Abstract:
An optical information recording/reproduction apparatus capable of eliminating a waste of learning time for spherical aberration learning and rationalizing the spherical aberration-correcting operation is provided. Specifically, the optical information recording/reproduction apparatus includes: a discrimination circuit for discriminating the kind of an optical disk, that is, whether a recording layer is a single-layer, or whether double-layers or an optical disk is a disk corresponding to red-laser or a disk corresponding to blue-laser; a correction device for correcting the aberration due to a change in thicknesses of the transparent substrate of an optical disk by changing intervals between a plurality of lenses; a learning circuit for searching a correction amount while changing intervals between the plurality of lenses; and a circuit for changing initial positions of intervals between the plurality of lenses at start of learning in accordance with a discrimination result by the discrimination circuit.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical information recording and reproduction apparatus for recording information in an optical recording medium such as an optical disk or reproducing the recorded information from the optical recording medium, particularly to the rationalization of a correction technique for correcting spherical aberration of an optical recording medium.  
         [0003]     2. Related Background Art  
         [0004]     In recent years, in the case of an optical disk apparatus, a technique corresponding to a change of making the wavelength of a light source shorter and a change of making the NA of an objective lens higher is vigorously studied in order to make the density of a disk higher. Locally, commercialization of an apparatus using a 405 nm-band semiconductor laser and an objective lens of NA=0.85 is started.  
         [0005]     Moreover, in order to make the capacity of a disk higher, a disk having two recording layers is used. However, when using the 405 nm-band semiconductor laser, its quantization noise, so-called LD noise becomes a problem and when using the objective lens of NA=0.85, spherical aberration due to error of the thickness of a transparent substrate or jump operation between the layers of the double-layer disk becomes a problem.  
         [0006]     Furthermore, the spherical aberration due to jump operation between the layers cannot be ignored for a DVD of red LD and NA (numerical aperture) of about 0.65.  
         [0007]     Therefore, when increasing output power, because of the characteristic of a semiconductor laser (hereafter abbreviated as “LD”), LD noises are lowered. Therefore, a technique for restraining LD noises by inserting an optical attenuation device when a single-layer disk is used is disclosed in Japanese Patent Application Laid-Open No. 2003-257072.  
         [0008]     Moreover, a technique for generating a spherical aberration by additionally using a beam expander and changing interval between lenses to offset the spherical aberration due to a thickness error of a transparent substrate is disclosed in Japanese Patent Application Laid-Open No. 2002-236252.  
         [0009]     However, the above conventional techniques have the following problems.  
         [0010]     That is, when inserting an optical filter between an LD and a collimator lens, this is effective for compacting an optical system but an optical path length between the LD and the collimator lens depends on presence or absence of the optical. filter. As a result, a case in which there is an optical filter is assumed as the reference state of the optical path length between the LD and the collimator lens, the LD is present at a defocus position viewed from the collimator lens when the optical filter is not inserted. Then, the light flux after the collimator lens becomes convergent light, and when condensing the light to a disk by the optical lens, a large spherical aberration occurs.  
         [0011]     However, a spherical aberration also occurs due to a thickness error of a transparent substrate of a disk or thickness difference between layers. Therefore, by using spherical aberration correcting means and searching the optimum state of the spherical aberration correcting means so that a signal quality serving as an index-signal becomes preferable, it is possible to correct spherical aberration occurring as a result.  
         [0012]     Therefore, when searching the optimum state of the spherical aberration correcting means (hereafter, the searching of the optimum state of the spherical aberration correcting means is referred to as “spherical aberration learning”), the optimum state is searched by using an initial state serving as a reference as a start point. However, as described above, particularly in the case of using an optical filter, the initial state is changed due to presence or absence of the optical filter. Therefore, in the case of spherical aberration learning, the range of the learning expands by at least a change of the initial state and the waste time of spherical aberration learning occurs.  
         [0013]     Moreover, even if a system between an LD and a collimator lens is not changed or even in the case of an apparatus capable of recording/reproducing a disk formed in accordance with a different format, for example, use of wavelengths different from each other, because the format differs, a spherical aberration amount to be corrected also differs. Therefore, it is necessary to widely set a learning range for spherical aberration learning, and by learning spherical aberration in accordance with the set range, waste of leaning time occurs.  
       SUMMARY OF THE INVENTION  
       [0014]     An object of the present invention is to provide an optical information recording/reproduction apparatus which eliminates a waste of learning time for spherical aberration learning and rationalizes the spherical aberration correcting operation.  
         [0015]     The present invention makes it possible to provide an optical information recording/reproduction apparatus which can eliminate a waste of learning time for spherical aberration learning by changing the initial position for learning every kind of an optical recording medium before the operation of the spherical aberration learning, and to rationalize the operation of spherical aberration correcting.  
         [0016]     Specifically, an optical information recording/reproduction apparatus of recording information by leading a light flux from a light source to an objective lens and condensing the light flux through a transparent substrate to the recording face of an optical recording medium with the objective lens, or reproducing the information based on the light returned from the optical recording medium, including:  
         [0017]     a discrimination circuit for discriminating the kind of the optical recording medium;  
         [0018]     a correction device for correcting the aberration due to a change of thicknesses of the transparent substrate by changing intervals between a plurality of lenses;  
         [0019]     a learning circuit for searching a correction amount while changing intervals of a plurality of lenses; and  
         [0020]     a circuit for changing initial positions of the intervals between the plurality of lenses at start of learning in accordance with a discrimination result by the discrimination circuit.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a block diagram showing a first embodiment of the present invention;  
         [0022]      FIGS. 2A and 2B  are illustrations showing a structure of a medium used for the first embodiment;  
         [0023]      FIG. 3  is a flowchart showing operations of the first embodiment;  
         [0024]      FIG. 4  is a graph showing a relation between a distance between the collimator lens groups (L) and a generated spherical aberration (W 40 ) of the first embodiment;  
         [0025]      FIG. 5  is a block diagram showing second embodiment of the present invention;  
         [0026]      FIG. 6  is a flowchart showing operations of a second embodiment; and  
         [0027]      FIG. 7  is a graph showing a relation between a distance between the collimator lens groups (L) and a generated spherical aberration (W 40 ) in the second embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Then, preferred embodiments for executing the present invention are described below in detail with referring to the accompanying drawings.  
       First Embodiment  
       [0029]      FIG. 1  is a block diagram showing a first embodiment of an optical information recording/reproduction apparatus of the present invention. First, the outline of an optical system is described below.  
         [0030]     A part of a beam emitted from an LD (semiconductor laser)  1  is reflected by a PBS (polarization beam splitter)  3  and condensed to a monitor PD (photodiode)  5  by a condensing leans  4 . An output of the monitor PD  5  is used for control of power output from the LD  1 . Reference numeral  25  denotes a signal detecting part for converting the photocurrent of the monitor PD  5  into a voltage signal.  
         [0031]     An optical filter  2  is set between the LD  1  and the PBS  3 . The optical filter  2  is a parallel flat plate provided with an optical thin film having a transmittance of 50%, which is constituted between the LD  1  and the PBS  3  so that it can be inserted and retreated according to necessity in accordance with driving by an optical attenuation device-driving mechanism  31  and kept in an inserted state in the case of initialization.  
         [0032]     A beam passing through the PBS  3  passes through a λ/4 plate  6  and enters a collimator lens  9  and becomes into almost a parallel light flux. The parallel light flux is condensed by an objective lens  10  and imaged on a recording layer through the transparent substrate of an optical disk  11 . Information is recorded on the optical disk  11  by modulation of an optical output by a modulation circuit not shown. Moreover, the information is reproduced by scanning an information track with a low output of the LD  1 , receiving the light reflected from the optical disk  11  by an RF servo PD  13  and conforming to the light receiving signal.  
         [0033]     The collimator lens  9  is constituted of two groups of lens-group  7  and  8  and has a configuration capable of providing variable spherical aberration for a beam condensed to the optical disk  11  by changing the distance between the lens-groups. Reference numeral  32  denotes a spherical aberration correcting device-driving mechanism (for example, stepping motor) for changing the distance between the lens groups by moving at least one of the lens-group  7  and  8  in the optical axis direction. Reference numeral  24  denotes a spherical aberration correcting device-driving part for driving the spherical-aberration correcting-device driving mechanism  32 .  
         [0034]     The optical disk  11  includes a single-layer disk having one a recording layer and a double-layer disk having two recording layers and is formed of a transparent substrate, recording layers, intermediate layer and substrate as shown in  FIGS. 2A and 2B .  FIG. 2A  shows the single-layer disk and  FIG. 2B  shows the double-layer disk. In the case of this embodiment, the optical disk  11  changes initial positions for learning start of the spherical aberration correcting means in the learning operation for searching an optimum spherical aberration correcting amount when the optical disk  11  is a single-layer disk and a double-layer disk.  
         [0035]     When assuming the recording layer of a single-layer disk as L 0 , the recording layer of a double-layer disk far from the objective lens  10  as L 0 ′ and the recording layer of the double-layer disk close to the objective lens as L 1 ′, the recording layer L 0  of the single-layer disk and the recording layer L 0 ′ of the double-layer disk are almost equal except for transmittance and reflectance viewed from the objective lens  10 . Moreover, in the case of the double-layer disk, an address is sequentially assigned from L 0 ′ to L 1 ′.  
         [0036]     In the case of this embodiment, the wavelength of the LD 1  is 405 nm, the focal distance of the collimator lens  9  is 13 mm, the distance between the groups of the collimator lens (distance between the collimator lens groups) is 0.8 mm for a reference, the numerical aperture of the objective lens  10  is 0.85 and the focal distance is 1.176 mm.  
         [0037]     Moreover, when the optical disk  11  is a single-layer disk, a transparent substrate has a refractive index of about 1.6 and a thickness of 100 μm, and a recording layer has a thickness of about 0.1 μm. When the optical disk  11  is a double-layer disk, the transparent substrate has a refractive index of about 1.6 and a thickness of 75 μm, each recording layer has a thickness of about 0.1 μm and an intermediate layer has a refractive index of about 1.6 and a thickness of about 25 μm.  
         [0038]     A beam reflected from the optical disk  11  enters the PBS  3  through the objective lens  10 , collimator lens  9  and λ/4 plate  6 . This incoming light flux is reflected by the PBS  3  and condensed on to the RF servo PD  13  by a sensor lens  12 . An information signal and a servo signal can be obtained by an output from the RF servo PD  13 . Moreover, a controller  22  is a control circuit for controlling each part in an apparatus, which controls the spherical aberration learning operation and the like to be described later.  
         [0039]     Then, a process from disk insertion to spherical aberration learning of this embodiment is described.  FIG. 3  is a flowchart showing the operation.  
         [0040]     First, the optical disk  11  is inserted into an apparatus (S 301 ). At this stage, a single-layer disk or double-layer disk is not known. In an initial state, the optical filter  2  is inserted between the LD  1  and PBS  3  as described above. When it is detected that the optical disk  11  is inserted, the controller  22  controls a laser driving circuit not shown to turn on the LD  1  (S 302 ) and under this state, sets the emission power of the objective lens  10  to 0.35 mW.  
         [0041]     In the case of this embodiment, a mechanism for suppressing LD noise is prepared for a case of a single-layer disk. When there is not the optical filter  2  between the LD  1  and PBS  3 , an output of the LD  1  when an output from the objective lens  10  corresponds to 0.35 mW approximately ranges between 2.4 and 3.0 mW and an output of the LD 1  approximately ranges between 4.8 and 6.0 mW by means of the optical filter  2 . An output of the LD  1  is set to a range between 4.8 and 6.0 mW. Also in the case of a double-layer disk, an output is almost the same. In this case, LD noise lowers to about −6 to −10 (dB) and S/N is improved to a large extent.  
         [0042]     Then, the controller  22  discriminates whether the inserted optical disk  11  is a single-layer disk or double-layer disk (S 303 ). Specifically, the controller  22  slightly vertically moves the objective lens  10  to detect the peak value of the sum of outputs from the RF servo PD  13  by a signal detecting part  21 . The controller  22  compares the output sum of the signal detecting part  21  with a preset reference voltage. When the output sum is higher than the reference voltage, the controller  22  discriminates a single-layer disk and when the output sum is lower than the reference voltage, it discriminates a double-layer disk.  
         [0043]     In the case of a single-layer disk, the controller  22  controls the spherical aberration correcting device-driving part  24  and sets the initial position of the distancedistance between the lens groups between the lens-group  7  and  8  of the collimator lens  9  to L=α by driving the spherical aberration driving mechanism  32  (S 304 ).  
         [0044]     As shown in  FIG. 1 , the collimator lens  9  is two-group configuration of the lens-group  7  and  8 . The relation between the distance between the lens groups (L) and the generated spherical aberration (W 40 ) when combining the collimator lens  9  with the objective lens  10  is shown by graphs in  FIG. 4 .  
         [0045]     In  FIG. 4 , the relation between the distance between the lens groups (L) and the generated spherical aberration (W 40 ) in recording/reproduction on the layers L 0 , L 0 ′ and L 1 ′ is plotted. As shown by the graphs in  FIG. 4 , it is found that the layer L 0  is shifted by the distance between the lens groups corresponding to the spherical aberration generated by inserting the optical filter  2 .  
         [0046]     The shift amount is about 0.1 mm when the a parallel flat plate constituting the optical filter  2  has a thickness of 1 mm, and about 0.15 mm when the parallel flat plate has a thickness of 1.5 mm. In the case of this embodiment, the thickness of the parallel flat plate of the optical filter  2  is set to 1 mm.  
         [0047]     Therefore, in the case of this embodiment, the reference value of the distance between the lens groups (L) of the collimator lens  9  is approximately equal to 0.68 mm for a single-layer disk. Moreover, in the case of a double-layer disk, the reference value is approximately equal to 0.55 mm for the layer L 0 ′ and 1.65 mm for the layer L 1 ′.  
         [0048]     Therefore, in this embodiment, in the case of a single-layer disk, it is normal that L nearly equal to 0.68 mm is used as an initialization value, and in the case of a double-layer disk, since L 0 ′ is used in accordance with an address, L nearly equal to 0.55 mm is used as the initialization value. In S 304 , the initialization value is set to α nearly equal to 0.68 mm.  
         [0049]     Then, the controller  22  controls each part and learns spherical aberration for searching an optimum distance between the lens groups at which spherical aberration disappears (S 305 ). In this case, the distance between the lens groups of the collimator lens  9  is set to the initialization value in accordance with the control by the controller  22  as described above.  
         [0050]     A reproduction signal amplitude value corresponding to the distance between the lens groups is detected by the signal detecting part  21  while changing the distance between the lens groups of the collimator lens  9  at predetermined intervals in a predetermined width (range) centering around the initial position. The controller  22  performs processing by relating the corresponding reproduction signal amplitude with the distance between the lens groups to detect a lend group distance of the collimator lens  9  at which the reproduction signal amplitude value is maximized. When the controller  22  detects the distance between the lens groups at which the reproduction signal amplitude is maximized, the controller  22  controls the spherical aberration correcting device-driving part  24  to set the part  24  to an optimum distance between the lens groups at which the reproduction signal amplitude value is maximized.  
         [0051]     In this case, the spherical aberration value becomes almost zero and spherical aberration is corrected. In the case of this embodiment, the above learning operation is performed by cutting a width of ±20 mm every 0.02 mm interval which corresponds to a width of ±10 μm and an interval of 1 μm in a transparent substrate thickness error.  
         [0052]     Then, the operation when discriminated as a double-layer disk in S 303  is described. In the case of the double-layer disk, the reflectance and absorption coefficient of a recording layer have almost a half of the case of a single-layer disk, and light quantity to be irradiated to the disk becomes about two times. Therefore, LD output power rises and LD noise is restrained. Consequently, the controller  22  controls an optical attenuation device-driving part  23  to retreat the optical filter  2  from the gap between the LD  1  and PBS  3  by driving the optical attenuation device-driving mechanism  31  (S 306 ).  
         [0053]     In this case, the LD  1  is once turned off, and after the optical filter  2  is retreated, the LD  1  is turned on again. The optical attenuation device-driving mechanism  31  is a mechanism for inserting or evacuating the optical filter  2  between the LD  1  and PBS  3 , and the optical attenuation device-driving portion  23  is a driving part for driving the optical attenuation device-driving mechanism  31  in accordance with control by the controller  22 .  
         [0054]     Then, the controller  22  controls the spherical aberration correcting device-driving part  24  to set the initial position of the distance between the lens groups of the collimator lens  9  to L=β by driving the spherical aberration correcting device-driving mechanism  32  (S 307 ). In the case of this embodiment, β is approximately equal to 0.55 mm as described above. This corresponds to the layer L 0 ′.  
         [0055]     Moreover, spherical aberration is learned similarly to the case of a single-layer disk (S 308 ). That is, the spherical aberration correcting device-driving portion  24  is controlled and a reproducing-signal amplitude value is detected by the signal detecting portion  21  while changing the distance between the lens groups at predetermined intervals in a predetermined width centering around the initial position. Then, a distance between the lens groups at which a reproduction signal amplitude is maximized is detected and stored in the controller  22 .  
         [0056]     Then, learning of the layer L 1 ′ is started (S 309 ) In this case, the controller  22  controls the spherical aberration correcting device-driving part  24  to set the initial position of the distance between the lens groups of the collimator lens  9  to L=γ. In the case of this embodiment, γ is approximately equal to 1.05 mm as described above.  
         [0057]     Then, spherical aberration for L=γ is similarly learned (S 310 ). That is, the controller  22  controls the spherical aberration correcting device-driving part  24  to detect a reproduction signal amplitude by the signal detecting part  31  while changing an distance between the lens groups at predetermined intervals in a predetermined width centering around an initial position. Moreover, the distance between the lens groups of the collimator lens  9  at which the reproduction signal amplitude is maximized is detected and stored in the controller  22 . Thus, learning of spherical aberration is completed.  
         [0058]     Thereafter, in case of recording or reproducing information in or from a double-layer disk, the controller  22  sets a distance between the lens groups to an optimum value corresponding to each layer to record or reproduce information in or from the layers L 0 ′ and L 1 ′.  
         [0059]     Thus because the initial position of the distance between the lens groups of the collimator lens  9  is changed in accordance with the kind of the optical disk  11  (single-layer disk or double-layer disk), whereby waste learning is not performed and it is possible to decrease the time of spherical aberration learning of an apparatus capable of avoiding LD noise.  
       Second Embodiment  
       [0060]      FIG. 5  is a block diagram showing a second embodiment of the present invention. In the case of this embodiment, initial positions of spherical aberration learning of spherical aberration correcting means are changed in accordance with the fact that an optical disk to be used is a disk corresponding to blue LD corresponding to blue LD or a disk corresponding to red LDdisk corresponding to red LD. First, the outline of an optical system when a disk to be used is a disk corresponding to blue LD is described.  
         [0061]     A part of a beam emitted from an LD (semiconductor layer)  41  is reflected by a composite SB  42  and condensed to a light-receiving area for a monitor of a PD (photodiode)  44  by a condensing lens  43 . This output is used for control of emission power of the LD  41 . PD  44  has a light-receiving area for a monitor and a RF servo area.  
         [0062]     The beam passing through the composite BS  42  is changed to an almost parallel light flux by a collimator lens  48  through a λ/4 plate  45  and moreover, the parallel light flux passes through a wavelength selection phase plate  49  and imaged on a recording layer through a transparent substrate of an optical disk  51  by an objective lens  50 . When information is read in the optical disk  51 , the information is recorded through modulation of an information light output by a modulation circuit not shown. Moreover, when reproducing the information, information track is scanned with a low output of the LD  41 , the reflected light is received and the information is reproduced in accordance with the light-receiving signal.  
         [0063]     When the optical disk  51  is a disk corresponding to blue LD, reproduction is performed in accordance with the light-receiving signal of the RF servo area of the PD  44 . When the optical disk  51  is a disk corresponding to red LD, reproduction is performed in accordance with a light-receiving signal condensed to a photodiode (not shown) in an integrated unit  61 . The same is applied when obtaining a servo signal. Moreover, when performing the learning operation to be described later, learning is similarly performed in accordance with a light-receiving signal in the RF servo area of the PD  44  in the case of a disk corresponding to blue LD, and learning is performed in accordance with a light-receiving signal of the photodiode in the integrated unit  61  in the case of a disk corresponding to red LD.  
         [0064]     In this case, a PBS film is formed on the separate face of the composite BS  42  no the LD  41  side to constitute an optical isolator in accordance with a combination with the λ/4 plate  45 . Moreover, the collimator lens  48  is constituted of two groups of lens-group  46  and  47  so as to be able to provide variable spherical aberration for a beam condensed to the optical disk  51  by changing the distance between the lens groups. Furthermore, the wavelength-selection phase plate  49  is held integrally with the objective lens  50 .  
         [0065]     A beam reflected by the optical disk  51  enters the composite BS  42  through the objective lens  50 , collimator lens  48  and λ/4 plate  45 . This incoming light flux is reflected by the composite BS  42  and condensed on the RF servo area of the PD  44  by a sensor lens  52 . An information signal and a servo signal can be obtained in accordance with an output from the RF servo area.  
         [0066]     In this case, the collimator lens  48  is constituted of two groups of the lens-group  46  and  47  as described above, which can provide spherical aberration for a beam condensed to the optical disk  51  by changing the distance between the lens groups. A spherical aberration correcting device-driving mechanism  71  is a driving mechanism for changing the distance between the lens groups by moving at least either of the lens-group  46  and  47  in the optical axis direction, and reference numeral  92  denotes a driving part for driving the spherical aberration correcting device-driving mechanism  71  under the control of the controller  81 . The spherical aberration correcting device-driving mechanism  71  uses, for example, a stepping motor.  
         [0067]     In the case of this embodiment, the wavelength of the LD  41  is 405 nm, the focal distance of the collimator lens  48  is 13 mm, the distance between the lens groups of the collimator lens  48  is 0.8 mm as a reference, the numerical aperture of the objective lens  50  is 0.85, and the focal distance of the lens  50  is 1.176 mm.  
         [0068]     The optical disk  51  includes a single-layer disk having one recording layer and a double-layer disk having two recording layers and is constituted of a transparent substrate, recording layers, an intermediate layer and a substrate similarly to the case of  FIG. 2 . Moreover, it is assumed that recording and reproduction are performed at a wavelength of 405 nm and objective-lens numerical aperture of 0.85.  
         [0069]     In this case, it is assumed that the recording layer of a single-layer disk is L 0 , the recording layer of a double-layer disk far from the objective lens  50  is L 0  and the recording layer close to the objective lens  50  is L 1 . In the case of the double-layer disk, an address is sequentially assigned from L 0  to L 1 .  
         [0070]     Moreover, in the case of the single-layer disk, the transparent substrate has a refractive index of about 1.6 and a thickness of 100 μm and the recording layer has a thickness of about 0.1 μm. In the case of the double-layer disk, the transparent substrate has a refractive index of about 1.6 and a thickness of 75 μm, each recording layer has a thickness of about 0.1 μm, and the intermediate layer has a refractive index of about 1.6 and thickness of 25 μm. Because the recording layer of the single-layer disk and the recording layer of the double-layer disk far from the objective lens are regarded to be almost the same, they are assumed as L 0  as a generic name.  
         [0071]     Then, the outline of an optical system when a disk to be used is a disk corresponding to red LD is described below. In the case of the integrated unit  61 , a red (660-nm band) LD chip, photodiode and preamplifier are integrated. Moreover, in the case of a hologram device  62 , a diffraction grating is set to the integrated unit  61  side, a polarized hologram structure is formed at the facing side, and the integrated unit  61  and the hologram device  62  are integrally held.  
         [0072]     A part of a beam emitted from the red (660 5 -nm band) LD chip in the integrated unit  61  passes through the composite BS  42  and condensed to the light-receiving area for a monitor of the PD  44  by the condensing lens  43 . This output is used for the control of the power emitted from the LD chip.  
         [0073]     The beam reflected by the composite BS42 is changed to almost a parallel light flux by the collimator lens  48  through the λ/4 plate  45 . The parallel light flux passes through the wavelength election phase plate  49  and is imaged on a recording layer through the transparent substrate of the optical disk  51  by the objective lens  50 . Information is recorded in accordance with modulation of an optical output by a modulation circuit not shown. When the information is reproduced, an information track is scanned with a low output, the light reflected from the track is condensed to a photodiode in the integrated unit  61  and the information is reproduced in accordance with the light-receiving signal.  
         [0074]     In this case, the wavelength selection phase plate  49  has an aperture-size limit function by a wavelength selection filter for using the objective lens  50  as NA=0.65 as publicly known as well as phase distribution for correcting initial spherical aberration generated when different from a designed wavelength and designed substrate thickness.  
         [0075]     The optical disk  51  includes a disk composed of one or two recording layers corresponding to a red LD and an objective-lens numerical aperture of 0.60 to 0.65, a transparent substrate, an intermediate layer and a substrate as described for the first embodiment.  
         [0076]     In this case, it is assumed that the recording layer of a single-layer disk of a red-LD-corresponding disk or the recording layer of a double-layer disk far from the objective lens  50  is a layer L 0 ′ and a recording layer of the double-layer disk close to the objective lens  50  is a layer L 1 ′. This represents that the recording layer of the single-layer disk and the recording layer of the double-layer disk far from the objective lens  50  have the same transparent substrate thickness viewed from the objective lens  50 . Moreover, in the case of the double-layer disk, an address is sequentially assigned from L 0 ′ to L 1 ′.  
         [0077]     The wavelength of the light from the integrated unit  61  is 660 nm, and the focal distance of the collimator lens  48  at the wavelength is about 13 mm because the lens  48  has an achromatic configuration, the distance between the lens groups of the collimator lens  48  is 0.8 mm as a reference, and the focal distance of the objective lens  50  is about 1.18 mm.  
         [0078]     Moreover, in the case of the optical disk  51 , the reference distance from the surface of the red LD corresponding disk is 0.6 mm for the layer L 0 ′ and 0.54 mm for the layer L 1 ′.  
         [0079]     Then, a process from disk insertion to spherical aberration learning of this embodiment is described below.  FIG. 6  is a flowchart showing operations of the process.  
         [0080]     First, the optical disk  51  is inserted (S 601 ). At this stage, it is unknown that the disk is a disk corresponding to red LD or disk corresponding to blue LD. When it is detected that the optical disk  51  is inserted, a controller  81  controls a laser driving circuit not shown to turn on a read LD in the integrated unit  61  (S 602 ).  
         [0081]     Moreover, the controller  81  controls each part to reproduce the disk information area of the optical disk  51  and discriminates a disk corresponding to red LD when disk information is obtained in accordance with a signal from a signal detecting part  91  and a disk corresponding to blue LD when the disk information is not obtained.  
         [0082]     Thus, the kind of a disk is discriminated in accordance with whether disk information can be reproduced or not. In this case, the signal detecting part  91  uses a signal in the RF servo area of the PD 44  as a voltage signal, and the controller  81  reproduces the disk information in accordance with the signal. Moreover, when the disk information can be reproduced, the information showing that the recording layer of the optical disk  51  is single-layer or double-layer is included in the disk information and it is found that the inserted disk is a single-layer disk or double-layer disk in accordance with the information.  
         [0083]     In the case of the disk corresponding to red LD, the controller  81  controls the spherical-aberration correcting device-driving part  92  to set the distance between the lens groups of the collimator lens  48  to an initial position L=γ by driving the spherical aberration correcting device-driving mechanism  71  (S 604 ).  
         [0084]     As shown in  FIG. 5 , the collimator lens  48  is constituted of two groups of lens-group  46  and  47  and the relation between the distance between the-lens groups (L) and the generated spherical aberration (W 40 ) according to a combination of the collimator lens  48  and the objective lens  50  through the wavelength selection phase plate  49  is shown by graph of  FIG. 7 .  
         [0085]     The relation between the distance between the lens groups (L) and the generated spherical aberration (W 40 ) in the case of the disk corresponding to red LD is plotted as the layers L 0 ′ and L 1 ′ in the graph. The reference value of the distance between the lens groups (L) of the collimator lens  48  is nearly equal to 0.68 mm for the layer L 0 ′ and nearly equal to 0.92 mm for the layer L 1 ′. Because it is normal that L 0 ′ is first used in view of an address, L nearly equal to 0.68 mm is used as an initialization value. Therefore, in this step, γ is set to about 0.68 is realized.  
         [0086]     Then, the controller  81  controls each part to perform the spherical aberration learning for searching an optimum distance between the lens groups (S 605 ). That is, similarly to the case of the first embodiment, the controller  81  controls the spherical aberration correcting device-driving part  92 , and corresponding reproduction signal amplitude is detected from a light-receiving signal of the photodiode of the integrated unit  61  while changing the distance between the lens groups of the collimator lens  48  at a predetermined interval in a predetermined width (range) centering around the initial position.  
         [0087]     The controller  81  performs processing by relating the distance between the lens groups of the collimator lens  48  with a reproduction signal amplitude, detects the distance between the lens groups of the collimator lens  48  when the reproduction signal amplitude is maximized and stores the detected distance between the lens groups in the controller  81 .  
         [0088]     In this case, a spherical aberration value becomes almost zero and spherical aberration is corrected. In this case, the above learning operation is performed by cutting a width of ±0.12 mm every 0.02 mm interval which corresponds to a width of ±30 μm and an interval of about 5 [m in a transparent substrate thickness error.  
         [0089]     Then, learning of the layer L 1 ′ is started (S 606 ). In this case, the controller  81  controls the spherical aberration correcting device-driving part  92  to set the distance between the lens groups of the collimator lens  48  to the initial position L=δ. In this case, δ is approximately equal to 0.92 mm as described above.  
         [0090]     When a single-layer disk is discriminated in accordance with the reproduced disk information, this step (S 606 ) and the next step (S 607 ) are unnecessary.  
         [0091]     Then, the controller  81  similarly performs spherical aberration learning (S 607 ). That is, the controller  81  controls the spherical aberration correcting device-driving part  92  to detect a reproduction signal amplitude while changing the distance between the lens groups at a predetermined interval in the above-described predetermined width centering around an initial position. Moreover, the distance between the lens groups of the collimator lens  48  at which the reproduction signal amplitude is maximized is detected and stored in the controller  81 .  
         [0092]     Thereafter, when recording or reproducing information in or from the double-layer disk, the controller  81  sets the distance between the lens groups of the collimator lens to an optimum value corresponding to each stored layer and records or reproduce information in or from each layer.  
         [0093]     Then, operations when a disk corresponding to blue LD is discriminated in S 603  are described. First, the controller  81  turns off a red LD (S 608 ).  
         [0094]     Moreover, the controller  81  turns on the LD  41  (blue LD) and reproduces disk information (S 609 ) The information showing whether the optical disk  51  is a single-layer disk or double-layer disk is included in the disk information.  
         [0095]     Then, the controller  81  controls the spherical aberration correcting device-driving part  92  to set the distance between the lens groups of the collimator lens  48  to the initial position L=α (S 610 ).  
         [0096]     The relation between the distance between the lens groups (L) and the generated spherical aberration (W 40 ) in accordance with a combination of the collimator lens  48  and the objective lens  50  through the wavelength selection phase plate  49  is shown by the graph of  FIG. 7 .  
         [0097]     In the case of the disk corresponding to blue LD, the relation between the distance between the lens groups (L) and the generated spherical aberration (W 40 ) is plotted as the layers L 0  and L 1 . The reference value of the distance between the lens groups. (L) of the collimator lens  48  is nearly equal to 0.55 mm for the layer L 0  and nearly equal to 1.05 mm for the layer L 1 . Therefore, because it is normal that a layer is used starting with the layer L 0  in view of an address, L nearly equal to 0.55 mm is used as an initialization value. In this step, α nearly equal to 0.55 mm is realized.  
         [0098]     Then, the controller  81  controls each part to similarly learn spherical aberration (S 611 ). That is, the controller  81  controls the spherical aberration correcting device-driving part  92  to detect a reproduction signal amplitude by the signal detecting part  91  while changing the distance between the lens groups at a predetermined interval in a predetermined width centering around an initial position. Moreover, an distance between the lens groups at which the reproducing signal amplitude is maximized is detected to store it in the controller  81 . In this case, the above learning operation is performed by cutting a width of ±0.20 mm every 0.02 mm interval which corresponds to a width of ±10 μm and an interval of about 0.02 mm in a transparent substrate thickness error.  
         [0099]     Then, learning of the layer L 1  is started (S 612 ). In this case, the spherical aberration correcting device-driving part  92  is controlled and the distance between the lens groups of the collimator lens  48  is set to an initial position L=β. In this case, β is approximately equal to 1.05 mm as described above.  
         [0100]     In this case, when a single-layer disk is discriminated in accordance with the reproduced disk information, this step (S 612 ) and the next step (S 613 ) are unnecessary.  
         [0101]     Then, the controller  81  similarly learns spherical aberration (S 613 ). That is, the controller  81  controls the spherical aberration correcting device-driving part  92  and detects a reproduction signal amplitude by the signal detecting part  91  while changing the distance between the lens groups at a predetermined interval in a predetermined width centering around an initial position. Moreover, the distance between the lens groups at which the reproducing signal amplitude is maximized is detected and stored in the controller  81 .  
         [0102]     Thereafter, when recording or reproducing information in or from the double-layer disk, the controller  81  sets the distance between the lens groups of the collimator lens to an optimum value corresponding to each of the stored layers, and the recording or reproduction of information is performed in each layer.  
         [0103]     Thus, in the case of this embodiment, initial positions of the distance between the lens groups of the collimator lens  48  are changed in accordance with the kind of a disk (disk corresponding to red LD or disk corresponding to blue LD). Therefore, it is possible to decrease the time of spherical aberration learning in an apparatus capable of recording/reproducing disks having different kinds from each other corresponding to different wavelengths and numerical apertures.  
         [0104]     Moreover, in the case of the above embodiment, spherical aberration is corrected by using a collimator lens constituted of two groups of lenses. However, it is also allowed to correct spherical aberration by setting an exclusive lens system, the so-called expander lens (constituted of a pair of lenses respectively capable of changing relative position of a lens) in an optical path without combining with the collimator lens.  
         [0105]     This application claims priority from Japanese Patent Application No. 2005-021449 filed Jan. 28, 2005, which is hereby incorporated by reference herein.