Patent Publication Number: US-2006018359-A1

Title: Structure for optical axis adjustment of laser diode and optical pickup apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a structure for optical axis adjustment of a laser diode which is applied as, for example, a light source of an optical pickup, and to an optical pickup apparatus.  
      In the invention, ‘substantially around’ includes ‘around,’ and ‘substantially along a virtual spherical surface’ includes ‘along a virtual spherical surface.’ 
      2. Description of the Related Art  
      An optical pickup apparatus that records, reproduces and deletes information of a recording medium such as a compact disk (abbreviated to CD), a digital versatile disk (abbreviated to DVD) and a Blu-ray Disk (abbreviated to BD) is practically used. As a light source of the optical pickup apparatus, a laser diode is applied {refer to Japanese Unexamined Patent Publication No. JP-A 5-81693 (1993), for example}.  FIG. 7  is a plan view illustrating the essential part of a conventional optical axis adjustment structure of an optical pickup apparatus, and  FIG. 8  is a side view illustrating the essential part of the conventional optical axis adjustment structure of the optical pickup apparatus.  
      The optical pickup apparatus has a housing  1 , a laser diode base  2 , a pressing plate  3  made of a spring member, a laser diode holder  4 , and a laser diode  5 . To the laser diode holder  4 , the laser diode  5  is firmly attached with an adhesive or the like. The laser diode holder  4  has a contact portion that is formed into a partially spherical shape (referred to as the spherical contact portion). The laser diode base  2  has a spherical pedestal that abuts against the spherical contact portion.  
      The laser diode holder  4  and the laser diode base  2  are fixed with four screws  6 . By tightening and loosening the four screws  6 , an inclination of the optical axis is adjusted. The laser diode base  2  is movably supported on the housing  1  by the pressing plate  3 . Thus, the optical axis on the plane of the laser diode  5  is adjusted.  
      In the conventional optical axis adjustment structure, the optical axis adjustment on the plane and the inclination adjustment of the optical axis must be successively performed. Moreover, as to the inclination adjustment of the optical axis, the adjustment itself takes a lot of time for tightening and loosening of the screws  6 . Therefore, in the conventional optical axis adjustment structure, it is impossible to easily perform the optical axis adjustment and the inclination adjustment of the optical axis, and moreover, the time for the assembly of the apparatus is long.  
     SUMMARY OF THE INVENTION  
      An object of the invention is to provide a structure for optical axis adjustment of a laser diode that makes it possible to easily perform optical axis adjustment and inclination adjustment of the optical axis, and shortens operation time necessary for assembling the apparatus.  
      The invention provides a structure for optical axis adjustment of a laser diode, comprising a housing, laser diode supporting means capable of supporting a laser diode, and pressing means for pressing and movably retaining the laser diode supporting means on the housing.  
      According to the invention, a optical axis adjustment structure comprises a housing, laser diode supporting means, and pressing means. The laser diode supporting means is capable of supporting the laser diode. The pressing means presses and movably supports the laser diode supporting means on the housing. When the laser diode and the laser diode supporting means should be moved, that is, should be adjusted, the following operation is produced. The laser diode supporting means is pressed on the housing at all times due to the pressing force of the pressing means, and moreover, moves relatively to the housing. It is possible to move the laser diode supporting means with respect to the housing over a specified short distance, without an influence by the pressing force. The optical axis of the laser diode is adjusted in this way. In this way, it is possible to easily perform optical axis adjustment and inclination adjustment of the optical axis with a simpler structure than the conventional structure. Therefore, it is possible to make the operation time necessary for the assembly of the apparatus shorter than in the conventional art.  
      Further, in the invention, it is preferable that the laser diode supporting means includes a base that is supported so as to be movable along one surface portion of the housing, and a laser diode holder that is tiltingly movably supported on the base and supports the laser diode.  
      According to the invention, the laser diode supporting means includes a base and a laser diode holder. The base is supported so as to be movable along one surface portion of the housing. The laser diode holder is supported on the base so as to be tiltingly movable, and supports the laser diode. Optical axis adjustment of the laser diode and inclination adjustment of the optical axis are thereby performed. In particular, since the laser diode holder is tiltingly movably supported on the base, it is possible to easily perform the optical axis adjustment. It is possible to adjust the optical axis of the laser diode and adjust inclination of the optical axis in this way. It is possible to easily perform the optical axis adjustment and the inclination adjustment of the optical axis with such a simple structure.  
      Furthermore, in the invention, it is preferable that the laser diode holder has one curved portion that faces the base and the other curved portion that faces the pressing means, and the one curved portion and the other curved portion are formed substantially along a virtual spherical plane substantially around the light emitting point of the laser diode.  
      According to the invention, the laser diode holder has one curved portion and the other curved portion. The one curved portion and the other curved portion are formed substantially along a virtual spherical plane substantially around the light emitting point. The one curved portion faces the base, and the other curved portion faces the pressing means. The other curved portion is pressed and supported by the pressing means, and the one curved portion abuts against the base and tilts. In a state where the laser diode holder abuts against the base in this manner, the inclination adjustment of the optical axis of the laser diode can be performed, and moreover, it can be pressed with the pressing means in order to support the state after the inclination adjustment.  
      Still further, in the invention, it is preferable that the one curved portion and the other curved portion of the laser diode holder have different radiuses of curvature;  
      According to the invention, the radius of curvature of the one curved portion and the radius of curvature of the other curved portion are different, so that the following operation is produced. It is possible to fix the radius of curvature of the one curved portion that faces the base, and change the radius of curvature of the other curved portion that faces the pressing means in various manners, thereby forming the other curved portion into an optimum shape for the pressing means and the laser diode. On the contrary, it is possible to fix the radius of curvature of the other curved portion, and change the radius of curvature of the one curved portion in various manners, thereby forming the one curved portion into an optimum shape for the base. Accordingly, it is possible to shorten the time for a change of design, and it is possible to reduce the cost of manufacture.  
      Still further, in the invention, it is preferable that the other curved portion of the laser diode holder is formed so as to have a larger radius of curvature than that of the one curved portion.  
      According to the invention, the radius of curvature of the one curved portion of the laser diode holder that abuts against the base is made to be smaller than the radius of curvature of the other curved portion. Conversely, the other curved portion has a larger radius of curvature than that of the one curved portion. Besides, the radius of curvature of the other curved portion is determined on the basis of the size of the laser diode and so on. Since the other curved portion is formed so as to have a larger radius of curvature than that of the one curved portion, it is possible to make a movement amount when moving the laser diode holder relatively to the base large, at the time of the inclination adjustment of the optical axis. It is possible to make the amount of relative movement of the laser diode holder necessary for inclination angle adjustment of the optical axis large. Consequently, it is possible to easily and promptly perform minute inclination adjustment of the optical axis.  
      Still further, in the invention, it is preferable that an abutting surface of the base that faces the one curved portion of the laser diode holder is formed into a circular cone shape.  
      According to the invention, an abutting surface of the base that faces the one curved portion of the laser diode holder is formed into a circular cone shape, whereby the following operation is produced. It is possible to form a gap between the circular cone portion of the base and the one curved portion of the laser diode holder. By applying an adhesive to the gap and curing the adhesive, it is possible to firmly fix the laser diode holder to the base.  
      Still further, the invention provides a structure for optical axis adjustment of a laser diode, comprising a housing, a laser diode having a cap portion which is formed partially into a spherical shape, and pressing means for pressing and movably supporting the laser diode on the housing via the cap portion.  
      According to the invention, an optical axis adjustment structure comprises a housing, a laser diode, and pressing means. A cap portion of the laser diode is formed partially into a spherical shape. The pressing means presses and movably supports the laser diode on the housing via the cap portion. When the laser diode should be moved, that is, should be adjusted, the following operation is produced. The laser diode is pressed on the housing at all times due to the pressing force of the pressing means, and moreover, moves relatively to the housing via the cap portion. It is possible to move the laser diode with respect to the housing over a specified short distance, without an influence by the pressing force. The optical axis of the laser diode is adjusted in this way. In particular, since it is possible to relatively and directly move the laser diode with respect to the housing via the cap portion, it is possible to remarkably reduce the number of components less than in the conventional art. Besides, the same effects as in claim  1  are obtained.  
      In the invention, it is preferable that the pressing means includes a pressing plate which is made of a spring member that is elastically deformable.  
      Still further, the invention provides an optical pickup apparatus provided with the structure for optical axis adjustment of the laser diode described above.  
      According to the invention, it is possible to realize an optical pickup apparatus that is provided with the structure for optical axis adjustment of the laser diode described above. As to the laser diode installed in the optical pickup apparatus, it is possible to easily perform the optical axis adjustment and the inclination adjustment of the optical axis with a simpler structure than the conventional structure, and it is possible to shorten the operation time necessary for assembly. Thus, it is possible to shorten the time for the assembly of the whole optical pickup apparatus and the time for optical axis adjustment, and moreover, it is possible to realize an optical pickup apparatus whose quality is higher than that of a conventional one. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other and further objects, features, and advantages of the invention will be more explicit from the following detailed description taken with reference to the drawings wherein:  
       FIG. 1  is a cross section view of the essential part of an optical pickup apparatus according to a first embodiment of the invention, taken on a virtual plane including an optical axis;  
       FIG. 2  is a plan view of the essential part of the optical pickup apparatus according to the first embodiment;  
       FIG. 3  is a side view showing the relation among a housing, laser diode supporting means, and pressing means;  
       FIG. 4  is a cross section view of the essential part of an optical pickup apparatus according to a second embodiment of the invention, taken on a virtual plane including the optical axis;  
       FIG. 5  is a cross section view illustrating, in a magnified manner, the essential part of a base whose abutting surface is formed into a circular cone shape;  
       FIG. 6  is a cross section view of the essential part of an optical pickup apparatus according to a third embodiment of the invention, taken on a virtual plane including the optical axis;  
       FIG. 7  is a plan view illustrating the essential part of a conventional structure for optical axis adjustment of an optical pickup apparatus; and  
       FIG. 8  is a side view illustrating the essential part of the conventional structure for optical axis adjustment of the optical pickup apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Now referring to the drawings, preferred embodiments of the invention are described below.  
       FIG. 1  is a cross section view of the essential part of an optical pickup apparatus  10  according to a first embodiment of the invention, taken on a virtual plane including an optical axis L 1 .  FIG. 2  is a plan view of the essential part of the optical pickup apparatus  10  according to the first embodiment.  FIG. 3  is a side view showing the relation among a housing  11 , laser diode supporting means  12 , and pressing means  13 . The optical pickup apparatus  10  (referred to as the first pickup apparatus  10 ) according to the first embodiment is applied to an apparatus that irradiates a light of a laser diode to a recording medium such as a compact disk (abbreviated to CD), a digital versatile disk (abbreviated to DVD) and a Blu-ray Disk (abbreviated to BD), and records information on the recording surface thereof, or reproduces information written on the recording surface of the recording medium.  
      The first pickup apparatus  10  comprises a laser diode  14  serving as a light source, a structure for optical axis adjustment, an optical system, an actuator, and a light receiving element. The structure for optical axis adjustment for adjusting the optical axis L 1  of the laser diode  14 , and mainly has the housing  11 , a laser diode holder base  15 , a laser diode holder  16 , and the pressing means  13  that includes first and second pressing plates  17 ,  18 . The laser diode holder base  15  is synonymous with ‘the base.’ 
      The housing  11  has a hole portion that is formed in order to ensure the path of a light from at least the laser diode  14 . On the housing  11 , along one surface portion  11   a  of the housing  11 , the base  15  is movably supported by a pair of first pressing plates  17 . The first pressing plates  17  are separately positioned at a specified distance in the x-direction expressed by an arrow x in  FIGS. 1 and 2 . Each of the first pressing plates  17  is made of a spring member that is capable of elastically deforming, one end portion thereof is fixed to the housing  11  with a screw  19 , and the other end portion of each of the first pressing plates  17  presses and supports the base  15 . A portion in the vicinity of the middle in the x-direction of each of the first pressing plates  17  is bent at a right angle with respect to the one end portion and the other end portion, by the thickness of the base  15 .  
      The other end portion of the first pressing plate  17  is cut off in the x-direction, so that the other end portion does not interfere with a screw  20  for fixing the second pressing plate  18  described hereinafter. In other words, the base  15  is capable of moving along the one surface portion  11   a  of the housing  11  in a state where it is pressed and supported on the housing  11  by the other end portions of the pair of first pressing plates  17 . The x-direction is synonymous with a direction that is perpendicular to the thickness direction of the first pickup apparatus  10  as well as along the one surface portion  11   a.  In the vicinity of the middle in the x-direction of the base  15 , a base hole portion that communicates with the hole portion of the housing  11  is formed, and the light path is ensured.  
      The laser diode holder  16  that is supported on the base  15  so as to be tiltingly movable and supports the laser diode  14  is disposed. The base  15  and the laser diode holder  16  correspond to the laser diode supporting means. That is to say, it is possible to support the laser diode  14  with the base  15  and the laser diode holder  16 . The laser diode holder  16  has a base-side spherical convex portion  16   a  that faces the base  15 , and moreover, a pressing-plate-side spherical convex portion  16   b  that faces the second pressing plate  18 . The base-side spherical convex portion  16   a  corresponds to the one curved portion, and the pressing-plate-side spherical convex portion  16   b  corresponds to the other curved portion. The base-side spherical convex portion  16   a  and the pressing-plate-side spherical convex portion  16   b  are formed substantially along a virtual spherical surface substantially around the light emitting point of the laser diode  14 . The base-side spherical convex portion  16   a  and the pressing-plate-side spherical convex portion  16   b  are formed so as to have different radiuses of curvature. In concrete, the pressing-plate-side spherical convex portion  16   b  is formed so as to have a larger radius of curvature than that of the base-side spherical convex portion  16   a.    
      The base  15  has a spherical concave portion  15   a  that abuts against the base-side spherical convex portion  16   a.  The base-side spherical convex portion  16   a  and the spherical concave portion  15   a  are formed so as to be slidable. To the base  15  integrated with the housing  11 , a pair of second pressing plates  18  are fixed with the screws  20 , respectively. The second pressing plates  18  are positioned each other so as to be isolated inside in the x-direction with respect to a pair of first pressing plates  17 . Each of the second pressing plates  18  is made of a spring member that is capable of elastically deforming, one end portion thereof is fixed to the base  15  with the screw  20 , and the other end portion thereof presses and supports the pressing-plate-side spherical convex portion  16   b  of the laser diode holder  16 . Due to the pressing force of the second pressing plates  18 , the laser diode holder  16  is supported on the housing  11  so as to be tiltingly movable and the base  15  so as to be capable of tilting.  
      At the time of the optical axis adjustment of the laser diode  14  along the one surface portion  11   a,  the laser diode holder  16  is grasped with a catcher (not shown) of an optical axis adjustment machine, and the base  15 , the second pressing plates  18 , the laser diode holder  16  and the laser diode  14  move relatively to the housing  11  in a state where they are supported on the housing  11  by the first pressing plates  17 . At the time of the inclination adjustment of the optical axis L 1  of the laser diode  14 , a rotation force around the light emitting point of the laser diode  14  is given with the catcher of the optical axis adjustment machine in the above state (the state right after the optical axis adjustment described above). In a state where the laser diode holder  16  and the laser diode  14  are supported on the base  15 , that is, on the housing  11  by the second pressing plates  18 , the base-side spherical convex portion  16   a  of the laser diode holder  16  and the spherical concave portion  15   a  of the base  15  slide. Thus; the inclination of the optical axis L 1  of the laser diode  14  is adjusted. After the adjustments finish, even if the grasp with the catcher is loosened, the laser diode holder  16  and the base  15  are supported in the position after the adjustments by the first and second pressing plates  17 ,  18 . In a state where the position after the adjustments is supported, it is possible to shift to an adhesion process as a post-process. In the adhesion process, the laser diode holder  16  is firmly fixed to the base  15  with an adhesive.  
      According to the structure for optical axis adjustment described above, the first and second pressing plates  17 ,  18  press and movably support the laser diode supporting means  12  on the housing  11 . When the laser diode  14  and the laser diode supporting means  12  should be moved, that is, should be adjusted, the following operation and effect are produced. The laser diode supporting means  12  is pressed on the housing  11  at all times due to the pressing force of the first and second pressing plates  17 ,  18 , and moreover, moves relatively to the housing  11 . It is possible to move the laser diode supporting means  12  with respect to the housing  11  over a specified short distance, without an influence by the pressing force. Thus, it is possible to easily perform the optical axis adjustment and the inclination adjustment of the optical axis of the laser diode  14  with a simpler structure than the conventional structure. Therefore, it is possible to make the operation time necessary for the assembly of the apparatus shorter than in the conventional art.  
      Further, the base-side spherical convex portion  16   a  of the laser diode holder  16  faces the base  15 , and the pressing-plate-side spherical convex portion  16   b  on the opposite side thereof faces the second pressing plate  18 . The pressing-plate-side spherical convex portion  16   b  is pressed and supported by the second pressing plate  18 , and the base-side spherical convex portion  16   a  abuts against the spherical concave portion  15   a  of the base  15  and tilts. In a state where the laser diode holder  16  abuts against the base  15 , the inclination adjustment of the optical axis L 1  of the laser diode  14  can be performed, and moreover, it can be pressed with the pressing means in order to support the state after the inclination adjustment.  
      In the laser diode holder  16 , the radius of curvature of the base-side spherical convex portion  16   a  and the radius of curvature of the pressing-plate-side spherical convex portion  16   b  are different, so that the following effect is produced. It is possible to fix the radius of curvature of the base-side spherical convex portion  16   a  that faces the base  15 , and change the radius of curvature of the pressing-plate-side spherical convex portion  16   b  that faces the second pressing plate  18  in various manners, thereby making one spherical shape optimum for the base  15 . Therefore, a change of design is easy. Accordingly, it is possible to shorten the time for a change of design, and reduce the cost of manufacture. In a case where the radius of curvature of the pressing-plate-side spherical convex portion  16   b  is made to be larger than the radius of curvature of the base-side spherical convex portion  16   a,  it is possible to make a movement amount when moving the laser diode holder  16  relatively to the base  15  large, at the time of the inclination adjustment of the optical axis L 1 . It is possible to make a relative movement amount of the laser diode holder  16  necessary for the inclination angle adjustment of the optical axis L 1  large. Consequently, it is possible to perform minute inclination adjustment of the optical axis L 1  easily and promptly.  
       FIG. 4  is a cross section view of the essential part of an optical pickup apparatus  10 A according to a second embodiment of the invention, taken on a virtual plane including the optical axis L 1 .  FIG. 5  is a cross section view illustrating, in a magnified manner, the essential part of a base  15 A whose abutting surface is formed into a circular cone shape. The same members as in the first embodiment will be denoted by the same reference numerals, and the detailed description thereof will be omitted. In the structure for optical axis adjustment of the optical pickup apparatus  10 A of the second embodiment, the abutting surface of the base  15 A that faces the base-side spherical convex portion  16   a  of the laser diode holder  16  is formed into a circular cone shape. Consequently, it is possible to form a gap δ between a circular cone portion  15   b  of the base  15 A and the base-side spherical convex portion  16   a  of the laser diode holder  16 . By filling up an adhesive to the gap δ and curing, it is possible to firmly fix the laser diode holder  16  to the base  15 A.  
       FIG. 6  is a cross section view of the essential part of an optical pickup apparatus  10 B according to a third embodiment of the invention, taken on a virtual plane including the optical axis L 1 . In the optical pickup apparatus  10 B according to the third embodiment, a structure for optical axis adjustment of a laser diode  21  has the housing  11 , the laser diode  21 , a laser diode holder  23 , and the first pressing plate  17  and a third pressing plate  22  that serve as the pressing means. A cap portion  21   a  of the laser diode  21  is formed into a partially spherical shape. The third pressing plate  22  presses and movably supports the laser diode  21  on the laser diode holder  23  integrated with the housing  11 , via the cap portion  21   a.  When the laser diode  21  should be moved, that is, should be adjusted, the following operation and effect are produced. The laser diode  21  is pressed on the housing  11  at all times due to the pressing force of the third pressing plate  22 , and moreover, moves relatively to the housing  11  via the cap portion  21   a.  It is possible to move the laser diode  21  with respect to the housing  11  over a specified short distance, without an influence by the pressing force. The optical axis of the laser diode  21  is adjusted in this way. In particular, since it is possible to move the laser diode  21  relatively and directly with respect to the housing  11  via the cap portion  21   a,  it is possible to make the component count less than in the conventional art. Besides, the same effects as in the first embodiment are produced.  
      As another embodiment of the invention, the base-side spherical convex portion and the pressing-plate-side spherical convex portion may be formed so as to have the same radius of curvature. It is also possible to make the radius of curvature of the base-side spherical convex portion larger than the radius of curvature of the pressing-plate-side spherical convex portion, on the contrary to the first embodiment.  
      The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and the range of equivalency of the claims are therefore intended to be embraced therein.