Patent Publication Number: US-2010124161-A1

Title: Optical pickup and optical information reproducing device

Description:
INCORPORATION BY REFERENCE 
     The present application claims priority from Japanese application JP2005-052245 filed on Feb. 28, 2005, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     The invention relates to an optical pickup for reproducing or recording information by irradiating a laser beam onto a disk-shaped information medium. A high density optical disk device using a blue-violet laser having a laser wavelength of a band of 405 nm, an objective lens having a numerical aperture of 0.85, and a BD (Blu-ray Disc) having a substrate thickness of 0.1 mm has been realized as a product. At present, a medium of a single-layered disc and a medium of a double-layered disc exist as BDs. According to the BD standard, in the double-layered disc, there is a difference of the substrate thickness of 25 μm between the first recording layer and the second recording layer. Further, in each recording layer of the double-layered disc or in the single-layered disc, the substrate thickness varies every disc and even in a single disc, the substrate thickness varies in dependence on a recording or reproducing position (in the BD standard, a variation of up to ±5 μm is permitted). If there is such a variation or difference of the substrate thickness as mentioned above, a spherical aberration occurs in a light spot on the disc recording surface and it is difficult to record and reproduce. To correct such a spherical aberration, the optical pickup is equipped with an optical element for spherical aberration correction such as a beam expander. A typical constructional example of such an element has been disclosed in, for example, a Patent Document 1 (JP-A-2002-304763 (pages 21-23,  FIGS. 1 ,  4 , and  6 )). 
     As a technique regarding the spherical aberration correction, for example, a technique in which a predetermined correction value of a spherical aberration correcting system is preliminarily stored in a ROM provided for the optical pickup and, upon recording and reproducing of the BD, the correcting system is driven on the basis of the correction value read out of the ROM has been disclosed in, for example, a Patent Document 2 (JP-A-2003-257069 (pages 1-7,  FIGS. 1 ,  2 , and  3 )). 
     SUMMARY OF THE INVENTION 
     In the optical disk device corresponding to the BD mentioned above, until the disc is loaded, information showing to which one of the single-layered disc and the double-layered disc such a disc corresponds or, even if the disc is the single-layered disc, information indicative of a degree of variation of the substrate thickness cannot be detected on the optical pickup side. When the disc is loaded into the device from such a state, in the optical pickup, there is executed aberration correction control in which a spherical aberration amount due to the substrate thickness error is detected, the optical element for the spherical aberration correction is driven in an optical axis direction from a certain initial position (not determined yet) and moved to a proper position, and the spherical aberration is reduced up to a level at which no trouble is caused in the recording and reproduction. However, in such correction control, there is the following problem: an initial setting position of the optical element for the spherical aberration correction is not preset and it takes time until the proper position of the optical element is searched for, or the aberration correction control fails and the recording and reproduction of the disc cannot be started. Under the condition that the use frequency of the single-layered disc and the first layer of the double-layered disc of the BDs is considered to be highest, solving the above problem is indispensable in order to improve use efficiency of a drive. In consideration of the above problem, it is an object of the invention to provide an optical information recording and reproducing device or an optical information recording device having high use efficiency. 
     The above object is accomplished by the inventions disclosed in Claims. 
     According to the invention, the optical information recording and reproducing device or optical information reproducing device having high use efficiency can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a diagram showing a construction of an optical pickup in the embodiment 1; 
         FIGS. 2A to 2C  are diagrams for explaining an objective lens  113  in the embodiment 1; 
         FIGS. 3A and 3B  are a diagram and a graph showing an example of a relation between a divergence angle of incident light to the objective lens  113  in the case of a BD medium and a wave front aberration of a converging spot  302  in the embodiment 1; 
         FIG. 4  is a diagram for explaining a layout and shape parameters of a beam expander element  110  in the embodiment 1; 
         FIG. 5  is a graph showing a relation between a substrate thickness of the BD medium and an interval between a concave lens  108  and a convex lens  109  which are necessary in the embodiment 1; 
         FIG. 6  is a graph showing an aberration correcting effect by the beam expander shown in Table 1; 
         FIG. 7  is a diagram for explaining detecting surfaces of a photodetector  118  and an error signal in the embodiment 1; 
         FIG. 8  is a diagram showing an example of a construction of a peripheral portion of the beam expander element  110  in the embodiment 1; 
         FIG. 9  is a flowchart showing an example of an assembling adjusting flow of a BD optical system in the embodiment 1; 
         FIG. 10  is a flowchart showing an example of a drive operating flow in the case of the BD medium in the embodiment 1; 
         FIGS. 11A and 11B  are graphs showing a focusing error signal in the embodiment 1; 
         FIGS. 12A and 12B  are graphs showing a focusing error signal in the embodiment 1; 
         FIG. 13  is a flowchart for explaining an operating flow in the case where a focal point is moved from an L 0  layer to an L 1  layer of the BD medium in the embodiment 1; 
         FIG. 14  is a flowchart showing an example of an assembling adjusting flow in a DVD optical system and a CD optical system in the embodiment 1; 
         FIG. 15  is a flowchart showing an example of a drive operating flow in the case of a DVD medium and a CD medium in the embodiment 1; 
         FIG. 16  is a diagram showing the first example in the embodiment 2; 
         FIG. 17  is a diagram showing an example of a construction of an optical information recording and reproducing device in the embodiment 3; 
         FIG. 18  is a diagram showing the second example in the embodiment 2; 
         FIG. 19  is a diagram showing the third example in the embodiment 2; and 
         FIG. 20  is a diagram showing the fourth example in the embodiment 2. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Although the following embodiments are considered as best modes for carrying out the invention, the invention is not limited to the following embodiments so long as the object of the invention is accomplished. 
     The embodiment 1 will be described hereinbelow.  FIG. 1  shows a construction of an optical pickup in the embodiment. It is the optical pickup which can cope with each medium of the BD, DVD, and CD and uses a common objective lens. Light emitted from a blue-violet laser  101  having a wavelength of a band of 405 nm passes through a beam shaping element  102  and a half wave plate  103 , is branched into a main beam and two sub beams by a diffraction grating  104  for the BD, and passes through a polarization beam splitter  105 . Parallel light is irradiated from a collimator lens  106  for the BD. The parallel light is reflected by a half mirror  107  and passes through a concave lens  108  and a convex lens  109 , its beam diameter is enlarged, and the resultant light is reflected by a rising mirror  111 . After that, the light is transmitted through a quarter wave plate  112  and an aperture restricting element  131  for the CD, is converged by an objective lens  113 , and reaches an information recording surface of an information recording medium  114  (in this case, a BD medium having one, two, or more recording layers). The objective lens  113  and the aperture restricting element  131  for the CD mounted in a common holder (not shown) and parallel movement in the surface oscillating direction and the radial direction of the information recording medium  114  and rotational movement in which the tangential direction of the information recording medium  114  is set to an axis can be executed by an actuator  134 . To compensate a spherical aberration which is caused in association with a substrate thickness error of the information recording medium  114 , a beam expander element  110  is constructed by a pair of the concave lens  108  and the convex lens  109  and can be moved in the optical axis direction shown by arrows  132  and  133  by an actuator  135 . The reflection return light from the information recording medium  114  is transmitted through the objective lens  113  and the quarter wave plate  112 , reflected by the rising mirror  111 , transmitted through the convex lens  109  and concave lens  108 , and reflected by the half mirror  107 . After that, the light is transmitted through the collimator lens  106 , is reflected by the polarization beam splitter  105 , is converged by a detecting lens  117 , and reaches a detecting surface of a photodetector  118  for the BD. An RF signal and servo signals (focusing error signal, DPP signal, and the like) are detected by the photodetector  118  for the BD and a spherical aberration error signal is formed on the basis of those signals and detected. A part of the parallel light emitted from the collimator lens  106  for the BD is transmitted through the half mirror  107 , is converged by a lens  115 , reaches a front monitor  116  for the BD, and a light emission amount of the blue-violet laser  101  is monitored. 
     Light emitted from a red laser  119  having a laser wavelength of a band of 660 nm is transmitted through an auxiliary collimator lens  120 , is branched into a main beam and two sub beams by a diffraction grating  121  for the DVD, and passes through a synthetic prism  122 , and thereafter, is reflected by a half mirror  123 . Parallel light is irradiated from a collimator lens  124 , is transmitted through the half mirror  107 , passes through the concave lens  108  and the convex lens  109 , its beam diameter is enlarged, and after that, the resultant light is reflected by the rising mirror  111 , transmitted through the quarter wave plate  112 , converged by the objective lens  113 , and reaches the information recording surface of the information recording medium  114  (in this case, the DVD medium having one or two recording layers). The reflection return light from the information recording medium  114  is transmitted through the objective lens  113  and the quarter wave plate  112 , reflected by the rising mirror  111 , transmitted through the convex lens  109  and concave lens  108 , and transmitted through the half mirror  107 . After that, the light is converged by the collimator lens  124  and a detecting lens  127 , and reaches a detecting surface of a photodetector  128  for the DVD/CD. An RF signal and servo signals (focusing error signal, DPP signal, and the like) are detected by the photodetector  128  for the DVD/CD. A part of the light transmitted through the synthetic prism  122  is transmitted through the half mirror  123 , is converged by a lens  125 , reaches a front monitor  126  for the DVD/CD, and a light emission amount of the red laser  119  is monitored. 
     Light emitted from an infrared laser  129  having a laser wavelength of a band of 780 nm is branched into a main beam and two sub beams by a diffraction grating  130  for the CD and is reflected by the synthetic prism  122  and the half mirror  123 . The parallel light is irradiated from the collimator lens  124 , is transmitted through the half mirror  107 , and enters the concave lens  108 . The concave lens  108  is moved in the direction shown by the arrow  132 . Divergent light is emitted from the convex lens  109 . After that, the light is reflected by the rising mirror  111 , transmitted through the quarter wave plate  112  and the aperture restricting element  131  for the CD, converged by the objective lens  113 , and reaches the information recording surface of the information recording medium  114  (in this case, the CD medium). Since an optical path until the reflection return light from the information recording medium  114  reaches the information recording surface of the photodetector  128  for the DVD/CD is the same as that of the DVD system as mentioned above, its explanation is omitted here. Although the red laser  119  and the infrared laser  129  are separately provided in  FIG. 1 , a laser of two wavelengths in which those lasers are integrated can be also used in order to simplify the optical system. In dependence on the specifications of the drive, for example, it is possible to use an optical system in which the blue-violet laser  101  and the red laser  119  are mounted without using the infrared laser  129 . 
     The objective lens  113  will now be described with reference to  FIGS. 2A to 2C .  FIG. 2A  shows the state where the light is converged in a BD double-layers medium  201 . Parallel light  202  having the wavelength of the band of 405 nm passes through the aperture restricting element  131  for the CD as it is and is converged by the operation of a refracting plane  203 . The objective lens  113  is designed so that a wave front aberration of a converging spot  206  is optimized at a substrate thickness t 1  (=0.0875 mm) in an intermediate layer  205  (shown in a broken line portion) comprising an L 0  layer having a substrate thickness of 0.1 mm and an L 1  layer having a substrate thickness of 0.075 mm. The objective lens  113  is designed so that grating grooves  204  formed concentrically on the refracting plane  203  do not have a diffraction function in such a manner that a numerical aperture of the refracting plane  203  is equal to 0.85 for the light having the wavelength of the band of 405 nm.  FIG. 2B  shows the state where the light is converged in a DVD medium  207 . Parallel light  208  having the wavelength of the band of 660 nm passes through the aperture restricting element  131  for the CD as it is, is diffracted by the grating grooves  204 , and is converged by the refracting plane  203 . The objective lens  113  is designed so that an aberration of a converging spot  209  is optimized at a substrate thickness t 2  (=0.6 mm). The objective lens  113  is designed so that grating grooves  204  are formed in a beam diameter range where the numerical aperture is equal to 0.65 for the light having the wavelength of the band of 660 nm in such a manner that the spherical aberration which is caused due to the wavelength difference of about 255 nm and the substrate thickness difference of about 0.5 mm from those in the case of the BD of  FIG. 2A  is set off.  FIG. 2C  shows the state where the light is converged in a CD medium  210 . As for divergent light  211  having the wavelength of the band of 780 nm, a beam diameter of the light entering the objective lens  113  is restricted by the aperture restricting element  131  for the CD and the numerical aperture of the objective lens  113  lies within a range from 0.45 to 0.5. The objective lens  113  is designed so that the light is diffracted by the grating grooves  204 , converged by the refracting plane  203 , and the aberration of the converging spot  212  is optimized at a substrate thickness t 3  (=1.2 mm). 
     As described in  FIG. 2A , in the case of the BD medium, the objective lens  113  is designed so that the wave front aberration of the converging spot  206  is optimized at the substrate thickness t 1  (=0.0875 mm). However, it is sufficiently considered that there are two kinds of BD media such as single-layered medium and double-layered medium and both of them are used at present and that at a point when the recording/reproduction of the double-layered medium is started, the use frequency of the L 0  layer of the first layer is highest. Therefore, it is necessary to set in such a manner that the wave front aberration of the converging spot becomes minimum at a reference value (=0.1 mm) of the substrate thickness of the single-layered medium and the substrate thickness of the LO layer of the double-layered medium. For this purpose, as shown in  FIG. 3A , it is necessary to allow predetermined divergent light  301  to enter the objective lens  113 .  FIG. 3B  shows an example of calculations executed to find which kind of divergent light should be made to enter in order to minimize a converging spot  302  at the substrate thickness of 0.1 mm. The wavelength is set to 405 nm, the numerical aperture of the objective lens  113  is set to 0.85, the refractive index of the substrate is set to 1.62, a distance L between an incident plane  303  of the objective lens  113  and a virtual light source  304  of the divergent light  301  is changed, and the wave front aberration of the converging spot  302  is calculated. An axis of abscissa indicates a divergence angle θ (°) of the incident light entering the objective lens  113  converted from the distance L. An axis of ordinate indicates a wave front aberration value (λ rms) of the converging spot  302 . A calculation result is as shown by a curve  305 . It will be understood from the result that by setting the divergence angle θ of the incident light to θ=0.16° , the wave front aberration value of the converging spot at the substrate thickness of 0.1 mm can be minimized and this value is suppressed to an enough small value of 0.0027 λ rms. 
     Specific examples of the beam expander element  110  designed on the basis of the result of  FIG. 3B  will be described hereinbelow.  FIG. 4  shows a layout and shape parameters of the concave lens  108  and the convex lens  109  of the beam expander element  110 . In this example, in the case of an initial interval B between the concave lens  108  and the convex lens  109 , parallel light  401  entering the concave lens  108  is magnified and emitted as parallel light  402  from the convex lens  109 . In this example, the convex lens  109  is fixed and when the concave lens  108  is moved in parallel in the optical axis direction from the initial interval B, the divergent light or converging light is emitted from the convex lens  109  and enters the objective lens  113 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Concave lens 
                 Convex lens 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Refractive index 
                 n = 1.60524 
                 n = 1.60524 
               
               
                   
                 Center thickness 
                 d1 = 1.2 mm 
                 d2 = 1.2 mm 
               
               
                   
                 Focal distance 
                 f1 = −8.225 mm 
                 f2 = 11.225 mm 
               
               
                   
                 Radius of 
                 R1 = −8.336 mm 
                 R3 = 24.9 mm 
               
               
                   
                 curvature 
                 R2 = 13.028 mm 
                 R4 = −9.173 mm 
               
               
                   
                 Aspherical 
                 R1 plane k = 2.25 
                 R4 plane k = −0.85 
               
               
                   
                 constant 
               
               
                   
                   
               
            
           
         
       
     
     Design values are as shown in Table 1. The initial interval B=2 mm and a distance C between the convex lens  109  and the incident plane of the objective lens is set to (C=15.7 mm).  FIG. 5  shows an example of calculations of the interval between the concave lens  108  and the convex lens  109  which are necessary to minimize the wave front aberration of the converging spot when the substrate thickness of the BD medium fluctuates. A straight line  501  shows the calculation result. It will be understood that it is sufficient to set the interval to 1.755 mm, for example, at the substrate thickness of 0.1 mm in the L 0  layer. 
     It will be understood that it is sufficient to set the interval to 2.25 mm, for example, at the substrate thickness of 0.075 mm in the L 1  layer. Further, the correctable substrate thickness error converted by the movement amount of 1 mm of the concave lens  108  is equal to 0.05 mm.  FIG. 6  shows an example of calculations of the substrate thickness of the BD medium and the wave front aberration of the converging spot. A curve  601  shows the case where the aberration correction by the beam expander element  110  is not made. When the substrate thickness is deviated from the design reference value of 0.0875 mm, the wave front aberration of the converging spot deteriorates suddenly. On the other hand, in the case where the aberration correction by the beam expander element  110  is made, the result is as shown by a curve  602 . It will be understood that even if the substrate thickness fluctuates by ±0.025 mm from the design reference value of 0.0875 mm, the wave front aberration of the converging spot is suppressed to an enough small value of 0.005 λ rms or less. 
     As shown in  FIG. 7 , in the photodetector  118  for the BD, as photodetecting surfaces, a main detecting surface  701  is formed in the center portion, sub detecting surfaces  702  and  703  are formed in the upper and lower portions, and the photodetector  118  has eight detecting surfaces A to D and E to H. Main light  704  in which the return light from the information recording medium  114  of O-order light branched by the diffraction grating  104  for the BD has been converged by the detecting lens  117  enters the eight detecting surfaces A to D. Primary light  705  branched by the diffraction grating  104  for the BD enters the eight detecting surfaces E and F. Sub light  706  in which the return light from the information recording medium  114  of -primary light branched has been converged by the detecting lens  117  enters the eight detecting surfaces G and H. An astigmatism method is used for detection of a focusing error. The error signal is obtained by an arithmetic operation of [A+C−(B+D)] and the RF signal is obtained by an arithmetic operation of [A+B+C+D]. 
       FIG. 8  shows an example of a construction of a peripheral portion of the beam expander element  110 . The convex lens  109  is fixed to a frame (not shown) and the concave lens  108  is attached to a holder  801  and supported by guide shafts  802  provided on the right and left sides. The holder  801  is connected to a lead screw  804  of a stepping motor  803  and is moved in parallel in the optical axis direction  132  or  133  by the rotational motion of the lead screw  804 . A position detecting sensor  805  to detect the position in the optical axis direction of the holder  801  including the concave lens  108  is attached to the frame (not shown) so as to face the holder  801 . Reference numeral  806  denotes a reflecting surface provided for the holder  801 . The position detecting sensor  805  is designed so as to have characteristics in which an output voltage linearly changes in accordance with a distance between the position detecting sensor  805  and the reflecting surface  806 . Although a contactless reflecting type sensor is used as a position detecting sensor  805  in  FIG. 8 , it is also possible to use another type such as contactless transmitting type, contact type using a potentiometer, or the like. 
     In the embodiment, when the optical pickup is assembled, adjustment is made, for example, in steps  901  to  908  shown in  FIG. 9 . First, a first reference disc accurately manufactured so that the substrate thickness is set to the same value of 0.1 mm as that of the L 0  layer is used, an interferometer, a spot observing apparatus, or the like is used, the stepping motor  803  is driven so that the converging spot obtained by the objective lens  113  enters the optimum state, and the initial position of the concave lens  108  is adjusted. Or, the optical pickup is set into the state where the focusing servo can be performed, the stepping motor  803  is driven so as to maximize an amplitude of the RF signal or optimize a jitter value and an error rate value, and the initial position of the concave lens  108  is adjusted. In this state, electrical adjustment is made on a circuit  807  side of the position detecting sensor  805  so that a first predetermined voltage V 1  is outputted from the circuit  807  (for example, the predetermined voltage V 1  is recorded into the circuit  807  or the like). Subsequently, a second reference disc accurately manufactured so that the substrate thickness is set to the same value of 0.075 mm as that of the L 1  layer is used and the position of the concave lens  108  is adjusted so that the converging spot by the objective lens  113  is set into the optimum state or a jitter value and the error rate value are optimized. After that, electrical adjustment is made on the circuit  807  side so that a second predetermined voltage V 2  is outputted from the circuit  807  (for example, the predetermined voltage V 2  is recorded into the circuit  807  or the like). 
     The operation of the drive of the optical pickup adjusted as mentioned above is, for example, as shown in steps  1001  to  1010  in  FIG. 10  and will be explained hereinbelow also with reference to  FIG. 8 . When a power source of the drive is turned on, a drive controller  809  refers to the circuit  807  of the position detecting sensor  805  and a driver circuit  808  of the stepping motor  803 . The stepping motor  803  is driven while observing the output voltage from the circuit  807 . When the voltage V 1  is outputted, the stepping motor  803  is stopped. In this state, the blue-violet laser  101  is turned on and a focusing acquisition is performed to the L 0  layer. When the initial position in the optical axis direction of the concave lens  108  is the optimum position, a good S-character curve  1101  is obtained as shown in  FIG. 11A . 
     However, when the initial position in the optical axis direction of the concave lens  108  is deviated from the optimum position, the spherical aberration occurs in the light spot on the disc and the light spot cannot be converged. Thus, the focusing error signal deteriorates as shown by as S-character curve  1102  or  1103  in  FIG. 11B  (the amplitude is decreased and an offset occurs) and there is a risk of failure in the focusing acquisition. To avoid such a situation, the initial position of the concave lens  108  is forcedly determined so that the first predetermined voltage V 1  is outputted from the circuit  807  of the position detecting sensor  805  (as described above) before the focusing acquisition is performed to the L 0  layer. By this method, the good S-character curve is obtained as shown in  FIG. 11A  and the focusing acquisition operation can be stably started. Further, actually, since the substrate thickness of the L 0  layer has a variation depending on a radial direction position of the disc, there is a possibility of fluctuation of the optimum position of the concave lens  108 . For example, while the focusing control is made, the position of the concave lens  108  is finely adjusted so that the amplitude of the RF signal obtained by photodetector  118  for the BD is maximized or the jitter and error rate value are optimized. Such fine adjustment is made, for example, when radial direction position of the disc of the optical pickup is changed. Since information regarding the optimum position of the concave lens  108  is obtained by the driving operation so far, it is stored into the drive controller  809  together with an operation history. When the disc is ejected from the drive and the power source is again turned on from the off state of the power source of the drive, or when the power source is again turned on from the off state of the power source of the drive while the disc is inserted in the drive, the obtained information is immediately transferred to the circuit  807  and the driver circuit  808  from the drive controller  809 . By constructing the system as mentioned above, such an effect that the stable driving operation can be executed in a short time and the use efficiency is improved can be obtained. 
     The case of subsequently moving the focal point to the L 1  layer from the state where the L 0  layer is recorded/reproduced in the double-layered medium will now be described. At this time, the concave lens  108  is located at the optimum position at the substrate thickness of 0.1 mm of the L 0  layer. Even if it is intended to move the focal point to the L 1  layer in this state, since there is a substrate thickness difference of 0.025 mm between the L 1  layer and the L 0  layer, the converging spot on the disc is blurred. In this state, the characteristics are as shown by an S-character curve  1202  in  FIG. 12B  as compared with an S-character curve  1201  in  FIG. 12A  which is obtained when the focal point is in-focused to the L 1  layer and the focusing acquisition cannot be performed, so that there is a risk of failure in the movement of the focal point to the L 1  layer. Therefore, the optical pickup is operated, for example, as shown in steps  1301  to  1306  in  FIG. 13 . When a command to move the focal point to the L 1  layer is sent to the optical pickup from the drive controller  809 , the position of the concave lens  108  is forcedly moved so that the second predetermined voltage V 2  is outputted from the detecting circuit  807  of the position detecting sensor  805  (as described above) before the focusing acquisition is performed to the L 1  layer. If the optical pickup is set into such a state, the good converging spot is obtained in the L 1  layer, the characteristics are as shown in the S-character curve  1201  shown in  FIG. 12A , and the focusing acquisition operation can be stably started. Further, actually, since the substrate thickness of the L 1  layer also has a variation depending on the radial direction position of the disc, there is a possibility of fluctuation of the optimum position of the concave lens  108 . For example, the position of the concave lens  108  is finely adjusted in a manner similar to the method described before in the operation in the L 0  layer. Information regarding the position of the concave lens  108  in the L 1  layer obtained by the driving operation so far is stored into the drive controller  809  together with the operation history. When the focal point is again moved to the L 1  layer, the obtained information is immediately transferred to the optical pickup from the drive controller  809 . In this manner, the focal point can be stably moved to the L 1  layer. Since the optimum position information of the concave lens  108  in the L 0  layer and the L 1  layer were obtained by the driving operation so far, by referring to those information, the stable operation can be executed even in the continuous focal point movement along in the L 0  layer→L 1  layer→L 0  layer. Although the convex lens  109  is fixed and the concave lens  108  is set to be movable in the embodiment, contrarily, it is also possible to fix the concave lens  108  and set the convex lens  109  to be movable. 
     The case of the BD medium has been described above. A case of the DVD medium and the CD medium will be described hereinbelow. As shown in  FIG. 1 , the beam expander element  110  is arranged on a common optical path between the red laser  119  having the laser wavelength of the band of 660 nm, the infrared laser  129  having the laser wavelength of the band of 780 nm, and the objective lens  113 . Therefore, in the case of recording/reproducing the DVD medium or the CD medium, the position of the concave lens  108  is set to a position different from that in the case of the BD medium. In the case of the DVD medium, since the objective lens  113  is designed as described with reference to  FIG. 2B , the initial position of the concave lens  108  is set so that the red parallel light emitted from the collimator lens  124  enters the concave lens  108  and the parallel light from the convex lens  109  is emitted. For example, when a trial calculation is performed by using the expander element shown in 
     Table 1 at the wavelength of 660 nm, it is sufficient to set the concave lens  108  to the position which is away from the convex lens  109  in the optical axis direction by 2.08 mm. 
     On the other hand, in the case of the CD medium, since the objective lens  113  is designed as described with reference to  FIG. 2C , although the infrared parallel light emitted from the collimator lens  124  enters the concave lens  108 , the initial position of the concave lens  108  is set so that the predetermined designed divergent light  211  is emitted from the convex lens  109 . For example, the objective lens designed so that a virtual light emitting point is located at the position which is away from a principal plane of the objective lens  113  by 90 mm at the wavelength of 780 nm is presumed. When a trial calculation is performed by using such an objective lens and the expander element shown in Table 1, it is sufficient to set the concave lens  108  to the position which is away from the convex lens  109  in the optical axis direction by 0.32 mm. 
     When the optical pickup is assembled, adjustment is made, for example, in steps  1401  to  1408  shown in  FIG. 14 . First, in the case of the DVD, a DVD reference disc manufactured so that the substrate thickness is set to the same value of 0.6 mm as that of the DVD medium is used, the interferometer, spot observing apparatus, or the like is used, and the initial position of the concave lens  108  is adjusted so that the converging spot by the objective lens  113  enters the optimum state. Or, the optical pickup is set into the state where the focusing servo can be performed and the initial position of the concave lens  108  is adjusted so as to optimize the jitter value and the error rate value. In this state, electrical adjustment is made on the circuit  807  side so that a third predetermined voltage V 3  is outputted from the detecting circuit  807  of the position detecting sensor  805 . Subsequently, a CD reference disc accurately manufactured so that the substrate thickness is set to the same value of 1.2 mm as that of the CD medium is used and the initial position of the concave lens  108  is adjusted so that the converging spot by the objective lens  113  is set into the optimum state or the jitter value and the error rate value are optimized. In this state, electrical adjustment is made on the circuit  807  side so that a fourth predetermined voltage V 4  is outputted from the circuit  807  of the position detecting sensor  805 . 
     The operation of the drive of the optical pickup adjusted as mentioned above is, for example, as shown in steps  1501  to  1506  in  FIG. 15  and will be explained hereinbelow also with reference to  FIG. 8 . When the disc is loaded into the drive and it is determined that this disc is the DVD medium (CD medium), the drive controller  809  refers to the circuit  807  of the position detecting sensor  805  and the driver circuit  808  of the stepping motor  803 . The stepping motor  803  is driven so that the predetermined voltage V 3  (V 4 ) is outputted from the circuit  807 , thereby deciding the position of the concave lens  108 . In this state, the focusing acquisition is performed. When the focusing operation becomes unstable during the operation, the optical axis direction position of the concave lens  108  is finely adjusted. The information regarding the position of the concave lens  108  is obtained by the driving operation so far and stored into the drive controller  809  together with the operation history. When the disc is ejected from the drive and the DVD medium (CD medium) is again used, the obtained information is immediately transferred to the optical pickup from the drive controller (not shown). By constructing the system as mentioned above, such an effect that the stable driving operation can be executed in a short time and the use efficiency is improved can be obtained. 
     In the embodiment, in the state before the disc is loaded, the state of the optical element for spherical aberration correction is preset so that the converging spot on the disc is optimized at the substrate thickness of 0.1 mm. This substrate thickness of 0.1 mm is a condition in which it is presumed that it is a reference value of the substrate thickness in the single-layered disc and the first layer of the double-layered disc of the BDs and the use frequency is highest. Thus, such a preset state can be set to a start point of the spherical aberration correction and the spherical aberration correction control after the disc was loaded can be most efficiently made. 
     As an embodiment 2, the optical pickup in which two objective lenses of an objective lens for the BD and a DVD/CD-compatible objective lens are mounted and which can cope with each medium of the BD, DVD, and CD will be described.  FIG. 16  shows the first example in the embodiment. In this example, an objective lens  1601  for the BD and a DVD/CD compatible objective lens  1603  are mounted on an axial sliding actuator  1602  of a rotary type. The objective lens to be used is switched as shown by arrows  1604  in accordance with a kind of information recording medium  114 . The DVD/CD compatible objective lens  1603  is designed so as to optimize the state of the converging spot on the recording surface of the information recording medium  114  when the parallel light enters. For example, when a trial calculation is performed by using the expander element shown in Table 1 at the wavelength of 780 nm, it is sufficient to set the concave lens  108  to the position which is away from the convex lens  109  in the optical axis direction by 2.1 mm. Since an optical system up to the objective lens  1601  for the BD or the DVD/CD compatible objective lens  1603  is common to that in  FIG. 1  of the embodiment 1 and has already been described in the embodiment 1, its explanation is omitted here. 
       FIG. 18  shows the second example in the embodiment. In the diagram, an X axis, a Y axis, and a 
     Z axis indicate a tangential direction, a radial direction, and a surface oscillating direction of the information recording medium, respectively. The upper stage shows an XY plan view and the lower stage shows an XZ plan view. In this example, the objective lens  1601  for the BD and the DVD/CD compatible objective lens  1603  are arranged in parallel with the X axis and mounted on a lens holder  1801  and a fine translation driving in the Y-axis direction and the Z-axis direction in the diagram and a fine rotational driving around the X axis and the Y axis can be performed by an actuator (not shown) including a driving coil  1802 . 
     The divergent light emitted from the blue-violet laser  101  passes through the polarization beam splitter  105 , is converted into the parallel light by the collimator lens  106  for the BD, reflected by a return mirror  1804 , transmitted through the beam expander element  110 , and reflected by a rising mirror  1803 . After that, the light passes through the quarter wave plate  112 , is converged by the objective lens  1601  for the BD, and reaches the information recording surface of the information recording medium  114  (in this case, the BD medium having one, two, or more recording layers). A part of the divergent light emitted from the blue-violet laser  101  is reflected by the polarization beam splitter  105 , is converged by the lens  115 , and reaches the front monitor  116  for the BD, and a light emission amount of the blue-violet laser  101  is monitored. The reflection return light from the information recording medium  114  passes through the objective lens  1601  for the BD and the quarter wave plate  112 , reflected by the rising mirror  1803 , transmitted through the beam expander element  110 , and reflected by the return mirror  1804 . After that, the light passes through the collimator lens  106 , is reflected by the polarization beam splitter  105 , is converged by the detecting lens  117 , and reaches a detecting surface of the photodetector  118  for the BD. 
     After the divergent light emitted from the red laser  119  passes through the synthetic prism  122 , it is reflected by the half mirror  123 . Parallel light is irradiated from a collimator lens  1805 . After that, the resultant light is reflected by the rising mirror  1803 , converged by the DVD/CD compatible objective lens  1603 , and reaches the information recording surface of the information recording medium  114  (in this case, the 
     DVD medium having one or two recording layers). The reflection return light from the information recording medium  114  passes through the DVD/CD compatible objective lens  1603 , is reflected by the rising mirror  1803 , and is transmitted through the collimator lens  1805  and the half mirror  123 . The light is converged by the detecting lens  127  and reaches the photodetecting surface of the photodetector  128  for the DVD/CD. 
     The divergent light emitted from the infrared laser  129  having the laser wavelength of the band of  780  nm is reflected by the synthetic prism  122  and the half mirror  123  and the parallel light is emitted from the collimator lens  1805 . After that, it is reflected by the rising mirror  1803 , is converged by the DVD/CD compatible objective lens  1603 , and reaches the information recording surface of the information recording medium  114  (in this case, the CD medium). Since the optical path until the reflection return light from the information recording medium  114  reaches the photodetecting surface of the photodetector  128  for the DVD/CD is substantially the same as that of the DVD optical system of the red laser  119 , its description is omitted here. 
       FIG. 19  shows the third example in the embodiment. In the diagram, the X axis, Y axis, and Z axis indicate the tangential direction, radial direction, and surface oscillating direction of the information recording medium, respectively. The upper stage shows an XY plan view and the lower stage shows a YZ plan view. In this example, the objective lens  1601  for the BD and the DVD/CD compatible objective lens  1603  are arranged in parallel with the Y axis and mounted on a lens holder  1901  and a fine translation driving in the Y-axis direction and the Z-axis direction in the diagram and a fine rotational driving around the X axis and the Y axis can be performed by an actuator (not shown) including a driving coil  1904 . A rising mirror  1902  for the BD reflects the BD light entering from the −X direction in the diagram and allows it to enter the objective lens  1601  for the BD. A rising mirror  1903  for the DVD/CD reflects the DVD/CD light entering from the Y direction in the diagram and allows it to enter the DVD/CD compatible objective lens  1603 . Since the other optical path is substantially the same as that in the second example, its description is omitted here. 
       FIG. 20  shows the fourth example in the embodiment. In the diagram, the X axis, Y axis, and Z axis indicate the tangential direction, radial direction, and surface oscillating direction of the information recording medium, respectively. A broken line section  2001  at the upper stage shows the optical pickup for the DVD/CD on which the DVD/CD optical system has been mounted. A broken line section  2002  at the lower stage shows the optical pickup for the BD on which the BD optical system has been mounted. Those optical pickups are enclosed in different pickup casings (not shown). 
     Although the red laser  119  and the infrared laser  129  are separately provided in  FIGS. 16 ,  18 ,  19 , and  20 , a double-wavelength laser in which those lasers are integrated can be used in order to simplify the optical system. For example, an optical system in which the blue-violet laser  101  and the red laser  119  have been mounted without using the infrared laser  129  can be also used in accordance with the specification of the drive. 
     The examples of the optical pickups have been described in the embodiments 1 and 2. An embodiment of an optical information recording and reproducing device on which the foregoing optical pickup has been mounted will now be described.  FIG. 17  shows a schematic block diagram of an information recording and reproducing device  1701  for executing reproduction or recording/reproduction of information. Reference numeral  1702  denotes an optical pickup described in the embodiments 1 and 2. A signal detected from the optical pickup  1702  is sent to a servo signal generating circuit  1703  and an information signal reproducing circuit  1704  in a signal processing circuit. In the servo signal generating circuit  1703 , a focusing control signal, a tracking control signal, and a spherical aberration detection signal suitable for an optical disk medium  1705  are formed from the signal detected by the optical pickup  1702 . On the basis of those signals, an ACT (not shown) in the optical pickup  1702  is driven by an ACT driving circuit  1706 , thereby controlling the position of an objective lens  1707 . In the servo signal generating circuit  1703 , the spherical aberration detection signal is generated from the optical pickup  1702 . On the basis of this signal, a correcting lens of a beam expander element (not shown) in the optical pickup  1702  is driven by a spherical aberration correction driving circuit  1708 . In the information signal reproducing circuit  1704 , an information signal recorded on the optical disk  1705  is reproduced from the signal detected from the optical pickup  1702 . The information signal is outputted to an information signal output terminal  1709 . A part of the signals obtained by the servo signal generating circuit  1703  and the information signal reproducing circuit  1704  are sent to a system control circuit  1710 . A recording signal for laser driving is sent from the system control circuit  1710  and a laser light source turn-on circuit  1711  is driven, thereby controlling the light emission amount and recording the recording signal onto the optical disk  1705  through the optical pickup  1702 . An access control circuit  1712  and a spindle motor driving circuit  1713  are connected to the system control circuit  1710  and radial direction position control of the optical pickup  1702  and rotation control of a spindle motor  1714  of the optical disk  1705  are made, respectively. In the case where the user makes control by a personal computer, a recorder for AV, or the like, he gives an instruction to a user input processing circuit  1715  from a user input device  1718  such as keyboard, touch panel, jog dial, or the like, thereby controlling the information recording and reproducing device  1701 . At this time, a processing state or the like of the information recording and reproducing device  1701  is processed by a display processing circuit  1716  and displayed by a display device  1717  such as liquid crystal panel, CRT, or the like. 
     While we have shown and described several embodiments in accordance with our invention, it should be understood that disclosed embodiments are susceptible of changes and modifications without departing from the scope of the invention. Therefore, we do not intend to be bound by the details shown and described herein but intend to cover all such changes and modifications within the ambit of the appended claims.