Patent Publication Number: US-8537867-B2

Title: Method for fabricating optical device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Divisional of application Ser. No. 13/192,752, filed Jul. 28, 2011, which is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2010-169867, filed on Jul. 28, 2010, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to an optical device and a method of fabricating an optical device. 
     (ii) Related Art 
     There is a demand for improving reliability of an optical device. The optical device controls temperature of each optical component with a temperature control device. Thus, optical characteristics of the optical component are stabilized. Japanese Patent Application Publication No. 2007-101700 discloses an optical device having a temperature control device. 
     SUMMARY 
     The temperature control device has a structure in which a plurality of peltier elements are sandwiched between an upper plate and a lower plate. Therefore, mechanical strength of the temperature control device is relatively low. It is necessary to reduce distortion of the temperature control device in order to secure the reliability of the optical device. 
     It is an object of the present invention to provide an optical device having high reliability and a method for fabricating the optical device. 
     According to an aspect of the present invention, there is provided an optical device including: a carrier having a first area and a second area, both edges of the second area having a wall of a step, one edge of the second area being adjacent to the first area, the first area having a first thickness, the second area having a second thickness larger than the first thickness; and a first optical component mounted on the first area of the carrier, the second area of the carrier being an absence area of a component. 
     According to another aspect of the present invention, there is provided a method for fabricating an optical device including: a first step of preparing a carrier having a first area and a second area, both edges of the second area having a wall of a step, one edge of the second area being adjacent to the first area, the first area having a first thickness, the second area having a second thickness larger than the first thickness; a second step of mounting the carrier on a temperature control device after the first step; and a third step of mounting a first optical component on the first area of the carrier after the second step. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an optical device in accordance with a comparative example; 
         FIG. 2  illustrates an optical device in accordance with an embodiment; 
         FIG. 3  illustrates a carrier in accordance with the embodiment; 
         FIG. 4  illustrates a carrier in accordance with the embodiment; 
         FIG. 5  illustrates a fabrication method in accordance with the embodiment; 
         FIG. 6  illustrates a fabrication method in accordance with the embodiment; 
         FIG. 7  illustrates a fabrication method in accordance with the embodiment; and 
         FIG. 8  illustrates another carrier. 
     
    
    
     DETAILED DESCRIPTION 
     A description will be given of a comparative example. 
     Comparative Example 
       FIG. 1  illustrates an optical device  200  that is an example of an optical device in accordance with a comparative example. The optical device  200  has a temperature control device  20 , a carrier  30 , an optical isolator  40 , a lens  41 , a sub-carrier  42 , and a semiconductor laser  50  in a space closed by a package  10  and a cap  11 . In  FIG. 1 , the temperature control device  20 , the carrier  30 , the optical isolator  40 , the lens  41 , the sub-carrier  42  and the semiconductor laser  50  are viewed by seeing through the package  10 . 
     The temperature control device  20  has a structure in which a plurality of peltier elements  20   b  are sandwiched between an upper plate  20   a  and a lower plate  20   c . The carrier  30  is provided on the temperature control device  20 . The optical isolator  40 , the lens  41  and the sub-carrier  42  are provided on the carrier  30 . The semiconductor laser  50  is provided on the sub-carrier  42 . The semiconductor laser  50 , the lens  41  and the optical isolator  40  are arranged in this order so that an output light of the semiconductor laser  50  passes through the optical components in the order. A holder  60  having a transparent member such as glass is provided at a position of the package  10  where a light is output from the optical isolator  40 . 
     As illustrated in  FIG. 1 , a thickness of an edge portion of the carrier  30  in a light-outputting direction is the same as that of an area of the carrier  30  where the optical isolator  40  is mounted. In this case, rigidity of the edge portion of the carrier  30  is relatively low. Therefore, the edge portion of the carrier  30  tends to warp when the edge portion is subjected to stress. The warp of the carrier  30  may distort the temperature control device  20  largely. 
     Embodiment 
     Next, a description will be given of an embodiment of the present invention.  FIG. 2  illustrates an optical device  100  in accordance with the embodiment. In  FIG. 2 , the same components have the same numeral as  FIG. 1 . In  FIG. 2 , the temperature control device  20 , the carrier  30 , the optical isolator  40 , the lens  41 , the sub-carrier  42  and the semiconductor laser  50  are viewed by seeing through the package  10 . The optical device  100  is different from the optical device  200  in a point that the carrier  30  has a different shape.  FIG. 3  and  FIG. 4  illustrate an enlarged view of the carrier  30  of  FIG. 2 .  FIG. 3  illustrates a perspective view of the carrier  30 .  FIG. 4  illustrates a side view of the carrier  30 . 
     A main body of the carrier  30  is, for example, made of iron-nickel-cobalt alloy (KOVAR). The carrier  30  may act as a first area  32 , a second area  31  and a third area  33 . The first area  32  is an area where the optical isolator  40  is mounted as a first optical component. The second area  31  has a thickness larger than that of the first area  32 . The second area  31  is positioned between the first area  32  and an edge of the carrier  30  in a light-outputting direction. Both edges of the second area  31  have a wall of a step. One edge of the second area  31  is adjacent to the first area  32 . The second area  31  is no component area where no components are mounted. In other words, the second area  31  is an absence area of a component. The third area  33  is an area where the lens  41  and the semiconductor laser  50  mounted on the sub-carrier  42  are mounted as a second optical component. 
     In the optical device  100 , the carrier  30  has the first area  32  having a first thickness and acting as component area where a component is mounted and the second area  31  having a second thickness larger than the first thickness and acting as no component area where no components are mounted. 
     The thickness of the carrier  30  is determined in view of corresponding a height direction of an optical component mounted thereon to a target. Therefore, freedom degree of designing of the thickness of the first area  32  is low, and the thickness of the first area  32  tends to be designed to be small. In contrast, in the embodiment, the rigidity of the edge portion of the carrier  30  is secured, because the second area  31  having the thickness larger than that of the first area  32  is provided. 
     It is not necessary to adjust the height of the second area  31 , because the second area  31  is the no-component area where no components are mounted. Normally, the thickness of the second area  31  is the same as that of the first area  32  as illustrated in  FIG. 1 . In accordance with the embodiment, the rigidity of the second area  31  acting as the edge portion of the carrier  30  is improved. Therefore, the warp of the carrier  30  is suppressed. And, the distortion of the temperature control device  20  is suppressed. A relatively thicker portion of the third area  33  has a thickness of 1000 μm, for example. A relatively thinner portion of the third area  33  has a thickness of 800 μm, for example. The second area  31  has a thickness of 1000 μm, for example. The first area  32  has a thickness of 500 μm, for example. 
     A description will be given of a method for fabricating the optical device  100 .  FIG. 5  though  FIG. 7  illustrate the method. The numerals are the same as  FIG. 2  through  FIG. 4 . 
     As illustrated in  FIG. 5 , an optical component is mounted on the carrier  30 . In concrete, the lens  41  and the sub-carrier  42  mounting the semiconductor laser  50  are mounted on the carrier  30 . A laser welding using YAG laser or the like or a soldering is used in the mounting process. In this stage, the optical isolator  40  is not mounted yet in order to suppress damage of the optical isolator  40  caused by the heat generated in the mounting process of the carrier  30  on the temperature control device  20 . 
     As illustrated in  FIG. 6 , the carrier  30  is mounted after the temperature control device  20  is mounted in the package  10 . A soldering is adopted in order to improve thermal conductivity between the temperature control device  20  and the carrier  30 . A solder such as SnAgCu-based material may be used for the soldering. A treatment temperature of the soldering is higher than a melting point of the solder, and is approximately 230 degrees C., for example. In the stage, the optical isolator  40  is not mounted on the carrier  30 . Therefore, the damage of the optical isolator  40  that is weak against heat is suppressed. 
     Next, as illustrated in  FIG. 7 , the optical isolator  40  is mounted on the carrier  30 . The optical isolator  40  is mounted through a laser welding process with use of a YAG laser. In the laser welding, a laser is irradiated at an interface between the carrier  30  and the optical isolator  40 . The temperature of the interface is increased only locally in the laser welding. Therefore, thermal damage of the optical isolator  40  is suppressed. However, the carrier  30  may be subjected to stress when the laser welding is performed. 
     The carrier  30  having the structure in accordance with the comparative example may warp because of the stress. The warp of the carrier  30  may cause warp of the upper plate  20   a  of the temperature control device  20 , because the carrier  30  and the temperature control device  20  are soldered with each other. This may cause large stress in the temperature control device  20 . In this case, the reliability of the temperature control device may be degraded. In a worst-case situation, the peltier element structuring the temperature control device  20  may be peeled and broken. 
     On the other hand, in the embodiment, the carrier  30  has the second area  31  having large thickness. Therefore, the rigidity of the edge portion of the carrier  30  is improved. This may suppress the warp of the carrier  30 . Thereby, degradation of the reliability or the breaking of the temperature control device  20  may be suppressed. After the processes, the optical device  100  is fabricated by sealing the package  10  with the cap  11 . 
     In a case where the laser of the laser welding is irradiated to both edges of the optical isolator  40  facing with each other, the stress is the largest in a direction connecting the both edges during the laser welding of the optical isolator  40 . On the other hand, the second area  31  has large rigidity in a longitudinal direction thereof. It is therefore possible to use the rigidity of the second area  31  effectively, if the laser is irradiated to both edges of the optical isolator  40  in the longitudinal direction of the second area  31  during the laser welding of the optical isolator  40 . 
     A difference of the warp of the carrier  30  was measured between the comparative example illustrated in  FIG. 1  and the embodiment as illustrated in  FIG. 2 . A sample of the embodiment was fabricated in accordance with the above-mentioned fabrication processes. Another sample of the comparative example was fabricated in accordance with the above-mentioned fabrication processes, but the carrier  30  has the structure in accordance with the comparative example. 
     The thickness of the edge portion (the second area  31 ) of the carrier  30  of the embodiment was 1000 μm. The thickness of the area (the first area  32 ) where the optical isolator  40  is mounted was 500 μm. The thickness of the edge portion (including the component area of the optical isolator  40 ) of the carrier  30  of the comparative example was 500 μm. The carrier was made of the same iron-nickel-cobalt alloy (KOVAR) in the embodiment and the comparative example. The condition of the irradiation of the YAG laser was the electrical power: 6.0 J and the irradiation time: 2.0 ms. 
     As the result of the measurement, in the comparative example, large warp appeared in the carrier. Both edges of the edge portion of the carrier having a small thickness were lifted by 10 μm on an average, compared to the condition before the welding. In contrast, in the embodiment, both edges of the first area  32  were lifted by only 4 μm on an average, compared to the condition before the welding. 
     The thickness of the second area  31  of the carrier  30  may be determined in a range where the edge portion of the carrier  30  has necessary rigidity. Although the thickness of the second area  31  of the carrier  30  was twice as the first area  32  in the above-mentioned measurement, the thickness of the second area  31  may be 1.5 times to 3 times as the first area  32 . 
     In a case where the second area  31  interrupts the optical axis, the second area  31  may have a cut-out area.  FIG. 8  illustrates another example of the carrier  30 . The same components have the same numerals as  FIG. 3 . The carrier  30  of  FIG. 8  has a structure in which the second area  31  is thicker than the third area  33 . A relatively thicker portion of the third area  33  has a thickness of 1000 μm, for example. A relatively thinner portion of the third area  33  has a thickness of 800 μm, for example. The second area  31  has a thickness of 1500 μm. for example. The first area  32  has a thickness of 500 μm, for example. As illustrated in  FIG. 8 , the cut-out area  34  of the second area is acting as a channel to allow passage of the optical axis. 
     The optical component mounted on the first area  32  of the carrier  30  and the optical component mounted on the third area  33  of the carrier  30  may be a lens, an etalon, a diffractive grating, a light-receiving element or the like. 
     The third area  33  is thicker than the first area  32  in the embodiment. However, the thickness of the third area  33  may be determined according to an optical axis of an optical component to be mounted or another design necessity. For example, the thickness of the third area  33  may be equal to or less than that of the first area  32 . However, the rigidity of an edge portion on the side of the third area  33  may be low, when the thickness of the third area  33  is equal to or less than that of the first area  32 . In this case, an area thicker than the third area  33  may be provided as a no-component area, as well as the second area  31 . Further, the third area  33  of the carrier  30  may not be provided, because the third area  33  is an area where the second optical component is to be mounted. 
     The present invention is not limited to the specifically disclosed embodiments and variations but may include other embodiments and variations without departing from the scope of the present invention.