Abstract:
In a container assembly for a laser diode module in which a temperature control device is not incorporated in advance, a heat-insulative casing is adapted to accommodate the laser diode module. A temperature detector is accommodated in the casing. A thermal coupling member is accommodated in the casing so as to thermally couple the laser diode module and the temperature detector. A heat-conductive plate member is attached to the casing. A heat transfer element is interposed between the thermal coupling member and the plate member so as to allow heat transfer therebetween. A sealing member is disposed between the casing and the plate member so as to seal the heat transfer element. A heat transfer controller causes the heat transfer element to control the heat transfer in accordance with a temperature of the thermal coupling member which is detected by the temperature detector.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a container for a laser diode module capable of performing a temperature control.  
         [0002]     For example, Japanese Patent Publication Nos. 5-90698A and 2003-142766A disclose laser diode modules that perform a temperature control. However, each of the laser diode modules disclosed in these documents is complex in structure, difficult to manufacture, and expensive because a temperature controlling device is incorporated in the laser diode module in advance.  
       SUMMARY OF THE INVENTION  
       [0003]     It is therefore an object of the invention to provide a module container assembly that is easy to manufacture, inexpensive, and capable of performing an effective temperature control on an uncooled laser diode module (i.e., no temperature control device is incorporated in advance).  
         [0004]     In order to achieve the above object, according to the invention, there is provided a container assembly for a laser diode module in which a temperature control device is not incorporated in advance, comprising: 
        a heat-insulative casing, adapted to accommodate the laser diode module;     a temperature detector, accommodated in the casing;     a thermal coupling member, accommodated in the casing so as to thermally couple the laser diode module and the temperature detector;     a heat-conductive plate member, attached to the casing;     a heat transfer element, interposed between the thermal coupling member and the plate member so as to allow heat transfer therebetween;     a sealing member, disposed between the casing and the plate member so as to seal the heat transfer element; and     a heat transfer controller, causing the heat transfer element to control the heat transfer in accordance with a temperature of the thermal coupling member which is detected by the temperature detector.        
 
         [0012]     Preferably, the container assembly further comprises: an optical fiber, adapted to lead light emitted from the laser diode module; and a board, on which the laser diode module is mounted. The casing is formed with a first opening closed by the optical fiber, a second opening closed by the board, and a third opening adapted to receive the heat transfer element and closed by the sealing member and the plate member.  
         [0013]     Here, it is preferable that: a gap between the optical fiber and the first opening is filled with an adhesive; and a gap between the board and the second opening is filled with an adhesive.  
         [0014]     Preferably, the temperature detector is a thermistor configured to vary a resistance value thereof in accordance with the temperature of the thermal coupling member. The heat transfer element is a Peltier element operable to change a direction of the heat transfer in accordance with a current inputted thereto. The heat transfer controller control the current so as to keep the resistance value constant.  
         [0015]     With the above configurations, it is easy to manufacture and capable of performing an effective temperature control on the uncooled laser diode module. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0017]      FIG. 1  is a perspective view of a laser transmission unit incorporating a laser diode module according to one embodiment of the invention;  
         [0018]      FIG. 2  is a perspective view showing a disassembled state of the laser transmission unit;  
         [0019]      FIG. 3  is a perspective view showing a disassembled state of the laser diode module;  
         [0020]      FIG. 4A  is a rear perspective view of a module container assembly incorporating the laser diode module;  
         [0021]      FIG. 4B  is a front perspective view of the module container assembly;  
         [0022]      FIG. 5A  is a top plan view of the module container assembly;  
         [0023]      FIG. 5B  is a partially sectional side view of the module container assembly;  
         [0024]      FIG. 5C  is a partially sectional bottom plan view of the module container assembly;  
         [0025]      FIG. 5D  is a rear view of the module container assembly;  
         [0026]      FIG. 5E  is a front view of the module container assembly; and  
         [0027]      FIG. 6  is a block diagram showing the schematic configuration of the laser transmission unit. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0028]     Embodiments of the invention will be described below in detail with reference to the accompanying drawings.  
         [0029]     As shown in  FIG. 1 , according to one embodiment of the invention, a laser transmission unit  1  comprises: a module container assembly  2 ; a heat sink  100 ; and a main board  102  including a driving circuit  30  and a temperature control circuit  32  for a laser diode module  200  (both are indicated by dashed lines) and other components.  
         [0030]     As shown in  FIGS. 2 and 3 , the module container assembly comprises: a module board  3  having a connector  232 ; a Peltier element  234 ; a heat-insulative casing  210 ; a thermistor  238 ; a heat-conductive plate  240 ; flat head screws  242 ; a moisture-proof packing  244 ; a module mount  246 ; pan head screws  248 ; and grounding member  250 .  
         [0031]     The laser diode module  200  comprises a sleeve  202  and a conductive flange  204 . The heat-insulative casing  210  is formed with a first opening  214 , a second opening  212 , a third opening  216 , first screw receiving portions  218  that have threaded holes and receive the flat head screws  242 , and second screw receiving portions  220  that likewise receive the pan head screws  248 .  
         [0032]     The heat sink  100  and ground patterns provided on the module board  3  and the main board  102  are connected to a ground for radio frequency signals (not shown).  
         [0033]     Using the above components, the laser transmission unit  1  converts, to an optical signal (laser light beam), a transmission signal that is input from the main board  102  and sends out the optical signal to the optical fiber  106  while performing a temperature control on the laser diode module  200 .  
         [0034]     As indicated by chain lines A and A′, the grounding member  250 , the module mount  246 , and the conductive flange  204  of the laser diode module  200  are together fastened to the second screw receiving portions  220  of the heat-insulative casing  210  with the pan head screws  248 . These components are thus housed in and fixed to the heat-insulative casing  210 .  
         [0035]     The Peltier element  234  is surrounded by the moisture-proof packing  244  and received by the heat-insulative casing  210  through the third opening  216 . And the Peltier element  234  is housed in the heat-insulative casing  210  so as to be interposed between the bottom face of the module mount  246  and the heat-conductive plate  240 .  
         [0036]     As indicated by chain lines B and B′, when the heat-conductive plate  240  is fixed to the first-screw receiving portions  218  of the heat-insulative casing  210  with the flat head screws  242 , the Peltier element  234  is sealed in by the moisture-proof packing  244 , the heat-insulative casing  210 , and the heat-conductive plate  240 . The Peltier element  234  and the module mount  246  are pressed against each other and are thereby thermally coupled to each other.  
         [0037]     If the flange  204  of the laser diode module  200  were separated from the ground for radio frequency signals, the operation characteristics of the laser diode module  200  might deteriorate. In view of this, as indicated by chain lines C and C′, projections of the grounding member  250  are inserted in and soldered to grounding holes  300  of the module board  3  and are thereby connected to a ground for radio frequency signals provided on the module board  3 .  
         [0038]     In this manner, the flange  204  is grounded via the grounding member  250 , the module board  3 , the main board  102 , and the heat sink  100 , whereby the operation characteristics of the laser diode module  200  are kept good.  
         [0039]     The external appearance of the module container assembly  2  with the above components combined together is as shown in  FIGS. 1 and 4 A through  5 E.  
         [0040]     As shown in  FIG. 6 , a transmission signal that is input from the main board  102  is input to the laser diode module  200  via the grounded module board  3 .  
         [0041]     Inputting a transmission signal to the laser diode module  200  via the module board  3  in this manner makes it possible to provide more stable characteristics for radio frequency signals than in a case that a transmission signal is directly input from the main board  102 .  
         [0042]     The temperature control circuit  32  and the driving circuit  30  on the main board  102  are connected to the thermistor  238  via the connector  232 .  
         [0043]     The heat-insulative casing  210  is made of a material that is high in heat insulation characteristics (e.g., ABS). The inside of the heat-insulative casing  210  has such a shape that an air layer is formed between the casing and the components such as the laser diode module  200  housed therein and those components are thermally insulated from the outside.  
         [0044]     The heat-insulative casing  210  is formed with the first opening  214  through which the optical fiber  106  is inserted, the second opening  212  through which the laser diode module  200  etc. are inserted, and the third opening  216  through which the Peltier element  234  is received to bring it into contact with the bottom face of the module mount  246 .  
         [0045]     One end of the optical fiber  106  is introduced through the first opening  214  to such a position as to come into contact with a light output window (not shown) of the metal casing of the laser diode module  200  housed in the heat-insulative casing  210  and to be able to receive laser light that is output from the laser diode module  200 .  
         [0046]     An adhesive fills the gap in the first opening  214  that is formed between the heat-insulative casing  210  and the optical fiber  108  whose one end portion is introduced in the heat-insulative casing  210 , whereby the heat-insulative casing  210  is sealed.  
         [0047]     The heat-insulative casing  210  may be plated with a metal. Where the heat-insulative casing  210  is plated with a metal and the plating portion is grounded, the laser diode module  200  housed inside is shielded and hence its operation characteristics are kept good.  
         [0048]     Further, if the metal plating gives the heat-insulative casing  210  a metallic luster, its emissivity comes close to  1  and the heat insulation characteristics are improved.  
         [0049]     An electrode  206  of the laser diode module  200  is attached to the module board  3  and the main board  102  (see  FIG. 1 ), which allows input of a radio frequency signal from the main board  102  to the laser diode module  200 .  
         [0050]     The module mount  246 , which is inserted between the laser diode module  200  and the Peltier element  234 , is made of a material that is high in thermal conductivity (e.g., pure copper) and connects the laser diode module  200  and the Peltier element  234  with good thermal coupling.  
         [0051]     The thermistor  238  is attached to the module mount  246 , and the thermistor  238  and the laser diode module  200  are thermally coupled to each other via the module mount  246 .  
         [0052]     The heat-conductive plate  240  made of a material having high thermal conductivity (e.g., pure copper) is attached to the heat sink  100  through an opening  103  of the main board  102 , whereby the heat sink  100  and the heat-conductive plate  240  are thermally coupled to each other. If necessary, electrical conduction between them is further secured.  
         [0053]     As described above, the first opening  214  of the heat-insulative casing  210  is sealed with the optical fiber  106  and the adhesive and its third opening  216  is sealed with the moisture-proof packing  244  and the heat-conductive plate  240 .  
         [0054]     Likewise, the module board  3  is put in the second opening  212  of the heat-insulative casing  210  and fixed to the heat-insulative casing  210  with an adhesive or the like, whereby the second opening  212  is sealed with the module board  3  and the adhesive.  
         [0055]     All the openings of the heat-insulative casing  210  are sealed in this manner, whereby the heat insulation characteristics of the inside of the heat-insulative casing  210  are kept good. Further, since the inside of the heat-insulative casing  210  is isolated from the external air, the internal components are not deteriorated by external moisture and condensation of leakage moisture does not occur.  
         [0056]     In the laser transmission unit  1  having the above structure, the components housed in the heat-insulative casing  210  are thermally insulated from the outside except via the Peltier element  234  and the laser diode module  200 , the thermistor  238 , the Peltier element  234 , the heat-conductive plate  240 , and the heat sink  100  are thermally coupled together.  
         [0057]     Further, electrical conduction is secured between the laser diode module  200 , the grounding member  250 , the ground patterns (not shown) on the module board  3  and the main board  102 , the heat-conductive plate  240 , and the heat sink  100 .  
         [0058]     The temperature control of the module container assembly  2  will be described below with reference to  FIG. 6 .  
         [0059]     The Peltier element  234  transfers heat from the heat sink  100  to the module mount  246  and the laser diode module  200  or vice versa in accordance with the direction and the value of a current that is supplied from the temperature control circuit  32 .  
         [0060]     The resistance of the thermistor  238 , which is thermally coupled to the laser diode module  200 , varies with a temperature variation of the laser diode module  200 . Therefore, if the voltage applied to the thermistor  238  is constant its current value varies with a temperature variation of the laser diode module  200 .  
         [0061]     The temperature control circuit  32 , which is connected to the thermistor  238  via the connector  232 , detects the value of the current flowing through the thermistor  238  (i.e., the resistance of the thermistor  238 ), and controls the direction and the value of the current supplied to the Peltier element  234  so that the detected current value (i.e., resistance) is always kept constant. In this manner, the temperature control circuit  32  keeps the temperature of the laser diode module  200  almost constant.  
         [0062]     More specifically, if the value of the current flowing through the thermistor  238  is smaller than a reference value, the temperature control circuit  32  transfers heat from the laser diode module  200  to the heat sink  100 , that is, cools the laser diode module  200 .  
         [0063]     Conversely, if the value of the current flowing through the thermistor  238  is larger than the reference value, the temperature control circuit  32  transfers heat from the heat sink  100  to the laser diode module  200 , that is, heats the laser diode module  200 .  
         [0064]     Since the temperature control circuit  32  always keeps the temperature of the laser diode module  200  constant, the characteristics of the laser diode module  200  are kept almost constant irrespective of the ambient temperature of the laser transmission unit  1 .  
         [0065]     Since the temperature control circuit  32  always keeps the temperature of the laser diode module  200  constant, the characteristics of the laser diode module  200  do not vary and are always kept good.  
         [0066]     Although laser diode modules are available whose temperature characteristics are kept good because of incorporation of a Peltier element, they are generally expensive as described the above.  
         [0067]     In contrast, the laser diode module  200  used in the laser transmission unit  1  does not incorporate a Peltier element in advance and hence is inexpensive. However, since the temperature control is performed by using the Peltier element  234  that is thermally coupled to the laser diode module  200 , the laser transmission unit  1  is given temperature characteristics that are equivalent to or better than those as would be obtained when an laser diode module incorporating a Peltier element is used.  
         [0068]     In the laser transmission unit  1 , the laser diode module  200  and the Peltier element  234  are thermally coupled to each other closely via the module mount  246 , the Peltier element  234  can be of a small size and of low power consumption.  
         [0069]     Since the laser diode module  200  is grounded via the grounding member  250  etc., whereas its characteristics are kept high it is thermally insulated from the outside except via the module mount  246 . As a result, the temperature control can be performed efficiently.  
         [0070]     Further, since the heat-insulative casing  210  is sealed, the laser diode module  200  is free of trouble due to condensation of moisture leaking into the heat-insulative casing  210 .  
         [0071]     Still further, the components (laser diode module  200 , module mount  246 , etc.) of the laser transmission unit  1  are small and can be manufactured as general-purpose modules that can easily be attached and detached.  
         [0072]     Therefore, even if the laser transmission unit  1  has many types of products, the same parts can be used in the many types of products and the many types of products can be manufactured at low costs.  
         [0073]     Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.