Abstract:
The light source package comprises a first light source for emitting a first light beam, a second light source for emitting a second light beam which is different from the first light beam, and a deflection arrangement which deflects the first and second light beam and releasing the deflected light beam as a third light beam. The deflection arrangement includes a first and second deflectors which deflects the first and second light beams such that the optical axes of the first and second deflected light beams are substantially coincide.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a semiconductor light source for emitting light beam of two different wavelengths and an optical pickup head apparatus and a data record/playback apparatus for storage, playing back, and erasing data on an optical disk.  
           [0003]    2. Description of the Related Art  
           [0004]    Optical disks are known as high-density, mass-storage mediums on which data is stored in the form of a pattern of bits. The optical disks are classified into various types depending on the contents of data and the application. Characteristic examples of the optical disks are digital audio disks, video disks, text file disks, data file disks and so forth. Their applications are now increased as spread in different fields. In particular, digital versatile disks (DVD) become popular and get focused as high-density optical disks for using 650 nm wavelength visible light emitted from a semiconductor laser. The DVD disks are available in different formats including read only DVD-ROM, once writable DVD-R, and rewritable DVD-RAM. Also, compact disk (CD) is widely known using a 780 nm wavelength infrared light emitted from a semiconductor laser. Similar to the DVD, the CD disks are available in different formats including read only CD-ROM, once rewritable CD-R, and multiply rewritable CD-RW.  
           [0005]    As both DVD and CD are popular, it is desired for the convenience of any user to play back data from not only DVD-ROM and CD-ROM but also DVD-R and CD-R with the use of a single data playback apparatus.  
           [0006]    The CD-R and DVD-R technologies are similar to each other in storage and playing back data on the basis of different levels of the reflectivity of colors. However, the reflectivity and the absorptance are optimized in narrow wavelength ranges about 780 nm and 650 nm respectively. This disallows CD-R data to be read and played back using the 650 nm wavelength light beam. Also, DVD-R data is hardly permitted to be read and played back using the 780 nm wavelength light beam. For compensation, each CD-R/DVD-R compatible type data record/playback apparatus has an optical pickup head equipped with a DVD-R accessible semiconductor laser and a CD-R accessible semiconductor laser.  
           [0007]    For minimizing the overall size and the production cost of the data record/playback apparatus, the optical pickup head should be decreased in the size and the cost. One of such techniques is proposed for integrating the above described two different wavelength semiconductor lasers into a single package to simplify the optical system of the optical pickup head.  
           [0008]    [0008]FIG. 16 illustrates an arrangement of a conventional optical pickup head apparatus  1600  such as disclosed in Japanese Patent Laid-open Publication (Heisei)10-289468. The optical pickup head apparatus  1600  has a light source  110  and a light source  120  both provided on a substrate  610  in a package  60  for emitting a beam of linearly polarized divergent light having a wavelength of 650 nm and a beam of linearly polarized divergent light having a wavelength of 780 nm respectively.  
           [0009]    The principle of a method of reading data from a storage medium  20  with the optical pickup head  1600  will now be explained. A light beam  100  emitted from the light source  110  or  120  is first directed to a beam composite means  30  which may be implemented by a polarizing prism (a birefringent plate) or a hologram. The beam composite means  30  aligns any light beam from either the light source  110  or the light source  120  with the optical axis. When the light beam  100  is received from the light source  120 , it is refracted or diffracted by the beam composite means  30  for deflection. The light beam  100  is then converted to a collimate light by a collimate lens  131 , circularly polarized by a {fraction (1/4)} wavelength plate  140 , passed through an aperture  15 , and converted to a beam of convergence light by an objective lens  132 . The light beam  100  is directed to an optical storage medium  20  and more specifically, passed through a transparent substrate  21  and focused on a data recording surface  22 . The light beam  100  is reflected on the data recording surface  22 , converted by the {fraction (1/4)} wavelength plate  140  to a polarized beam shifted 90 degrees from the onward beam, passed through the beam composite means  30 , and received by deflecting means  40  (a polarizing hologram) before guided to a photo detecting means  50 . A signal produced by the photo detecting means  50  is used as a data signal indicative of the data for generating the focusing error signal and the tracking error signal which are then supplied to an actuator  16  for focusing and tracking control.  
           [0010]    It is common in the data record/playback apparatus for rewritable disks such as DVD-RAM that the tracking control signal is unstable because of shallow pits of the disks. For compensation, a diffraction grating (not shown) is provided for generating three different diffracted lights to determine the focusing error signal and the tracking error signal.  
           [0011]    As the conventional optical pickup head apparatus  1600  includes the beam composite means  30  of a polarizing prism or hologram and the {fraction (1/4)} wavelength plate  140  for handling the polarized light, its optical system will significantly increase in the cost.  
           [0012]    When the transparent substrate  21  of the optical storage medium  20  is birefringent, the light beam reflected on the optical storage medium  20  may be deflected by the beam composite means  30  and hardly received by the photo detecting means  50  which thus fails to read data from the optical storage medium  20 .  
           [0013]    Also, while the two light sources  110  and  120  are provided on the single substrate  610 , there may be less a room for the diffraction grating which is arranged for generating three different diffracted lights and should be controlled properly. The overall dimensions of the optical pickup head apparatus itself will be increased.  
         SUMMARY OF THE INVENTION  
         [0014]    It is hence an object of the present invention to provide a semiconductor light source package, an optical pickup head apparatus, and an optical data apparatus where a non-polarizing prism is used for minimizing the number of components and thus the overall cost. It is another object of the present invention to provide an optical pickup head apparatus and an optical data apparatus where desired data can be read out from an optical storage medium  20  while the tracking error signal is appropriately produced, even though the transparent substrate of the optical storage medium is birefringent.  
           [0015]    A light source package according to the present invention comprises: a first light source which emits a first light beam; a second light source which emits a second light beam which is different from the first light beam; and a deflection arrangement which deflects the first and second light beams and releases the deflected light beam as a third light beam, wherein the deflection arrangement includes a first deflector which deflects the first light beam and a second deflector which deflects the second light beam such that the optical axis of the first deflected light beam from the first deflector and the optical axis of the second deflected light beam from the second deflector substantially coincide.  
           [0016]    An optical pickup head apparatus according to one aspect of the present invention comprises: a first light source which emits a first light beam having a wavelength λ 1 ; a second light source which emits a second light beam having a wavelength λ 2  which is different from the wavelength λ 1 ; a diffractor which generates a plurality of light beams from the light beam emitted from the light source; a light converging unit which converges the plurality of light beams received from the diffractor on an optical storage medium; a beam splitter which deflects the plurality of light beams converged and reflected on the optical storage medium; and a photodetector which receives deflected light beams from the beam splitter and outputs a signal relative to intensity of the deflected light beam, wherein the diffractor includes a first pattern and a second pattern provided at an angle to each other, the first pattern having a higher diffraction efficiency of a beam having a wavelength λ 1  than that having a wavelength λ 2  and the second pattern having a higher diffraction efficiency of a beam having a wavelength λ 2  than that having a wavelength λ 1 .  
           [0017]    An optical pickup head apparatus according to another aspect of the present invention comprises a beam splitter which deflects a light beam converged and reflected on a optical storage medium; and a photodetector which generates and releases a signal indicative of the intensity of each of the deflected light beams received from the beam splitter, wherein the beam splitter is a holographic optical element including a first holographic pattern and a second holographic pattern, the first holographic pattern having a higher diffraction efficiency of a beam having a wavelength λ 1  than that having a wavelength λ 2  and the second holographic pattern having a higher diffraction efficiency of a beam having a wavelength λ 2  than that having a wavelength λ 1 .  
           [0018]    Also, a data record/playback apparatus of the present invention may be provided, which comprises: one of optical pickup head apparatuses according to the present invention; a drive which varies the position of the optical pickup head apparatus relative to a data storage medium; and an electric signal processor responsive to a signal received from the optical pickup head apparatus which performs an arithmetic operation to reconstruct a desired data. Accordingly, an optical data apparatus can be implemented which allows the intensity of each light received by its photodetector to remain unchanged when an optical storage medium to be played back is partially birefringent, hence ensuring improved playback of data.  
           [0019]    Also, during the assembling of the optical pickup head apparatus, the diffraction grating is adjustably positioned to match one of any two formats, CD and DVD, of the optical storage medium while its adjustment for the other format is automatically done at the same time. As a result, the optical pickup head apparatus will highly be improved in the productivity. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    These and other object and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:  
         [0021]    [0021]FIG. 1 is a diagram of an arrangement of a semiconductor light source package according to Embodiment 1 of the present invention;  
         [0022]    [0022]FIG. 2 is a schematic diagram of a prism in Embodiment 1;  
         [0023]    [0023]FIG. 3 is a diagram of an arrangement of an optical pickup head apparatus according to Embodiment 2 of the present invention;  
         [0024]    [0024]FIG. 4 is a schematic diagram of a holographic optical element in Embodiment 2;  
         [0025]    [0025]FIG. 5 is a schematic diagram of elements of a photodetector in Embodiment 2;  
         [0026]    [0026]FIG. 6 is a diagram of an arrangement of an optical pickup head apparatus according to Embodiment 3 of the present invention;  
         [0027]    [0027]FIG. 7 is a schematic diagram of elements  14   a  to  14   d  of a photodetector  14  in Embodiment 3 where a group of diffracted lights  71   a  to  71   c  are aligned with another group of diffracted lights  72   a  to  72   c;    
         [0028]    [0028]FIG. 8 is a diagram of an arrangement of an optical pickup head apparatus according to Embodiment 4 of the present invention;  
         [0029]    [0029]FIG. 9 is a diagram of an arrangement of an optical pickup head apparatus according to Embodiment 5 of the present invention;  
         [0030]    [0030]FIG. 10A is a schematic diagram of a group of beams  4   a  to  4   c  on the data recording surface of an optical storage medium;  
         [0031]    [0031]FIG. 10B is a schematic diagram of a group of beams  5   a  to  5   c  on the data recording surface of an optical storage medium;  
         [0032]    [0032]FIG. 11A is a schematic diagram of a grating pattern  61  of a diffraction grating  6 ;  
         [0033]    [0033]FIG. 11 B is a schematic diagram of a grating pattern  62  of a diffraction grating  6 ;  
         [0034]    [0034]FIG. 12 is a diagram of an arrangement of an optical pickup head apparatus according to Embodiment 6 of the present invention;  
         [0035]    [0035]FIG. 13A is a schematic diagram of a group of beams  4   a  to  4   c  on the data recording surface of an optical storage medium;  
         [0036]    [0036]FIG. 13B is a schematic diagram of a group of beams  5   a  to  5   c  on the data recording surface of an optical storage medium;  
         [0037]    [0037]FIG. 14 is a diagram of an arrangement of an optical pickup head apparatus according to Embodiment 7 of the present invention;  
         [0038]    [0038]FIG. 15 is a diagram of an arrangement of an optical data apparatus according to Embodiment 8 of the present invention; and  
         [0039]    [0039]FIG. 16 is a schematic diagram of a conventional optical pickup head apparatus. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]    Embodiments 1 to 8 of the present invention will be described referring to the accompanying drawings. Like components are denoted by like numerals throughout the drawings.  
         [0041]    (Embodiment 1)  
         [0042]    This embodiment incorporates a semiconductor light source package having a prism with the first and the second reflecting surface. The prism is arranged such that the optical axis for a first wavelength light beam reflected on the first reflecting surface substantially coincides with the optical axis for a second wavelength light beam reflected on the second reflecting surface.  
         [0043]    [0043]FIG. 1 illustrates an arrangement of the semiconductor light source package  10  of Embodiment 1. The semiconductor light source package  10  comprises a semiconductor laser light source  1  for a laser beam of a wavelength λ 1 , another semiconductor laser light source  2  for a laser beam of a wavelength λ 2 , and a prism  3 . The semiconductor laser light source  1  emits a linearly polarized divergent light beam  4  having the wavelength λ 1  for reading out data from an optical storage medium of DVD format such as DVD-R. It is assumed in this specification that the wavelength λ 1  is 650 nm. Similarly, the semiconductor laser light source  2  emits a linearly polarized divergent light beam  5  having the wavelength λ 2  for reading out data from an optical storage medium of CD format such as CD-R. It is thus assumed that the wavelength λ 2  is 780 nm. The two semiconductor laser light sources  1  and  2  are mounted in a single package  10 .  
         [0044]    The prism  3  has three reflecting surfaces  31 ,  32 , and  33 . The reflecting surface  31  is a dichroic mirror which is wavelength-selective and fully transmits a beam of the wavelength λ 1  while reflects a beam of the wavelength λ 2 . The reflecting surface  32  is a total reflection mirror which fully reflects a beam of the wavelength λ 1 . The reflecting surface  33  is a total reflection mirror which fully reflects beams of the wavelengths λ 1  and λ 2 . The prism  3  is arranged for aligning the optical axis of a light beam having the wavelength λ 1  reflected on the reflecting surface  32  substantially with the optical axis of a light beam having the wavelength λ 2  reflected on the reflecting surface  31 . As a result, two lights of the wavelengths λ 1  and λ 2  reflected on the reflecting surface  33  run substantially along the same optical axis.  
         [0045]    The light beams reflected on the two reflecting surfaces  31  and  32  may be released out from the prism  3  before reflected on the reflecting surface  33 . In that case, the outgoing lights from the prism  3  are shifted 90 degrees clockwisely from the outgoing direction shown in FIG. 1. The outgoing direction of light from the prism  3  may arbitrarily be determined by adjusting the position of the semiconductor light source package  10 . Embodiment 7 incorporates an optical pickup head apparatus using the prism  3  as will be described later.  
         [0046]    [0046]FIG. 2 illustrates the prism  3 . The prism  3  comprises two glass substrates  35  and  36 . The total reflecting surface  33  and the dichroic surface  31  are provided by vacuum vapor deposition on the lower and upper sides of the glass substrate  36  respectively while the total reflecting surface  32  is provided by the same technique on the upper side of the glass substrate  35 . The reflecting surfaces  32  and  33  consist of metal films while the dichroic surfaces  31  is a multi-layer dielectric. The two glass substrates  35  and  36  having the reflecting surfaces  31  to  33  are bonded at an interface  34  to each other. The two bonded glass substrates are then cut along the lines  41  to form a unit of the prism  3 . In brief, the prism  3  is made from two plane-parallel glass plates. The prism  3  is hence lower in the cost than any conventional prism fabricated by polishing, thus contributing to the cost down of the semiconductor light source package  10 .  
         [0047]    As the light beam is deflected by the prism  3 , its direction hardly be displaced when the wavelength is changed and its light source will be improved in the operational reliability.  
         [0048]    Also, as the semiconductor light source package  10  allows the two light beams  4  and  5  from the prism  3  to run along the same optical axis, the two light sources can be identified as a single light source. Accordingly, when the semiconductor light source package  10  is installed in an optical pickup head apparatus, the adjustment over the light sources will be as highly simplified as with the single light source.  
         [0049]    Moreover, the semiconductor light source package  10  is compatible with a multi-color laser pointer.  
         [0050]    (Embodiment 2)  
         [0051]    This embodiment is in the form of an optical pickup head apparatus with no use of the  114  wavelength plate  140  (FIG. 16).  
         [0052]    [0052]FIG. 3 illustrates an arrangement of the optical pickup head apparatus  300  of Embodiment 2. The optical pickup head apparatus  300  comprises a semiconductor light source package  10 , a holographic optical element  64 , a collimate lens  8 , an objective lens  9 , and a photodetector  12 .  
         [0053]    While the positional relationship between the two semiconductor laser light sources  1  and  2  in the semiconductor light source package  10  is not concerned in Embodiment 1, the distance between the two semiconductor laser light sources  1  and  2  in this embodiment is  2  mm, for example. As the light source  2  is positioned closer to the collimate lens  8  than the light source  1 , any spherical aberration caused by a difference in the thickness of the substrate  21  between the optical storage mediums  20  can be corrected. The refractivity of the prism  3  is 1.51, for example.  
         [0054]    The operation of the optical pickup head apparatus  300  reading out data from the optical storage medium  20  will now be explained. The optical pickup head apparatus  300  initiates the irradiation of one of the two semiconductor laser light sources  1  or  2  in accordance with the type of the optical storage medium  20 . When the optical storage medium  20  is a DVD, the semiconductor laser light source  1  emits a light beam  4 . The light beam  4  is reflected on the reflecting surface  32  of the prism  3  as its optical path is turned and passed through the dichroic surface  31 . On the other hand, when the optical storage medium  20  is a CD, the semiconductor laser light source  2  emits a light beam  5 . The light beam  5  is received by the prism  3  where it is reflected on the dichroic surface  31 . Thus, the light beam  5  substantially coincides with the optical axis of the light beam  4  transmitted through the reflecting surface  31 . Each of the two light beams  4  and  5  is then reflected on the reflecting surface  33  as its optical path is deflected and converted to a collimate light by the collimate lens  8  having a focusing distance of 20 mm. The collimated light  4  or  5  is converged by the objective lens  9  having a focusing distance of 3 mm, passed through the transparent substrate  21  of the optical storage medium  20 , and focused on the data recording surface  22 . The thickness t of the transparent substrate is 1.2 mm in the CD format and 0.6 mm in the DVD format.  
         [0055]    The light beam  4  or  5  is reflected on the data recording surface  22  of the optical storage medium  20 . The light beam  4  or  5  is then passed through the objective lens  9  and the collimate lens  8  and transmitted to the holographic optical element  64  where it is converted to a diffracted light  71  or  72  which is then received by the photodetector  12 .  
         [0056]    [0056]FIG. 4 illustrates an arrangement of the holographic optical element  64 . The holographic optical element  64  has three regions  64   a  to  64   c.  The light beam  4  or  5  entering the holographic optical element  64  is diffracted by the regions  64   a  to  64   c.  The axis  64   d  extends in parallel with a separation line between the two regions  64   b  and  64   c  and is arranged such that it can be in parallel with the track on the data recording surface when projected with the light beam  4  or  5 .  
         [0057]    [0057]FIG. 5 shows a light receiving side of the photodetector  12 . The light receiving side of the photodetector  12  comprises four elements  12   a  to  12   d.  The elements  12   a  to  12   d  receive the diffracted lights  71   a  to  71   c  and  72   a  to  72   c.  The diffracted lights  71   a  and  72   a,    71   b  and  72   b,  and  71   c  and  72   c  are generated by their respective regions  64   a,    64   b,  and  64   c  of the holographic optical element  64  (FIG. 4).  
         [0058]    As signal outputs  112   a  to  112   d  of the elements  12   a  to  12   d  are produced based on the intensities of the incident light, the focusing error signal can be calculated as  112   a - 112   b  by Foucault method. Similarly, the tracking error signal can be obtained by differential phase detection method of comparing the phases of  112   a  and  112   c.  The detection methods of those signals are well-known and will be explained in no more detail.  
         [0059]    The optical pickup head apparatus of this embodiment permits the intensity of each light received by the photodetector to remain unchanged even if the optical storage medium carries birefringent factors and can thus be improved in the performance of data playback.  
         [0060]    In this embodiment, the reflecting surface  31  is a dichroic mirror for increasing the efficiency of light transmission. When the intensity of incident light is sufficient, the reflecting surface  31  may be implemented by a half-mirror which is not wavelength-selective. Also, a wavelength-selective aperture filter may be provided between the collimate lens  8  and the objective lens  9  for limiting the aperture for the wavelength of 780 nm. The objective lens  9  may be a specific lens having different curvatures partially to realize the adequate aberration for DVD and CD. The optical pickup head apparatus  300  (FIG. 3) may further be reduced in the overall dimensions when the photodetector and the light sources are formed in a single unit.  
         [0061]    (Embodiment 3)  
         [0062]    This embodiment incorporates an optical pickup head apparatus which employs a holographic optical element for aligning the diffracted lights from different light sources with each other on a photodetector.  
         [0063]    [0063]FIG. 6 illustrates an arrangement of the optical pickup head apparatus  600  of Embodiment 3. This apparatus is differentiated from the optical pickup head apparatus  300  (FIG. 3) of Embodiment 2 by the fact that the holographic optical element  64  (FIG. 3) is replaced by another holographic optical element  65  while the photodetector  12  is replaced by another photodetector  14 . The other components are identical to those of the optical pickup head apparatus  300  (FIG. 3) and will be explained in no more detail.  
         [0064]    The holographic optical element  65  comprises a couple of patterns  66  and  67  provided on the upper and lower sides of a single substrate. The pattern  66  generates a diffracted light  71 . The pattern  67  generates a diffracted light  72 . FIG. 7 shows four elements  14   a  to  14   d  of the photodetector  14  where a group of diffracted lights  71   a  to  71   c  are aligned with another group of diffracted lights  72   a  to  72   c  respectively. The grating pitch and the spatial frequency axis of the holographic optical element  65  (FIG. 6) are selectively determined such that the diffracted lights  71  and  72  are aligned with each other on the photodetector  14 . The characteristics of the patterns  66  and  67  (FIG. 6) are substantially equal to those of the regions  64   a  to  64   c  (FIG. 4).  
         [0065]    Returning back to FIG. 6, the pattern  66  generates the diffracted light from a light beam having the wavelength λ 1  emitted from the light source  1  but no diffracted light from a light beam having the wavelength λ 2  emitted from the light source  2 . In other words, the pattern  66  has a higher level of diffraction efficiency for the wavelength λ 1  than for the wavelength λ 2 . This can be implemented by optically increasing the grating depth to an integer multiple of λ 2 . As a result, the amount of stray light can be minimized thus improving the efficiency of use of light. Similarly, the pattern  67  generates the diffracted light from the light beam having the wavelength λ 2  emitted from the light source  2  but no diffracted light from the light beam having the wavelength λ 1  emitted from the light source  1 . The pattern  67  has a higher level of diffraction efficiency for the wavelength λ 2  than for the wavelength λ 1 . This can be implemented by optically increasing the grating depth to an integer multiple of 1.  
         [0066]    The photodetector  14  is smaller in the size than the photodetector  12  (FIG. 3). This is realized by the two diffracted lights  71  and  72  aligned with each other and thus the four elements  14   a  to  14   d  minimized in the dimensions. As the optical pickup head apparatus  600  of this embodiment is favorably reduced in the overall dimensions with its elements minimized in the size, it can be applicable to any data playback apparatus which requires a minimum of the size and a higher speed of the operation.  
         [0067]    While the focusing error signal is obtained by well-known Foucault method in this embodiment, it may be determined by any other appropriate manner such as spot size detection. The photodetector  14  may be arranged for receiving conjugate lights  71  and  72  from the holographic optical element  65 . This will double the efficiency of use of light, hence contributing to the higher signal-to-noise ratio of the optical pickup head apparatus.  
         [0068]    As the two patterns  66  and  67  are provided in a combination, the photodetector  14  can be controlled to a desired size and located to a desired position. Even if the optical pickup head apparatus is limited in the external configuration, the freedom of designing its optical system will be large enough to satisfy the requirements of any application such as vehicle-mounted or portable model.  
         [0069]    (Embodiment 4)  
         [0070]    This embodiment is in the form of an optical pickup head apparatus which employs a specific holographic optical element, similar to that of Embodiment 3, for aligning the diffracted lights from different light sources with each other on a photodetector.  
         [0071]    [0071]FIG. 8 illustrates an arrangement of the optical pickup head apparatus  800  of embodiment 4. This apparatus is differentiated from the optical pickup head apparatus  600  of Embodiment 3 (FIG. 6) by the fact that the holographic optical element  65  (FIG. 6) is replaced by another holographic optical element  68  while the two light sources  1  and  2  (FIG. 3) are replaced by a pair of light sources  1   a  and  2   a  which are assembled in a semiconductor light source package  810 . The other components are identical to those of the optical pickup head apparatus  600  (FIG. 6) and will be explained in no more detail.  
         [0072]    The two light sources  1   a  and  2   a  are monolithic semiconductor lasers mounted on a single semiconductor substrate for emitting light beams having a wavelength of 780 nm and a wavelength of 650 nm respectively. The distance between the two lasers is 100 μm, for example. The holographic optical element  68  like the holographic optical element  65  (FIG. 6) comprises a couple of patterns  69  and  70 . The pattern  69  generates a diffracted light  71 . The pattern  70  generates a diffracted light  72 . Similarly, the grating pitch and the spatial frequency axis of the hologram  68  are selectively determined such that the diffracted lights  71  and  72  from their respective patterns  69  and  70  are aligned with each other on the photodetector  14  as shown in FIG. 7.  
         [0073]    While the two light sources are spaced from each other, their two diffracted lights can successfully be aligned with each other on the photodetector  14 . This allows the optical pickup head apparatus of this embodiment to be minimized in the overall dimensions. Also, as the light sources are associated with no prism, the optical pickup head apparatus will be lower in the production cost.  
         [0074]    (Embodiment 5)  
         [0075]    This embodiment incorporates a diffraction grating which has a pair of grating patterns arranged where when its position is determined relative to one of two storage mediums such that two or more diffracted lights fall in a desired positional relationship, its position relative to the other storage medium can automatically be set.  
         [0076]    [0076]FIG. 9 illustrates an optical pickup head apparatus  900  of Embodiment 5. This apparatus is differentiated from the optical pickup head apparatus  300  (FIG. 3) of Embodiment 2 by the fact that the holographic optical element  64  and the photodetector  12  (FIG. 3) are replaced by a half-mirror  7  and another photodetector  13  respectively, while a diffraction grating  6  is set between the prism  3  and the half-mirror  7 , and while a concave lens  11  is provided between the half-mirror  7  and the photodetector  13 .  
         [0077]    The diffraction grating  6  comprises a couple of grating surfaces  61  and  62 . The distance from the light source  2  to the grating surface  61  is 10 mm, for example. In operation, a light beam  4  or  5  is passed through the prism  3  and received by the diffraction grating  6 . The light beam  4  or  5  from the diffraction grating  6  is expressed as three beams  4   a  to  4   c  or  5   a  to  5   c.  The three beams are reflected on the half-mirror  7 , converted into a converged light by the objective lens  9 , and focused on the data recording surface  22  of an optical storage medium  20 . The light beam  4  or  5  is then reflected on the data recording surface  22 , passed back through the objective lens  9  and the collimate lens  8 , and transmitted through the half-mirror  7 . As the light beam  4  or  5  is transmitted through the half-mirror  7 , it is astigmatized before passed through the concave lens  11  tilted from the optical axis. This allows coma aberration provided by the half-mirror  7  to be eliminated. The light beam  4  or  5  is finally received by the photodetector  13  as three beam components  4   a  to  4   c  or  5   a  to  5   c  which are then used for producing the focusing error signal and the tracking error signal as will be explained later.  
         [0078]    The relationship between the optical storage medium  20 , the light beams  4   a  to  4   c  or  5   a  to  5   c,  and the diffraction grating  6  is now explained.  
         [0079]    [0079]FIGS. 10A and 10B show the relation between a group of beams  4   a  to  4   c  and tracks on the data recording surface  22  of an optical storage medium  20  and between another group of beams  5   a  to  5   c  and the tracks respectively. As shown in FIG. 10A, the beams  4   a  to  4   c  are located along the track of the optical storage medium  20  of CD-ROM format. The CD-ROM carries a record in the form of a row of pits, each pit measuring 0.8 μm to 3.0 μm in length, 0.5 μm in width, and 0.1 μm in depth. The tracking pitch tp 1  is 1.6 μm. The beams  4   a  to  4   c  are generated by the diffraction grating  6  and classified into a zero-order diffracted light  4   a,  a positive first-order diffracted light  4   b,  and a negative first-order diffracted light  4   c.  The angle between the line extending across the three beams  4   a  to  4   c  and the track is θ 1 . The displacement L 1   b  of the beam  4   b  from the beam  4   a  along the tracking pitch is equal to tp¼ or 0.4 μm. Similarly, the displacement L 1   c  of the beam  4   c  from the beam  4   a  along the tracking pitch is equal to tp¼ or 0.4 μm. The three diffracted lights can be controlled to hold their positional relationship by the diffraction grating  6  being turned. This technique is well-known as three-beam method for generating the tracking error signal.  
         [0080]    [0080]FIG. 10B schematically shows the beams  5   a  to  5   c  focused on the track of the optical storage medium  20  of DVD-RAM format. The DVD-RAM carries a record in the form of a row of dark and light mark, each mark measuring 0.6 μm to 2.8 μm in length and 0.6 μm in width. The tracking pitch tp 2  is 0.74 μm. The storage medium unlike the DVD-ROM has a guide groove which is 1.48 μm (=tp2×2) in the pitch gp 2  and 0.07 μm in the depth. The dark and light marks are developed in and between the grooves. The beams  5   a  to  5   c  are generated by the diffraction grating  6  and classified into a zero-order diffracted light  5   a,  a positive first-order diffracted light  5   b,  and a negative first-order diffracted light  5   c.  The angle between the line extending across the three beams  5   a  to  5   c  and the track is θ 2 . The displacement L 2   b  of the beam  5   b  from the beam  5   a  along the tracking pitch is also equal to tp 2  (=gp{fraction (2/2)}) or 0.74 μm. Similarly, the displacement L 2   c  of the beam  5   c  from the beam  5   a  along the tracking pitch is equal to tp 2  (=gp{fraction (2/2)}) or 0.74 μm. This technique is well-known as differential push-pull method for generating the tracking error signal as will be explained later in more detail.  
         [0081]    The angles θ 1  and θ 2  are determined based on a tilt of the grating patterns  61  and  62  of the diffraction grating  6  respectively being tilted as is explained below referring to FIG. 11. The diffraction grating  6  is controlled in the arrangement and position such that the angle between the diffracted lights and the track is duly maintained.  
         [0082]    [0082]FIGS. 11A and 11B illustrate the grating patterns  61  and  62  of the diffraction grating  6 . FIG. 11A shows the grating pattern  61  and FIG. 11B shows the grating pattern  62 . The diffraction grating  6  is made by molding a resin material which has a refractivity of 1.52. The distance b (FIG. 9) between the two grating patterns  61  and  62  is 1 mm. The grating patterns of the diffraction grating  6  are designed such that each set of the diffracted beams  4   a,    4   b,  and  4   c  (FIG. 10A) and  5   a,    5   b,  and  5   c  (FIG. 10B) are spaced substantially at equal intervals on the data recording surface of an optical storage medium  20 . As the three beams are spaced at equal intervals, the elements of the photodetector  13  can be reduced in the size.  
         [0083]    The grating pattern  61  shown in FIG. 11A is arranged with its grating depth of integral multiples of λ 2  optically for generating no diffraction of a light beam having the wavelength λ 2  while generating the diffracted lights from a light beam having the wavelength λ 1 . The grating pattern  62  shown in FIG. 11B is arranged with its grating depth of integral multiples of λ 1  optically for generating no diffraction of the light beam having the wavelength λ 1  while generating the diffracted lights from the light beam having the wavelength λ 2 . For example, the grating depth may be 2.3 μm and 1.9 μm, respectively. The pitches P 1  and P 2  of the grating are 74 μm and 83 μm respectively.  
         [0084]    The axis  61  a shown in FIGS. 11A and 11B is a reference axis for fabricating the diffraction grating  6 . The diffraction grating  6  is designed such that the angle between the reference axis  61   a  and the spatial frequency axis  61   b  of the grating pattern  61  is θ 1  and the angle between the reference axis  61 a and the spatial frequency axis  62   b  of the grating pattern  62  is θ 2 . As the two grating patterns  61  and  62  of the diffraction grating  6  are fabricated at once, the relationship between the two angles θ 1  and θ 2  can always be maintained constant. As described with FIG. 10A, the angle θ 1  is defined between the line extending across the beams  4   a  to  4   c  and the tracks on the data recording surface  22  of the optical storage medium  20 . Similarly, as described with FIG. 10B, the angle θ 2  is defined between the line extending across the beams  5   a  to  5   c  and the tracks. Accordingly, when the diffraction grating  6  is simply turned relative to one of the two storage mediums, CD and DVD, to position the three diffracted lights such that relationships between the displacements L 1   b  and L 1   c  (FIG. 10A) or between the displacements L 2   b  and L 2   c  (FIG. 10B) are satisfied, the positioning of the head to the other storage medium can automatically be completed. As a result, the process of adjusting the optical axis can significantly be simplified, thus contributing to the higher productivity of the optical pickup head apparatus. Also, as the diffraction grating  6  has two patterns on both sides thereof, its size can be equal to that of a conventional one pattern grating hence allowing the optical pickup head apparatus including two light sources to be minimized in the overall dimensions.  
         [0085]    A method of producing the focusing error signal and the tracking error signal with the use of diffracted lights generated by the above manner will be explained. Referring back to FIG. 9, the photodetector  13  comprises eight elements  13   a  to  13   h.  The elements  13   a  to  13   d  accept the beams  4   a  and  5   a,  the elements  13   e  and  13   f  accept the beams  4   b  and  5   b,  and the elements  13   g  and  13   h  accept the beams  4   c  and  5   c.  The elements  13   a  to  13   h  respectively generate and output electric signals I 13   a  to I 13   h  relative to intensities of the received beam. For any type of the optical storage medium, the focusing error signal is obtained from the four signals I 13   a  to I 13   d  of their respective elements  13   a  to  13   d  by an astigmatic method as expressed (I 13   a +I 13   c )−(I 13   b +I 13   d ).  
         [0086]    The tracking error signal is calculated as (I 13   e +I 13   f )−(I 13   g +I 13   h ) when the optical storage medium is a CD such as CD-ROM. On the other hand, the tracking error signal is obtained by using differential phase detection method when the optical storage medium is a DVD-ROM, and is calculated as (I 13   a +I 13   d )−(I 13   b +I 13   c )+k·{(I 13   e +I 13   g )−(I 13   f +I 13   h )} when the optical storage medium is a DVD-RAM, where value k is a coefficient for correcting the amplitude of the signal relative to the diffraction efficiency of the diffraction grating  6 . When the storage medium is a DVD-RAM, the tracking error signal may be (I 13   a +I 13   d )−(I 13   b +I 13   c ). As the objective lens is moved in response to the tracking action, an offset signal may occur. The offset signal can be subtracted by the above operation called differential push-pull method. The focusing error signal and the tracking error signal are produced in the above described manners.  
         [0087]    While the angle θ 2  is determined to match the DVD-RAM format in this embodiment, it may be controlled by varying the spatial frequency axis of the grating pattern  62  to have an optimum value of L 1   b  and L 1   c  (FIG. 10A) (for DVD-R, the optimum of L 1   b  and L 1   c  is 0.37 μm). In a data playback apparatus having light sources for different wavelengths of light or storage mediums of different types, the optical pickup head apparatus of this embodiment can be appropriated with an optical system modified to satisfy the optical requirements of the data playback apparatus. The optical system described above is an example and its angle between  61   a  and  61   b  or  62   a  and  62   b  may arbitrarily be designed while the grating pitch P 1  or P 2  is adjusted. The concave lens  11  may be eliminated depending on the optical requirements.  
         [0088]    (Embodiment 6)  
         [0089]    This embodiment is in the form of an optical pickup head apparatus which has a specific diffraction grating arranged to inhibit significant declination of the tracking error signal.  
         [0090]    [0090]FIG. 12 illustrates the optical pickup head apparatus  1200  of Embodiment 6. This apparatus is differentiated from the optical pickup head apparatus  900  (FIG. 9) of Embodiment 5 by the fact that the diffraction grating  6  (FIG. 9) is replaced by another diffraction grating  63 . The diffraction grating  63  allows the positional relationship between the spots of diffracted light beams  4   a  to  4   c,    5   a  to  5   c  focussed on the optical storage medium  20  and the tracks of an optical storage medium  20  to be different. Further, the diffraction grating  63  also allows the elements of a photodetector  13  to receive light beams  4   a  to  4   c  and  5   a  to  5   c  in different position. The diffraction grating  63  is designed for generating the diffracted light beams  4   a  to  4   c  and  5   a  to  5   c  from irradiation of the light source  1  and the light source  2  respectively.  
         [0091]    [0091]FIGS. 13A and 13B show the positional relationship between the beams  4   a  to  4   c  and the tracks on the data recording surface  22  of the optical storage medium  20  and between the beams  5   a  to  5   c  and the same respectively. As shown in FIG. 13A, the beams  4   a  and  4   c  are focussed on the track of the optical storage medium  20  of CD-R format. The CD-R format has a groove pitch gp 1  of 1.6 μm and carries a row of data marks developed in a groove or between grooves. The data mark measures 0.8 μm to 3.0 μm in length and 0.6 μm in width. Unlike DVD-RAM, this format has the groove pitch gp 1  arranged identical to a track pitch tp 1 . The diffracted light beams  4   a  to  4   c  generated by the diffraction grating  63  are classified into a zero-order diffracted light  4   a,  a positive first-order diffracted light  4   b,  and a negative first-order diffracted light  4   c.  The diffraction grating  63  is tilted to θ 3  such that the displacement L 1   b  or L 1   c  of the beam  4   b  or  4   c  from the beam  4   a  along the tracking pitch is equal to 0.8 μm (=tp{fraction (1/2)}).  
         [0092]    [0092]FIG. 11B schematically illustrates the beams  5   a  to  5   c  focussed on the track of the optical storage medium  20  of DVD-RAM format. As the displacement L 2   b  or L 2   c  of the beam  5   b  or  5   c  from the beam  5   a  along the tracking pitch is provided on one grating pattern of the diffraction grating  63 , its angle θ 3  for DVD can automatically be set by the adjustment of the beams relative to the track on the CD. The displacement is 0.67 μm. This is smaller than the displacement 0.74 μm of Embodiment 2 and may slightly decline the amplitude of the tracking error signal but not develop any offset signal. The DVD-RAM format also includes 0.62 μm of a tracking pitch standard. For reading out data from the disk with 0.62 μm of the tracking pitch not 0.74 μm, the optical pickup head apparatus  1200  (FIG. 12) of this embodiment can preferably be used. This is because this embodiment inhibits significant declination of the tracking error signal throughout a range of the applicable storage mediums.  
         [0093]    The diffraction grating  63  of this embodiment which is provided as a single unit allows the diffracted light beams  4   a  to  4   c  or  5   a  to  5   c  to be aligned in a straight row on the photodetector  13 . The tracking error signal is obtained by differential phase detection method of comparing the phases of I 13   a  to I 13   d  when the storage medium is a DVD-ROM and otherwise, by differential push-pull method as expressed by (I 13   a +I 13   d )−(I 13   b +I 13   c )+k 1 {(I 13   e −I 13   f )+k 2 ·(I 13   g −I 13   h ). The values k 1  and k 2  are coefficients for correcting the amplitude of the signal according to the diffraction efficiency of the diffraction grating  63  and the reflectivity of the optical storage medium  20 .  
         [0094]    The optical pickup head apparatus  1200  (FIG. 12) of this embodiment is favorably applicable to a data record/playback apparatus which can record data onto disks such as CD-R and DVD-RAM. The optical pickup head apparatus  1200  (FIG. 12) like the optical pickup head apparatus  600  (FIG. 6) of Embodiment 3 allows the diffraction grating  63  (FIG. 12) to be adjusted for one of the two formats, CD and DVD, so that the other format can automatically be enabled for playback, hence making the step of adjustment simplified.  
         [0095]    (Embodiment 7)  
         [0096]    This embodiment incorporates an optical pickup head apparatus which has a prism arranged for optimum use when light beams emitted from two different light sources are different in the astigmatism.  
         [0097]    [0097]FIG. 14 illustrates the optical pickup head apparatus  1400  of Embodiment 7. This apparatus is differentiated from the optical pickup head apparatus  1200  (FIG. 12) of Embodiment 6 by the fact that the prism  3  (FIG. 12) is replaced by another prism  37 .  
         [0098]    The prism  37  has a total reflecting surface  39  and a dichroic surface  38  which is wavelength selective. A light beam  4  emitted from the light source  1  is reflected on the total reflecting surface  39  and passed through the dichroic surface  38 . On the other hand, a light beam  5  emitted from the light source  2  is reflected on the dichroic surface  38 . Both the light beams  4  and  5  run along the same path after the prism  37 .  
         [0099]    The light beam  4  from the light source  1  possesses substantially an astigmatic difference of 20 μm such as a gain waveguide laser beam and is directed to the prism  37  where its astigmatic difference is eliminated. The light beam  5  from the light source  2  is not passed through the prism  37  and has no astigmatism. When there is an astigmatic difference between the two light beams from their respective light sources, one of the two light beams is corrected in the astigmatic difference. This permits the two light beams from the prism  37  to be decreased in the astigmatism, thus contributing the improvement of the reading of data from any optical storage medium  20 . More specifically, when there is a difference in the astigmatism between the two light beams from their respective light sources, the optical pickup head apparatus of this embodiment can favorably be used.  
         [0100]    The optical pickup head apparatus  1400  like the optical pickup head apparatus  1200  (FIG. 12) of Embodiment 6 has a diffraction grating  63  arranged adjustable for one of the two formats, CD and DVD, so that the other format can automatically be enabled for playback, hence making the step of adjustment simplified.  
         [0101]    The optical system may be modified and changed without departing from the scope of the present invention.  
         [0102]    (Embodiment 8)  
         [0103]    This embodiment is in the form of an optical data apparatus employing the optical pickup head apparatus of any of the foregoing embodiments.  
         [0104]    [0104]FIG. 15 illustrates the optical data apparatus  1500 . An optical storage medium  20  loaded on the optical data apparatus  1500  is rotated by an optical storage medium drive  81 . The optical pickup head apparatus  80  supplies an electric circuit  83  with a signal corresponding to its relative position on the optical storage medium  20 . The electric circuit  83  amplifies or calculates the signal to slightly move the optical pickup head apparatus  80  or an objective lens in the pickup head apparatus  80 . A drive  82  is provided for driving the optical pickup head apparatus  80  and an objective lens drive  85  is provided for driving the objective lens in the pickup head apparatus. The drive  82  or  85  performs a focusing/tracking servo control operation over the optical storage medium  20  to write, read, or delete data on the optical storage medium  20 . An interface  84  connects the apparatus with a power supply or an external power source. More particularly, the electric circuit  83 , the drive  82  for the pickup head apparatus, the optical storage medium drive  81  and the objective lens drive  85  are energized through the interface  84 . The interface or connecting terminals to the power supply or external source may be provided in each of the drives or circuits.  
         [0105]    As set forth above, the present invention permits the non-polarizing prism to align the optical axis of a first wavelength light substantially with the optical axis of a second wavelength light reflected on the second reflecting surface of the prism. As a result, the two non-polarized light beams are received as if emitted from one signal light source. When this light source arrangement is used in an optical pickup head apparatus, the need of a conventional {fraction (1/4)} wavelength plate will successfully be eliminated. This allows the assembly and adjustment of optical components to be simplified during the production of an optical pickup head apparatus as easy as of a conventional optical pickup head apparatus which has a single light source.  
         [0106]    Even if the optical storage medium is partially birefringent, the intensity of light received by the photodetector can remain unchanged, hence ensuring appropriate playback of data on the data apparatus.  
         [0107]    Also, during the assembling of the optical pickup head apparatus, the diffraction grating is adjustably positioned to match one of any two formats, CD and DVD, of the optical storage medium while its adjustment for the other format is automatically done at the same time. As a result, the optical pickup head apparatus will highly be improved in the productivity.  
         [0108]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.