Patent Publication Number: US-2007104076-A1

Title: Optical pickup

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical pickup of an optical disk device.  
      2. Description of the Related Art  
      An optical disk device for reproducing/recording an optical disk such as a CD or DVD has an optical pickup installed therein. In the related art, there has been developed an optical pickup, which is adapted for recording/reproducing different kinds of disks.  
      For example, a DVD recorder uses an optical pickup adapted for recording a DVD and reproducing a CD.  FIGS. 7 and 8  show an optical system of an optical pickup for a DVD recorder.  FIG. 7  is a side elevation, and  FIG. 8  is a top plan view.  
      A laser beam is emitted from a laser diode  1 . The laser diode  1  has a configuration shown in  FIG. 9 . A sub-mount  5  is fixed on a base  4  protruding from a principal face  3 a of a disc-shaped stem  3 . A monolithic laser diode (hereinafter called as “monolithic LD”)  6  is arranged on a leading end of the upper portion of the sub-mount  5 , and a PIN diode is formed on the sub-mount  5  at the back of the monolithic LD  6 . The monolithic LD  6  emits laser beams of different wavelengths including a DVD wavelength (e.g., a band of 650 nm) and a CD wavelength (e.g., a band of 780 nm). The PIN diode  7  is an element for receiving the laser beam emitted backward from the monolithic LD  6  thereby to detect the intensity, so as to perform the APC (Automatic Power Control), i.e., the control to make constant the outputs of the laser beams emitted from the monolithic LD  6 . A plurality of terminals  2  extend through the stem  3  and are connected with the monolithic LD  6  and the PIN diode  7  through lead wires  8  so that the drive currents are fed to the individual diodes through the terminals  2 . Additionally, the principal face  3 a of the stem  3  is equipped with a cap (not shown) for covering the structure which is positioned on the side closer to the base  4  than the stem  3 .  
       FIG. 10  is a view showing the periphery of the monolithic LD  6  and viewed from the side of the laser beam emitting direction (in the direction of arrow L in  FIG. 9 ). The monolithic LD  6  has a structure integrated into one chip so that it can output two kinds of wavelengths including the DVD wavelength (e.g., the band of 650 nm) and for the CD wavelength (e.g., the band of 780 nm). The structure includes a common negative electrode  9 , a GaAs substrate  10 , an active layer  11 , a DVD-side p-electrode  14 , and a CD-side p-electrode  15 . On the GaAs substrate  10 , there are laminated various layers containing the active layer, the lowest layer of which is connected with the DVD-side p-electrode  14  and the CD-side p-electrode  15 . A DVD light emitting point  12  and a CD light emitting point  13  are formed in the active layer  11 . The DVD-side p-electrode  15  is connected with a DVD-side positive electrode  16  formed on the sub-mount  5 , and the CD-side p-electrode  15  is connected with a CD-side positive electrode  17  formed on the sub-mount  5 . The common negative electrode  9  is connected with the GaAs substrate  10 . When an electric current is fed to the electrodes, the DVD recording laser beam (having the wavelength of 650 nm) is emitted from the DVD light emitting point  12 , and the CD reproducing laser beam (having the wavelength of 780 nm) is emitted from the CD light emitting point  13 . The DVD recording laser beam has a higher output than that of the CD reproducing laser beam (e.g., the DVD recording laser beam has an output of 135 mW whereas the CD reproducing laser beam has an output of 8 mW). The DVD light emitting point  12  and the CD light emitting point  13  are highly precisely positioned, because the positions are determined by a semiconductor wafer process.  
      The DVD recording laser beam or the CD reproducing laser beam, emitted from the laser diode  1  thus configured, is divided through a grating  18  into one main beam and two sub-beams. Moreover, the laser beam having passed through a PBS (Polarized Beam Splitter)  19  and a quarter-wavelength plate  20  is reflected by a launching mirror  21  into a collimator lens  22 . The laser beam having entered the collimator lens  22  is introduced as a parallel beam into an aperture  23 . This aperture  23  has such a wavelength selectivity that it passes the DVD recording laser beam (of the wavelength of 650 nm) as it is but restricts the CD recording laser beam (of the wavelength of 780 nm). The laser beam having passed through the aperture  23  is condensed by an objective lens  24  onto the recording face of a disk  25 .  
      The laser beam reflected by the disk  25  is passed through the objective lens  24 , the aperture  23  and the collimator lens  22 , and is reflected by the launching mirror  21  through the quarter-wavelength plate  20  into the PBS  19 . The laser beam to enter the PBS  19  has passed twice through the quarter-wavelength plate  20  so that it is reflected by the PBS  19  into a cylindrical lens  26 .  
      The cylindrical lens  26  has a curved concave surface, as shown in  FIG. 11A  and is arranged such that the concave surface faces the PBS  19 .  FIG. 11B  views the cylindrical lens  26  in the direction of arrow A is  FIG. 8 . As thus viewed, the cylindrical lens  26  is arranged at such an inclination that a center line S is inclined from a vertical direction by 45 degrees in the plane of the drawing.  
      The laser beam thus having passed through the cylindrical lens  26  is received by a photo-detector  27 .  FIG. 12  views the photo-detector  27  in the direction of arrow B in  FIG. 8 . The photo-detector  27  has a structure, in which light receiving portions for the laser beams of the two wavelengths are formed on one silicon substrate  28 . Alight receiving portion  30  having quartered light receiving faces receives the main beam of the DVD recording laser beam. The light receiving portions  29  and  31  having halved light receiving faces receive the sub-beams of the DVD recording laser beam. A light receiving portion  33  having quartered light receiving faces receives the main beam of the CD reproducing laser beam. Light receiving portions  32  and  34  having no divided light receiving face receive the sub-beam of the CD reproducing laser beam. The laser beams received by those individual light receiving portions are converted into electric signals, which are used to generate RF signals recorded in the disk, focus error signals and tracking error signals.  
      Here, the optical pickup thus configured has the following problems.  
       FIG. 13  is a diagram showing the behaviors of a laser beam emission from the aforementioned monolithic LD  6 . The laser beam emitted from the DVD light emitting point  12  or the CD light emitting point  13  has an intensity distribution of an elliptical pattern extended orthogonally to the active layer  11  as to reflect the shape of the light emitting point of the active layer  11 . The distribution of the intensity of light of the laser beam has a Gaussian distribution in directions both parallel and orthogonal to the active layer  11 . The angle of the portion, at which the intensity of light takes a predetermined ratio (e.g., a half value) or more to the peak value, will be called the “irradiation angle”. The irradiation angle (θ// in  FIG. 13 ) parallel to the active layer  11  will be called the “parallel irradiation angle”, and the irradiation angle (θ ⊥  in  FIG. 13 ) orthogonal to the active layer  11  will be called the “orthogonal irradiation angle”.  FIG. 14  shows the distributions of the intensities of lights of the CD reproducing laser beam and the DVD recording laser beam of a higher output than that of the CD reproducing laser beam, which are orthogonal to the active layer  11 . The DVD recording laser beam of the higher output has a small orthogonal emission angle and a steep distribution, whereas the CD reproducing laser beam of the lower output has a large orthogonal emission angle and a gentle distribution.  
       FIG. 15  is a schematic side elevation of the monolithic LD  6 . As shown in  FIG. 15 , the emission direction of a laser beam emitted from at least one of the emission points of the monolithic LD  6 , which has a light intensity peak value, may be deviated orthogonally relative to the active layer  11  of the monolithic LD  6  from a reference axis on the optical path from each light emitting point of the monolithic LD  6  to either the center of the light receiving portion  30  (for the DVD main beam) or the light receiving portion  33  (for the CD main beam) of the photo-detector  27 . This angle of deviation will be called the “emission angle” (i.e., Δ θ ⊥  in  FIG. 15 ). This deviation is caused by the manufacturing errors of the light emitting point of the monolithic LD  6  and the mounting errors of the monolithic LD  6  itself.  
      The upper face diagram of the distribution of the intensity of light just after emitted from the objective lens  24  of the case, in which the deviation angle deviates orthogonally relative to the active layer from the reference axis, as shown in  FIG. 15 , is presented in  FIG. 16A . The sectional side elevations of the distribution of the intensity of light just after emitted from the objective lens  24  of the cases, in which the emission direction does not deviate from the reference axis and deviates as shown in  FIG. 15 , are presented in  FIG. 16B . Here, letters Dob in  FIG. 16  designate the diameter of the laser beam just after emitted from the objective lens  24 . When the emission direction of the laser beam thus deviates orthogonally to the active layer from the reference axis, the intensity of light just after emitted from the objective lens  24  stopped down by the aperture  23  or the fixing member of the objective lens  24  deviates in the intensity of light and in the center of gravity.  
      In response to this deviation of the distribution of the intensity of light just after emitted from the objective lens  24 , the distribution of the intensity of light in the light receiving portion of the photo-detector  27  also deviates. The distribution of the intensity of light and the center-of-gravity position (i.e., a mark X) in the light receiving portion  30  (for the DVD main beam) and the light receiving portion (for the CD main beam) of the case, in which the emission direction deviates orthogonally to the active layer from the reference axis, as shown in  FIG. 15 , are shown in  FIG. 17A . When the emission direction of the laser beam thus deviates orthogonally to the active layer from the reference axis, the distribution of the intensity of light in the light receiving portion deviates in a Y-axis direction, and the center-of-gravity of the intensity of light also deviates in the Y-axis direction from the center of the light receiving portion.  
      If the four light receiving faces of the light receiving portion  30  are designated by a, b, c and d and if the four light receiving faces of the light receiving portion  33  are designated by A, B, C and D, as shown in  FIG. 17A , the photo-detector  27  has to be so adjusted that the light receiving balances expressed by the following Formulas (1) and (2) may be ideally 0: 
 
 PDY   1 =(( I   a   +I   b )−( I   c   +I   d ))/( I   a   +I   b   +I   c   +I   d )×100   (1) 
 
 PDY   2 =(( I   A   +I   B )−( I   C   +I   D ))/( I   A   +I   B   +I   C   +I   D )×100   (2) 
 
      Here: PDY 1  [%]: Light receiving balance of the DVD light receiving portion; PDY 2  [%]: Light receiving balance of the CD light receiving portion; and Ii: Intensity of light on the light receiving face i.  
      The case, as shown in  FIG. 17A , in which the adjustment is so made by moving the photo-detector  27  in the Y-axis direction that the center-of-gravity of the intensity of light in the light receiving portion  30  or the DVD light receiving portion may be positioned at the center of the light receiving portion  30 , is shown in  FIG. 7B . As a result, the light receiving balance (of Formula (1)) in the light receiving portion  30  or the DVD light receiving portion is 0. In the light receiving portion  33  or the CD light receiving portion, however, the center-of-gravity deviation of the intensity of light from the center of the light receiving portion  33  resides so that the light receiving balance (of Formula (2)) does not correspondingly become 0 but resides. This residual is called the “light receiving balance residual”. Due to the manufacturing errors of the light emitting point of the monolithic LD or the mounting errors of the monolithic LD itself, the emission angle of the laser beam disperses between the optical pickups. Depending the magnitude of the emission angle, the center-of-gravity deviation of the intensity of light in the state of  FIG. 17A  may be so large as to cause the aforementioned light receiving balance residual after the movement adjustment of the photo-detector  27  to exceed an allowable range. If the light receiving balance residual exceeds the allowable range, an adjustment is required because the reading of the disk or the servo action is adversely affected. However, the light receiving balance residual cannot be eliminated by the rotation adjustment of the photo-detector  27 . Therefore, the optical system other than the photo-detector  27  has to be so adjusted that the light receiving balance residual may be within the allowable range, but this adjustment becomes a cause for raising the cost.  
      JP-A-2003-22543 discloses that the deviation of the light receiving balance due to the deviation of the emission direction of the laser beam from the LD from the reference axis parallel to the active layer is adjusted by inclining the LD thereby to adjust the light receiving balance. However, this adjustment has to be made for every optical pickups, thereby to raise the cost.  
     SUMMARY OF THE INVENTION  
      In view of the problems thus far described, the present invention has been conceived to provide an optical pickup capable of suppressing the rise in the cost.  
      In order to achieve the aforementioned object, according to the invention, there is provided an optical pickup comprising: a monolithic laser diode; and a photo-detector having each light receiving portion formed on one substrate and corresponding to each laser beam emitted from the monolithic laser diode,  
      wherein the monolithic laser diode is arranged such that each light emitting point belonging to the monolithic laser diode is positioned on each reference axis, and such that each reference axis is inclined from the direction orthogonal to each laminar face containing the each light emitting point and in the direction orthogonal to the active layer by an angle of an average value of the angular deviation of the emission direction orthogonal to the active layer at the light emitting point belonging to the monolithic laser diode.  
      For example, the invention may be embodied by an optical pickup comprising: a laser diode including a stem, a base protruded from the principal face of the stem, a sub-mount arranged on the base, and a monolithic laser diode arranged over the sub-mount; and a photo-detector having each light receiving portion formed on one substrate and corresponding to each laser beam emitted from the monolithic laser diode, wherein the mounting face of the base for mounting the sub-mount is formed by such an angle with respect to an axis orthogonal to the principal face of the stem as corresponds to an average value of the angular deviation of the emission direction orthogonal to an active layer at a light emitting point belonging to the monolithic laser diode; and the laser diode is arranged such that each light emitting point belonging to the monolithic laser diode is positioned on each reference axis, and such that each reference axis and the axis orthogonal to the principal face of the step are substantially parallel to each other.  
      For example, the invention may also be embodied by an optical pickup comprising: a laser diode including a stem, a base protruded from the principal face of the stem, a sub-mount arranged on the base, and a monolithic laser diode arranged over the sub-mount; an LD holder having a hole for inserting the laser diode; and a photo-detector having each light receiving portion formed on one substrate and corresponding to each laser beam emitted from the monolithic laser diode, wherein the hole belonging to the LD holder is formed such that the axis extending through the center of the hole is inclined from the axis parallel to the upper face and the lower face of the LD holder by such an angle as corresponds to an average value of the angular deviation of the emission direction orthogonal to an active layer at a light emitting point belonging to the monolithic laser diode; and the LD holder having the laser diode inserted thereinto is arranged such that each light emitting point belonging to the monolithic laser diode is positioned on each reference axis, and such that each reference axis and the axis parallel to the upper face and the lower face of the LD holder are substantially parallel to each other.  
      For example, the invention may also be embodied by an optical pickup comprising: a laser diode including a stem, abase protruded from the principal face of the stem, a sub-mount arranged on the base, and a monolithic laser diode arranged over the sub-mount; an LD holder having a hole for inserting the laser diode and protrusions formed on the upper face and the lower face; an LD spring having a base portion and leaf portions formed by folding the two ends of the base portion; and a photo-detector having each light receiving portion formed on one substrate and corresponding to each laser beam emitted from the monolithic laser diode, wherein the hole belonging to the LD holder is formed such that the axis extending through the center of the hole is substantially parallel to the upper face and the lower face of the LD holder; the leaf portions have holes for fitting the protrusions therein, and in that the LD spring is arranged such that the leaf portions are substantially parallel to each reference axis; and the LD holder having the laser diode inserted thereinto is fixed on the LD spring by fitting the protrusions in the holes belonging to the leaf portions, such that each light emitting point belonging to the monolithic laser diode is positioned on each reference axis, and such that each reference axis is inclined from the direction orthogonal to each laminar face containing the each light emitting point and in the direction orthogonal to the active layer by an angle of an average value of the angular deviation of the emission direction orthogonal to the active layer at the light emitting point belonging to the monolithic laser diode.  
      For example, the invention may also be embodied by an optical pickup comprising: a laser diode including a stem, a base protruded from the principal face of the stem, a sub-mount arranged on the base, and a monolithic laser diode arranged over the sub-mount; an LD holder having a hole for inserting the laser diode and protrusions formed on the upper face and the lower face; an LD spring having a base portion and first and leaf portions formed by folding the end portions of the base portion substantially perpendicularly; a base portion for retaining the LD spring; and a photo-detector having each light receiving portion formed on one substrate and corresponding to each laser beam emitted from the monolithic laser diode, wherein the hole belonging to the LD holder is formed such that the axis extending through the center of the hole is substantially parallel to the upper face and the lower face of the LD holder; the first and second leaf portions have holes for fitting the protrusions therein, and in that the LD holder having the laser diode inserted thereinto is fixed by the LD spring such that the first leaf portion and the upper face of the LD holder, and the second leaf portion and the lower face of the LD holder are substantially parallel to each other; the base portion has a stiffening face, against which the base portion is brought into abutment, and in that the stiffening face is inclined from the axis orthogonal to each reference axis by an angle corresponding to an average value of the angular deviation of the emission direction orthogonal to the active layer at the light emitting point belonging to the monolithic laser diode; and the base portion is brought into abutment against the stiffening face such that each light emitting point belonging to the monolithic laser diode may be positioned on each reference axis, and in that the LD spring, on which the LD holder having the laser diode inserted thereinto is fixed, is retained by the base portion.  
      According to the optical pickup thus constituted, the average light receiving balance residual between the optical pickups can be suppressed to a small value, and the optical pickups, of which the light receiving balance residual exceeds the allowable range, can be suppressed in number, to make unnecessary an adjustment after the movement adjustment of the photo-detector thereby to suppress the rise in the cost.  
      The optical pickup of the invention can suppress the rise in the cost. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIGS. 1A and 1B  are a top plan view and a side elevation of an optical pickup according to an embodiment the invention;  
       FIG. 2  is an exploded perspective view of a laser diode mounting portion of the optical pickup;  
       FIG. 3  is a sectional side elevation of a laser diode according to a first embodiment of the invention;  
       FIG. 4  is a sectional side elevation of a laser diode and an LD holder according to a second embodiment of the invention;  
       FIG. 5  is a sectional side elevation of a laser diode, an LD holder and an LD spring according to a third embodiment of the invention;  
       FIG. 6  is a sectional side elevation of a laser diode, an LD holder, an LD spring and a wall portion of a base portion according to a fourth embodiment of the invention;  
       FIG. 7  is a side elevation of an optical system in an optical pickup;  
       FIG. 8  is a top plan view of the optical system;  
       FIG. 9  is a perspective view of a laser diode;  
       FIG. 10  is a view of the periphery of a monolithic LD and taken from the side of the laser beam emitting direction;  
       FIGS. 11A and 11B  are views showing a cylindrical lens;  
       FIG. 12  is a diagram showing a photo-detector;  
       FIG. 13  is a diagram showing the behaviors of a laser beam emission from the monolithic LD;  
       FIG. 14  is a diagram showing the distributions of the intensities of lights emitted from the monolithic LD, which are orthogonal to an active layer;  
       FIG. 15  is a diagram showing the deviation of a laser beam in the emission direction orthogonal to the active layer from a reference axis, which is emitted from the monolithic LD;  
       FIGS. 16A and 16B  are diagrams showing the center-of-gravity deviation of such a laser beam just after emitted from an objective lens and accompanying the deviation of the emission direction orthogonal to the active layer from the reference axis as is emitted from the monolithic LD; and  
       FIGS. 17A and 17B  are diagrams showing the light receiving balance adjustments by adjusting the movements of the photo-detector. 
    
    
     DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS  
      Embodiments of the invention are described with reference to the accompanying drawings. An optical pickup for a DVD recorder is taken as an example.  FIG. 1A  is a top plan view of an optical pickup according to an embodiment of the invention, and  FIG. 1B  is a side elevation of the optical pickup (a laser diode  1  is detached in  FIG. 1B  from the optical pickup).  FIG. 2  is an exploded perspective view, viewed from above a portion of the laser diode  1  to be mounted on a base portion  38 , of the optical pickup. Here, the configuration of the optical system of the optical pickup is similar to the aforementioned one shown in  FIG. 7  and FIG. B.  
      The laser diode  1  has the aforementioned configuration, as shown in  FIG. 9 , in which a cap  35  is so mounted on the principal face  3 a of the stem  3  as to cover the structure of a monolithic LD  6 , a sub-mount  5  and so on, positioned closer to a base  4  than a stem  3 . The cap  35  is provided, in the front face of the cap  35 , with a hole for passing the laser beam.  
      An LD holder  36  is provided with holes  36   a  and  36   b,  which extend longitudinally therethrough such that the hole  36   a  has a larger diameter than that of the hole  36   b.  The laser diode  1  is mounted on the LD holder  36  by press-fitting the stem  3  into the hole  36   a  so that the principal face  3   a  of the stem  3  may come into abutment against an abutment face  36   c  positioned at the boundary between the hole  36   a  and the hole  36   b.  At this time, the cap  35  is covered with the hole  36   b.  Moreover, protrusions  36   f  are formed at the substantially transverse center portions on the upper face  36   d  and the lower face  36   e  of the LD holder  36 .  
      An LD spring  37  is a leaf spring formed of a metal sheet. The LD spring  37  includes a base portion  37   a  and leaf portions  37   b  and  37   c  formed by folding it at the upper and lower ends of the base portion  37   a  substantially perpendicularly to the base portion  37   a  into a generally C-shape in a side view. Moreover, the LD spring  37  is folded into a generally L-shape in a side view oppositely of the leaf portion  37   c  from the lower end of the base portion  37   a  thereby to form retaining portions  37   e  transversely across the leaf portion  37   c.  A hole  37   f  is formed in the substantially central portion of the base portion  37   a.  In the substantially transverse center portions of the leaf portions  37   b  and  37   c,  there are formed holes  37   d,  in which the protrusions  36   f  of the LD holder  36  are fitted to hold the LD spring  37  on the LD holder  36 .  
      The base portion  38  is provided therein with a grating  18 , a PES  19 , a quarter-wavelength plate  20 , a launching mirror  21 , a collimator lens  22  and a cylindrical lens  26  (see  FIG. 8 ), and a photo-detector  27  (see  FIG. 8 ) is mounted on the side face. Over the base portion  38 , moreover, there is positioned a lens holder  39 , which is provided with an aperture  23  (see  FIG. 7 ) and an objective lens  24 . The base portion  38  is provided at its one end with a wall portion  38   a,  which is equipped with a generally U-shaped opening  38   b  at its transversely central portion. The LD spring  37  is fixed on the base portion  38  by hooking the retaining portions  37   e  of the LD spring  37  on the transversely two side lower portions of the wall portion  38   a  across the opening  38   b  while bringing the base portion  37   a  of the LD spring  37  on an stiffening face  38   c  of the wall portion  38   a.    
      As described above, the laser diode  1  is integrated with the base portion  38 . The laser beam, as emitted from the laser diode  1 , passes through the hole of the cap  35 , the holes  36   a,    36   b  and  37   f  and the opening  38   b  and through the optical system in the base portion  38  so that it is emitted from the objective lens  24 . The laser beam is reflected by the disk  25  to enter the objective lens  24  again, and passes through the optical system in the base portion  38  so that it is received by the photo-detector  27  mounted on the side face of the base portion  38 .  
      Next, embodiments of the individual structures for achieving the object of the invention are described on the optical pickup having the structure thus made.  
     First Embodiment  
       FIG. 3  is a sectional side elevation of the laser diode  1  according to a first embodiment. By the aforementioned structure, the laser diode  1  is integrated with the base portion  38  by the LD holder  36  and the LD spring  37 , although not shown.  
      Here, the monolithic LD  6  has the emission direction precisions on the individual light emitting points as its specifications. The emission direction precisions orthogonal to the active layer are expressed with the average value and the dispersion of the angular deviation orthogonal to the active layer of the emission direction in the direction orthogonal to the laminar face containing the light emitting points. Here, the average value of the angular deviation of the emission direction at a light emitting point  12  for the DVD orthogonal to the active layer is designated by θ A .  
      The sub-mount  5  is mounted on the upper leading end of the base  4  protruded from the stem  3 , and the monolithic LD  6  is mounted on the upper leading end of the sub-mount  5 . The cap  35  is mounted on the principal face  3   a  of the stem  3  and provided in its front face with a hole  35   a  for passing the laser beam therethrough. A mounting face  4   a  for mounting the sub-mount  5  is inclined by −θ A  with respect to the axis orthogonal to the principal face  3   a  of the stem  3 . As shown in  FIG. 3 , moreover, the laser diode  1  is so arranged and integrated with the base portion  38  that the individual light emitting points of the monolithic LD  6  are positioned on the individual reference axes, and that the individual reference axes are substantially parallel to the axis orthogonal to the principal face  3   a  of the stem  3 .  
      As a result, the monolithic LD  6  is arranged to deviate the individual reference axes by θ A  orthogonally to the active layer from the direction orthogonal to the individual laminar faces containing the individual light emitting points, so that the average emission direction of the DVD light emitting point  12  is aligned with the reference axis. In case, therefore, the laser beam emitted from the DVD light emitting point  12  is received by a light receiving portion  30  (for the DVD main beam) of the photo-detector  27 , the center of gravity of the intensity of light is aligned on the average with the center of the light receiving portion  30  so that the light receiving balance becomes substantially 0 on the average. If the average value of the angular deviation of the emission direction of a CD light emitting point  13  is then equal to the same value θ A  as that of the DVD light emitting point  12 , the average emission direction of the CD light emitting point  13  is also aligned with the reference axis, and the light receiving balance in a light receiving portion  33  (for the CD main beam) of the photo-detector  27  also becomes substantially 0 on the average, so that the average light receiving balance residual becomes substantially 0.  
      In case the average value of the angular deviation of the emission direction of the CD light emitting point  13  is different from that of the DVD light emitting point  12 , the average emission direction of the CD light emitting point  13  deviates from the reference axis. As has been described with reference to  FIG. 14 , however, the CD reproducing laser beam of a lower output than that of the DVD recording laser beam has a large orthogonal irradiation angle so that the distribution of the intensity of light orthogonal to the active layer becomes gentle. Even if the average emission direction deviates from the reference axis, therefore, the center-of-gravity deviation of the intensity of light of the light receiving portion  33  (for the CD main beam) of the photo-detector  27  from the center of the light receiving portion as well as the light receiving balance deviation is small. As a result, the average light receiving balance residual is so small as to raise no problem.  
      According to this first embodiment, the average light receiving balance residual between the optical pickups can be suppressed to a small value, and the optical pickups, of which the light receiving balance residual exceeds the allowable range, can be suppressed in number, to make unnecessary an adjustment after the movement adjustment of the photo-detector thereby to suppress the rise in the cost.  
     Second Embodiment  
       FIG. 4  is a sectional side elevation of a laser diode  1  and an LD holder  36  according to a second embodiment. By the aforementioned structure, the laser diode  1  and the LD holder  36  are integrated with the base portion  38  by the LD spring  37 , although not shown.  
      In the laser diode  1 , the base  4  is protruded substantially orthogonally to the principal face  3   a  of the stem  3 . The sub-mount  5  is mounted on the upper leading end of the base  4 , and the monolithic LD  6  is mounted on the upper leading end of the sub-mount  5 . The cap  35  is mounted on the principal face  3   a  of the stem  3  and provided in its front face with the hole  35   a  for passing the laser beam therethrough.  
      As in the foregoing first embodiment, the average value of the angular deviation of the emission direction at the light emitting point  12  of the monolithic LD  6  orthogonal to the active layer is designated by θ A . At this time, the hole  36   a  and the hole  36   b  are so formed that the axis extending through the centers of the hole  36   a  and the hole  36   b  of the LD holder  36  may be inclined by −θ A  from the axis parallel to the upper face  36   d  and the lower face  36   e  of the LD holder  36 . Moreover, the stem  3  is so press-fitted in the hole  36   a  as to bring the principal face  3   a  of the stem  3  into abutment against the abutment face  36   c.  As shown in  FIG. 4 , moreover, the ID holder  36  having the laser diode  1  press-fitted therein is so arranged and integrated with the base portion  38  that the individual light emitting points of the monolithic LD  6  are positioned on the individual reference axes, and that the individual reference axes are substantially parallel to the axis parallel to the upper face  36   d  and the lower face  36   e  of the LD holder  36 .  
      As a result, the monolithic LD  6  is arranged to deviate the individual reference axes by θ A  orthogonally to the active layer from the direction orthogonal to the individual laminar faces containing the individual light emitting points, so that the average emission direction of the DVD light emitting point  12  is aligned with the reference axis. In case, therefore, the laser beam emitted from the DVD light emitting point  12  is received by the light receiving portion  30  (for the DVD main beam) of the photo-detector  27 , the center of gravity of the intensity of light is aligned on the average with the center of the light receiving portion  30  so that the light receiving balance becomes substantially 0 on the average. If the average value of the angular deviation of the emission direction of the CD light emitting point  13  is then equal to the same value θ A  as that of the DVD light emitting point  12 , the average emission direction of the CD light emitting point  13  is also aligned with the reference axis, and the light receiving balance in the light receiving portion  33  (for the CD main beam) of the photo-detector  27  also becomes substantially 0 on the average, so that the average light receiving balance residual becomes substantially 0. Even in case the average value of the angular deviation of the emission direction of the CD light emitting point  13  is different from that of the DVD light emitting point  12 , the average light receiving balance deviation is suppressed to a small value for the aforementioned reasons.  
      According to this second embodiment, the average light receiving balance residual between the optical pickups can be suppressed to a small value, and the optical pickups, of which the light receiving balance residual exceeds the allowable range, can be suppressed in number, to make unnecessary an adjustment after the movement adjustment of the photo-detector thereby to suppress the rise in the cost,  
     Third Embodiment  
       FIG. 5  is a sectional side elevation of a laser diode  1 , an LD holder  36  and an LD spring  37  according to a third embodiment. By the aforementioned structure, the laser diode  1 , the LD holder  36  and the LD spring  37  are integrated with the base portion  38  by the retaining portions  37   e  of the LD spring  37 .  
      In the laser diode  1 , the base  4  is protruded substantially orthogonally to the principal face  3   a  of the stem  3  The sub-mount  5  is mounted on the upper leading end of the base  4 , and the monolithic LD  6  is mounted on the upper leading end of the sub-mount  5 . The cap  35  is mounted on the principal face  3   a  of the stem  3  and provided in its front face with the hole  35   a  for passing the laser beam therethrough.  
      In the LD holder  36 , the hole  36   a  and the hole  36   b  are so formed that the axis extending through the centers of the hole  36   a  and the hole  36   b  of the LD holder  36  may be substantially parallel to the upper face  36   d  and the lower face  36   e  of the LD holder  36 . Moreover, the stem  3  is so press-fitted in the hole  36   a  as to bring the principal face  3   a  of the stem  3  into abutment against the abutment face  36   c.  Moreover, the protrusions  36   f  are formed at longitudinally displaced positions on the upper face  36   d  and the lower face  36   e  of the LD holder  36 .  
      The holes  37   d  are individually formed at the longitudinally displaced positions in the leaf portion  37   b  and the leaf portion  37   c  of the LD spring  37 . As shown in  FIG. 5 , moreover, the LD spring  37  is so arranged that the leaf portions  37   b  and  37   c  may be substantially parallel to the individual reference axes, and is integrated with the base portion  38  by the retaining portions  37   e.  As in the foregoing first embodiment, the average value of the angular deviation of the emission direction at the light emitting point  12  of the monolithic LD  6  orthogonal to the active layer is designated by θ A . As shown in  FIG. 5 , moreover, the protrusions  36   f  are so fitted in the holes  37   d  that the monolithic LD  6  may be arranged such that the individual light emitting points of the monolithic LD  6  are positioned on the individual reference axes, and that the individual reference axes are deviated by θ A  orthogonally to the active layer from the directions orthogonal to the individual laminar faces containing the individual light emitting points, and the LD holder  36  having the laser diode  1  press-fitted therein is fixed on the LD spring  37  and integrated with the base portion  38 .  
      As a result, the monolithic LD  6  is arranged to deviate the reference axes by θ A  orthogonally to the active layer from the direction orthogonal to the laminar faces containing the DVD light emitting points  12 , so that the average emission direction of the DVD light emitting point  12  is aligned with the reference axis. In case, therefore, the laser beam emitted from the DVD light emitting point  12  is received by the light receiving portion  30  (for the DVD main beam) of the photo-detector  27 , the center of gravity of the intensity of light is aligned on the average with the center of the light receiving portion  30  so that the light receiving balance becomes substantially 0 on the average. If the average value of the angular deviation of the emission direction of the CD light emitting point  13  is then equal to the same value θ A  as that of the DVD light emitting point  12 , the average emission direction of the CD light emitting point  13  is also aligned with the reference axis, and the light receiving balance in the light receiving portion  33  (for the CD main beam) of the photo-detector  27  also becomes substantially 0 on the average, so that the average light receiving balance residual becomes substantially 0. Even in case the average value of the angular deviation of the emission direction of the CD light emitting point  13  is different from that of the DVD light emitting point  12 , the average light receiving balance deviation is suppressed to a small value for the aforementioned reasons.  
      According to this third embodiment, the average light receiving balance residual between the optical pickups can be suppressed to a small value, and the optical pickups, of which the light receiving balance residual exceeds the allowable range, can be suppressed in number, to make unnecessary an adjustment after the movement adjustment of the photo-detector thereby to suppress the rise in the cost.  
     Fourth Embodiment  
       FIG. 6  is a sectional side elevation of a laser diode  1 , an LD holder  36 , an LD spring  37  and a wall portion  38   a  of the base portion  38  according to a fourth embodiment.  
      In the laser diode  1 , the base  4  is protruded substantially orthogonally to the principal face  3   a  of the stem  3 . The sub-mount  5  is mounted on the upper leading end of the base  4 , and the monolithic LD  6  is mounted on the upper leading end of the sub-mount  5 . The cap  35  is mounted on the principal face  3   a  of the stem  3  and provided in its front face with the hole  35   a  for passing the laser beam therethrough.  
      In the LD holder  36 , the hole  36   a  and the hole  36   b  are so formed that the axis extending through the centers of the hole  36   a  and the hole  36   b  of the LD holder  36  may be substantially parallel to the upper face  36   d  and the lower face  36   e  of the LD holder  36 . Moreover, the stem  3  is so press-fitted in the hole  36   a  as to bring the principal face  3   a  of the stem  3  into abutment against the abutment face  36   c.  Moreover, the protrusions  36   f  are formed at longitudinally displaced positions on the upper face  36   d  and the lower face  36   e  of the LD holder  36 .  
      The leaf portion  37   b  and the leaf portion  37   c  of the LD spring  37  are substantially orthogonal to the base portion  37   a,  and the holes  37   d  are individually formed in the leaf portion  37   b  and the leaf portion  37   c  at the longitudinally identical positions. Moreover, the protrusions  36   f  are so fitted in the holes  37   d  that the upper face  36   d  of the LD holder  36  and the leaf portion  37   b,  and the lower face  36   e  of the LD holder  36  and the leaf portion  37   c  may be substantially parallel to each other, and the LD holder  36  having the laser diode  1  press-fitted therein is fixed on the LD spring  37 .  
      As in the foregoing first embodiment, the average value of the angular deviation of the emission direction at the light emitting point  12  of the monolithic LD  6  orthogonal to the active layer is designated by θ A . At this time, as shown in  FIG. 6 , the stiffening face  38   c  belonging to the base portion  38  is formed such that it is inclined by −θ A  from the axis perpendicular the individual reference axes. Moreover, the LD spring  37  holding the LD holder  36  having the laser diode  1  press-fitted therein is fixed on the base portion  38  by bringing the base portion  37   a  of the LD spring  37  into abutment against the stiffening face  38   c  so that the individual light emitting points of the monolithic LD  6  may be positioned on the individual reference axes, and by hooking the retaining portions  37   e  on the two side lower portions of the wall portion  38   a  across the opening  38   b.    
      As a result, the monolithic LD  6  is arranged to deviate the individual reference axes by θ A  orthogonally to the active layer from the direction orthogonal to the individual laminar faces containing the individual light emitting points, so that the average emission direction of the DVD light emitting point  12  is aligned with the reference axis. In case, therefore, the laser beam emitted from the DVD light emitting point  12  is received by the light receiving portion  30  (for the DVD main beam) of the photo-detector  27 , the center of gravity of the intensity of light is aligned on the average with the center of the light receiving portion  30  so that the light receiving balance becomes substantially 0 on the average. If the average value of the angular deviation of the emission direction of the CD light emitting point  13  is then equal to the same value  6  A as that of the DVD light emitting point  12 , the average emission direction of the CD light emitting point  13  is also aligned with the reference axis, and the light receiving balance in the light receiving portion  33  (for the CD main beam) of the photo-detector  27  also becomes substantially 0 on the average, so that the average light receiving balance residual becomes substantially 0. Even in case the average value of the angular deviation of the emission direction of the CD light emitting point  13  is different from that of the DVD light emitting point  12 , the average light receiving balance deviation is suppressed to a small value for the aforementioned reasons.  
      According to this fourth embodiment, the average light receiving balance residual between the optical pickups can be suppressed to a small value, and the optical pickups, of which the light receiving balance residual exceeds the allowable range, can be suppressed in number, to make unnecessary an adjustment after the movement adjustment of the photo-detector thereby to suppress the rise in the cost.