JP2010009727A - Optical pickup and optical disk device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup for preventing variation in power of optical beams emitted from a light source caused by variation in coupling efficiency of the optical pickup during reproduction, and suppressing variations in laser noise, peak power during high frequency superimposition and the life of the light source, and to provide an optical pickup device. <P>SOLUTION: The optical pickup includes a light source 31, an objective lens 32 for converging optical beams emitted from the light source 31 on an optical disk 2, and an optical attenuator disposed between the light source 31 and the objective lens 32 to attenuate the amount of the optical beam emitted from the light source 31 to guide the optical beam to the objective lens 32. The optical attenuator includes a liquid crystal element 34 for changing the polarized state of the optical beam and a polarization separation part 35a receiving the optical beam passing through the liquid crystal element 34. An optical attenuation factor is variably reduced by changing the polarized state of the optical beam by the liquid crystal element 34. The optical attenuator is controlled so as to have an optical attenuation factor corresponding to variation in coupling efficiency of the optical pickup. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical pickup that records and / or reproduces an information signal on an optical disc, and an optical disc apparatus using the optical pickup.

  Recent optical discs are remarkable for high density and high transfer technology. For example, an optical disc capable of recording and reproducing signals using a light beam having a wavelength of about 405 nm by a violet semiconductor laser such as a BD (Blu-ray Disc (registered trademark)) (hereinafter referred to as “high-density recording optical disc”). Is proposed).

  In addition, as the transfer rate has been increased, as the example of CD (Compact Disc) and DVD (Digital Versatile Disc) has been increased, the double speed has already been put to practical use in, for example, the professional disc system XDCAM. ing. In the future, there is a tendency to shift to 4 × speed and 8 × speed. When the speed is increased, it is obvious that the required recording light power at that time increases, and more so, in the case of a multilayer optical disc having two or more layers.

  In such an optical pickup that performs recording and / or reproduction with respect to an optical disk capable of high density and high transfer, the problem is the reliability of the laser, that is, the lifetime.

  The reliability of the laser depends on the laser case temperature and the output light power, and the reliability tends to be inferior when the multi-layer optical disk has a high transfer rate. Here, it is generally known that reliability is improved by lowering the laser case temperature or reducing the output power.

  On the other hand, laser noise, which is one of noise factors when reproducing an optical disk, depends on output power, and the laser power decreases as the output power increases. This point will be described with reference to FIG. In FIG. 9, the horizontal axis indicates the laser power (hereinafter also referred to as “original power”) of the light beam emitted from the light source, and the vertical axis indicates RIN (dB / Hz) corresponding to the original power (original power). Is shown. Here, RIN (Relative Intensity Noise) indicates a value per 1 Hz of a relative value of fluctuation power with respect to a certain laser power. Such a curve indicating the relationship between the laser power and the RIN is also referred to as “Power vs Rin curve” below. According to FIG. 9, the laser noise depends on the output power, and it can be confirmed that the laser noise decreases as the output power increases.

  Further, during reproduction, high frequency superposition is generally applied in order to eliminate the influence of the return light to the laser. Here, the relationship between the high frequency superimposed waveform and the original power of the laser will be described with reference to FIGS. 10 shows a high frequency superimposed waveform when the laser source power is 2.5 mW, and FIG. 11 shows a high frequency superimposed waveform when the laser source power is 4.5 mW. 10 and 11, the vertical axis indicates the objective lens output power [mW], and W10 and W11 each indicate a high frequency superposition frequency, for example, about 300 MHz. When the original power is small, the high-frequency superimposed waveform is unimodal (first relaxation vibration) and has a large peak power, as shown in FIG. However, in this high frequency superimposed waveform, when the original power is increased from the state shown in FIG. 10, the second and third so-called humps of the relaxation vibration, that is, the rising portion of the power is generated as shown in FIG. As a result, the peak power decreases. Such a hump starts to appear at a point where the RIN slightly deteriorates from a monotonous decrease in the Power vs RIN curve. For example, in FIG. 9, the portions are about 3 mW and 5.5 mW. This is apparent with reference to the light emission waveform at the time of high frequency superposition shown in FIGS.

  The peak power at the time of high frequency superimposition is related to the reproduction durability, that is, the degree of deterioration of recorded data when the same track is still, and is also defined in the BD standard. The laser of the BD system is a blue-violet laser with a wavelength of 405 nm, and the noise of the laser itself is generally larger than that of a red laser with a wavelength of about 650 nm used for DVDs and the like.

  For example, an optical attenuator consisting of a liquid crystal element, ND filter, etc. was adopted as a method for constructing a system that realizes high output during recording and low noise during reproduction to support high transfer / multilayer optical disks. There is something. This is because an element having a different transmittance, in other words, a light attenuation factor, is inserted in the middle of the optical path, and at the time of recording, the transmittance is increased, that is, the light attenuation factor is reduced to reduce the light attenuation factor. High power is obtained. On the other hand, at the time of reproduction, the laser power is increased by reducing the transmittance, that is, by increasing the attenuation factor, thereby reducing the laser noise.

  This optical attenuator is realized by, for example, a method of mechanically switching between two types of ND filters having transmittance, or a method of switching the attenuation rate by switching the voltage applied to the liquid crystal element.

  The mechanical optical attenuator is a method of switching between two types of transmittance, that is, using one having a large transmittance during recording and one having a small transmittance during reproduction. In general, an optical attenuator composed of a liquid crystal element is one that changes an attenuation factor according to an applied voltage. However, two types of voltages corresponding to two modes for reproduction and recording are switched and used. . That is, in both of the systems, a fixed attenuation rate is set at the time of reproduction and at the time of recording.

  However, if the attenuation factor is fixed at the time of reproduction, for example, the laser original power is different even if the same reproduction power is obtained due to the optical efficiency inherent in the optical pickup. The optical efficiency of this optical pickup is also called coupling efficiency, and is determined by the divergence angle of a light beam such as laser light emitted from a light source, the transmittance and optical loss of the optical components constituting the optical pickup, and the like. That is, if the original power of the light source varies, there is a problem that the laser noise, the peak power of the high frequency superimposed waveform, the life, etc. vary, which affects the system performance.

Japanese Patent Application Laid-Open No. 2004-272962

  The object of the present invention is to make the operating point of the power of the light beam emitted from the light source during reproduction due to variations in the coupling efficiency unique to the optical pickup substantially constant, laser noise, peak power at the time of high frequency superimposition, and light source lifetime. It is an object to provide an optical pickup and an optical disc apparatus that can suppress the variation of the optical disc.

  In order to solve the above-described problems, an optical pickup according to the present invention includes a light source that emits a light beam having a predetermined wavelength, an objective lens that collects the light beam emitted from the light source on the optical disc, and a reflection by the optical disc. A photodetector that detects the reflected light beam, and an optical attenuator that is provided between the light source and the objective lens, and that attenuates the amount of the light beam emitted from the light source and guides it to the objective lens. The optical attenuator includes a liquid crystal element that changes a polarization state of the light beam, and a polarization separation unit on which the light beam that has passed through the liquid crystal element is incident, and the polarization state of the light beam is changed by the liquid crystal element. By changing the optical attenuation factor, the optical attenuation factor is variably attenuated, and the optical attenuator is controlled to have an optical attenuation factor corresponding to the variation in the coupling efficiency of the optical pickup.

  An optical disc apparatus according to the present invention includes a drive unit that holds and rotates an optical disc, and an optical pickup that records and / or reproduces an information signal with respect to the optical disc that is rotationally driven by the drive unit. The optical pickup used in this optical disc apparatus is the same as described above.

  The present invention realizes the suppression of laser noise, peak power at the time of high frequency superposition, and life variation by changing the optical attenuation factor with an optical attenuator according to the coupling efficiency of the optical pickup, and good recording Realize playback characteristics.

  Hereinafter, an optical pickup and an optical disc apparatus to which the present invention is applied will be described in detail with reference to the drawings. The embodiments described below are specific examples, and the scope of the present invention is not limited to these embodiments.

  As shown in FIG. 1, an optical disc apparatus 1 to which the present invention is applied includes an optical pickup 3 for recording and reproducing information on an optical disc 2 as an optical recording medium, and a spindle motor as a driving means for rotating the optical disc 2. 4. The optical disc apparatus 1 also includes a feed motor 5 that moves the optical pickup 3 in the radial direction of the optical disc 2 as a drive unit for the optical pickup 3.

  The optical disk 2 used here is, for example, an optical disk such as a CD (Compact Disc), a CD-R (Recordable), a CD-RW (ReWritable) using a semiconductor laser having an emission wavelength of about 785 nm. The optical disc 2 is, for example, an optical disc such as a DVD (Digital Versatile Disc), DVD-R (Recordable), DVD-RW (ReWritable), DVD + RW (ReWritable) using a semiconductor laser having an emission wavelength of about 655 nm. The optical disc 2 is a high-density recording optical disc such as a BD (Blu-ray Disc (registered trademark)) capable of high-density recording using a semiconductor laser having a shorter emission wavelength of about 405 nm (blue-violet).

  In the optical disc apparatus 1, the spindle motor 4 and the feed motor 5 are driven and controlled in accordance with the disc type by a servo control unit 9 that is controlled based on a command from a system controller 7 that also serves as disc type discriminating means. At this time, the optical disc 2 is driven at a predetermined rotational speed.

  The optical pickup 3 irradiates the recording surface of the optical disc 2 with a light beam, and detects the reflected light beam from the recording surface of this light beam. The optical pickup 3 supplies a signal corresponding to each light beam to the preamplifier 14 based on the reflected light beam from the recording surface of the optical disc 2.

  The preamplifier 14 generates a focus error signal by an astigmatism method or the like based on an output from the photodetector, and generates a tracking error signal by a three beam method, a DPD method, a DPP method, or the like. Further, the preamplifier 14 generates an RF signal and outputs the RF signal to the signal modulation & ECC block 15. Further, the preamplifier 14 outputs a focus error signal and a tracking error signal to the servo control unit 9.

  The signal modulation & ECC block 15 performs the following processing on the digital signal input from the interface 16 or the D / A / A / D converter 18 when recording data on an optical disc such as a BD. I do. Specifically, the signal modulation & ECC block 15 performs error correction processing using an error correction method such as LDC-ECC and BIS, and then performs modulation processing such as the 1-7PP method. The signal modulation & ECC block 15 performs error correction processing according to an error correction method such as PC (Product Code) when recording data on an optical disk such as a DVD, and then performs modulation processing such as 8-16 modulation. Do. Further, when recording data on an optical disk such as a CD, the signal modulation & ECC block 15 performs error correction processing by an error correction method such as CIRC, and then performs modulation processing such as 8-14 modulation processing. Then, the signal modulation & ECC block 15 outputs the modulated data to the laser control unit 21. Further, when reproducing each optical disk, the signal modulation & ECC block 15 performs demodulation processing based on the RF signal input from the preamplifier 14, further performs error correction processing, and converts the interface 16 or data to D / A. , Output to the A / D converter 18.

  When data is compressed and recorded, a compression / decompression unit may be provided between the signal modulation & ECC block 15 and the interface 16 or the D / A / A / D converter 18. In this case, the data is compressed by a method such as MPEG2 or MPEG4.

  The servo controller 9 receives a focus error signal and a tracking error signal from the preamplifier 14. The servo control unit 9 generates a focus servo signal and a tracking servo signal so that the focus error signal and the tracking error signal become zero, and an objective lens such as a biaxial actuator that drives the objective lens based on these servo signals. Drive control of the drive unit. Further, a synchronization signal or the like is detected from the output from the preamplifier 14, and the spindle motor is servo-controlled by CLV (Constant Linear Velocity), CAV (Constant Angular Velocity), or a combination of these. The servo control unit 9 controls the optical attenuation rate in the optical pickup 3 in accordance with the type of the optical disk 2 to be recorded and / or reproduced, the LCD monitor result as described later, and the like.

  The laser control unit 21 controls the laser light source of the optical pickup 3. In particular, in this specific example, the laser control unit 21 performs control to vary the output power of the laser light source between the recording mode and the reproduction mode. Further, it is possible to perform control so as to vary the output power of the laser light source depending on the type of the optical disc 2. In this case, the laser control unit 21 switches the laser light source of the optical pickup 3 in accordance with the type of the optical disc 2 detected by the disc type determination unit 22.

  The disc type discriminating unit 22 can detect a different format of the optical disc 2 by detecting a change in the amount of reflected light from the surface reflectance between optical discs, the difference in shape and shape, and the like.

  Each block constituting the optical disc apparatus 1 is configured to be able to perform signal processing based on the specification of the optical disc 2 to be mounted, according to the detection result in the disc type discriminating unit 22.

  The system controller 7 controls the entire apparatus according to the type of the optical disk 2 determined by the disk type determination unit 22. The system controller 7 performs control based on address information and table information (TOC) recorded in premastered pits and grooves in the innermost periphery of the optical disc in response to an operation input from the user. Here, the system controller 7 specifies a recording position and a reproduction position of the optical disc on which recording and reproduction are performed, and controls each unit based on the identified position.

  The optical disk apparatus 1 configured as described above rotates the optical disk 2 by the spindle motor 4 and drives and controls the feed motor 5 in accordance with a control signal from the servo control unit 9. The optical disc apparatus 1 records and reproduces information with respect to the optical disc 2 by moving the optical pickup 3 to a position corresponding to a desired recording track of the optical disc 2.

  Specifically, when recording / reproducing is performed by the optical disc apparatus 1, the servo control unit 9 rotates the optical disc 2 by CAV, CLV, or a combination thereof. The optical pickup 3 irradiates a light beam from a light source, detects a returning light beam from the optical disc 2 by a photodetector, and generates a focus error signal and a tracking error signal. The optical pickup 3 performs focus servo and tracking servo by driving the objective lens by the objective lens driving mechanism based on the focus error signal and the tracking error signal.

  When recording is performed by the optical disc apparatus 1, a signal from the external computer 17 is input to the signal modulator / demodulator & ECC block 15 through the interface 16. The signal modulator / demodulator & ECC block 15 adds a predetermined error correction code as described above to the digital data input from the interface 16 or the A / D converter 18, and further performs a predetermined modulation process and then a recording signal. Is generated. The laser control unit 21 controls the laser light source of the optical pickup 3 based on the recording signal generated by the signal modulator / demodulator & ECC block 15 and records it on a predetermined optical disk.

  When the information recorded on the optical disc 2 is reproduced by the optical disc apparatus 1, the signal modulator / demodulator & ECC block 15 demodulates the signal detected by the photodetector. If the recording signal demodulated by the signal modulator / demodulator & ECC block 15 is for data storage of a computer, it is output to the external computer 17 via the interface 16. Accordingly, the external computer 17 can operate based on the signal recorded on the optical disc 2. If the recording signal demodulated by the signal modulator / demodulator & ECC block 15 is for audio / visual use, it is converted from digital to analog by the D / A converter 18 and supplied to the audio / visual processing unit 19. The audio / visual processing unit 19 performs audio / visual processing and outputs the audio / visual signal to an external speaker or monitor (not shown) via the audio / visual signal input / output unit 20.

  Next, the optical pickup 3 used in the above-described optical disc apparatus will be described in detail with reference to FIG.

  As shown in FIG. 2, an optical pickup 3 to which the present invention is applied condenses a light source 31 such as a semiconductor laser element that emits laser light of a predetermined wavelength and a light beam emitted from the light source 31 onto an optical disc 2. An objective lens 32. The optical pickup 3 includes an anamorphic prism having a collimator lens 33, a liquid crystal element (hereinafter also referred to as “LCD”) 34, and a polarization beam splitter film surface 35 a between the light source 31 and the objective lens 32. 35.

  The polarization beam splitter film surface 35a transmits part of the incident light beam according to the polarization state of the incident light beam and reflects the remaining light beam, and functions as a polarization separation unit. The liquid crystal element 34 changes the polarization state of the light beam. The liquid crystal element 34 and the polarization beam splitter film surface 35a change the polarization state of the light beam by the liquid crystal element 34, and adjust the amount of light beam that travels to the optical disc 2 side through the polarization beam splitter film surface 35a. To do. That is, here, the polarization beam splitter film surface 35a adjusts the amount of light beam transmitted to the optical disc 2 side when the light beam whose polarization state is changed by the liquid crystal element 34 is incident. As described above, the liquid crystal element 34 and the polarization beam splitter film surface 35 a function as an optical attenuator that attenuates the light amount of the light beam emitted from the light source 31. The ratio of attenuation by the optical attenuator, that is, the optical attenuation ratio is obtained by subtracting from 1 the ratio of the amount of light beam guided to the optical disc 2 side with respect to the amount of light beam emitted from the light source 31 and incident. It is. The attenuation may include a state where light is transmitted as it is, that is, a state where the light attenuation factor is zero. In other words, the optical attenuator is condensed on the optical disk 2 with respect to the total light amount emitted from the light source 31 by changing the polarization state of the light beam by the liquid crystal element 34 and attenuating the light beam at a predetermined ratio. The optical coupling efficiency, which is the ratio of the amount of light to be changed, is changed.

  The optical attenuator controls the liquid crystal element 34 in the recording mode to decrease the optical attenuation factor, and controls the liquid crystal element 34 in the reproduction mode to increase the optical attenuation factor.

  This optical attenuator can reduce laser noise during reproduction, and the optical attenuation factor is not constant but variable. The optical attenuator is controlled so as to have an optical attenuation factor corresponding to variations in individual coupling efficiency CE unique to the optical pickup 3 as will be described later. That is, the optical attenuator is configured to suppress variations in the laser source power during reproduction due to variations in the coupling efficiency CE inherent to the optical pickup 3. That is, the optical attenuator determines the power of the light beam 31 emitted from the light source 31 by making the optical attenuation rate R variable according to the variation in coupling efficiency CE for each unit as will be described later. The operating point of the driving voltage can be in a desired range. Such an optical attenuator can make the operating point (original power P0) of the power of the light source 31 substantially constant by setting the optical attenuation factor R according to CE. Thereby, this optical attenuator suppresses variations in laser noise, peak power at the time of high frequency superposition, life, and the like.

  The optical pickup 3 includes a branch amount detection element 36 as an optical attenuation factor detection unit (hereinafter also referred to as “LCD monitor”) for detecting the optical attenuation factor of the optical attenuator including the liquid crystal element 34 and the like. . That is, the branch amount detection element 36 is disposed at a position where a light beam branched from the light beam guided to the objective lens 32 and the optical disc 2 side by the polarization beam splitter film surface 35a is incident. A diffusion plate 37 is provided between the branch amount detection element 36 and the polarization beam splitter film surface 35a. The branch amount detection element 36 detects the light amount of the light beam transmitted through the polarization beam splitter film surface 35a and guided to the optical disc 2 by detecting the light beam reflected by the polarization beam splitter film surface 35a and passing through the diffusion plate 37. To do. As described above, the branch amount detection element 36 monitors the optical branch amount, that is, detects the light attenuation rate of the optical attenuator.

  The optical pickup 3 includes, for example, a phase plate 38 that is a half-wave plate, a beam splitter 39 that is a light separation element, a light emission power detection element 40 such as an FPD (front photodiode), and a quarter wavelength. A plate 41. The light emission power detection element 40 is an element for detecting the light emission power of the light source 31. A condensing lens for condensing the light beam guided from the beam splitter 39 onto the light emission power detection element 40 may be provided between the light emission power detection element 40 and the beam splitter 39. Further, a beam expander or a raising mirror may be arranged between the beam splitter 39 and the quarter wavelength plate 41.

  The optical pickup 3 also includes a detection lens group 42, a cylindrical lens 43, and light serving as a light detection means for detecting a return light beam reflected from the optical disk and separated from the forward light beam by the beam splitter 39. And a detector 44. The detection lens group 42 includes, for example, a collimator lens and a holographic plate. In the optical pickup 3, each optical component described above is configured by being individually mounted.

  In the optical pickup 3, a temperature sensor 45 may be provided in order to control the liquid crystal element 34 according to the temperature. A signal indicating the detection result detected by the temperature sensor 45 is sent to the system controller 7. When the temperature sensor 45 is provided, the liquid crystal element 34 is driven according to the result detected by the temperature sensor 45 as described later. Thereby, even if the recording and / or reproducing power changes depending on the temperature, it is possible to cope with this change.

  Next, the optical path of the light beam emitted from the light source 31 in the optical pickup 3 will be described with reference to FIG. The linearly polarized light beam emitted from the light source 31 is incident on the collimator lens 33 to be a parallel light beam, and is incident on the liquid crystal element 34. The light beam that has passed through the liquid crystal element 34 is sequentially incident on the anamorphic prism 35, the phase plate 38, and the beam splitter 39.

  At this time, the anamorphic prism 35 shapes the cross-sectional shape of the light beam emitted from the light source 31 from an ellipse to a substantially circular shape. That is, the light beam emitted from the light source 31 is linearly polarized light and has an elliptical cross-sectional shape in which the polarization state indicated by the arrow P in FIG. Then, the light beam is incident from the incident surface of the anamorphic prism 35 inclined with respect to the minor axis direction of the cross-sectional shape, so that the beam diameter is expanded in the minor axis direction, and is substantially circular. Shaped into a light beam.

  The incident light beam that has entered the beam splitter 39 through the anamorphic prism 35 and the phase plate 38 is approximately against a planar reflecting surface that is inclined with respect to the optical axis of the incident light beam that the beam splitter 39 has. It is in a P-polarized state. The phase plate 38 is rotated and adjusted around the optical axis so that the polarization state of the incident light beam is P-polarized light with respect to the reflection surface of the beam splitter 39.

  The light beam incident on the beam splitter 39 passes through the separation surface 39a at a constant ratio of, for example, about 95% or less and is incident on the quarter wavelength plate 41. Here, the light beam reflected by the separation surface 39 a of the beam splitter 39 enters the light emission power detection element 40. The incident light beam that has passed through the beam splitter 39 passes through the quarter-wave plate 41 to become circularly polarized light, and is condensed on the recording surface of the optical disc 2 by the objective lens 32.

  Then, the reflected light beam reflected by the recording surface of the optical disc 2 passes through the objective lens 32 and is transmitted through the quarter-wave plate 41, so that a straight line in a direction orthogonal to the polarization state of the light beam in the outgoing optical path. The polarized light is returned to the beam splitter 39. At this time, the reflected light beam is substantially in the S-polarized state with respect to the separation surface 39 a of the beam splitter 39, and substantially the entire amount is reflected by this separation surface 39 a and separated from the optical path from the light source 31. Is done. The reflected light beam separated from the optical path from the light source 31 is converted into convergent light by the detection lens group 42, and is given astigmatism by the cylindrical lens 43 to obtain a focus error signal by the astigmatism method. The light enters the photodetector 44. An RF signal, a focus error signal, a tracking error signal, and the like are generated based on a signal output from the photodetector 44 that has received the reflected light beam.

  In this optical pickup 3, the light attenuation rate of the light beam emitted from the light source 31 is appropriately variably controlled by the action of the liquid crystal element 34 as an optical attenuator and the polarization beam splitter film surface 35a of the anamorphic prism 35. The That is, the light beam emitted from the light source 31 is transmitted with an appropriate transmittance according to the reproduction mode and the recording mode, and is guided to the optical disc 2 side. In the recording mode, the light is guided to the optical disc 2 with a smaller light attenuation rate, that is, a larger transmittance than in the reproduction mode.

  In the optical pickup 3, a current for driving the semiconductor laser element chip of the light source 31 is supplied from the laser control unit 21.

  The liquid crystal element 34 changes the polarization state of the incident light beam based on an applied voltage (hereinafter also referred to as “liquid crystal applied voltage”) and emits the light beam. The applied voltage to the liquid crystal element 34 is controlled by the servo control unit 9. The light beam transmitted through the liquid crystal element 34 enters the anamorphic prism 35 in a state where the polarization state is changed.

  The polarization beam splitter film surface 35a of the anamorphic prism 35 has a planar shape having a predetermined angle with respect to the optical axis of the incident light beam, transmits substantially 100% of the P-polarized light, and approximately 100 of the S-polarized light. % Reflection. Therefore, for example, when recording is performed on the optical disc 2 (hereinafter, also referred to as “recording mode”), the polarization state of the light beam emitted from the liquid crystal element 34 is set to a state substantially close to the P-polarization direction. A light amount of about 95% is transmitted through the polarizing beam splitter film surface 35a. When the optical disk 2 is reproduced (hereinafter also referred to as “reproduction mode”), the polarization state of the light beam emitted from the liquid crystal element 34 is changed from the P-polarization direction, for example, 30. % Of light passes through the polarizing beam splitter film surface 35a. At this time, the remaining light amount of, for example, about 70% is reflected from the polarization beam splitter film surface 35a and guided to the branch amount detection element 36 side. Here, the rate of transmission through the polarization beam splitter film surface 35 a is determined by the angle at which the polarization state is rotated by the liquid crystal element 34.

  The light beam reflected by the polarization beam splitter film surface 35a of the anamorphic prism 35 is received by the branch amount detection element 36 serving as the light attenuation rate detection means via the diffusion plate 37.

  The output of the branch amount detection element 36 corresponds to the product of the light emission output of the light source 31 and the light branching rate on the polarization beam splitter film surface 35a of the anamorphic prism 35. It corresponds to the rate. In this optical pickup 3, when the light attenuation factor is small, the amount of light incident on the branch amount detection element 36 decreases, and when the light attenuation factor is large, the amount of light incident on the branch amount detection element 36 increases. It has become. The amount of light incident on the branch amount detection element 36 is an amount proportional to the product of 100%-[passage rate of optical coupling efficiency variable means (%)] and "laser emission power". The output of the branch amount detection element 36 is sent to the preamplifier 14 as shown in FIG.

  The light beam transmitted through the anamorphic prism 35 enters the beam splitter 39. The beam splitter 39 is a light emission power detecting element for monitoring the light beam emitted from the light source 31 to the recording surface of the optical disc via the objective lens 32 and the light quantity of the light beam guided to the recording surface. The light beam incident on 40 is separated at a constant ratio. The output of the light emission power detecting element 40 is sent to the laser control unit 21, and an auto power control operation is executed. That is, the laser control unit 21 controls the light emission output of the light source 31 so that the output from the light emission power detection element 40 becomes a predetermined value. By this control, the amount of irradiation light on the recording surface of the optical disc 2 is made constant. Note that, as will be described later, the irradiation light amount that is a predetermined value on the recording surface of the optical disc 2 is a different value between the recording mode and the reproduction mode, and also varies depending on the type of the optical disc.

  The light beam that has passed through the beam splitter 39 is incident on the objective lens 32 as described above. The objective lens 32 irradiates the incident light beam by converging it to a certain point on the recording surface of the optical disc 2. The objective lens 32 is driven in the focus direction and the tracking direction by a biaxial actuator or the like (not shown). As a result, the objective lens 32 focuses the light beam so that it is in focus on the recording surface of the optical disc 2 and causes the focused light beam to follow a track on the recording surface of the optical disc 2.

  In addition, the system controller 7 uses a signal indicating the temperature sent from the temperature sensor 45 to transmit a predetermined light through the servo control unit 9 so that the power operating point of the light source 31 becomes constant as will be described later. Control the attenuation rate.

  The optical pickup 3 described above uses a liquid crystal element 34 as an optical attenuator for reducing laser noise during optical disc reproduction. The optical pickup 3 is characterized in that the liquid crystal applied voltage is not fixed in the binary mode in the recording mode and the reproduction mode, but is controlled by varying it according to the coupling efficiency CE of the optical pickup 3 during reproduction or the like. It is. With this feature, the optical pickup 3 can suppress variations in the laser source power during reproduction, and can suppress variations in peak power, reliability, and life when laser noise and high frequency are superimposed. This will be described in detail below. . The optical pickup 3 enables closed-loop control based on the output of the branch amount detection element 36 that monitors the optical attenuation rate. Further, since the optical pickup 3 can be set to an arbitrary optical attenuation factor, it can be controlled not only during reproduction but also during recording. In the following, the advantages of the closed loop control and the advantages of increasing the LCD (liquid crystal element) response speed and reducing the mode switching time by overdrive at the time of mode switching will be described.

  First, the relationship between the applied voltage of the liquid crystal element 34 and the optical attenuation factor characteristic of the optical attenuator composed of the liquid crystal element and the polarizing beam splitter film surface 35a will be described with reference to FIG. In FIG. 3, the horizontal axis indicates a liquid crystal applied voltage (also referred to as “LCDDRV”), and the vertical axis indicates a light attenuation rate (also referred to as “ATT rate”). In FIG. 3, L1 indicates the light attenuation rate characteristic of the light attenuator with respect to the voltage applied to the liquid crystal element 34.

  Here, first, conventional binary fixed control for comparison with the present invention will be described. In the binary fixing control for fixing the values of the two modes consisting of the reproduction mode and the recording mode, for example, 0.5V is set during reproduction as shown by Pa in FIG. 3, and during recording as shown by Pb in FIG. This voltage is applied as 9V. In such a case, as shown in FIG. 3, the reproduction attenuation rate is 0.3, and the recording attenuation rate is about 0.95.

  Next, the relationship between the voltage applied to the liquid crystal element 34, the voltage characteristic of the branch amount detecting element 36 as the attenuation rate monitor, and the voltage characteristic of the light emission power detecting element 40 when the relationship shown in FIG. This will be described with reference to FIG. 4, L2 indicates the voltage characteristic (also referred to as “VMON”) of the branch amount detection element 36 with respect to the voltage applied to the liquid crystal element 34, that is, the monitor voltage characteristic of the optical attenuation factor. The output of the photodetector constituting the element 36 is I / V converted. 4 indicates a voltage characteristic of the light emission power detection element 40 with respect to the voltage applied to the liquid crystal element 34 (also referred to as “VFPD”), that is, a voltage characteristic for monitoring the irradiation power to the objective lens 32. Specifically, L3 indicates the I / V output of the front photodiode (FPD) constituting the light emission power detection element 40. Further, the horizontal axis in FIG. 4 indicates the liquid crystal applied voltage (also referred to as “LCDDRV”). Also, the vertical axis in FIG. 4 shows the voltage (VMON) characteristic of the branch amount detection element 36 for L2, and the voltage (VFPD) characteristic of the light emission power detection element 40 for L3. .

  As described above, the branch amount detection element 36 functions as an attenuation rate monitor. The branch amount detection element 36 as the attenuation rate monitor is also used for state confirmation in binary control, and is used for recording / reproducing operation. Is more stable.

  That is, the voltage of the branch amount detection element 36 as an attenuation rate monitor is constantly monitored, and a state can be confirmed by providing a threshold value for comparison. Specifically, the state of the liquid crystal element 34 can be confirmed by determining whether the voltage of the branch amount detecting element 36 is equal to or higher than a threshold value, and after the state is confirmed, the mode can be shifted to the reproduction / recording mode.

  In particular, this monitoring is required in the switching operation from the reproduction mode to the recording mode from the high attenuation rate (hereinafter also referred to as “LCD CLOSE”) to the low attenuation rate (hereinafter also referred to as “LCD OPEN”). . That is, since the response speed of the liquid crystal element 34 is finite and the switching time of the liquid crystal element 34 itself is not zero, in this switching operation from reproduction to recording, the laser that makes the recording power without being completely in the LCDOPEN state is destroyed. There is a possibility that. This is because the light source 31 emits more power than necessary because of the large attenuation rate. The branch amount detection element 36 as described above can detect the state of the liquid crystal element 34, and after confirming this state, switching to the laser power during recording can prevent laser destruction. Even in the conventional binary fixed control as described above, the problem at the time of mode switching and the like can be solved, but it is difficult to solve the problem due to the variation of the laser source power as described above.

  The optical pickup 3 to which the present invention is applied has the advantages of the binary fixing control as described above, and controls the optical attenuation factor variably instead of being fixed at the time of reproduction or the like in order to solve the problems of the binary fixing control. Is. As a result, the optical pickup 3 constructs a stable optical disk drive system by suppressing variations in laser noise, peak power at the time of high frequency superposition, and laser life. This will be described in detail below.

  In the optical pickup 3, the emission power control emitted from the light source 31 is based on the voltage obtained by the I / V conversion of the light emission power detection element 40 disposed in the middle of the optical path. This obtained voltage is a voltage proportional to the power. Hereinafter, the control using the output of the light emission power detecting element 40 is also referred to as auto power control (APC).

  In general, the relationship between the emission power and the light emission power detection element 40 is measured for each optical pickup. Specifically, the relationship between the output power and the output voltage of the front photodiode (FPD) constituting the light emission power detection element 40 is stored as ki (V / mW). This is because the element sensitivity of the light emission power detection element 40 and the coupling efficiency of the optical pickup are not exactly the same for each optical pickup.

  Specifically, it is common to adjust k1 (V / mW) to a fixed value by adjusting the gain of an I / V amplifier of an FPD (front photodiode) constituting the light emission power detection element 40. is there. On the other hand, when the power to be set is, for example, P1 (mW), the laser control unit 21 as the APC performs control so that the FPD output of the light emission power detection element 40 becomes P1 × k1 (V).

  Next, k1 indicating this relationship will be described more specifically. The measurement of k1 (V / mW) is performed by using at least two points of power (P1, P2) by constant current driving light emission (hereinafter also referred to as “CC light emission”) instead of auto power control. Then, the output powers P1 and P2 of the objective lens 32 and the I / V amplifier outputs V1 and V2 of the font photodiode (FPD) constituting the light emission power detection element 40 at that time are measured with an optical power meter. Further, the laser currents I1 and I2 of the light source 31 at that time are also measured.

From the output powers P1 and P2 and the output voltages V1 and V2 thus obtained, k1 can be calculated by the following equation (1). Further, the differential efficiency η1 of the laser by the light source 31 when the optical system is used can be calculated from the laser currents I1 and I2 by the following equation (2). Furthermore, if the differential efficiency as a single laser is η0 (mW / mA), η0 and the obtained η1 and the coupling efficiency CE have the relationship of the following equation (3).
k1 = (V2-V1) / (P2-P1) (V / mW) (1)
η1 = (P2-P1) / (I2-I1) (mW / mA) (2)
CE = η1 / η0 (3)

  Incidentally, the coupling efficiency CE in the optical pickup 3 is determined by the laser divergence angle of the light beam emitted from the light source 31, the transmittance of the optical components constituting the optical pickup 3, the optical loss, and the like. It is determined in consideration of the spot shape and the like.

  Next, the laser emitted from the light source 31 is similarly made to emit light at a certain power by CC light emission, and the voltage applied to the liquid crystal element 34 is changed at every step. At this time, when the FPD output voltage of the light emission power detection element 40 is measured, the characteristic as shown in L3 of FIG.

  In general light attenuation control, a fixed value is adopted at two voltage points where the light attenuation rate is in a uniform range and hardly affected by temperature change, for example, at positions such as Pa and Pb shown in FIG. The method is chosen. Here, as a specific attenuation ratio, the attenuation ratio at the time of LCDClose in Pa shown in FIG. 3 is about 0.3, and the attenuation ratio at the time of LCDOpen in Pb shown in FIG. 3 is about 0.95.

  When the optical attenuation factor during reproduction (LCD Close) is fixed at 0.3, the original power P0 of the laser when the reproduction power is 0.3 mW is obtained by using the coupling efficiency CE and the optical attenuation factor R, P0 = 0. 3 / (CE × R) is satisfied. When R = 0.3, P0 = 0.3 / (CE × 0.3) = 1 / CE.

  Here, in consideration of variation, when the coupling efficiency CE is set to CE = 0.10 to 0.20, the laser source power P0 is P0 = 1 / (0.10 to 0.20) = 5.0 to 10 mW, and the operating point will be different. As described above, if the operating points are different, the laser noise (RIN), the peak power at the time of high frequency superposition, the lifetime, and the like are not uniform. This is a specific problem of the conventional binary fixed control described above.

  On the other hand, in order to make the operating point of the laser source power substantially the same, the light attenuation factor may be made variable. The operating point must be determined in consideration of the power vs RIN curve of the laser to be used, the laser noise allowed in the system, the peak power of the high frequency superimposed waveform, and the like. Also, from the viewpoint of life, the power at the operating point should be small.

  In the example of FIG. 9 described above, 5 mW before the second hump of the superimposed waveform begins to appear is considered to be appropriate as the operating point. Further, the relationship of R = 0.3 / (P0 × CE) is obtained from the above relational expression. Therefore, in order to set the operating point to 5 mW, when CEmax = 0.20, the optical attenuation factor is 0.3 mW / 5 mW × 0.20 (CEmax) = 0.3, and CEmin = 0.10. In this case, the light attenuation factor is 0.3 mW / 5 mW × 0.10 (CEmin) = 0.6. That is, in order to set the operating point to 5 mW, the light attenuation factor may be made variable in the range of 0.3 to 0.6. Specifically, it is possible to make the operating point constant by determining the light attenuation rate according to the coupling efficiency CE of each optical pickup and driving the liquid crystal element 34 to achieve this light attenuation rate. Become.

  As described above, the relationship between the voltage applied to the liquid crystal element 34 and the light attenuation rate is such that the light source 31 emits light with a constant current (CC) drive power and the liquid crystal (LCD) applied voltage is varied in a certain step. can get. That is, this relationship can be understood by varying the applied voltage of the liquid crystal in a certain step between 0 to 9 V, for example, and measuring the FPD voltage of the light emission power detection element 40 and the monitor voltage of the branch amount detection element 36 at that time.

  The monitor voltage of the branch amount detection element 36 increases when the light attenuation factor is large, and the voltage increases due to an increase in the light branched to the branch amount detection element 36 as a monitor. The characteristics are opposite to those of the FPD voltage.

  In the example described here, when VFPD9, VMON9, VFPDn, and VMONn are set as follows, the following relationship is obtained. That is, the FPD voltage of the light emission power detection element 40 at the time of the minimum optical attenuation rate, which is the liquid crystal applied voltage 9V, is VFPD9, and the monitor voltage of the branch amount detection element 36 at that time is VMON9. Further, the FPD voltage of the light emission power detection element 40 when the liquid crystal applied voltage is nV is VFPDn, and the monitor voltage of the branch amount detection element 36 at that time is VMONn. When set in this way, the optical attenuation factor ATTn at nV satisfies the relational expression ATTn = 0.95 × VFPDn / VFPD9 = 0.95 × VMON9 / VMONn. In this case, “0.95” is because the minimum light attenuation factor is not 0.9 but 0.95.

  In this way, when the liquid crystal application voltage is varied in an allowable step of 0 to 9 V and the above measurement is performed, the relationship between the liquid crystal application voltage and the light attenuation factor (LCD application voltage vs. light attenuation factor) can be determined.

  As described above, since the relationship between the coupling efficiency CE, the liquid crystal (LCD) applied voltage, and the optical attenuation factor can be obtained for each optical pickup, the operating point, that is, the laser source power during reproduction is almost the same. It becomes possible to do. Specifically, the servo control unit 9 controls the optical attenuator composed of the liquid crystal element 36 on the basis of the intrinsic coupling efficiency CE stored in the servo control unit 9 itself or the system controller 7, so that the laser source The power can be the same.

  The optical pickup 3 to which the present invention is applied includes a light source 31, an objective lens 32, a photodetector 44, and an optical attenuator. The optical attenuator includes a liquid crystal element 34 and a polarized beam as a polarization separation unit. It is characterized by having a splitter film surface 35a. This optical pickup 3 has the following effects by the configuration in which the photodetector is controlled so as to have an optical attenuation factor corresponding to the variation in coupling efficiency inherent to the optical pickup 3. In other words, the optical pickup 3 realizes suppression of variations in laser noise, peak power at the time of high frequency superimposition, and laser lifetime by changing the optical attenuation rate according to the coupling efficiency, and stable recording / reproduction characteristics. Realize. Thus, the present invention realizes a stable recording / reproducing system.

  Further, in the optical pickup 3 to which the present invention is applied, the optical attenuator is configured so as to suppress variations in the power of the light beam emitted from the light source 31 during reproduction due to variations in the coupling efficiency of the optical pickup. It has the characteristics. The optical pickup 3 makes the power operating point of the light source 31 constant by making the light attenuation rate variable according to the variation in individual coupling efficiency. With this configuration, the optical pickup 3 can surely suppress variations in laser noise, peak power during high frequency superposition, and laser lifetime.

  In the above, an example in which the open control is employed has been described. However, it is also possible to perform a closed loop control in which the monitor voltage of the branch amount detection element 36 that is an LCD monitor is made constant. Furthermore, this closed loop control can also suppress a change in attenuation rate due to a temperature change. In general, the liquid crystal element is easily affected by temperature, and the liquid crystal element 34 constituting the optical pickup 3 described above is no exception.

  Here, FIG. 5 and FIG. 6 show characteristic examples of the light attenuation rate characteristic (L1) with respect to the liquid crystal applied voltage and the voltage characteristic (L2) of the branch amount detection element 36 for each temperature described with reference to FIGS. . 5 and 6, the horizontal axis represents the liquid crystal applied voltage (LCDDRV). Further, L10 in FIG. 5 indicates the optical attenuation factor characteristic of the optical attenuator with respect to the voltage applied to the liquid crystal element 34 at 0 ° C. L11 indicates the light attenuation rate characteristic of the light attenuator with respect to the voltage applied to the liquid crystal element 34 at 25 ° C. L12 indicates the optical attenuation factor characteristic of the optical attenuator with respect to the voltage applied to the liquid crystal element 34 at 50 ° C. The vertical axis in FIG. 5 indicates the light attenuation rate (ATT rate). Further, L20 in FIG. 6 indicates the voltage characteristic of the branch amount detection element 36 with respect to the voltage applied to the liquid crystal element 34 at 0 ° C. L21 indicates the voltage characteristic of the branch amount detection element 36 with respect to the voltage applied to the liquid crystal element 34 at 25 ° C. L22 indicates the voltage characteristic of the branch amount detection element 36 with respect to the voltage applied to the liquid crystal element 34 at 50 ° C. The vertical axis in FIG. 6 represents the voltage (VMON) characteristics of the branch amount detection element 36.

  As described above, in the case of the method using the binary recording / reproducing control that is normally performed, the optical attenuation rate (ATT rate) is a flat region where the temperature does not change, for example, the Pa shown in FIG. , Pb is set to binary. On the other hand, in the optical pickup 3, depending on the coupling efficiency, the optical attenuation rate (ATT rate) may be an operating point that is affected by a temperature change. It should be noted that the coupling efficiency is less than twice the change of 0.1 to 0.2. As described above, in the open control, there is a possibility that the light attenuation rate (ATT rate) changes due to the temperature change, but by adopting the closed loop control using the LCD monitor voltage VMON of the branch amount detection element 36 as the detection value. , The influence of temperature change can be suppressed. This is because the branch amount detection element 36 uses a photodetector and has a temperature characteristic much lower than that of the liquid crystal element 34.

  Specifically, in the optical pickup 3 that enables the closed loop control, the system controller 7, the servo control unit 9, and the preamplifier 14 described above are configured as shown in FIG. The system controller 7 has a light attenuation rate vs. VMON table 7a indicating a relationship (light attenuation rate vs. VMON) between the light attenuation rate and the monitor voltage VMON of the branch amount detection element 36 as an LCD monitor. Further, the system controller 7 includes a reference voltage determination unit 7b for determining a reference voltage serving as a reference. In the light attenuation rate vs. VMON table 7a, the relationship between the light attenuation rate obtained from the above-described relationship between the LCD applied voltage vs. the light attenuation rate and the monitor voltage VMON (light attenuation rate vs. VMON) is stored as a table. Then, the reference voltage determination unit 7b of the system controller 7 determines a reference voltage (also referred to as “Ref voltage”) that serves as a reference for comparison with the LCD monitor output voltage at the optical attenuation rate desired to be set during reproduction. To the comparator 9a.

  The preamplifier 14 is provided with an I / V amplifier 14a for I / V converting the output from the photodetector of the branch amount detecting element 36 as an LCD monitor. The I / V amplifier 14a generates a result detected by the branch amount detection element 36 as a monitor voltage VMON, and supplies it to a comparator 9a described later.

  The servo controller 9 includes a comparator 9a, a square wave oscillator 9b, and a liquid crystal element voltage control amplifier (also referred to as “VCA”) 9c. Here, the applied voltage of the liquid crystal element 34 is AC driving, not DC, and 1 kHz square wave driving.

  As described above, the reference voltage is input to the comparator 9a from the reference voltage determination unit 7b, and the monitor voltage VMON is input from the I / V amplifier 14a. The comparator 9a performs an operation (VMON-Ref voltage) for subtracting the reference voltage from the monitor voltage VMON, and supplies the result to the liquid crystal element voltage control amplifier 9c. The liquid crystal element voltage control amplifier 9 c supplies the liquid crystal element 34 with a liquid crystal application voltage (LCD drive voltage) for driving the liquid crystal element 34. When the output of the comparator 9a is +, that is, when the LCD monitor voltage is large, the liquid crystal element voltage control amplifier 9c means that the light attenuation factor is larger than the target, so that the LCD applied voltage is increased in polarity. Set to. On the other hand, the liquid crystal element voltage control amplifier 9c is when the output of the comparator 9a is-. That is, when the LCD monitor voltage is small, it means that the light attenuation rate is small, and therefore, the polarity is set so that the LCD applied voltage is lowered. The output of the comparator 9a is input as a control voltage to the liquid crystal element voltage control amplifier 9c, and the liquid crystal element voltage control amplifier 9c gives an amplification degree according to the control voltage. The liquid crystal element voltage control amplifier 9c receives a 1 kHz square wave from the square wave oscillator 9b. The liquid crystal element voltage control amplifier 9c changes the Ac signal amplitude of 1 kHz, which is an input signal from the square wave oscillator 9b, in accordance with the output voltage and polarity from the comparator 9a. And a predetermined light attenuation rate is obtained. As described above, the servo control unit 9 including the liquid crystal element voltage control amplifier 9 c and the like controls the optical attenuator including the liquid crystal element 36 based on the signals from the branch amount detection element 36 and the system controller 7.

  The optical pickup 3 can suppress the change in the optical attenuation rate (ATT rate) due to the temperature change by controlling the LCD monitor voltage VMON to be constant by such closed loop control.

  As described above, the optical pickup 3 to which the present invention is applied is characterized in that it is configured to suppress a change in attenuation rate due to a temperature change by being controlled to be closed. Specifically, the optical pickup 3 compares the reference voltage with the monitor voltage and determines the voltage applied to the liquid crystal element 34 according to the result, thereby suppressing the change in the optical attenuation factor due to the temperature change. As a result, the optical pickup 3 realizes stable recording / reproducing characteristics regardless of temperature changes.

  Note that the liquid crystal response speed at the time of switching can be improved by performing the closed loop control. That is, as described above, by performing the closed loop control in which the LCD monitor voltage is compared with the reference voltage as a reference, it is possible to set an arbitrary optical attenuation ratio, and it is possible to control not only during reproduction but also during recording. The mode transition time can be shortened.

  Specifically, as shown in FIG. 8, the comparator 9a and the liquid crystal element voltage control amplifier 9c are configured so that the liquid crystal applied voltage is applied up to the allowable voltage of the liquid crystal element 34 as the dynamic range of the closed loop control. May be. FIG. 8A shows the applied voltage V1 during reproduction, and FIG. 8B shows the applied voltage V2 during recording. The broken line portion in FIG. 8B indicates a state where overdrive is performed, and V3 indicates the maximum allowable applied voltage.

  Accordingly, when switching from the reproduction mode to the recording mode, overdrive, that is, by applying up to about the maximum allowable applied voltage V3 larger than the applied voltage V2 during recording, as shown in FIG. Response speed can be improved. In FIG. 8C, the solid line LR indicates the liquid crystal applied voltage during reproduction, the solid line LW indicates the liquid crystal applied voltage during recording, and the solid line LRW indicates the liquid crystal applied voltage when shifting from reproduction to recording. Shows changes. A broken line LOD in FIG. 8C shows a change in the liquid crystal applied voltage when overdriven. In FIG. 8C, the horizontal axis indicates time, and the vertical axis indicates the monitor voltage VMON. FIG. 8C shows that by performing overdrive as indicated by the broken line in FIG. 8B, the subsequent time from reproduction to recording can be shortened.

  This is because the liquid crystal response speed generally depends on the liquid crystal applied voltage (LCDDRV voltage) and becomes faster as the voltage is higher. The liquid crystal response speed also depends on the ambient temperature, and the response speed becomes slower as the temperature is lower. In mode switching in the overdrive state by such closed loop control, the mode switching time is shortened compared to normal switching. As a result, the memory capacity until the actual recording starts can be reduced, and the cost can be reduced particularly in an AV recorder or the like that requires real-time performance.

  The optical pickup 3 to which the present invention is applied is controlled by a closed loop, and when the mode is switched from the reproduction mode to the recording mode, the maximum allowable applied voltage V3 in which the applied voltage of the liquid crystal element 34 is larger than the applied voltage V2 in the recording mode is applied. It is set as the structure. As a result, the optical pickup 3 can increase the liquid crystal response speed and shorten the mode switching time. In other words, the optical pickup 3 realizes real-time performance as an optical disc apparatus, reduces memory capacity, and realizes cost reduction.

  As described above, the optical pickup 3 to which the present invention is applied can make the operating point of the laser original power during reproduction due to variations in the optical coupling substantially constant, and the variations in the laser noise, the peak power at the time of high frequency superimposition, and the variations in the lifetime. Is suppressed, and stable recording and reproduction can be achieved. That is, according to the optical pickup 3, the laser noise is not only dependent on the power, but also has individual differences, but the configuration in which the operating point is the same has a merit in reducing variation factors and is good. Recording / reproducing characteristics can be realized.

  In addition, the optical pickup 3 to which the present invention is applied enables the closed loop control for comparing the LCD monitor voltage and the reference voltage by the branch amount detecting element 36 capable of monitoring the optical attenuation rate, and can be set to an arbitrary optical attenuation rate. Is possible.

  Further, the optical pickup 3 to which the present invention is applied can suppress the change in the optical attenuation rate (ATT rate) due to the temperature change by performing the closed loop control. Further, in the optical pickup 3, the liquid crystal application voltage is overdriven at the time of mode switching, the mode switching time is shortened, and the memory capacity required at the time of switching transition can be reduced.

  The optical disc apparatus 1 to which the present invention is applied is characterized in that it includes a driving means and an optical pickup, and includes the optical pickup 3 described above as an optical pickup. This optical disc apparatus 1 realizes suppression of laser noise, peak power at the time of high frequency superimposition, and variation in lifetime by changing the optical attenuation factor with an optical attenuator according to the coupling efficiency of the pickup, and is favorable. Realizes recording and playback characteristics.

It is a block diagram which shows the structure of the optical disk apparatus to which this invention is applied. It is an optical path diagram showing an optical system of an optical pickup to which the present invention is applied. It is a figure which shows the relationship between the applied voltage LCDDRV of a liquid crystal element, and an optical attenuation factor (ATT rate) characteristic. It is a figure which shows the relationship between the applied voltage LCDDRV of a liquid crystal element, the voltage characteristic VFPD of the light emission power detection element as a monitor of the irradiation power to an optical disk, and the voltage characteristic VMON of the branch amount detection element as a liquid crystal monitor. It is a figure which shows the relationship between the applied voltage LCDDRV of a liquid crystal element, and optical attenuation factor (ATT rate) characteristic when temperature is 0 degreeC, 25 degreeC, and 50 degreeC. It is a figure which shows the relationship between the applied voltage LCDDRV of a liquid crystal element when the temperature is 0 degreeC, 25 degreeC, and 50 degreeC, and the voltage characteristic VMON of the branch amount detection element as a liquid crystal monitor. It is a block diagram which shows the structure which enables the closed loop control in the example which enables the closed loop control of the optical pick-up to which this invention is applied. It is a figure for demonstrating performing overdrive at the time of mode switching, (a) shows the applied voltage in reproduction | regeneration mode, (b) shows the applied voltage and maximum permissible applied voltage in recording mode. (C) is a figure which shows that mode switching time is shortened by performing overdrive. It is a figure for demonstrating the relationship between the original power of a laser light source, and a laser noise, and is a figure which shows the relationship between an original power and a RIN value. In a general laser light source, it is a figure which shows the high frequency superimposed waveform made into the state with a large peak power when high frequency superimposition is applied. FIG. 11 is a diagram illustrating that when the original power of the laser light source is increased with respect to the state illustrated in FIG. 10, second and third rising portions of relaxation vibration are generated and the peak power is decreased.

Explanation of symbols

1 optical disk device, 2 optical disk, 3 optical pickup, 4 spindle motor, 5 feed motor, 7 system controller, 9 servo controller, 31 light source, 32 objective lens, 33 collimator lens, 34 liquid crystal element, 35 anamorphic prism, 35a Polarization beam splitter film surface, 36 branching amount detection element, 37 diffuser plate, 38 phase plate, 39 beam splitter, 39a separation surface, 40 emission power detection element, 41 1/4 wavelength plate, 42 detection lens group, 43 cylindrical lens, 44 photodetectors, 45 temperature sensors

Claims (7)

A light source that emits a light beam of a predetermined wavelength;
An objective lens for condensing the light beam emitted from the light source onto the optical disc;
A photodetector for detecting a reflected light beam reflected by the optical disc;
An optical attenuator provided between the light source and the objective lens, and attenuating the light amount of the light beam emitted from the light source to guide the objective lens;
The optical attenuator includes a liquid crystal element that changes a polarization state of the light beam and a polarization separation unit on which the light beam that has passed through the liquid crystal element is incident, and the polarization state of the light beam is changed by the liquid crystal element. By damaging the light attenuation rate variably,
The optical pickup is controlled such that the optical attenuator has an optical attenuation factor corresponding to variations in coupling efficiency of the optical pickup.   The optical attenuator reduces the optical attenuation according to the variation in the coupling efficiency of the optical pickup so as to suppress the variation in the power of the light beam emitted from the light source during reproduction due to the variation in the coupling efficiency of the optical pickup. 2. The optical pickup according to claim 1, wherein the operating point of the power of the light source is made substantially constant by changing the rate. Furthermore, it comprises a light attenuation rate detector that detects the light attenuation rate of the light attenuator,
The optical pickup according to claim 1, wherein the optical attenuator is closed-loop controlled based on an output of the optical attenuation factor detector. The polarization separation unit guides a part of the light beam to the objective lens at a ratio according to the polarization state of the light beam that has passed through the liquid crystal element, and the remaining light beam from the light beam guided to the objective lens. Branch,
4. The light according to claim 3, wherein the light attenuation rate detection unit detects the light attenuation rate of the light attenuator by receiving a light beam branched from the light beam guided to the objective lens by the polarization separation unit. pick up.   The optical pickup according to claim 3, wherein the optical attenuator suppresses a change in attenuation rate due to a temperature change by being controlled in a closed loop.   The optical attenuator is closed-loop controlled, and when the mode is switched from the reproduction mode to the recording mode, the maximum allowable applied voltage that is larger than the applied voltage in the recording mode is applied to the liquid crystal element, thereby shortening the mode switching time. The optical pickup according to claim 3. Driving means for holding and rotating the optical disc;
An optical pickup that records and / or reproduces an information signal with respect to the optical disk rotated and driven by the driving means,
The optical pickup includes a light source that emits a light beam having a predetermined wavelength,
An objective lens for condensing the light beam emitted from the light source onto the optical disc;
A photodetector for detecting a reflected light beam reflected by the optical disc;
An optical attenuator provided between the light source and the objective lens, and attenuating the light amount of the light beam emitted from the light source to guide the objective lens;
The optical attenuator includes a liquid crystal element that changes a polarization state of the light beam, and a polarization separation unit on which the light beam that has passed through the liquid crystal element is incident, and the polarization state of the light beam is changed by the liquid crystal element. By damaging the light attenuation rate variably,
An optical disc apparatus in which the optical attenuator is controlled so as to have an optical attenuation factor corresponding to variations in coupling efficiency of the optical pickup.

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