Patent Publication Number: US-2011075887-A1

Title: Lens shift measuring apparatus, lens shift measuring method, and optical module manufacturing method

Description:
BACKGROUND 
     This application is based on Japanese patent application No. 2009-224989, the content of which is incorporated hereinto by reference. 
     TECHNICAL FIELD 
     The present invention relates to a lens shift measuring apparatus, a lens shift measuring method, and an optical module manufacturing method. 
     RELATED ART 
     For example, in a CAN package of an optical semiconductor element that is used for optical communication, it is general to perform packaging using a cap (hereinafter, referred to as lens cap) where a lens is hermetic sealed to a central portion, in order to obtain optical coupling with an optical fiber or optical coupling with a receptacle to connect the optical fiber. The lens cap is hermetic sealed by resistance welding with respect to a disk-like block (stem) where a chip, such as a laser diode, is mounted. 
     When the lens cap is hermetic sealed, the stem and the lens cap are positioned on the basis of the external positions thereof and are welded to each other. In this case, if the lens is eccentric to the cap, since the position of the lens with respect to a light emission point of the laser diode that is mounted on the center of the stem is shifted, the position of a focusing spot of the laser diode where light is focused by the lens may also be shifted from the center of the CAN package. 
     As such, if the position of the focusing spot of the laser diode is shifted from the center of the CAN package, in the following processes, when the CAN package is bonded to the optical fiber or the receptacle to constitute an optical module (optical semiconductor device), time is needed to adjust an optical axis or optical coupling efficiency of the optical module is lowered. 
     For this reason, when the optical semiconductor element for the optical module is assembled, before the CAN package is sealed, it is needed to previously measure a lens eccentric amount of the lens cap and exclude the lens cap having an eccentric amount out of the standard, or to perform position correction according to the measured eccentric amount when the CAN package is sealed. Accordingly, a technology for measuring the lens eccentricity of the lens cap becomes important. 
     In Japanese Laid-open patent publication No. 2005-221471, a lens eccentricity measuring apparatus that measures an eccentric amount of a lens is described. This lens eccentricity measuring apparatus has a lens eccentricity measuring jig that holds the lens, when the eccentricity of the lens is measured. The lens eccentricity measuring jig includes a mounting table on which a lens-attached member where the lens is held in a frame body is mounted, a holding member that contacts an outer edge of the frame body of the lens-attached member provided on the mounting table and positions the lens-attached member, and a rotating mechanism that rotates the lens-attached member. 
     Measurement by the lens eccentricity measuring apparatus that is disclosed in Japanese Laid-open patent publication No. 2005-221471 is performed as follows. First, the lens-attached member is mounted on the mounting table, measurement light is irradiated onto the lens of the lens-attached member through a pinhole while the lens-attached member is rotated by the rotating mechanism, and plural image data is obtained by imaging returned light from a surface of the lens. Next, an eccentric amount of the lens with respect to the frame body of the lens-attached member is calculated by executing image processing on the image data. Specifically, if the trace of the position of a virtual image of a point light source from which light is irradiated onto the lens through the pinhole is detected by executing image processing on the plural image data and the position of the virtual image does not change, it is determined that the lens is not eccentric. Meanwhile, if the position of the virtual image changes and forms the circular trace, it is determined that the lens is eccentric and a radius of the trace is calculated as the eccentric amount of the lens with respect to the frame body. 
     SUMMARY 
     However, the present inventor has recognized as follows. According to the technology that is disclosed in Japanese Laid-open patent publication No. 2005-221471, the following problems occur. 
     First, since the eccentric amount of the lens is measured by rotating the lens-attached member, the rotating mechanism that rotates the lens-attached member is needed, the apparatus configuration is complicated, and a manufacturing cost increases. 
     The plural image data is acquired in the course of rotating the lens-attached member and the eccentric amount is calculated on the basis of the processing result of the image data. For this reason, a measurement time may be needed. 
     Since the measurement light is irradiated onto the surface of the lens and the position of the reflected light (returned light) is detected, the shift of the optical axis of the lens that occurs when the lens is mounted to be inclined to the frame body cannot be measured. For this reason, the position shift of the focusing spot of the laser diode by the lens when the optical module is assembled cannot be accurately estimated. 
     As such, it is difficult to calculate the position shift amount of the focusing spot of the lens due to the eccentricity of the lens with respect to the frame body and calculate the position shift amount of the focusing spot of the lens due to the inclination of the lens with respect to the frame body in short time, using an apparatus having the simple configuration. 
     In one embodiment, there is provided a lens shift measuring apparatus, including: an irradiating unit which irradiates light onto a lens-attached member having a lens and a frame body to hold the lens, such that a reflected light from the frame body and a focusing spot formed by focusing light transmitted through the lens by the lens is generated; an imaging unit which includes the lens-attached member in an imaging range; and an image processing unit that executes image processing on an imaging result obtained by the imaging unit and calculates a shift of the lens, wherein the imaging unit images the reflected light from the frame body and the light transmitted through the lens, and the image processing unit executes, as the image processing, a first process, in which, a position of a predetermined portion of the frame body is calculated on the basis of an imaging result of the reflected light, a second process, in which, a position of the focusing spot is calculated on the basis of an imaging result of the light transmitted through the lens, and a third process, in which, a shift amount of the position of the focusing spot with respect to the predetermined portion is calculated on the basis of processing results of the first and second processes, as the shift of the lens. 
     According to the lens shift measuring apparatus, the position of the predetermined portion of the frame body may be calculated on the basis of the imaging result of the reflected light from the frame body of the lens-attached member, the position of the focusing spot by the lens may be calculated on the basis of the imaging result of the light transmitted through the lens, and the shift amount of the position of the focusing spot with respect to the predetermined portion of the frame body may be calculated on the basis of the calculated positions. Accordingly, the shift amount of the position of the focusing spot due to the shift of the lens (eccentricity or inclination of the lens with respect to the frame body) may be calculated without rotating the lens-attached member. That is, a rotating mechanism that rotates the lens-attached member is unnecessary, and the shift amount of the position of the focusing spot due to the eccentricity or the inclination of the lens with respect to the frame body may be calculated as the shift of the lens, using an apparatus having the simple configuration. 
     Further, imaging does not need to be performed over plural times in the course of rotating the lens-attached member, and only one-time imaging maybe performed in a state in which the position of the lens-attached member is fixed. Alternatively, one-time imaging may be performed with respect to each of the reflected light from the frame body and the light transmitted through the lens, in a state in which the position of the lens-attached member is fixed. For this reason, the shift amount of the position of the focusing spot may be measured in short time. 
     Since the position of the focusing spot of the light focused by the lens is calculated on the basis of the imaging result of the light transmitted through the lens, the position shift of the focusing spot due to the inclination of the lens may be calculated. 
     That is, the position shift amount of the focusing spot of the lens due to the eccentricity of the lens with respect to the frame body and the position shift amount of the focusing spot of the lens due to the inclination of the lens with respect to the frame body may be calculated in short time using an apparatus having the simple configuration. 
     In another embodiment, there is provided a lens shift measuring method including: calculating a position of a predetermined portion of a frame body, on the basis of an imaging result obtained by imaging reflected light from the frame body, in a state in which light is irradiated onto a lens-attached member having a lens and the frame body to hold the lens, such that the reflected light from the frame body is generated; calculating a position of a focusing spot, on the basis of an imaging result obtained by imaging light transmitted through the lens, in a state in which the light is irradiated onto the lens-attached member, such that the focusing spot formed by focusing the light transmitted through the lens by the lens is generated; and calculating a shift amount of the position of the focusing spot with respect to the predetermined portion as a shift of the lens. 
     In another embodiment, there is provided an optical module manufacturing method including: calculating a position of a predetermined portion of a frame body, on the basis of an imaging result obtained by imaging reflected light from the frame body, in a state in which light is irradiated onto a lens-attached member having a lens and the frame body to hold the lens, such that the reflected light from the frame body is generated; calculating a position of a focusing spot, on the basis of an imaging result obtained by imaging light transmitted through the lens, in a state in which the light is irradiated onto the lens-attached member, such that the focusing spot formed by focusing the light transmitted through the lens by the lens is generated; 
     calculating a shift amount and a shift direction of a position of the focusing spot with respect to the predetermined portion as a shift of the lens; and bonding a stem of a stem unit, which has the stem, a carrier provided on the stem, and a light emitting element provided on the carrier, to the frame body of the lens-attached member. In the bonding of the stem of the stem unit to the frame body, a relatively positions of the stem unit and the lens-attached member are corrected such that the shift amount calculated by the calculating of the shift amount and the shift direction of the position of the focusing spot is corrected, and the stem and the frame body are bonded to each other. 
     According to the invention, the position shift amount of the focusing spot of the lens due to the eccentricity of the lens with respect to the frame body and the position shift amount of the focusing spot of the lens due to the inclination of the lens with respect to the frame body may be calculated in short time using a lens shift measuring apparatus having the simple configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic front cross-sectional view of a lens shift measuring apparatus according to a first embodiment; 
         FIG. 2  is a diagram showing an image of a lens cap (lens-attached member) that is obtained by imaging epi-illumination light; 
         FIG. 3  is a diagram showing an image of a lens cap (lens-attached member) that is obtained by imaging transmissive illumination light; 
         FIGS. 4A and 4B  are schematic front cross-sectional views of a lens cap (lens-attached member) showing the position shift of a focusing spot by the lens shift.  FIG. 4A  shows the case where the lens is eccentric, and  FIG. 4B  shows the case where the lens is inclined; 
         FIG. 5  is a flowchart showing a flow of the operation of a lens shift measuring method according to the first embodiment; 
         FIG. 6  is a diagram showing image processing for calculating the central position of the lens cap (lens-attached member), which shows a state in which three or more windows are disposed in an image; 
         FIG. 7  is a diagram showing an example of a change curved line of brightness of an image in a radial direction in the window of  FIG. 6 ; 
         FIG. 8  is a diagram showing a curved line that is obtained by performing primary differentiation on the change curved line of  FIG. 7 ; 
         FIG. 9  is a schematic cross-sectional view showing an example of an optical module that is manufactured by an optical module manufacturing method according to the first embodiment; 
         FIG. 10  is a schematic front cross-sectional view of a lens shift measuring apparatus according to a second embodiment; 
         FIG. 11  is a flowchart showing a flow of the operation of a lens shift measuring method according to the second embodiment; and 
         FIG. 12  is a schematic front cross-sectional view of a lens shift measuring apparatus according to a first modification. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes. 
     Embodiments of the present invention will be explained below, referring to the attached drawings. Note that any similar constituents will be given the same reference numerals or symbols in all drawings, and explanations therefor will not be repeated. 
     First Embodiment  
       FIG. 1  is a schematic front cross-sectional view of a lens shift measuring apparatus  100  according to a first embodiment.  FIG. 5  is a flowchart showing a flow of the operation of a lens shift measuring method according to the first embodiment.  FIG. 9  is a schematic cross-sectional view showing an example of an optical module  150  that is manufactured by an optical module manufacturing method according to the first embodiment. 
     The lens shift measuring apparatus  100  according to the embodiment includes an irradiating unit (for example, configured using an epi-illumination light source  7  to illuminate epi-illumination light and a transmissive illumination light source  1  to illuminate transmissive illumination light) that irradiates light onto a lens-attached member (for example, lens cap  20 ) that has a lens  21  and a frame body (for example, cap  22 ) to hold the lens  21 , such that a reflected light from the frame body and a focusing spot  30  (see  FIGS. 4A and 4B ) formed by focusing light transmitted through the lens  21  by the lens  21  is generated. The lens shift measuring apparatus  100  further includes an imaging unit (for example, color CCD camera  8 ) that includes the lens-attached member in an imaging range and an image processing unit (for example, color image processing unit  9 ) that calculates the shift of the lens  21  by executing image processing on an imaging result obtained by the imaging unit. The imaging unit images the returned light from the frame body and the light transmitted through the lens  21 . In the image processing that is executed by the image processing unit, the following first to third processes are included. In the first process, the position of a predetermined portion (for example, center of a sheet-like portion  22   a  of the cap  22 ) in the frame body is calculated on the basis of an imaging result of the reflected light. In the second process, the position of the focusing spot  30  is calculated on the basis of an imaging result of the light transmitted through the lens  21 . In the third process, a shift amount of the position of the focusing spot  30  with respect to the predetermined portion is calculated on the basis of the processing results of the first and second processes, as the shift of the lens  21 . 
     In the lens shift measuring method according to the embodiment, the following first to third processes are executed. In the first process, the position of the predetermined portion (for example, center of the sheet-like portion  22   a  of the cap  22 ) in the frame body is calculated on the basis of the imaging result obtained by imaging the reflected light from the frame body, in a state in which the light is irradiated onto the lens-attached member (for example, lens cap  20 ) that has the lens  21  and the frame body (for example, cap  22 ) to hold the lens  21 , such that the reflected light from the frame body is generated. In the second process, the position of the focusing spot  30  is calculated on the basis of the imaging result obtained by imaging the light transmitted through the lens  21 , in a state in which the light is irradiated onto the lens-attached member, such that the focusing spot  30  formed by focusing the light transmitted through the lens  21  by the lens  21  is generated. In the third process, the shift amount of the position of the focusing spot  30  with respect to the predetermined portion is calculated as the shift of the lens  21 . 
     In the optical module manufacturing method according to the embodiment, the following first to fourth processes are executed. In the first process, the position of the predetermined portion (for example, center of the sheet-like portion  22   a  of the cap  22 ) in the frame body is calculated on the basis of the imaging result obtained by imaging the reflected light from the frame body, in a state in which the light is irradiated onto the lens-attached member (for example, lens cap  20 ) that has the lens  21  and the frame body (for example, cap  22 ) to hold the lens  21 , such that the reflected light from the frame body is generated. In the second process, the position of the focusing spot  30  is calculated on the basis of the imaging result obtained by imaging the light transmitted through the lens  21 , in a state in which the light is irradiated onto the lens-attached member, such that the focusing spot  30  formed by focusing the light transmitted through the lens  21  by the lens  21  is generated. In the third process, a shift amount and a shift direction of the position of the focusing spot  30  with respect to the predetermined portion are calculated as the shift of the lens  21 . In the fourth process, a stem  161  of a stem unit  153  that has the stem  161 , a carrier  162  provided on the stem  161 , and a light emitting element (for example, laser diode  163 ) provided on the carrier  162  and the frame body (for example, cap  22 ) of the lens-attached member (for example, lens cap  20 ) are bonded to each other. In the fourth process, the relative positions of the stem unit  153  and the lens-attached member are corrected, such that the shift amount calculated by the third process is corrected, and the stem  161  and the frame body are bonded to each other. 
     Hereinafter, the configuration of the first embodiment will be described in detail. 
     First, the configuration of the lens shift measuring apparatus  100  will be described. 
     As shown in  FIG. 1 , the lens shift measuring apparatus  100  according to the first embodiment includes a color CCD (Charge Coupled Device) camera  8  as the imaging unit, a color image processing unit  9 , and an imaging lens unit  10 . 
     The imaging lens unit  10  has an epi-illumination light source  7  that emits epi-illumination light (first light), a half mirror  6 , and an imaging lens  5 . 
     The lens shift measuring apparatus  100  further includes a mounting table  4  where a lens cap (lens-attached member)  20  is mounted, a transmissive illumination light source  1  that emits transmissive illumination light (second light), a pinhole plate  2  where a pinhole  2   a  is formed, and a collimator lens (converting unit)  3 . 
     In this case, the lens cap  20  has a lens  21  and a cap  22  as a frame body to hold the lens  21 . 
     The cap  22  has a sheet-like portion  22   a , a wall-like portion  22   b , and a flange portion  22   c , as shown in  FIG. 2 . The sheet-like portion  22   a  that is a substantially flat portion in the form of plate to hold the lens  21  at the center has a circular external shape. The wall-like portion  22   b  is formed in a tubular shape (for example, cylindrical shape) and has one end (upper end of  FIG. 1 ) that is connected to a circumferential edge of the sheet-like portion  22   a , such that its central axis is orthogonal to the sheet-like portion  22   a . The flange portion  22   c  is a portion having a flange shape that is formed to protrude from the other end (lower end of  FIG. 1 ) of the wall-like portion  22   b  to the outer circumferential side. The cap  22  is formed of a metal and substantially does not cause the epi-illumination light and the transmissive illumination light to pass through the cap. 
     The lens cap  20  is mounted on the mounting table  4 . The mounting table  4  is formed of, for example, a transparent member such as a transparent resin or glass, and transmits the transmissive illumination light from the transmissive illumination light source  1 . This mounting table  4  is disposed between the transmissive illumination light source  1 , a pinhole plate  2 , and the collimator lens  3  and the color 
     CCD camera  8 . The lens cap  20  is mounted on the mounting table  4 , such that the flange portion  22   c  becomes a lower portion and the sheet-like portion  22   a  and the lens  21  become an upper portion. 
     The pinhole  2   a  is disposed on a focus of the collimator lens  3 . The pinhole  2   a  causes a portion of transmissive illumination light emitted from the transmissive illumination light source  1  to pass through the pinhole, thereby converging the transmissive illumination light. The collimator lens  3  converts the transmissive illumination light, which has passed through the pinhole  2   a  (which is converged by the pinhole  2   a ), into parallel light and causes the parallel light to be incident on the lens  21 . That is, the collimator lens  3  converts the transmissive illumination light irradiated from the transmissive illumination light source  1  into the parallel light, before the transmissive illumination light reaches the lens  21 . The transmissive illumination light source  1 , the pinhole  2   a , and the collimator lens  3  constitute a second irradiating unit. 
     In this case, the transmissive illumination light that is converted into the parallel light by the collimator lens  3  is irradiated over a sufficiently wide range to be incident on an entire surface of a bottom surface of the lens  21 . That is, if the lens cap  20  is mounted on the mounting table  4  such that the lens cap  20  is within a field of view of the imaging lens unit  10 , the transmissive illumination light that is converted into the parallel light by the collimator lens  3  is irradiated is incident on the entire surface of the bottom surface of the lens  21 , regardless of arrangement of the lens cap  20  on the mounting table  4 . 
     According to an ideal structure of the lens cap  20 , an optical axis of the lens  21  is matched with a central axis of the tubular wall-like portion  22   b . The transmissive illumination light source  1 , the pinhole  2   a , the collimator lens  3 , the mounting table  4 , and the lens cap  20  are disposed, such that the transmissive illumination light converted into the parallel light by the collimator lens  3  becomes light in a direction where an optical axis thereof is almost matched with the optical axis of the lens  21  of the lens cap  20  having the ideal structure. That is, the second irradiating unit (transmissive illumination light source  1 , pinhole  2   a , and collimator lens  3 ) irradiates the transmissive illumination light from a direction where almost straight view of the lens  21  is enabled. 
     However, due to a manufacturing error of the lens cap  20 , the central position of the lens  21  may be shifted from the center of the sheet-like portion  22   a  or the lens  21  may be inclined with respect to the sheet-like potion  22   a . When the lens  21  is mounted to be inclined with respect to the sheet-like portion  22   a , the optical axis of the lens  21  is shifted from the optical axis of the transmissive illumination light that is converted into the parallel light by the collimator lens  3 . 
     For example, the collimator lens  3  is disposed below the mounting table  4 , the pinhole plate  2  is disposed on the lower side of the collimator lens  3 , the transmissive illumination light source  1  is disposed on the lower side of the pinhole plate  2 , and the transmissive illumination light source  1  emits (irradiates) the transmissive illumination light upward. In this case, an irradiation direction of the transmissive illumination light with respect to the lens  21  is the same as a direction in which light from the laser diode  163  is irradiated onto the lens  21 , when the lens cap  20  is assembled as the optical module  150  (to be described below). 
     Meanwhile, the half mirror  6  reflects the epi-illumination light, which is emitted from the epi-illumination light source  7 , to the side of the lens cap  20 . The reflected light of the epi-illumination light is irradiated onto the lens cap  20  through the imaging lens  5 . The epi-illumination light source  7 , the half mirror  6 , and the imaging lens  5  constitute the first irradiating unit. 
     In this case, the reflected light of the epi-illumination light is irradiated over a sufficiently wide range, such that the reflected light is irradiated onto an entire surface of the lens cap  20 . That is, if the lens cap  20  is mounted on the mounting table  4  such that the lens cap  20  is within a field of view of the imaging lens unit  10 , the reflected light of the epi-illumination light is irradiated onto the entire surface of the lens cap  20 , regardless of arrangement of the lens cap  20  on the mounting table  4 . 
     The epi-illumination light source  7 , the half mirror  6 , the imaging lens  5 , the mounting table  4 , and the lens cap  20  are disposed such that the reflected light of the epi-illumination light from the half mirror  6  is irradiated to be almost vertical to the sheet-like portion  22   a  of the lens cap  20 . That is, the first irradiating unit (the epi-illumination light source  7 , the half mirror  6 , and the imaging lens  5 ) irradiates the epi-illumination light onto the lens cap  20 , such that the epi-illumination light is irradiated to be almost vertical to the sheet-like portion  22   a.    
     For example, the epi-illumination light source  7  emits (irradiates) the epi-illumination light in a horizontal direction (rightward direction of  FIG. 1 ), the half mirror  6  is disposed on the side (right side in  FIG. 1 ) of the epi-illumination light source  7  and reflects the epi-illumination light downward, the imaging lens  5  is disposed below the half mirror  6 , and the mounting table  4  is disposed below the imaging lens  5 . 
     In the case of this embodiment, the imaging lens unit  10  constitutes a coaxial epi-illumination optical system. That is, the imaging lens unit  10  has the imaging lens  5  and the half mirror  6  that is disposed between the imaging lens  5  and the color CCD camera  8 . The imaging lens unit  10  is configured such that the epi-illumination light from the epi-illumination light source  7  is incident on the imaging lens  5  by the half mirror  6 . 
     In this case, an irradiation direction of the epi-illumination light with respect to the lens cap  20  becomes a direction that is opposite to an irradiation direction of the transmissive illumination light. Thereby, the reflected (returned) light of the epi-illumination light from the sheet-like portion  22   a  and the transmissive illumination light transmitted through the lens  21  may be imaged by one color CCD camera  8  to be fixedly disposed. 
     The color CCD camera  8  images a color image of the lens cap  20  that is projected by the imaging lens unit  10 . In the imaging lens unit  10 , lens magnification is set such that a lens of the color CCD camera  8  is focused on a top surface (top surface of the sheet-like portion  22   a ) of the lens cap  20 . The number of gray-scale levels of images that may be imaged by the color CCD camera  8  may be arbitrarily set. For example, the number of gray-scale levels may be 256 gray-scale levels, 128 gray-scale levels or 64 gray-scale levels for each color (for example, for each color of red, blue, and green). 
     To the color image processing unit  9 , a color image of an imaging result obtained by the color CCD camera  8  is input. The color image processing unit  9  executes image processing on the color image imaged by the color CCD camera  8  and calculates the shift (eccentricity or inclination) of the lens  21  with respect to the sheet-like portion  22   a.    
     In this case, the transmissive illumination light that is incident on the lens  21  is focused by the lens  21  and forms a focusing spot  30  ( FIGS. 4A and 4B ) above the lens  21 . 
     The color CCD camera  8  images an image (see  FIG. 3 ) including the focusing spot  30 , through the half mirror  6  and the imaging lens  5  of the imaging lens unit  10 . That is, the imaging lens  5  images the transmissive illumination light transmitted through the lens  21 , in the color CCD camera  8 . 
     Meanwhile, the epi-illumination light that is irradiated onto the lens cap  20  is reflected on a top surface of the sheet-like portion  22   a.    
     The color CCD camera  8  images an image (see  FIG. 2 ) including the reflected (returned) light from the sheet-like portion  22   a , through the half mirror  6  and the imaging lens  5  of the imaging lens unit  10 . That is, the imaging lens  5  images the epi-illumination light reflected from the sheet-like portion  22   a , in the color CCD camera  8 . 
     In the case of the embodiment, the wavelengths of the transmissive illumination light irradiated from the transmissive illumination light source  1  and the epi-illumination light irradiated from the epi-illumination light source  7  are different from each other. The reflected light of the epi-illumination light from the lens cap  20  and the transmissive illumination light including the focusing spot  30  are imaged by the color CCD camera  8  at one time. The color CCD camera  8  outputs a color image corresponding to an imaging result to the color image processing unit  9 . The color image processing unit  9  executes filter processing on the color image, thereby extracting an image (hereinafter, referred to as transmissive illumination image) based on the transmissive illumination light and an image (hereinafter, referred to as epi-illumination image) based on the epi-illumination light. 
     The color image processing unit  9  executes image processing on the epi-illumination image and calculates the position of a predetermined portion (for example, center of the sheet-like portion  22   a  of the cap  22 ) of the cap  22 . Meanwhile, the color image processing unit  9  executes image processing on the transmissive illumination image and calculates the position of the focusing spot  30  of the transmissive illumination light that is focused by the lens  21 . The color image processing unit  9  calculates a shift amount and a shift direction of the position of the focusing spot  30  with respect to the central position of the sheet-like portion  22   a.    
     Next, the operation will be described. The operation description also corresponds to the description of a lens shift measuring method according to the embodiment. 
     In the embodiment, first, the transmissive illumination light is irradiated from the transmissive illumination light source  1  and the epi-illumination light is irradiated from the epi-illumination light source  7 . 
     In this state, the transmissive illumination light that is irradiated from the transmissive illumination light source  1  is converged by the pinhole  2   a  and is converted into parallel light by the collimator lens  3 . The reason why the transmissive illumination light is caused to pass through the pinhole  2   a  is that a light source diameter of the illumination light source is generally large and it is difficult to obtain parallel light with high precision by only the collimator lens  3 . Letting the transmissive illumination light through the pinhole  2   a  disposed on the focus of the collimator lens  3 , the transmissive illumination light can be converted into the parallel light with high precision. 
     The transmissive illumination light that is converted into the parallel light by the collimator lens  3  transmits the mounting table  4  and is irradiated onto the lens cap  20 , from the lower side. The transmissive illumination light passes through the inside of the wall-like portion  22   b  of the lens cap  20 , is incident on the lens  21  from the lower side, is focused by the lens  21 , and forms the focusing spot (see  FIGS. 4A and 4B ) above the lens  21 . 
     In this case, the focal distance of the lens  21  of the lens cap  20  that is used in packaging of the optical semiconductor element is generally short in a high-performance optical module (for example, the lens  21  is an aspherical lens made of a material with a high refractive index) where high coupling efficiency is required at the high speed and the long transmission distance, for example, less than 1 mm at most. For this reason, the focusing spot  30  of the transmissive illumination light that is formed by the lens  21  is positioned within the distance less than 1 mm at most, above the lens  21 , and the height difference between the focusing spot  30  and the top surface of the cap  22  is within a depth of field of the imaging lens unit  10 . For this reason, if the color CCD camera  8  performs imaging through the imaging lens unit  10 , the color CCD camera  8  can focus the lens on the focusing spot  30  while focusing the lens on the top surface of the sheet-like portion  22   a  of the cap  22  and can perform imaging. That is, in the embodiment, the lens cap  20  (for example, the lens  21  is an aspherical lens made of a material with a high refractive index) where the focal distance of the lens  21  is short is set as a measurement object. 
     The lens  21  of the lens cap  20  is designed to be optimized in a near-infrared region corresponding to the wavelength of the laser diode. In this case, the wavelength of the transmissive illumination light from the transmissive illumination light source  1  is also preferably the wavelength (red color in the case of a visible light region) close to near infrared rays. If the wavelength (color) of the transmissive illumination light is set as a red color, the wavelength (color) of the epi-illumination light from the epi-illumination light source  7  is preferably set as a green color or a blue color. 
     Meanwhile, the epi-illumination light that is irradiated from the epi-illumination light source  7  is reflected to the side of the lens cap  20  (lower side) by the half mirror  6 , and is irradiated onto the lens cap  20  through the imaging lens  5 . The epi-illumination light is reflected on the top surface of the lens cap  20  and is imaged on an imaging surface of the color CCD camera  8  though the imaging lens  5  and the half mirror  6 . That is, the color CCD camera  8  images the entire lens cap  20  through the imaging lens unit  10 , by the epi-illumination light. 
     The outer diameter of the cap  22  that is used in a standard package of the optical semiconductor element is about 3 to 4 mm. An imaging surface of the color CCD camera  8  that is generally on the market has a rectangular shape in which the length of one side is about 5 to 8 mm. For this reason, optical magnification of the imaging lens unit  10  is set to about 1 to 2×. 
     In the case of the embodiment, the color CCD camera  8  acquires an image where illumination light of both the transmissive illumination light source  1  and the epi-illumination light source  7  is synthesized as a color image by one-time imaging. The image that is obtained by the imaging is output to the color image processing unit  9 . In the case of the embodiment, an image based on only the transmissive illumination light from the transmissive illumination light source  1  and an image based on only the epi-illumination light from the epi-illumination light source  7  are extracted by filter processing in the color image processing unit  9 . 
     An image in a frame A of  FIG. 2  is an image that is extracted with a color of the epi-illumination light. Since a correspondence relationship between the image in the frame A and the individual unit of the lens cap  20  is shown outside the frame A of  FIG. 2 , a sectional shape of the lens cap  20  is shown. 
     Since the image lens unit  10  is focused on the top surface of the sheet-like portion  22   a  of the cap  22 , a circular edge (outline B) of the top surface of the sheet-like portion  22   a  can be clearly observed. Meanwhile, since the imaging lens unit  10  is not focused on the top surface of the flange portion  22   c  of the cap  22 , an edge thereof (outline C) is unclear. Since an outer shape of the lens  21  is a curved surface, the reflected light of the epi-illumination light is not returned from most of the lens  21 . For this reason, an image that corresponds to the lens  21  is viewed dark as a whole. Since a central portion of the lens  21  is almost orthogonal to the optical axis of the epi-illumination light, the reflected light is returned from the central portion and an image corresponding to the central portion becomes a bright point. However, when the lens  21  is inclined to the cap  22 , the bright point is shifted from the position of the focusing spot  30  formed by focusing the light by the lens  21 . For this reason, it is not preferable to measure the eccentricity of the lens  21  on the basis of the position of the bright point. 
     In the embodiment, the positions of plural points in a clear circular edge (outline B) of the top surface of the sheet-like portion  22   a  of the cap  22  are detected, and the central position of the sheet-like portion  22   a  of the lens cap  20  is calculated on the basis of the detected positions of the plural points (which will be described in detail below). 
       FIG. 3  shows an image that is extracted with a color of the transmissive illumination light from the transmissive illumination light source  1 . The cap  22  is formed of a metal and does not transmit the transmissive illumination light. Meanwhile, the transmissive illumination light that has passed through the lens  21  is focused by the lens  21  and forms the focusing spot  30  (refer to  FIGS. 4A and 4B ) above the lens  21 . An image that corresponds to the focusing spot  30  becomes a small bright point (white portion of a central portion of  FIG. 3 ). 
     The color image processing unit  9  detects the deviation (shift) of the position of the spot position (white portion of the central portion of  FIG. 3 ) of the transmissive illumination light and the central position of the lens cap  20  described above as the shift of the lens  21  of the lens cap  20 . 
       FIGS. 4A and 4B  are schematic front cross-sectional views of the lens cap  20  showing the position shift of the focusing spot  30  caused by the shift of the lens  21 . 
       FIG. 4A  shows a state in which the lens  21  is eccentric horizontally with respect to the cap  22 . If the parallel transmissive illumination light is irradiated from the lower side of the lens cap  20 , the transmissive illumination light is focused by the lens  21  and forms the focusing spot  30 . 
     The position of the focusing spot  30  is shifted from the center D of the sheet-like portion  22   a  of the cap  22  by the amount of eccentricity E 1  of the lens  21 . In this case, the lens vertex (position of a central bright point of the lens  21  shown in  FIG. 2 ) where a curved surface of the lens  21  becomes horizontal and the position of the focusing spot  30  formed by the lens  21  are matched with each other. 
       FIG. 4B  shows a state in which the lens  21  is inclined with respect to the cap  22 . The position of the focusing spot  30  of the transmissive illumination light that is focused by the lens  21  is horizontally shifted from the center D of the sheet-like portion  22   a  of the cap  22  by the shift amount E 2  according to the inclination of the optical axis of the lens  21 . In this case, the vertex of the lens  21  and the position of the focusing spot  30  formed by the lens  21  are not matched with each other. 
     The lens shift measuring apparatus  100  according to the embodiment measures a shift amount and a shift direction of the position of the focusing spot  30  to suppress the position shift of the focusing spot of the laser diode  163 , when the laser diode  163  is sealed by the lens cap  20 . If this point is considered, it is important to be able to measure the position shift of the focusing spot  30  due to the inclination of the lens  21  as well as the position shift of the focusing spot  30  due to the eccentricity of the lens  21 . According to the lens shift measuring apparatus  100  according to the embodiment, since the position of the focusing spot  30  formed by focusing the transmissive illumination light by the lens  21  is detected, the position shift of the focusing spot  30  due to the inclination of the lens  21  can be easily measured. 
     Next, a flow of image processing for calculating the shift of the lens  21  from the obtained image will be described with reference to a flowchart of  FIG. 5 . 
     The image processing shown in  FIG. 5  includes processes of steps S 1  to S 8  to be described below. In step S 1 , a color image of the lens cap  20  where the transmissive illumination light and the epi-illumination light are irradiated is imaged by the color CCD camera  8 , and the color image of the lens cap  20  that is obtained by the imaging is output from the color CCD camera  8  to the color image processing unit  9 . The processes of steps S 2  to S 8  are executed by the color image processing unit  9 . First, instep S 2 , the color image that is imaged in step S 1  is positioned. In step S 3 , only a color of the epi-illumination light is extracted from the color image positioned in step S 2 . In step S 4 , an edge of the top surface of the sheet-like portion  22   a  of the cap  22  is detected from the image extracted with the color of the epi-illumination light in step S 3 . In step S 5 , the central position (that is, central position of the sheet-like portion  22   a ) of a circular shape that is formed by the edge detected in step S 4  is calculated. In step S 6 , only a color of the transmissive illumination light is extracted from the color image that is positioned in step S 2 . In step S 7 , the position of the focusing spot  30  of the transmissive illumination light that is focused by the lens  21  is detected from the image extracted with the color of the transmissive illumination light in step S 6 . In step S 8 , a shift amount and a shift direction of the position of the lens  21  with respect to the central position of the sheet-like portion  22   a  are calculated from the central position of the sheet-like portion  22   a  of the cap  22  obtained in step S 5  and the position of the focusing spot  30  obtained in step S 7 . 
     Hereinafter, the processes of steps S 2  to S 8  that are executed by the color image processing unit  9  will be described in detail. 
     In step S 2 , the image of the lens cap  20  that is imaged in step S 1  is positioned. The positioning is performed to accurately dispose windows (region to execute image processing) disposed in an image in the following processes with respect to the image of the lens cap  20  to some degree. This positioning is performed using a method, such as pattern matching. 
     In the pattern matching, for example, correlation values of a reference image previously stored and held by the color image processing unit  9  and the image of the lens cap  20  obtained by imaging are calculated, and similarity of both the images is calculated. For example, a correlation value with the reference image at each position is calculated while the image of the lens cap  20  obtained by the imaging is sequentially moved little by little, and the image of the lens cap  20  obtained by the imaging is positioned at the position where both the images are most matched with each other. 
     Next, in step S 3 , filter processing for extracting an image of a color of the epi-illumination light from the image of the lens cap  20  positioned in the previous step S 2  is executed. By this processing, the image that is shown in the frame A of  FIG. 2  is obtained. 
       FIG. 6  shows image processing for calculating the central position of the sheet-like portion  22   a  of the lens cap  20 , which shows a state in which three or more windows (for example, eight windows  11   a  to  11   h ) are disposed in the image. 
     In step S 4 , as shown in  FIG. 6 , the windows  11   a  to  11   h  are disposed in three places or more (in the embodiment,  8  places) in an outer circumferential portion of the sheet-like portion  22   a  of the cap  22  to the image obtained in the previous step S 3 . In each of the windows  11   a  to  11   h , a portion that becomes brighter from the center of the lens cap  20  to the outside is detected as the edge of the sheet-like portion  22   a.    
     A curved line L 1  shown in  FIG. 7  shows an example of a change curved line of brightness of an image in a radial direction of the sheet-like portion  22   a . That is, the curved line L 1  shows an example of a change in the brightness of an image from the central side of the sheet-like portion  22   a  to the outside, in any one of the windows  11   a  to  11   h  of  FIG. 6 . 
     In  FIG. 2 , a portion (outline B) that is viewed dark in a circular shape along outer circumference of the sheet-like portion  22   a  corresponds to a portion  41  that becomes dark in the curved line L 1  of  FIG. 7 . The edge of the sheet-like portion  22   a  corresponds to a portion  42  that becomes brighter in the curved line L 1  of  FIG. 7 . In order to accurately detect the portion  42  corresponding to the edge of the sheet-like portion  22   a , differentiation is performed on the curved line L 1  as will be described below. 
     A curved line L 2  shown in  FIG. 8  is a curved line that is obtained by performing primary differentiation on the curved line L 1  of  FIG. 7  in a radial direction. 
     The curved line L 2  of  FIG. 8  becomes negative in a portion  44  ( FIG. 8 ) that corresponds to a portion  43  ( FIG. 7 ) where brightness negatively changes (becomes dark) in the curved line L 1  of  FIG. 7 , and becomes positive in a portion  46  ( FIG. 8 ) that corresponds to a portion  45  ( FIG. 7 ) where brightness positively changes (becomes bright). 
     In order to detect the portion  42  (edge of the sheet-like portion  22   a ) that becomes brighter in  FIG. 7 , for example, in  FIG. 8 , a threshold value F is set, it is determined whether a differential value becomes maximized or a secondary differential value becomes zero in a region where a value becomes equal to or more than the threshold value F, and the edge position G of the sheet-like portion  22   a  is calculated. 
     By determine the edge position G for each of the windows  11   a  to  11   h  in  FIG. 6 , three or more (for example, eight) edge positions G that are different from each other can be calculated. The edge positions G are arranged in a circular shape along outer circumference of the sheet-like portion  22   a.    
     In step S 5 , the central position of the sheet-like portion  22   a  of the cap  22  is calculated on the basis of the three or more (for example, eight) edge positions G detected in the previous step S 4 . Since a minimum of three edge positions G are needed to calculate the center of the circle from the edge positions G on the circumference, the number of windows that is set in step S 4  is three minimum. When the number of windows is equal to or more than four, an approximate circle may be calculated from each edge position G using a least-square method and the center thereof may be used as the center of the sheet-like portion  22   a  of the cap  22 . In step S 4 , if the number of windows to detect the edge positions G is increased, improvement of measurement precision of the central position of the sheet-like portion  22   a  may be expected by an averaging effect. 
     Meanwhile, in step S 6 , filtering process for extracting an image of a color of the transmissive illumination light from the image of the lens cap  20  positioned in the previous step S 2  is executed. By this processing, for example, an image shown in  FIG. 3  is obtained. 
     In the image based on the transmissive illumination light shown in  FIG. 3 , only the focusing spot  30  (see  FIGS. 4A and 4B ) of the transmissive illumination light that is focused by the lens  21  shines bright. For this reason, in step S 7  subsequent to step S 6 , the position of the focusing spot  30  can be easily detected using general pattern matching or gravity center calculation. That is, the position of the focusing spot  30  with respect to the edge position G can be detected using the plural edge positions G calculated in the previous step S 4 . 
     The processes of steps S 3  to S 5  and the processes of steps S 6  and S 7  may be executed at individual timings or may be executed in parallel in a temporal sequence. 
     In step S 8 , on the basis of the central position of the sheet-like portion  22   a  of the cap  22  calculated in the previous step S 5  and the position of the focusing spot  30  calculated in the previous step S 7 , a position shift amount and a position shift direction of the focusing spot  30  with respect to the central position are calculated. 
     A series of image processing of steps S 2  to S 8  may be perfectly realized by functions of a general-purpose image processing apparatus that is generally on the market. 
     Next, before an optical module manufacturing method according to the embodiment is described, the configuration of the optical module  150  will be described with reference to  FIG. 9 . 
     As shown in  FIG. 9 , the optical module  150  has a CAN package  151  and a receptacle  152 . 
     The CAN package  151  has a stem  161 , a carrier  162 , a laser diode  163  as a light emitting element, and the lens cap  20 . On a mounting surface  161 A of the stem  161 , a block  165  is formed to protrude from the mounting surface  161 A. On a side of the block  165 , the carrier  162  is fixed. The carrier  162  is an insulating substrate on which the laser diode  163  is mounted. On the carrier  162 , the laser diode  163  is fixed. As such, when the carrier  162  and the laser diode  163  are mounted on the block  165 , the position of the block  165  is designed such that a light emission point of the laser diode  163  is positioned at the center of the mounting surface  161 A. The laser diode  163  irradiates laser light  164  in a direction orthogonal to the mounting surface  161 A of the stem  161 . The components (the carrier  162  and the laser diode  163 ) on the stem  161  are hermetic sealed by the lens cap  20 . 
     The receptacle  152  has a tubular fixing portion  171  and an optical connector inserting portion  172 . The optical connector inserting portion  172  is formed in a cylindrical joint shape. In an inner portion of the optical connector inserting portion  172 , for example, an SMF (Single Mode Fiber) stub  173  is inserted and fixed. If an optical connector  180  is inserted into the optical connector inserting portion  172  and a front end of the optical connector  180  is bumped against a right end face of the SMF stub  173  in  FIG. 9 , the optical connector  180  may be positioned in the optical connector inserting portion  172 . In a positioning state, an optical fiber  181  in the optical connector  180  and an SMF (Single Mode Fiber)  174  in the SMF stub  173  are coaxially positioned. 
     Next, the optical module manufacturing method according to the embodiment will be described. 
     First, the lens cap  20  described above is prepared. Next, the shift amount and the shift direction of the position of the focusing spot  30  with respect to the central position are calculated as the shift of the lens  21  with respect to the central position of the sheet-like shape  22   a  of the cap  22  of the lens cap  20 , using the lens shift measuring method described above. 
     When the lens cap  20  is mounted at the defined position of the stem  161 , the shift amount and the shift direction are matched or correlated with a shift amount and a shift direction in which a focusing spot (not shown in the drawings) formed by focusing the irradiated light from the laser diode  163  by the lens  21  is shifted from the central position of the sheet-like portion  22   a.    
     Meanwhile, the stem unit  153  is previously configured by fixing the carrier  162  on the stem  161  and mounting the laser diode  163  on the carrier  162 . 
     Next, the relative positions of the stem unit  153  and the lens cap  20  are corrected (corrected from the defined position described above) such that the shift amount calculated by the lens shift measuring method is corrected, and the components (the carrier  162  and the laser diode  163 ) on the stem  161  are hermetic sealed by the lens cap  20 . That is, the stem unit  153  and the lens cap  20  are bonded to each other, in a state in which the position of the lens cap  20  with respect to the stem unit  153  is corrected from the defined position by the same amount (distance) as the calculated shift amount in a direction opposite to the calculated shift direction. Specifically, the stem  161  and the flange portion  22   c  of the cap  22  are bonded by resistance welding. Thereby, the CAN package  151  that has the stem unit  153  and the lens cap  20  is configured. 
     Next, the optical connector  180  is inserted into the optical connector inserting portion  172  of the receptacle  152  and the optical fiber  181  in the optical connector  180  is aligned to the laser diode  163 . In this case, since the position of the focusing spot  30  formed by focusing the irradiated light from the laser diode  163  by the lens  21  is corrected in advance, the aligning can be easily performed, and optical coupling efficiency of the laser diode  163  and the receptacle  152  (SMF stub  173  of the receptacle  152 ) can be sufficiently obtained. 
     Next, the receptacle  152  and the CAN package  151  are mutually fixed at the aligned positions. The CAN package  151  is fixed to inner circumference of the tubular fixing portion  171  of the receptacle  152  by adhesion with an adhesive agent. 
     In this way, the optical module  150  can be manufactured. 
     According to the first embodiment described above, the central position in the sheet-like portion  22   a  may be calculated on the basis of the imaging result of the epi-illumination light that is reflected from the sheet-like portion  22   a  of the lens cap  20 , the position of the focusing spot  30  of the transmissive illumination light by the lens  21  may be calculated on the basis of the imaging result of the transmissive illumination light transmitted through the lens  21 , and the shift amount and the shift direction of the position of the focusing spot  30  with respect to the center of the sheet-like portion  22   a  may be calculated on the basis of the calculated positions. 
     Accordingly, the shift amount and the shift direction of the position of the focusing spot  30  due to the shift of the lens  21  (eccentricity or inclination of the lens  21  with respect to the cap  22 ) may be calculated without rotating the lens cap  20 . That is, a rotating mechanism that rotates the lens cap  20  is unnecessary, and the shift amount and the shift direction of the position of the focusing spot  30  due to the eccentricity or the inclination of the lens  21  with respect to the cap  22  may be calculated using an apparatus having the simple configuration. 
     Instead of measuring the lens eccentricity from the trace of the center of the lens when the lens is rotated, the image of the lens cap  20  is processed and the shift of the lens  21  is measured from the central position of the sheet-like portion  22   a  of the cap  22  and the position of the focusing spot  30 . Therefore, a high-speed measurement is enabled and the shift direction as well as the shift amount can be easily calculated. 
     That is, imaging does not need to be performed over plural times in the course of rotating the lens cap  20 , and only one-time imaging may be performed in a state in which the position of the lens cap  20  is fixed. For this reason, the shift amount and the shift direction of the position of the focusing spot  30  can be measured in short time. Since the position of the focusing spot  30  of the transmissive illumination light focused by the lens  21  is calculated on the basis of the imaging result of the transmissive illumination light transmitted through the lens  21 , the position shift of the focusing spot  30  due to the inclination of the lens  21  may be also calculated. 
     Specifically, since the position of the focusing spot  30  formed by focusing the transmissive illumination light corresponding to the parallel light by the lens  21  is calculated, the shift amount of the focusing spot  30  due to the inclination of the optical axis of the lens  21  can be accurately measured, even when the lens  21  is inclined with respect to the cap  22 . 
     In the lens shift measuring apparatus  100  according to the embodiment, one object is to reduce the position shift of the focusing spot by the laser light  164  emitted from the laser diode  163  in the optical module  150  when the lens cap  20  is assembled as the optical module  150 . For this reason, it is important to accurately measure the shift amount of the position of the focusing spot  30  due to the inclination of the lens  21  and the shift amount of the position. In the case of the lens cap  20  where an aspheric lens aiming at high optical coupling efficiency is used as the lens  21 , since a decrease in the optical coupling efficiency due to the shift of the light emission point of the laser diode  163  from the optical axis of the lens  21  is notable, the position of the lens  21  needs to be strictly managed. In the embodiment, since the position shift amount of the focusing spot  30  can be accurately measured, position correction of the lens  21  when the CAN package  151  is hermetic sealed by the lens cap  20  can be accurately performed. Therefore, sufficient optical coupling efficiency can be obtained even when the lens  21  is the aspheric lens. 
     As such, the shift amount of the position of the focusing spot  30  of the lens  21  due to the eccentricity of the lens  21  with respect to the cap  22  and the shift amount of the position of the focusing spot  30  of the lens  21  due to the inclination of the lens  21  with respect to the cap  22  may be calculated in short time using the lens shift measuring apparatus  100  having the simple configuration. 
     The transmissive illumination light is converted into the parallel light by the pinhole  2   a  and the collimator lens  3  and is irradiated over a sufficiently wide range as described above. And the epi-illumination light is also irradiated over a sufficiently wide range as described above. For this reason, if the lens cap  20  is disposed in a field of view of the imaging lens unit  10 , the measured shift amount is not affected by the position. Accordingly, a positioning mechanism that accurately positions the lens cap  20  at the predetermined position is not needed. 
     The wavelengths of the transmissive illumination light and the epi-illumination light are set to be different from each other, the color image of the lens cap  20  is imaged by the color CCD camera  8  in a state where the transmissive illumination light and the epi-illumination light are irradiated, and the image based on the transmissive illumination light and the image based on the epi-illumination light are extracted from the color image, using the color image processing unit  9 . By executing image processing on the extracted images, the position of the focusing spot  30  and the central position in the sheet-like portion  22   a  are calculated. Accordingly, since the transmissive illumination light and the epi-illumination light do not need to be switched, a control device for switching is not needed, and the lens shift measuring apparatus  100  can be configured at a low cost. Since only one-time imaging may be performed, an imaging time can be reduced. 
     Second Embodiment  
       FIG. 10  is a schematic front cross-sectional view of a lens shift measuring apparatus  200  according to a second embodiment.  FIG. 11  is a flowchart showing a flow of the operation of a lens shift measuring method according to the second embodiment. 
     In the first embodiment, the example of the case where the wavelengths of the epi-illumination light and the transmissive illumination light are set to be different from each other, the image of the color of the epi-illumination light and the image of the color of the transmissive illumination light are extracted from the color image obtained by one-time imaging, and the image processing is executed respectively, has been described. Meanwhile, in the second embodiment, an example of the case where imaging based on the epi-illumination light and imaging based on the transmissive illumination light are performed at different timings will be described. 
     In the case of the embodiment, the wavelengths of the epi-illumination light from the epi-illumination light source  7  and the transmissive illumination light from the transmissive illumination light source  1  do not need to be different from each other. The wavelengths of the epi-illumination light and the transmissive illumination light maybe equal to each other or different from each other. 
     In the case of the embodiment, the lens shift measuring apparatus  200  includes a CCD camera  90 , instead of the color CCD camera  8  (refer to  FIG. 1 ). The CCD camera  90  does not need to image a color image and may image a monochrome image. The number of gray-scale levels of images that may be imaged by the CCD camera  90  is arbitrary, and may be, for example, 256 gray-scale levels, 128 gray-scale levels or 64 gray-scale levels. 
     In the case of the embodiment, the lens shift measuring apparatus  200  has an image processing unit  91 , instead of the color image processing unit  9 . The image processing unit  91  does not need to process a color image and may process a monochrome image. 
     The lens shift measuring apparatus  200  according to the embodiment further includes a control unit  93 , an illumination control unit  92 , and an elevating mechanism  94 . 
     The control unit  93  controls the operation of the image processing unit  91 , the illumination control unit  92 , and the elevating mechanism  94 . 
     The illumination control unit  92  individually turns on/off the transmissive illumination light source  1  and the epi-illumination light source  7 , under the control of the control unit  93 . 
     In this case, the CCD camera  90  and the imaging lens unit  10  are mutually integrally provided. For example, the elevating mechanism  94  relatively elevates the CCD camera  90  and the imaging lens unit  10  with respect to the mounting table  4 . The elevating mechanism  94  may be configured to change the distances of the CCD camera  90  and the imaging lens unit  10  and the mounting table  4  in a vertical direction. For example, the elevating mechanism  94  may be configured to elevate the mounting table  4  or configured to elevate the CCD camera  90  and the imaging lens unit  10  and the mounting table  4  respectively. 
     In the case of the embodiment, an image of the lens cap  20  is imaged by the CCD camera  90  through the imaging lens unit  10 . The CCD camera  90  outputs an image of an imaging result to the image processing unit  91 . The image processing unit  91  executes image processing on the image input from the CCD camera  90 . 
     In the first embodiment described above, the lens cap  20  (for example, the lens  21  is an aspherical lens made of a material with a high refractive index) where the focal distance of the lens  21  is short is set as the measurement object. Meanwhile, in the second embodiment, the lens cap  20  (for example, the lens  21  is a cheap ball lens made of a material with a common refractive index) where the focal distance of the lens  21  is long may be set as the measurement object. That is, in the case of the lens cap  20  where the focal distance of the lens  21  is long, the height difference between the focusing spot  30  and the top surface of the cap  22  may be out of a depth of field of the image lens unit  10 . However, if the elevating mechanism  94  is used to elevate the imaging lens unit  10  and the CCD camera  90  to the position where the lens is focused on the focusing spot  30 , the focusing spot  30  can be clearly imaged. 
     Hereinafter, the operation of the embodiment will be described with reference to  FIG. 11 . The operation description also corresponds to the description of a lens shift measuring method according to the embodiment. 
     First, the control unit  93  transmits a control signal, which instructs to turn off the transmissive illumination light source  1  and turn on the epi-illumination light source  7 , to the illumination control unit  92 . The illumination control unit  92  that receives the control signal turns off the transmissive illumination light source  1  and turns on the epi-illumination light source  7 . Accordingly, the epi-illumination light that is emitted from the epi-illumination light source  7  is irradiated onto the lens cap  20  through the half mirror  6  and the imaging lens  5 . In this stage, the vertical positions of the imaging lens unit  10  and the CCD camera  90  are controlled such that the lens of the CCD camera  90  of the imaging lens unit  10  is focused on the top surface (top surface of the sheet-like portion  22   a ) of the lens cap  20 . 
     In this state, the control unit  93  transmits a first trigger signal to the image processing unit  91 . The image processing unit  91  that receives the first trigger signal acquires an image that is imaged by the CCD camera  90 . That is, when the CCD camera  90  is of a digital output type, the image processing unit  91  transmits an imaging command to the CCD camera  90 , and the CCD camera  90  that receives the imaging command images an image of the lens cap  20 , generates image data, and outputs the generated image data to the image processing unit  91 . Meanwhile, when the CCD camera  90  is a type of an analog output, the image processing unit  91  converts an analog video signal, which is input from the CCD camera  90 , into image data, and obtains the image data (step S 11 ). 
     Next, the image processing unit  91  executes processes of steps S 12  to S 14 . 
     First, in step S 12 , the image of the lens cap  20  that is imaged in the previous step S 11  is positioned, similarly to the process of step S 2  ( FIG. 5 ) in the first embodiment. 
     Next, in step S 13 , the edge position of the sheet-like portion  22   a  of the cap  22  is detected, similarly to the process of step S 4  ( FIG. 5 ) in the first embodiment. 
     Next, in step S 14 , the central position of the sheet-like portion  22   a  of the cap  22  is calculated, similarly to the process of step S 5  ( FIG. 5 ) in the first embodiment. 
     Next, the control unit  93  transmits a command to the elevating mechanism  94 . Next, the elevating mechanism  94  elevates the imaging lens unit  10  and the CCD camera  90  to the position where the lens is focused on the focusing spot  30  (step S 15 ). 
     Next, the control unit  93  transmits a control signal, which instructs to turn on the transmissive illumination light source  1  and turn off the epi-illumination light source  7 , to the illumination control unit  92 . The illumination control unit  92  that receives the control signal turns on the transmissive illumination light source  1  and turns off the epi-illumination light source  7 . Accordingly, the transmissive illumination light that is emitted from the transmissive illumination light source  1  is incident on the lens  21  through the pinhole  2   a  and the collimator lens  3 , and the transmissive illumination light is focused by the lens  21  and the focusing spot  30  is formed above the lens  21 . 
     In this state, the control unit  93  transmits a second trigger signal to the image processing unit  91 . The image processing unit  91  that receives the second trigger signal acquires an image that is imaged by the CCD camera  90  (step S 16 ). 
     Next, the image processing unit  91  executes processes of steps S 17  and S 18 . 
     First, in step S 17 , the position of the focusing spot  30  is calculated, similarly to the process of step S 7  ( FIG. 5 ) in the first embodiment. 
     Next, in step S 18 , the shift amount and the shift direction of the position of the focusing spot  30  with respect to the central position of the sheet-like portion  22   a  of the cap  22  are calculated, similarly to the process of step S 8  ( FIG. 5 ) in the first embodiment. 
     Next, in step S 19 , the control unit  93  transmits a command to the elevating mechanism  94 . Next, the elevating mechanism causes the imaging lens unit  10  and the CCD camera  90  to descend to the position where the lens is focused on the top surface of the cap  22  (step S 15 ). 
     In the embodiment, similarly to the first embodiment, the lens cap  20  (for example, the lens  21  is an aspherical lens made of a material with a high refractive index) where the focal distance of the lens  21  is short may be set as the measurement object. When such lens cap  20  is set as the measurement object, among the above-described processes, the processes of steps S 15  and S 19  may not be executed. If only such lens cap  20  is set as the measurement object, the lens shift measuring apparatus  200  that does not have the elevating mechanism  94  may be configured. 
     Since the optical module manufacturing method according to the embodiment is the same as that of the first embodiment, the description will not be repeated. 
     According to the second embodiment described above, the same effect as that of the first embodiment may be obtained. In addition, the illumination control unit  92  is used to switch the irradiation of the transmissive illumination light from the transmissive illumination light source  1  and the irradiation of the epi-illumination light from the epi-illumination light source  7  in a temporal sequence, and the central position of the sheet-like portion  22   a  of the cap  22  and the position of the focusing spot  30  are calculated from the individual image data. Therefore, the CCD camera  90  and the image processing unit  91  may use a monochrome type, instead of a color type, and the CCD camera  90  and the image processing unit  91  may be manufactured at a low cost. 
       FIG. 12  is a schematic front cross-sectional view of a lens shift measuring apparatus  300  according to a first modification. In the above-described embodiments, the imaging lens unit  10  has the imaging lens  5  and the half mirror  6  that is disposed in the middle of the optical path between the imaging lens  5  and the imaging unit (color CCD camera  8  or CCD camera  90 ), but the present invention is not limited to this example. For example, as shown in  FIG. 12 , pseudo coaxial epi-illumination where the half mirror  6  is disposed in the middle of an optical path between the imaging lens  5  and the lens cap  20  may be used. 
     It is apparent that the present invention is not limited tot the above embodiments, and may be modified and changed without departing from the scope and spirit of the invention.