Abstract:
An optical disc apparatus includes a light source for emitting laser light, a light source drive unit for driving said light source, an optical element for splitting the laser light into a plurality of light fluxes, an optical element drive unit for controlling the optical element, an element for focusing the laser light onto the optical disc, and a detection unit for detecting the laser light reflected by the optical disc. Reproduction of the optical disc is performed by switching effectiveness and ineffectiveness of a function of splitting the light flux of the optical element, and adjustment of an outgoing laser power is performed.

Description:
INCORPORATION BY REFERENCE 
     The present application claims priority from Japanese application JP-2009-192721 filed on Aug. 24, 2009, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an optical disc apparatus for reproducing an optical disc using laser light. 
     As background technology, for example, there is technology disclosed in JP-A-8-30989. In JP-A-8-30989, it is disclosed a method where “a tracking error signal by a push-pull method is selected in tracking-servo leading-in”, and “tracking control is performed based on tracking error signals by a three-beam method after servo leading-in”. 
     SUMMARY OF THE INVENTION 
     In reproducing an optical disc, as a method for making a light spot following a track on the optical disc, there have been used a DPP (differential Push-Pull) method or a three-beam method. The DPP method is a method for splitting laser light to a main beam (light flux) and sub-beams using a diffraction grating, and generating a main push-pull signal by the main beam, and a sub-push-pull signal by the sub-beams. By multiplying the sub-push-pull signal by a coefficient to compensate sensitivity for a lens shift, and using a signal subtracted from the main push-pull signal as the tracking error signal, an offset caused by the lens shift can be compensated, and the light spot can be made to follow the center of a track. The three-beam method is a method for splitting the laser light to the main beam and the sub-beams by using the diffraction grating, in which an intensity change of the signal generated by the sub-beams is used as the tracking error signal. 
     In the DPP method or the three-beam method, the main beam is used for recording and reproduction, and the sub-beams are used only for tracking servo. Because the power control of the laser light is performed for laser light usually before the beam splitting, when a light intensity ratio of the main beam and the sub-beams differs from a designed value, there is a problem of deterioration of recording and reproduction performance. That is, when the light intensity of the main beam is high, signals which have been recorded in a disc could be deteriorated, while in the case of low light intensity, the deterioration of reproduction performance is generated by a decrease in signal amplitude. Such deviation from the designed value is caused by a variation of the characteristics of the diffraction grating, or the like. 
     It is an object of the present invention to provide an optical disc apparatus or an optical disc reproducing method, which is capable of compensating the variation of the light intensity ratio of the main beam and the sub-beams. 
     The above object can be achieved, as one example, by the invention described in the appended claims. 
     According to the present invention, it is possible to compensate the variation of light intensity ratio of the main beam and the sub-beams, and obtain reproduction performance according to a designed value. 
     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a block configuration diagram representing one embodiment of an optical disc apparatus according to the present invention. 
         FIG. 1B  is a configuration diagram of a detector of an optical disc apparatus according to the present invention. 
         FIG. 2A  is an example of a schematic view of a light spot on a recording-type optical disc. 
         FIG. 2B  is an example of a schematic view of a light spot on a reproduction exclusive optical disc. 
         FIG. 3  is an example of a flow chart from inserting an optical disc into an optical disc apparatus according to the present invention to starting reproduction. 
         FIG. 4  is an example of a flow chart representing actions of an optical disc apparatus according to the present invention, when temperature varies from starting of reproduction. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Explanation will be given below on embodiments of the present invention with reference to drawings. 
     It should be noted that, “outgoing power” hereafter represents the power of laser light outwent from an objective lens. In addition, “emission power” represents the power of laser light which a laser diode emits. 
     EXAMPLE 1 
       FIG. 1A  is a block configuration diagram showing one embodiment of an optical disc apparatus according to the present invention. Here, descriptions on blocks not participating directly to the present embodiment were omitted. 
     A microcomputer  101  performs communication with a host apparatus such as a PC through an interface such as ATAPI not shown. In addition, the microcomputer  101  performs emission control for a laser driver  102 , and the laser driver  102  outputs current to drive a laser diode  103  corresponding to a control of the microcomputer  101 . The laser diode  103  emits an emission power corresponding to a drive current of the laser driver  102 . A power monitor  105  detects an emission power of the laser diode  103  via a beam splitter  104 , converts the detected power to a voltage value, and outputs it to the microcomputer  101 . The emission power detected here is a total light intensity before splitting the laser light using a diffraction grating  106 . The diffraction grating  106  switches the laser light to one beam and three beams corresponding to a control of a diffraction grating driver  107 . As a method for switching the one beam and the three beams, for example, it is considered a method for inserting and pulling out the diffraction grating  106  in a laser light path. An element to switch the laser light to the one beam and the three-beams is not especially limited to by the inserting and pulling out the diffraction grating mechanically in this way, but the laser light may be switched to the one beam and the three-beams by switching characteristics of an optical element by an optical element or an electrical element. An objective lens  108  focuses the laser light onto an optical disc  109 . 
     The laser light reflected at the optical disc  109  retains disc information as a light intensity. In performing reproduction, the laser light is reflected by a polarizing beam splitter  110 , and focused onto the detector  111 . The detector  111  detects the laser light focused, and outputs a signal corresponding to the intensity of the laser light to a waveform equalizer  112 . The waveform equalizer  112  performs a processing such as equalization, amplification for a signal waveform detected by the detector  111 , and outputs the signal waveform to a signal processor  113 . The signal processor  113  performs a signal processing such as analogue/digital conversion, equalization, and decoding, for the signal waveform output by the waveform equalizer  112 , and outputs a data thus decoded to the microcomputer  101 . 
     In an example of  FIG. 1A , blocks  102  to  108 ,  110  and  111  within a frame indicated by a dotted line shall be mounted on an optical pickup. It should be noted that, although  FIG. 1A  showed an example of mounting the laser diode  103  and the power monitor  105  in a separated way, a power monitor may be packaged, and a laser diode which outputs the detected power to the microcomputer  101  may be used. In addition, in the present specification, an example of controlling the diffraction grating  106  by the diffraction grating driver  107  was shown, however, the diffraction grating  106  may be driven by the microcomputer  101  without using the diffraction grating driver  107 . In addition, although an example of the diffraction grating  106  was shown as an element to split the laser light, however, the laser light may be split using a liquid crystal element or the like. 
       FIG. 1B  is an example representing the detector  111  in detail. The detector  111  is provided with a main detector  114  which receives reflected light of the main beam, and a sub-detector  115  which receives reflected light of the sub-beams. 
       FIG. 2A  shows a schematic view of a light spot focused onto an optical disc when the function of the diffraction grating was made effective. On the optical disc, a groove  201  and a land  202  are engraved, and they function as guides to make the optical spot followed.  203  and  204  each represents the optical spot of the main beam and the sub-beams split using the diffraction grating, and the light intensity ratio of both is typically about 15:1. Reflected light of the main beam is received at the main detector  114  of  FIG. 1B , and reflected light of the sub-beams is received at the sub-detector  115 . Because a reproduced signal is generated only at the main-detector  114 , when the light intensity ratio of the main beam to the sub-beams is smaller than a designed value, reduction of reproduction performance is incurred. On the other hand, when the light intensity ratio of the main beam is higher than a designed value, data which has been recorded on the optical disc could be erased. The sub-detector generates a sub-push-pull signal in the case of the DPP method, and in the case of the three-beam method, it generates a tracking error signal. Because only one beam outwent from the objective lens, when the function of the diffraction grating was made ineffective, only the spot  203  by the main beam is light-focused on the optical disc. 
     Here, although an example in which data is recorded in the groove  201  was shown in the present specification, it may be recorded in the land  202 , or it may be recorded in both of the groove and the land. 
     In addition, although  FIG. 2A  represented an example of a recording-type optical disc, in the case of a read-only compact disc, pits  205  function as a guide as represented in  FIG. 2B . 
       FIG. 3  represents an example of a flow chart from inserting an optical disc into the optical disc apparatus according to the present invention to starting reproduction. Here, descriptions on actions not directly participating to the present embodiment were omitted. 
     In a step  301 , a disc is loaded. In a step  302 , laser light is emitted. In a step  303 , the function of the diffraction grating is made ineffective, and one beam outgoes from the objective lens. The outgoing power in this case can be adjusted to a desired power of, for example, 0.3 mW or the like, by monitoring with the power monitor  105  in  FIG. 1A . After starting servo-control such as focus or tracking in a step  304 , an amplitude of a reproduced signal is measured in a step  305 . In a step  306 , the function of the diffraction grating is made effective to form the three beams. In a step  307 , the reproduced signal amplitude is measured, while maintaining the emission power of the laser in the step  302  as it is. By comparing the reproduced signal amplitude in this case and the reproduced signal amplitude measured in the step  305 , the light intensity ratio of the main beam and the sub-beams can be obtained. For example, when the reproduced signal amplitude measured in the step  305  was 300 mV, and the reproduced signal amplitude measured in the step  307  was 250 mV, it is understood that the light intensity ratio of the main beam and the sub-beams (sub:main:sub) is 1:10:1. In a step  308 , the outgoing power of the laser light is adjusted, based on the light intensity ratio thus obtained. As described above, when the light intensity ratio of the main beam and the sub-beams is 1:10:1, for example, in order to outgo the main beam at an intensity of 0.3 mW, the total outgoing power may be adjusted so as to be 0.36 mW. After performing the above adjustment, reproduction is started in a step  309 . Here, a place for measuring the reproduced signal amplitude may be a user data region, or may be a place where a signal for test has been recorded in advance such as an OPC region or a pre-write region. 
     As described above, the light intensity ratio of the main beam and the sub-beams can be obtained by switching the function of effective-ineffective of the diffraction grating and reproduction at the desired reproduction power is possible, so that the quality or the reliability of reproduction can be improved. 
     In addition, a data reproduced by switching the one beam and the three beams may be a user data in the user data region, or may be a data in a trial writing region used in the adjustment of the recording power or the like. 
       FIG. 4  shows an example of a flow chart representing actions of the optical disc apparatus according to the present invention, when temperature varies from starting reproduction. 
     In a step  401 , reproduction is started. In a step  402 , an internal temperature of the optical disc apparatus is measured, for example, with a sensor installed inside a drive, or a sensor installed at the optical pickup. A specific portion for measuring the temperature comprises the peripherals of an element with high temperature dependency, such as the laser diode, the diffraction grating, the liquid crystal element. When the temperature measured in the step  402  has changed equal to or more than a specified value of temperature measured at the previous measurement time, the diffraction grating is made ineffective in a step  403 , and the reproduced signal amplitude is measured in a step  404 . In a step  405 , the diffraction grating is made effective, and the reproduced signal amplitude is measured in a step  406 . By comparing the reproduced signal amplitude in this case and the reproduced signal amplitude measured in the step  404 , a light intensity ratio of the main beam and the sub-beams can be obtained. In a step  407 , outgoing power of the laser light is adjusted, based on the light intensity ratio obtained, and the reproduction is started in a step  408 . For the measurement of the reproduced signal amplitude, the user data region may be used, or it may be performed by transferring it to a place where a signal for testing has been recorded in advance, such as the OPC region, or the pre-write region. In addition, before making the diffraction grating ineffective in the step  403 , the emission power of the laser diode may be decreased to a predetermined value. This is because of the prevention of deterioration of the signal recorded in the disc due to an increased outgoing power by outgoing in one beam. 
     Although, in the present specification, an example of adjusting the outgoing laser power when the temperature changed was shown, the adjustment may be performed also when the action was changed from recording to reproduction. This is because the recording is considered to increase the temperature of the laser diode and change the emission characteristics. 
     It should be noted that, the present invention should not be limited to the above embodiments, and should contain various modified embodiments. For example, the above embodiments are those for explaining the invention in detail so as to explain the present invention for easy-understanding, and therefore, the present invention should not necessarily be limited to the one provided with all configurations explained. In addition, it is possible to substitute a part of a configuration of a certain embodiment with a configuration of other embodiment, and it is also possible to add a configuration of other embodiment to a configuration of a certain embodiment. In addition, it is possible to add, delete or substitute other configurations for a part of a configuration of each embodiment.