Abstract:
A method for connecting an optical waveguide and an optical semiconductor device and an apparatus for connecting the same, capable of removing a working error and getting a high optical coupling coefficiency. The method consisting of the steps of: moving the optical semiconductor device to the substrate so as to overlap the pair of the first positioning marks and the pair of the second positioning marks; obtaining an actual distance from the outgoing surface to the pair of the second positioning marks, based on an image photographed by allowing the infrared ray to transmit through the substrate and the optical semiconductor device; obtaining an error between the actual distance and a designed distance previously set, by subtracting the designed distance between the outgoing surface of the optical semiconductor device and the pair of the second positioning marks from the actual distance; moving the pair of the second positioning marks relative to the pair of the first positioning marks by a quantity equal to the error so as to cancel the error; and jointing the optical semiconductor device to the substrate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for connecting an a optical waveguide and an optical semiconductor device and an apparatus for connecting the same, particularly to an improvement of a passive alignment system. 
     2. Description of the Prior Arts 
     There has existed an electric-optical conversion device called an optical module, which is constituted by integrating an optical semiconductor device such as a semiconductor laser diode and an optical waveguide such as an optical fiber. 
     In fabricating the optical module, it is an important challenge to allow an emitted light from the optical semiconductor device to be incident onto the optical waveguide with minimal waste and to increase optical coupling coefficiency. 
     As methods to connecting the optical semiconductor device and the optical waveguide, there have existed an active alignment method and a passive alignment method. 
     The active alignment method is the one performed as follows. Specifically, an optical semiconductor device is actually made to emit a light and the emitted light is incident onto an optical waveguide. Relative positions of the optical semiconductor device and the optical waveguide with respect to each other are finely adjusted so as to maximize an intensity of the emitted light from the optical waveguide, thus connecting the optical semiconductor device and the optical waveguide. 
     On the other hand, the passive alignment method is performed as follows. Specifically, the optical semiconductor device is actually not made to emit a light, but alignment marks previously formed in both of the optical semiconductor device and the optical waveguide are made to be coincident with each other. Thus finely adjusting the relative positions of the optical semiconductor device and the optical waveguide with respect to each other to connect them. 
     In Japanese Patent Laid-Open No. Hei 7 (1995)-43565, published on Feb. 14, 1995, a method to connect the optical waveguide and the optical semiconductor device using the passive alignment method is disclosed. A technology written in the gazette will be described as a first conventional example. 
     FIG. 10 is a perspective view showing a method for connecting an optical waveguide and an optical semiconductor device of the first conventional example. 
     In FIG. 10, an optical semiconductor device  102  is loaded onto a sub substrate  101 . A thin film for shielding infrared ray is formed entirely on an overall bottom surface  102   a  of the optical semiconductor device  102  other than regions of markers  161  and  162 . The sub substrate  101  has a thin film for shielding infrared ray only at regions of markers  131  and  132 , and accommodates an optical fiber  104  in its V-shaped groove  105 . 
     Next, the infrared ray (not shown) is made to transmit through the sub substrate  101  upward from an infrared ray source (not shown) provided below the sub substrate  101 , and the markers  131 ,  132 ,  161  and  162  are photographed by an infrared ray camera (not shown) provided above the sub substrate  101 . 
     FIG. 11 is a schematic view showing a photographed image in the first conventional connection method. 
     In FIG. 11, the photographed image of the markers  131 ,  132 ,  161  and  162  undergoes an image processing, and relative positions of the optical semiconductor device  102  and the sub substrate  101  with respect to each other are corrected so that areal centers of gravity of the markers  131  and  132  and areal centers of gravity of the markers  161  and  162  are coincident with each other. Thereafter, the optical semiconductor device  102  is loaded onto the sub substrate  101  and jointed to the sub substrate  101 , whereby a precision in the connection of the optical semiconductor device  102  and the optical fiber  104  is increased. 
     Moreover, in Japanese Patent Laid-Open No. Hei 8 (1996)-111600, published on Apr. 30, 1996, a high precision mounting method using a passive alignment method for controlling relative positions of an optical semiconductor device and an optical waveguide based on an overlapping state of polygonal markers is disclosed. A technology written in the gazette is described as a second conventional example. 
     FIG. 12 is a perspective view showing a method for connecting an optical waveguide and an optical semiconductor device of a second conventional example. 
     In FIG. 12, an optical semiconductor device  228  is loaded onto a silicon substrate  225 . In the optical semiconductor device  228 , first markers having parallelogram-shape which allow an infrared ray R (FIG. 13) to transmit through are perforated, and second markers  238  are formed on a bottom surface. An infrared ray R is shielded in other regions than the region of the markers  238 . In the silicon substrate  225 , a rectangular-shaped holes, which allows the infrared ray R to transmit through, are perforated, and first markers  237  are formed. The infrared ray R is shielded in other regions than the region of the markers  237 . 
     FIG. 13 is a perspective view showing an apparatus for connecting the optical waveguide and the optical semiconductor device of the second conventional example. 
     In FIG. 13, the infrared ray R is irradiated upward from an infrared-ray source  222  located below the silicon substrate  225  and the optical semiconductor device  228 , and an image of the infrared ray R having transmitted through the silicon substrate  225  and the optical semiconductor device  228  is photographed by an infrared-ray camera  231 . 
     FIG. 14 is a schematic view showing an infrared-ray-photographed image in the method for connecting the optical guide and the optical semiconductor device of the second conventional example. 
     Based on the photographed image as shown in FIG. 14, a deviation of the first and second markers  236  and  238  from each other is obtained, and a parts-moving stage  226  (FIG. 13) and a substrate moving stage  223  (FIG. 13) are controlled so as to make coincident the first and second markers  236  and  238  with each other, thus positioning the silicon substrate  225  and the optical semiconductor device  228 . 
     Moreover, the image of the infrared ray R having transmitted through the first and second markers  236  and  238  is taken out by a half mirror  233  (FIG.  13 ), and measured by an optical intensity detector  235  (FIG.  13 ). The silicon substrate  225  and the optical semiconductor device  228  are fixed at a position where an intensity of the image comes to be maximum or minimum, whereby a positioning precision of the silicon substrate  225  and the optical semiconductor device  228  is increased. 
     As a still another conventional example, in Japanese Patent Laid-Open No. Hei 9 (1997)-205255, published on Aug. 5, 1997, an optical semiconductor device using an passive alignment method, in which areal centers of gravity of alignment marks provided respectively on a semiconductor laser chip and a sub-mount are made to be coincident with each other, and a method for manufacturing the same are disclosed. 
     Moreover, in Japanese Patent Laid-Open No. Hei 9 (1997)-292542, published on Nov. 11, 1997, an optical part mounting substrate using a passive alignment method, in which alignment marks provided respectively on a semiconductor laser chip and an optical part fixing member are detected thus mounting one on another, is disclosed. 
     However, the connection methods for the optical waveguide and the optical semiconductor device in the conventional examples have the following problems. 
     In the first conventional example shown in FIG. 10, when a working error exists on an outgoing surface  102   b  of the optical semiconductor device  102 , a distance from the outgoing surface  102   b  of the optical semiconductor device  102  to an incident surface  104   a  of the optical fiber  104  shifts from a designed distance. Thus, an optical coupling coefficiency of the optical semiconductor device  102  and the optical fiber  104  reduces. 
     The reason is as follows. Specifically, when the optical semiconductor device  102  such as a laser diode is manufactured, after markers  161  and  162  are formed, the outgoing surface  102   b  is formed by performing a cleavage processing for the optical semiconductor device  102 . Since this cleavage processing is performed in such manner that a breakable semiconductor is split so as to obtain the outgoing surface  102   b , a working error of the outgoing surface  102   b  with respect to the markers  161  and  162  cannot be made to be 10 μm or less. On the other hand, in the case of the optical semiconductor device  102  for which a high optical output power and a high optical coupling coefficiency are needed, a distance from the outgoing surface  102   b  of the optical semiconductor device  102  to the incident surface  104   a  of the optical fiber  104  must be reduced to about 3 μm. It is nevertheless difficult to meet the requirement as long as the cleavage processing is adopted. 
     Moreover, the distance from the outgoing surface  102   b  of the optical semiconductor device  102  to the incident surface  104   a  of the optical fiber  104  cannot be obtained as designed, and there is a problem that the optical coupling coefficiency is low. 
     The reason is as follows. Specifically, if a slit  110  for deciding the position of an incident surface  107   a  of a sub substrate  107  is formed by grinding the sub substrate  107  in a mechanical working manner, a working error of 5 μm or more is created. Similarly, even if the incident surface  104   a  of the optical fiber  104  is polished so as to smooth it using a blade saw, the working error of 5 μm or more is created. Specifically, the working error of 10 μm or more in total exists. 
     There have been these problems in any of the foregoing conventional examples. 
     Any of the foregoing conventional examples discloses simply the technology in which the areal center of gravity of the alignment marks are made to be coincident with each other, or the technology in which the positioning is controlled based on the overlapping state of the alignment markers. When the foregoing working error of the outgoing surface exists or the foregoing working error of the incident surface exists, any of the foregoing conventional examples cannot aim at removing the working errors, and does not disclose concrete method to remove the working errors. 
     Accordingly, any of the foregoing conventional examples cannot remove the foregoing working errors in principle. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a method for connecting an optical waveguide and an optical semiconductor device and an apparatus for connecting the optical waveguide and the optical semiconductor device, capable of removing a working error and getting a high optical coupling coefficiency. 
     A first aspect of the method is that: a method for connecting an optical waveguide for guiding light and an optical semiconductor device having an outgoing surface for emitting the light, the optical waveguide being formed in a first region on a top surface of a substrate, on which a pair of first positioning marks are formed for transmitting or shielding an infrared ray only at specified spots in a second region adjacent to the first region, and the optical semiconductor device having a bottom surface on which a pair of second positioning marks for transmitting or shielding the infrared ray are formed thereof, the second positioning marks being concentric and having a different diameter from that of the first positioning marks and an inverted pattern shape to that of the first positioning marks. The method consisting of the steps of: moving the optical semiconductor device to the substrate so as to overlap the pair of the first positioning marks and the pair of the second positioning marks; obtaining an actual distance from the outgoing surface to the pair of the second positioning marks, based on an image photographed by allowing the infrared ray to transmit through the substrate and the optical semiconductor device; obtaining an error between the actual distance and a designed distance previously set, by subtracting the designed distance between the outgoing surface of the optical semiconductor device and the pair of the second positioning marks from the actual distance; moving the pair of the second positioning marks relative to the pair of the first positioning marks by a quantity equal to the error so as to cancel the error; and jointing the optical semiconductor device to the substrate. 
     A second aspect of a method is that: a method for connecting an optical waveguide and an optical semiconductor device, the optical waveguide being laid in a groove formed on a top surface of a substrate on which a pair of first positioning marks are formed for transmitting or shielding an infrared ray only at specified spots and having one end surface thrusted to a thrust end surface, that is one end of the groove, so as to be positioned, and the optical semiconductor device having a bottom surface, in which a pair of second positioning marks for transmitting or shielding the infrared ray are formed, the second positioning marks being concentric and having a different diameter from that of the first positioning marks and an inverted pattern shape to that of the first positioning marks. The method consisting of the steps of: moving the optical semiconductor device to the substrate so as to overlap the pair of the first positioning marks and the pair of the second positioning marks; obtaining an actual distance from an outgoing surface of the optical semiconductor device to the thrust end surface, based on an image photographed by allowing the infrared ray to transmit through the substrate and the optical semiconductor device; obtaining an error between the actual distance and a designed distance previously set, by subtracting the designed distance between the outgoing surface of the optical semiconductor device and the thrust end surface of the slit from the actual distance; moving the pair of the second positioning marks relative to the pair of the first positioning marks by a quantity equal to the error so as to cancel the error; and jointing the optical semiconductor device to the substrate. 
     A first aspect of the apparatus is that: an apparatus for connecting an optical waveguide for guiding light and an optical semiconductor device having an outgoing surface for emitting the light, the optical waveguide being formed in a first region on a top surface of a substrate, on which a pair of first positioning marks are formed for transmitting or shielding an infrared ray only at specified spots in a second region adjacent to the first region, and the optical semiconductor device having a bottom surface on which a pair of second positioning marks for transmitting or shielding the infrared ray are formed thereof, the second positioning marks being concentric and having a different diameter from that of the first positioning marks and an inverted pattern shape to that of the first positioning marks. The apparatus consisting of: a stage for moving relatively the substrate and the optical semiconductor device; a light source for irradiating the infrared ray; a camera for photographing an image formed by the infrared ray irradiated from the light source and transmitted through the substrate and the optical semiconductor device; and a control unit for controlling the stage based on the image from the camera. The control unit drives the stage so as to overlap the pair of the first positioning marks and the pair of the second positioning marks; obtains an actual distance from the outgoing surface to the pair of the second positioning marks, based on the image photographed from the camera; obtains an error between the actual distance and a designed distance previously set, by subtracting the designed distance between the outgoing surface of the optical semiconductor device and the pair of the second positioning marks from the actual distance; and moves the pair of the second positioning marks relative to the pair of the first positioning marks by driving the stage by a quantity equal to the error so as to cancel the error. 
     A second aspect of an apparatus is that: an apparatus for connecting an optical waveguide and an optical semiconductor device, the optical waveguide being laid in a groove formed on a top surface of a substrate on which a pair of first positioning marks are formed for transmitting or shielding an infrared ray only at specified spots and having one end surface thrusted to a thrust end surface, that is one end of the groove, so as to be positioned, and the optical semiconductor device having a bottom surface, in which a pair of second positioning marks for transmitting or shielding the infrared ray are formed, the second positioning marks being concentric and having a different diameter from that of the first positioning marks and an inverted pattern shape to that of the first positioning marks. The apparatus consisting of: a stage for moving relatively the substrate and the optical semiconductor device; a light source for irradiating the infrared ray; a camera for photographing an image formed by the infrared ray irradiated from the light source and transmitted through the substrate and the optical semiconductor device; and a control unit for controlling the stage based on the image from the camera. The control unit drives the stage so as to overlap the pair of the first positioning marks and the pair of the second positioning marks; obtains an actual distance from the pair of the second positioning marks to the thrust end surface, based on the image from the camera; obtains an error between the actual distance and a designed distance previously set, by subtracting the designed distance between the pair of the second positioning marks of the optical semiconductor device and the thrust end surface of the slit from the actual distance, and moves the pair of the second positioning marks relative to the pair of the first positioning marks by driving the stage by a quantity equal to the error so as to cancel the error. 
     In the conventional examples, the relative positions of the substrate and the optical semiconductor device are controlled so that first and second positioning marks are made to be simply coincident with each other. Compared to the conventional examples, according to the methods and the apparatuses of the present invention as described above, the present invention is characterized as follows. The first and second positioning marks are once overlapped, and the actual distance from the positioning mark of the optical semiconductor device to either the outgoing surface of the optical semiconductor device or the thrust end surface of the slit of the substrate is measured. Then an error is obtained by subtracting a designed distance previously set from the actual distance obtained, and the optical semiconductor device is moved by the quantity equal to the error so as to cancel the error, thus jointing the optical semiconductor device to the optical waveguide substrate. 
     Since the constitutions and the technique described above are adopted in the present invention, the distance between the outgoing surface of the optical semiconductor device and the incident surface of the optical waveguide can be always made to be coincident wits the designed distance precisely. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings. 
     FIG. 1 is a perspective view showing a structure of connecting an optical waveguide and an optical semiconductor device according to a first embodiment of the present invention. 
     FIG. 2 is a schematic side view showing a structure of an apparatus for realizing the apparatus for connecting the optical waveguide and the optical semiconductor device according to the FIG. 1 embodiment. 
     FIG. 3 is a schematic view showing a photographed image at the time of starting a method for connecting the optical waveguide and the optical semiconductor device according to the FIG. 1 embodiment. 
     FIG. 4 is a flowchart showing processes in the method for connecting the optical waveguide and the optical semiconductor device according to the FIG. 1 embodiment. 
     FIG. 5 is a schematic view showing a photographed image at the time of completing the method for performing a method for connecting the optical waveguide and the optical semiconductor device according to the FIG.,  1  embodiment. 
     FIG. 6 is a perspective view showing a structure of connecting an optical waveguide and an optical semiconductor device according to a second embodiment of the present invention. 
     FIG. 7 is a schematic view showing a photographed image at the time of starting a method for connecting the optical waveguide and the optical semiconductor device according to the FIG. 6 embodiment. 
     FIG. 8 is a flowchart showing processes in the method for connecting the optical waveguide and the optical semiconductor device according to the FIG. 6 embodiment. 
     FIG. 9 is a schematic view showing a photographed image at the time of completing the method for performing a method for connecting the optical waveguide and the optical semiconductor device according to the FIG. 6 embodiment. 
     FIG. 10 is a perspective view showing a method for connecting an optical waveguide and an optical semiconductor device of a first conventional example. 
     FIG. 11 is a schematic view showing a photographed image in the first conventional connection method. 
     FIG. 12 is a perspective view showing a method for connecting an optical waveguide and an optical semiconductor device of a second conventional example. 
     FIG. 13 is a schematic side view showing an apparatus for connecting the optical waveguide and the optical semiconductor device of the second conventional example. 
     FIG. 14 is a schematic view showing an infrared-ray-photographed image in the method for connecting the optical waveguide and the optical semiconductor device of the second conventional example. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     (First Embodiment) 
     As a first embodiment, an optical module in which an optical waveguide  5  is formed on an optical waveguide substrate  1  will be described. 
     FIG. 1 is a perspective view showing a structure of connecting an optical waveguide and an optical semiconductor device of a first embodiment of the present invention. 
     In FIG. 1, the optical waveguide substrate  1  is a plane-shaped substrate formed of a silicon material and the like. The optical waveguide  5  made of a transparent material such as SiO 2  is formed on a top surface  1   a  of the optical waveguide substrate  1  by coating the optical waveguide  5  thereon by means of a Chemical Vapor Deposition (CVD) method or the like. The optical waveguide  5  takes a straight-line shape. 
     On a tip of the optical waveguide  5 , an incident surface  5   a  for allowing light to be incident thereonto is formed along an optical axis  5   x  so as to be perpendicular to the optical waveguide  5 . A step portion  1   b  is formed at a position of the top surface  1   a  of the optical waveguide substrate  1  so as to cross the incident surface  5   a . A mounting portion  1   c  is formed on a portion of the optical waveguide substrate  1  farther ahead of the tip of the optical waveguide  5 , the step portion  1   b  intervening therebetween. On the surface of the mounting portion  1   c , an electrode pad  3  which takes a rectangular shape having a protruding portion  3   a  in its center portion when viewed from the above is formed on an extended line of the optical waveguide  5 , by a technique such as etching. 
     Moreover, first positioning marks  4   a  and  4   b  taking a round shape, which is formed of a thin film for shielding infrared ray R (FIG.  2 ), are formed on both sides of the protruding portion  3   a  of the electrode pad  3  so as to sandwich the protruding portion  3   a  therebetween. 
     In FIG. 1, the optical semiconductor device  2  is a semiconductor device which emits light such as a laser beam from a light-emitting portion  2   c  along an optical axis  2   x , and a thin film for shielding the infrared ray R (FIG. 2) is formed on the entire surface of a bottom surface  2   a  thereof. In this thin film, regions formed by removing partially the thin film for shielding the infrared ray R, which surround the first positioning marks  4   a  and  4   b  of the optical waveguide substrate  1  and have a diameter larger than that of the first positioning marks  4   a  and  4   b , are formed as second positioning marks  6   a  and  6   b.    
     Note that an outline shape of a squared-shaped portion  3   b  excluding the protruding portion  3   a  from the region which takes a rectangular shape having a protruding portion  3   a  in its center portion on the optical waveguide substrate  1  is formed so as to fit it with an outline shape of the bottom surface  2   a  of the optical semiconductor device  2 . 
     Moreover, in order to make coincident a vertical height of the optical axis  5   x  of the optical waveguide  5  with a vertical height of the optical axis  2   x  of the optical semiconductor device  2 , the mounting portion  1   c  of the optical waveguide substrate  1  is formed by etching and the like to be somewhat lower than the region where the optical waveguide  5  is formed. 
     FIG. 2 is a schematic side view showing a structure of an apparatus for connecting the optical waveguide and the optical semiconductor device according to the FIG. 1 embodiment. 
     The connection apparatus shown in FIG. 2 constitutes of a substrate-moving stage  23  for mounting the optical waveguide substrate  1  thereon, a parts-moving stage  26  for holding the optical semiconductor device  2  thereunder, an image processing unit  27 , a control unit  29 , an infrared-ray light source  50  and an infrared-ray camera  51 . 
     The substrate-moving stage  23  is a plane stage placed on a horizontal plane and mounts the optical waveguide substrate  1  thereon. The substrate-moving stage  23  moves the optical waveguide substrate  1  placed thereon to an arbitrary position in response to a drive signal Sd from the control unit  29 . 
     The parts-moving stage  26  is a three-dimensional stage which holds the optical semiconductor device  2  with its arm at a tip bottom surface thereof and is movable with a degree of freedom in X, Y and Z-directions. The parts-moving stage  26  moves the optical semiconductor device  2  held with its arm to an arbitrary position on the horizontal plane in response to the drive signal Sd from the drive unit  29 , and moves the optical semiconductor device  2  vertically. 
     The image processing unit  27  obtains positions between specified images in a photographed image based on an image signal Sv from the infrared-ray camera  51 , and outputs it as an actual distance signal Sds. 
     The control unit  29  performs a computation based on an actual distance L (FIG. 3) indicated by the actual distance signal Sds and a designed distance Lo (FIG. 3) previously stored therein, and outputs the drive signal Sd to the substrate-moving stage  23  and the parts-moving stage  26 . 
     The infrared-ray light source  50  is provided below the substrate-moving stage  23  so as to face upward, and irradiates the infrared ray R upward. 
     The infrared-ray camera  51  is provided above the parts-moving stage  26  so as to face downward, and photographs the infrared ray R having transmitted through the optical waveguide substrate  1  and the optical semiconductor device  2 , thus outputting it as the image signal Sv to the image processing unit  27 . 
     Next, a method for connecting the optical waveguide and the optical semiconductor device of this embodiment will be described. 
     FIG. 3 is a schematic view showing a photographed image at the time of starting a method for performing a method for connecting the optical waveguide and the optical semiconductor device according to the FIG. 1 embodiment. 
     FIG. 4 is a flowchart showing processes in the method of connecting the optical waveguide and the optical semiconductor device according to the FIG. 1 embodiment. 
     In FIG. 3, the L denotes an actual distance from the outgoing surface  2   b  of the optical semiconductor device  2  to centers of the positioning marks  4   a ,  4   b ,  6   a  and  6   b . The Lo denotes a designed distance from the outgoing surface  2   b  of the optical semiconductor device  2  to the centers of the positioning marks  4   a ,  4   b ,  6   a  and  6   b . The α denotes a working error of the outgoing surface  2   b  of the optical semiconductor device  2 . 
     First, the optical semiconductor device  2  is moved onto the optical waveguide substrate  1  so that each of the centers of the first positioning marks  4   a  and  4   b  of the optical waveguide substrate  1  is made to be coincident with each of the centers of the second positioning marks  6   a  and  6   b  of the optical semiconductor device  2  respectively (step S 1 ). 
     Next, as shown in FIG. 2, the infrared ray R is irradiated onto the bottom surface of the optical waveguide substrate  1  from the infrared-ray light source  50  disposed below the optical waveguide substrate  1  so as to face upward. The infrared ray R is allowed to transmit through the optical waveguide substrate  1  and the optical semiconductor device  2 . 
     The infrared ray R having transmitted through the optical waveguide substrate  1  and the optical semiconductor device  2  is photographed by the infrared-ray camera  51  disposed above the optical semiconductor device  2  so as to face downward. The photographed infrared ray R is supplied to the image processing unit  27  as the image signal Sv (step S 2 ). 
     Thus, as shown in FIG. 3, the positioning marks  4   a ,  4   b ,  6   a ,  6   b  and the outgoing surface  2   b  of the optical semiconductor device  2  are photographed. 
     The image processing unit  27  (FIG. 2) performs an image processing such as a binary processing based on the photographed image indicated by the image signal Sv (FIG.  2 ), and detects the positions of the positioning marks  4   a ,  4   b ,  6   a  and  6   b  and the position of the outgoing surface  2   b  of the optical semiconductor device  2  (step S 3 ). 
     Subsequently, based on the detected positions of the positioning marks  4   a ,  4   b ,  6   a  and  6   b  and the outgoing surface  2   b , the image processing unit  27  (FIG. 2) obtains the actual distance L from the center of the positioning marks  4   a ,  4   b ,  6   a  and  6   b  to the outgoing surface  2   b  of the optical semiconductor device  2 , and outputs it as the actual distance signal Sds (FIG.  2 ). 
     The control unit  29  (FIG. 2) subtracts the designed distance Lo between the centers of the positioning marks  4   a ,  4   b ,  6   a  and  6   b  and the outgoing surface  2   b  of the optical semiconductor device  2  from the actual distance L indicated by the actual distance signal Sds, thus obtaining an error α (=L−Lo). Note that the designed distance Lo is previously set in the control unit  29  (FIG.  2 ). 
     Next, in FIG. 2, the control unit  29  generates the drive signal Sd for driving the substrate-moving stage  23  and the parts-moving stage  26  by a quantity equal to the error α so as to cancel the error α (FIG.  3 ). Note that the drive signal Sd may drive any one of the substrate-moving stage  23  and the parts-moving stage  26  or may drive the both of them. The control unit  29  then outputs the drive signal Sd (step S 4 ). 
     The drive signal Sd is supplied to the substrate-moving stage  23  and the parts-moving stage  26 , or the drive signal Sd is supplied to any one of the substrate-moving stage  23  and the parts-moving stage  26 . The parts-moving stage  26  is moved by the quantity equal to the error α (FIG. 3) in a direction of the arrow A (FIG. 3) so as to cancel the error α (FIG.  3 ). Alternatively, the substrate-moving stage  23  is moved by the quantity equal to the error α (FIG. 3) in a direction opposite to the arrow A (FIG.  3 ). Still alternatively, by combining the means above, the parts-moving stage  26  and the substrate-moving stage  23  are relatively moved with respect to each other (step S 5 ). 
     FIG. 5 is a schematic view showing a photographed image at the time of completing the method for performing a method for connecting the optical waveguide and the optical semiconductor device according to the FIG. 1 embodiment. 
     As shown in FIG. 5, since the second positioning marks  6   a  and  6   b  of the optical semiconductor device  2  are moved relative to the first positioning marks  4   a  and  4   b  of the optical waveguide substrate  1  by the quantity equal to the error α in the direction to cancel the errors α, a distance between the incident surface  5   a  (FIG. 1) of the optical waveguide  5  (FIG. 1) and the outgoing surface  2   b  (FIG. 1) of the optical semiconductor device  2  (FIG. 1) will be made to be coincident with the designed distance accurately. 
     Finally, the parts-moving stage  26  is made to descend so as to mount the optical semiconductor device  2  on the optical waveguide substrate  1 , thus jointing the optical semiconductor device  2  and the optical waveguide substrate  1  to each other by a method such as soldering and the like (step S 6 ). 
     As described above, according to this embodiment, the optical semiconductor device  2  is moved onto the optical waveguide substrate  1 , and the infrared ray R is allowed to transmit through the optical semiconductor device  2  and the optical waveguide substrate  1 . The actual distance L between the outgoing surface  2   b  and the centers of the positioning marks  4   a ,  4   b ,  6   a  and  6   b  is obtained, and the optical semiconductor device  2  is moved by the quantity equal to the error a between the actual distance L and the designed distance Lo previously set, in the direction to cancel the error α. Thereafter, the optical semiconductor device  2  and the optical waveguide substrate  1  are jointed to each other. 
     Thus, the working error α of the outgoing surface  2   b  of the optical semiconductor device  2  is cancelled, and the optical axis  2   x  of the optical semiconductor device  2  and the optical axis  5   x  of the optical waveguide  5  will be made to be coincident with each other accurately. 
     (Second Embodiment) 
     As a second embodiment, an optical module using an optical fiber  9  as the optical waveguide will be described. Since the optical semiconductor device  2  and the apparatus for connecting the optical semiconductor device  2  and the optical waveguide substrate  1  shown in FIG.,  2  have the same structure as those in the first embodiment, descriptions for them is omitted. In this embodiment, the optical waveguide substrate  1  of FIG. 2 is replaced by a sub substrate  7 . 
     FIG. 6 is a perspective view showing a structure of connecting an optical waveguide and an optical semiconductor device according to a second embodiment of the present invention. 
     In FIG. 6, the sub substrate  7  is made of a silicon material and the like. An electrode pad  3  for mounting the optical semiconductor device  2  thereon is formed on one side of a top surface of the sub substrate  7 . The electrode pad  3  takes a rectangular shape having a protruding portion  3   a  in its center portion by a technique such as etching. First positioning marks  4   a  and  4   b  having a round shape are formed on both sides of the protruding portion  3   a  of the electrode pad  3  so as to sandwich the protruding portion  3   a.    
     A V-shaped groove  8  having a V character-shaped vertical cross section is formed on the other side of the top surface of the sub substrate  7  along the extended line of the protruding portion  3   a  of the electrode pad  3  by a technique such as anisotropic etching. The V-shaped groove  8  is formed to a depth so that a vertical height of an optical axis  9   x  of the optical fiber  9  and a vertical height of an optical axis  2   x  of the optical semiconductor device  2  are coincident with each other. 
     A slit  10  perpendicular to the V-shaped groove  8  is formed on an end surface of the V-shaped groove  8  of the electrode pad  3  side. The slit  10  is formed by processing the top surface  7   a  of the sub substrate  7  by cutting using a blade saw and the like and by polishing. An end surface of the slit  10  on the electrode pad  3  side serves as a thrust end surface  10   a.    
     In the sub substrate  7  formed as described above, the optical fiber  9  is laid in the V-shaped groove  8 , and the incident surface  9   a  that is an end surface of the optical fiber  9  on the electrode pad  3  side is thrusted to the thrust end surface  10   a , whereby the optical fiber  9  is positioned in the V-shaped groove  8 . 
     FIG. 7 is a schematic view showing a photographed image at the time of starting a method for connecting the optical waveguide and the optical semiconductor device according to the FIG. 6 embodiment. 
     FIG. 8 is a flowchart showing processes in the method for connecting the optical waveguide and the optical semiconductor device according to the FIG. 6 embodiment. 
     In FIG. 7, the L denotes an actual distance from the outgoing surface  2   b  of the optical semiconductor device  2  to centers of the positioning marks  4   a ,  4   b ,  6   a  and  6   b . The Lo denotes a designed distance from the outgoing surface  2   b  of the optical semiconductor device  2  to the centers of the positioning marks  4   a ,  4   b ,  6   a  and  6   b . The α denotes a working error of the outgoing surface  2   b  of the optical semiconductor device  2 . 
     The D denotes an actual distance from the outgoing surface  2   b  of the optical semiconductor device  2  to the thrust end surface  10   a  of the slit  10 . The Do denotes a designed distance from the outgoing surface  2   b  of the optical semiconductor device  2  to the thrust end surface  10   a  of the slit  10 . The β denotes a working error of the thrust end surface  10   a  of the slit  10  of the sub substrate  7 . 
     First, the optical semiconductor device  2  is moved onto the sub substrate  7  so that each of the centers of the first positioning marks  4   a  and  4   b  of the sub substrate  7  are made to be coincident with each of the centers of the second positioning marks  6   a  and  6   b  of the optical semiconductor device  2  respectively (step S 11 ). 
     Next, as shown in FIG. 2, the infrared ray R is irradiated onto the bottom surface of the sub substrate  7  from the infrared-ray light source  50  disposed below the sub substrate  7  so as to face upward. The infrared ray R is allowed to transmit through the sub substrate  7  and the optical semiconductor device  2 . 
     The infrared ray R having transmitted through the sub substrate  7  and the optical semiconductor device  2  is photographed by the infrared-ray camera  51  disposed above the optical semiconductor device  2  so as to face downward. The photographed infrared ray R is supplied to the image processing unit  27  as the image signal Sv (step S 12 ). 
     Thus, as shown in FIG. 7, the positioning marks  4   a ,  4   b ,  6   a ,  6   b , the outgoing surface  2   b  of the optical semiconductor device  2  and the slit  10  are photographed. Note that the whole of the slit  10  is photographed as a shadow. The reason is that since the slit  10  is formed by cutting processing, the bottom surface of the slit  10  is not a smooth but an uneven plane. 
     The image processing unit  27  (FIG. 2) performs an image processing such as a binary processing based on the photographed image indicated by the image signal Sv. The image processing unit  27  (FIG. 2) detects the position of the outgoing surface  2   b  of the optical semiconductor device  2 , the positions of the positioning marks  4   a ,  4   b ,  6   a  and  6   b  and the position of the thrust end surface  10   a  of the slit  10 , respectively (step S 13 ). 
     Furthermore, the image processing unit  27  (FIG. 2) obtains the actual distance (L+D) from the centers of the positioning marks  6   a ,  6   b  of the optical semiconductor device  2  to the thrust end surface  10   a  a of the slit  10  by a method to count what quantity equal to the number of pixels indicating that spaces among the positions of the detected outgoing surface  2   b , the detected positioning marks  4   a ,  4   b ,  6   a  and  6   b  and the thrust end surface  10   a  separate from each other. The image processing unit  27  (FIG. 2) outputs it as the actual distance signal Sds. 
     The control unit  29  (FIG. 2) subtracts the designed distance (Lo+Do) between the outgoing surface  2   b  of the optical semiconductor device  2  and the thrust end surface  10   a  of the slit  10  from the actual distance (L+D) indicated by the actual distance signal Sds (FIG.  2 ), thus obtaining an error (α+β)={(L+D)−(Lo+Do)}. Note that the designed distance (Lo+Do) is previously set in the control unit  29  (FIG.  2 ). 
     Next, in FIG. 2, the control unit  29  generates the drive signal Sd for driving the substrate-moving stage  23  and the parts-moving stage  26  by a quantity equal to the error (α+β) (FIG. 7) in a direction to cancel the error (α+β) (FIG.,  7 ). Note that the drive signal Sd may drive any one of the substrate-moving stage  23  and the parts-moving stage  26  or may drive the both of them. The control unit  29  then outputs the drive signal Sd (step S 14 ). 
     The drive signal Sd is supplied to the substrate-moving stage  23  and the parts-moving stage  26 , or the drive signal Sd is supplied to any one of the substrate-moving stage  23  and the parts-moving stage  26 . The parts-moving stage  26  is moved by a quantity equal to the error (α+β) (FIG. 9) in a direction of the arrow B (FIG. 9) so as to cancel the error (α+β) (FIG.  9 ). Alternatively, the substrate-moving stage  23  is moved by the quantity equal to the error (α+β) (FIG. 9) in a direction opposite to the arrow B (FIG.  9 ). Still alternatively, by combining the means above, the parts-moving stage  26  and the substrate-moving stage  23  are relatively moved with respect to each other (step S 15 ). 
     FIG. 9 is a schematic view showing a photographed image at the time of completing the method for connecting the optical waveguide and the optical semiconductor device according to the FIG. 6 embodiment. 
     In FIG. 9, since the optical semiconductor device  2  is moved relative to the sub substrate  7  by the quantity equal to the error (α+β) in the direction to cancel the error (α+β), the actual distance (L+D) between the thrust end surface  10   a  of the slit  10  of the sub substrate  7  and the outgoing surface  2   b  of the optical semiconductor device  2  will be made to be coincident with the designed distance accurately. 
     Finally, the parts-moving stage  26  (FIG. 2) is made to descend so as to mount the optical semiconductor device  2  on the sub substrate  7 , and the optical semiconductor device  2  and the sub substrate  7  are jointed to each other by a method such as soldering and the like (step S 16 ). 
     Thus, the working error α of the outgoing surface  2   b  of the optical semiconductor device  2  and the working error β of the thrust end surface  10   a  of the slit  10  are cancelled, and the distance between the outgoing surface  2   b  of the optical semiconductor device  2  and the incident surface  10   a  of the slit  10  will be made to be coincident with the designed distance accurately. 
     In the foregoing embodiments, the example in which the optical semiconductor device  2  is not rotated relative to the optical waveguide substrate  1  or the sub substrate  7  was described. In other words, these examples in which the distance between the first positioning mark  4   a  and the second positioning mark  6   a  is equal to the distance between the first positioning mark  4   b  and the second positioning mark  6   b  ware described. Compared to these examples, in the case where the optical semiconductor device  2  is rotated relative to the optical waveguide substrate  1  or the sub substrate  7 , in other words, in the case where the distance between the first positioning mark  4   a  and the second positioning mark  6   a  is different from the distance between the first positioning mark  4   b  and the second positioning mark  6   b , an error of the distance between the first positioning mark  4   a  and the second positioning mark  6   a  and an error of the distance between the first positioning mark  4   b  and the second positioning mark  6   b  are respectively obtained. By moving them so as to cancel all of these errors, the rotation of the optical semiconductor device  2  can be cancelled. 
     In the first embodiment, the error α was obtained from the optical waveguide substrate  1 . In the second embodiment, the error (α+β) was obtained from the sub substrate  7 . On the contrary, the error (α+β) may be obtained from the optical waveguide substrate  1 , and the error α may be obtained from the sub substrate  7 . 
     In the foregoing embodiments, the first positioning marks  4   a  and  4   b  shield the infrared ray R, and the second positioning marks  6   a  and  6   b  allows the infrared ray R to transmit therethrough. On the contrary, the first positioning marks  4   a  and  4   b  may allow the infrared ray R to transmit therethrough, and the second positioning marks  6   a  and  6   b  may shield the infrared ray R. 
     Although the infrared ray R was used as the light, which transmits through the optical waveguide substrate  1 , the optical semiconductor device  2  and the sub substrate  7 , any beam of light other than the infrared ray R may be employed. In this case, the transmission of the infrared ray and the shield thereof in each embodiment can be replaced with the transmission of this beam of light and the shield thereof. It suffices that instead of the infrared-ray light source  50  and the infrared-ray camera  51 , a light source for emitting this beam of light and a camera for photographing this beam of light are used. 
     As described above, according to the present invention, the positioning marks are provided in both of the optical semiconductor device and one of the optical waveguide substrate and the sub substrate, and the infrared ray is allowed to transmit through them, thus obtaining the image. The obtained image is processed, and the actual distance from the centers of the positioning marks to either the outgoing surface of the optical semiconductor device or the thrust end surface of the optical waveguide is obtained. The optical semiconductor device and the optical waveguide are relatively moved by the quantity equal to the error between the actual distance and the designed distance in the direction to cancel this error. Then, the optical semiconductor device and the optical waveguide are jointed to each other. Accordingly, the working error of the outgoing surface of the optical semiconductor device and the working error of the incident surface of the optical waveguide are absorbed, and hence the distance between the outgoing surface of the optical semiconductor device and the incident surface of the optical waveguide is made to be coincident with the designed distance accurately. Then, the optical semiconductor device and the optical waveguide are joined to each other. Thus, the optical coupling coefficiency can be significantly increased. 
     Moreover, the positioning marks are formed in both of the optical semiconductor substrate and one of the optical waveguide substrate or the sub substrate, and the image obtained by allowing the infrared ray to transmit through them is processed, thus obtaining the actual distance from the centers of the positioning marks on the optical semiconductor device to either the outgoing surface of the optical semiconductor device or the thrust end surface of the optical waveguide. The optical semiconductor device and the optical waveguide are relatively moved by the quantity equal to the error between the actual distance and the designed distance in the direction to cancel the error, and then the optical semiconductor device and the optical waveguide are jointed to each other. Accordingly, the working error of the outgoing surface of the optical semiconductor device and the working error of the incident surface of the optical waveguide are absorbed, and hence the distance between the outgoing surface of the optical semiconductor device and the thrust end surface of the optical waveguide is made to be coincident with the designed distance accurately. Thus, the optical coupling coefficiency can be significantly increased. 
     Although the preferred embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and alternations can be made therein without departing from spirit and scope of the inventions as defined by the appended claims.