waveguide element  332  and is packaged in an upper portion of the lens holder  320 . A non-spherical lens may be employed as the lens  340 . 
   The stem  314  supports the lower end of the lens holder  320  and serves as a substrate for the optical elements housed in the outer cap  310 . A photodiode  312  and a plurality of metal lead wires  350  for operating a semiconductor laser  313  protrude downward from a lower surface of the stem  314 . The metal lead wires  350  connected to the semiconductor laser  313  serve as conductors for the high-frequency electrical signals that are input into the semiconductor laser  313  from the photodiode  312 . 
   Referring to  FIGS. 4 and 5 , the outer cap  310  is assembled with the stem for covering the upper surface of the stem  314 . The outer cap  310  has a hole  316  formed through a central portion thereof, so that the input and output optical signals can be transmitted and received through the hole  316 . Further, a view window  317  is disposed just under the hole  316 . The view window  317  prevents foreign material from coming into the outer cap  310  and allows the input and output optical signals to pass through the view window  317 . 
   In the outer cap  310 , optical elements such as the photodiode  312 , the semiconductor laser  313 , and a wavelength division multiplexing filter  315  are enclosed. The photodiode  312  receives the input optical signal  360  and converts it to an electrical signal. The semiconductor laser  313  modulates the electrical signal into the output optical signal  370 . The wavelength division multiplexing filter  315  separates the input optical signal  360  and the output optical signal  370  from each other and transmits them through their own respective paths. 
   The wavelength division multiplexing filter  315  is inclined at a predetermined angle and placed at a location where the input optical signal  360  and the output optical signal  370  intersect each other, so as to selectively transmit or reflect the input optical signal  360  and the output optical signal  370 . That is, the wavelength division multiplexing filter  315  is a device for separating the input optical signal  360  and the output optical signal  370  from each other, so as to prevent them from being superimposed upon one another and allow them to proceed along their individual optical paths without experiencing interference from one another. 
   The inner cap  311  is mounted in the outer cap  310 , having an inclined section  311  a extending from the inner cap at the same inclination angle as the inclination angle of the wavelength division multiplexing filter  315 . Further, the inner cap  311  encloses the photodiode  312 , thereby isolating the photodiode  312  from the other components contained within the outer cap  310 . This feature effectively intercepts any scattered or diffusion-reflected lights which may be introduced into the photodiode  312  from outside of the inner cap  311  by isolating the photodiode  312  from the exterior. In other words, the inner cap  311  prevents generation of noise and optical crosstalk by intercepting the scattered or diffusion-reflected lights. It is preferable that the inner cap  311  be made from material so as to prevent electromagnetic waves from reaching the photodiode  312  thereby preventing the electromagnetic waves from interfering with the electrical signal. Further, the inclined section  311  a has a hole formed therein, through which the input optical signal  360  or the output optical signal  370  can be received or transmitted, respectively. 
   The wavelength division multiplexing filter  315  is placed on the inclined section  311  a whereby the wavelength division multiplexing filter is at the same inclination angle with respect to the inner cap  311  and the other components of the bi-directional optical transceiver module, thereby bypassing any adjustment to the inclination angle of the wavelength division multiplexing filter that would be necessary for a conventional bi-directional transceiver module. Accordingly, this feature reduces assembly time. 
   Referring to  FIG. 6  showing a construction of a bi-directional optical transceiver module having double caps according to a preferred embodiment of the present invention, the bi-directional optical transceiver module includes an optical fiber  442 , a lens holder  420  serving as a body tube and having a cylindrical construction, a lens  440  disposed at an upper portion in the lens holder  420 , a stem  414  supporting a lower end of the lens holder  420 , an outer cap  410  disposed on the stem  414 , and an inner cap  411  mounted in the outer cap  410 . 
   The optical fiber  442  is assembled with the lens holder  420 . The optical fiber  442  serves as a medium through which an input optical signal  460  or an output optical signal  470 . 
   As described above, in a bi-directional optical transceiver module having outer and inner caps according to the present invention, the time for assembly is reduced, any optical crosstalk is reduced, and electromagnetic waves generated in a semiconductor laser  413  are prevented from reaching the photodiode, so that a photodiode may efficiently generate electrical signals without interference from any crosstalk or electromagnetic waves. 
   In a bi-directional optical transceiver module according to the present invention, an inner cap having an inclined section  411   a  with a wavelength division multiplexing filter  415  disposed thereon, having the same inclination angle as the inclined portion of the inner cap, all contained within an outer cap so that the wavelength division multiplexing filter can be easily assembled reducing time for the assembly process. Further, in the bi-directional optical transceiver module, the inner cap is made of material encapsulating a photodiode  412  and preventing interference from electromagnetic waves in the operation of the photodiode. Without such interference the photodiode is more efficient and precise in converting an optical signal into an electrical signal. The inner cap also prevents any scattered or diffusion-reflected lights from reaching the photodiode by isolating the photodiode, thereby minimizing the optical crosstalk. 
   While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.