JP2008071445A - Optical recording/reproducing device and optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems wherein the effect of high-frequency superposition decreases and noise increases, a peak level becomes high, and a recording layer deteriorates and data are erased by mistake, when an operating current is increased or decreased for changing the quantity of emitted light by a pickup having a means for varying the quantity of light if an attenuation optical element, or the like is used according to the optimum quantity of light on the media surface of an optical disk to be reproduced. <P>SOLUTION: In the optical reproducing device or optical pickup mounted with a means for attenuating the quantity of light, and an LD 2 for performing high-frequency superposition in reproduction, a laser beam from the LD 2 is attenuated by an ND filter 20 for obtaining an optimum quantity of reproduction light, and return light to the LD2 is attenuated by the ND filter 20, when an optical disk 1 is a single-layered disk, thus maintaining the quantity of emission light of the LD 2 in reproduction nearly constant, also maintaining the level of high-frequency superposition of the drive current of the LD2 nearly constant, and hence preventing laser noise from increasing, the recording layer from deteriorating, and data from being erased erroneously. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical recording / reproducing apparatus and an optical pickup, and more particularly to an optical recording / reproducing apparatus and an optical pickup for recording / reproducing information using a laser beam on a rewritable optical recording medium such as a single-layer disc or a single-sided dual-layer disc. About.

  FIG. 5 is a block diagram showing the main part of an example of a conventional optical recording / reproducing apparatus. In the figure, an optical disk 1 is a rewritable optical recording medium capable of recording or reproducing information using laser light. Laser light emitted from a semiconductor laser (hereinafter referred to as LD) 2 is transmitted through a collimator lens 18. Then, after being diffracted by the diffraction grating 19, the light is incident on the polarization beam splitter 16 and reflected, the optical path is changed, the light is incident on the collimator lens 3 to be parallel light, and a combination of a semitransparent half mirror and a prism is used. The light beam is almost transmitted by the beam splitter 4 which is a component, further passes through the quarter-wave plate 5 and is focused on the recording layer of the optical disc 1 by the objective lens 6 to form a light spot. The collimator lens 3 is configured to be movable in the optical axis direction by a motor 17.

  Further, the light incident on the beam splitter 4 and partially reflected here is condensed on the photodetector 9 by the condenser lens 7. The light received by the photodetector 9 is converted into an electric signal having a level corresponding to the received light level, amplified by the amplifier 11, and the level of the received light signal becomes a predetermined level by an APC (Automatic Power Control) circuit 13. In addition, the laser power of the LD 2 is controlled via the LD driving circuit 14. At the time of recording, the light intensity of the laser light emitted from the LD 2 is modulated by the recording information, and the recording information is recorded on the optical disc 1. Further, at the time of reproduction, the LD 2 is driven by a constant amplitude drive signal in which the high frequency signal from the high frequency superposition oscillator 15 is superimposed in the laser drive circuit 14.

  The spot light irradiated on the optical disc 1 is reflected on the optical disc 1. This reflected light is incident on the quarter-wave plate 5 through the objective lens 6. The reflected light incident on the quarter-wave plate 5 is converted into a linearly polarized S wave whose polarization plane is orthogonal to the P wave at the time of irradiation, passes through the beam splitter 4, and further passes through the collimator lens 3 to be polarized. The light enters the beam splitter 16.

  The linearly polarized light that has entered the polarization beam splitter 16 is an S wave, so that it is transmitted, is incident on the condenser lens 8, is condensed here, and is received by the photodetector 10. The light received by the photodetector 10 is converted into an electrical signal of a level corresponding to the received light level, and the recording information signal is detected and focused in a reproduction signal processing system or servo control system (not shown) via the amplifier 12. It is used for detection of error signals and tracking error signals.

  By the way, in the above-described configuration, the polarization beam splitter 16 and the quarter wavelength plate 5 function as an optical isolator for separating the laser beam irradiated from the LD 2 onto the optical disc 1 and the reflected light from the optical disc 1. In the ideal state, the return of reflected light to the LD 2 is prevented 100%.

  However, in practice, part of the light returns to the LD 2 due to the deviation of the quarter-wave plate 5 from the ideal state and the birefringence of the optical disk substrate, and so-called laser noise occurs. When a part of the laser light reflected by the recording layer is returned to the semiconductor laser 2, this return light causes power fluctuation of the LD 2, which is transmitted as noise to the photodetector 10, resulting in an adverse effect on video / audio. Will be affected.

  Further, the power fluctuation of the LD 2 is also caused by temperature fluctuation, and the high frequency superposition method is widely used as the most simple and effective method for reducing such noise. That is, by setting an optimum high-frequency superimposition level from the high-frequency superposition oscillator 15 to the LD 2, stable reproduction signal characteristics that are not influenced by the output change of the laser light can be obtained.

On the other hand, in the case of a recordable optical disk device, the reflectance of the optical disk is as low as 8% to 14% compared to 50% to 80% of a reproduction type optical disk (ROM disk), and the amount of return light is considerably smaller than that of a ROM disk device. However, since the reproduction output is reduced by 20 dB, laser noise is a problem. In addition, in a recordable optical disc apparatus, it is necessary to use a high output LD (for example, 120 mW) for recording and reproduction. However, as shown in FIG. 6, an LD with a large output generally has a relative intensity when using a small output. Noise (hereinafter referred to as RIN) is large, and the reproduction C / N is deteriorated. FIG. 6 is a graph showing the relationship between the output power of the LD and the noise. The horizontal axis represents the laser power, and the vertical axis represents the RIN characteristic of the laser. The RIN of the laser is a parameter representing the temporal fluctuation of the laser beam. When the average optical output of the LD is Po, the fluctuation of the optical output is δP, and the measurement bandwidth is Δf,
RIN = 10 × Log {(δP / Po) 2 / Δf} [dB / Hz]
It is represented by

  Another method for reducing laser noise is to increase the output to a sufficient level so that the RIN of the laser is reduced. A method of attenuating the laser output with an attenuating optical element during reproduction of a single-layer disc is disclosed. (For example, see Patent Documents 1 and 2).

  Patent Document 1 has a means for changing the amount of light, and at the time of reproduction, the laser output power is increased to suppress LD quantization noise, and at the same time, the laser power applied to the disk is attenuated by an attenuation optical element to keep it low. In addition, it is disclosed to prevent deterioration of the recording layer and erasure of data. In Patent Document 2, the laser light emitted from the laser light source and applied to the optical disk is attenuated by the attenuating optical element only at the time of low power operation such as reproduction of a single-layer disk or reproduction at a standard speed. It has been disclosed to reduce the wasteful power consumption of the laser light source and the reduction in the lifetime of the laser light source by preventing the attenuating optical element from attenuating during high power operation such as reproducing a disk or the like.

JP 2003-257072 A Japanese Patent Laid-Open No. 2004-199755

  However, when reproducing a recordable single-layer disc, noise is suppressed by superimposing a high-frequency current on the drive current of the LD. However, it is described in Patent Documents 1 and 2 according to the optimum light amount on the surface of the optical disc to be reproduced. When the output light amount is changed by increasing / decreasing the operating current by a pickup having a light amount variable means using the attenuating optical element or the like, the waveform and peak level to which high frequency superposition is applied change. For this reason, the effect of high-frequency superimposition is reduced and noise is increased, or conversely, the superimposition level is too large and the peak level is increased, causing deterioration of the recording layer and erroneous data erasure.

  If the change in the amount of emitted light from the LD is relatively small, the change in the state of high frequency superposition is small. For example, in response to the change in the reproduction speed, the LD output can be output without using the means for changing the amount of light for reproduction laser power. When changed, the occurrence of the above-mentioned problem is small if it is in a range lower than the change rate of the variable means.

  The present invention has been made in view of the above points, and among a plurality of types of optical discs having different reproduction light amounts, the laser output during playback is substantially the same during playback of any type of optical disc, and at the same time, By keeping the high frequency superposition state of the drive current of the light source (LD) the same, laser noise can be reduced, reproduction C / N can be improved, recording layer deterioration and erroneous data erasure can be prevented. An object of the present invention is to provide an optical recording / reproducing apparatus and an optical pickup compatible with a two-layer disc.

  In order to achieve the above object, an optical recording / reproducing apparatus according to a first aspect of the present invention modulates laser light emitted from a semiconductor laser with recording information during recording, and then applies it to an optical recording medium through a predetermined first optical system. Irradiated recording information is recorded, and at the time of reproduction, an optical recording in which an optimum reproduction light quantity is determined through a predetermined first optical system with laser light emitted from a semiconductor laser driven by a drive signal on which a high frequency is superimposed. Optical recording / reproduction for irradiating a medium and converting reflected light reflected from the optical recording medium into an electric signal through a predetermined second optical system and reproducing information recorded on the optical recording medium from the electric signal Regardless of the type of optical recording medium that is selected from a plurality of types of optical recording media for which the optimum amount of reproducing light is determined at the time of reproduction, the apparatus always provides a substantially constant average light amount from the semiconductor laser. Corresponding to the type of optical recording medium to be reproduced and selected from a plurality of types of optical recording media, a laser driving means for generating a driving signal for emitting light is determined for the type of optical recording medium A light attenuating means for inserting an optical attenuating element having a light amount attenuation ratio set so as to obtain an optimum reproduction light amount into the first optical system or holding it outside the first optical system. Features.

  In this invention, regardless of the type of optical recording medium to be reproduced, the average amount of laser light emitted from the semiconductor laser as the light source is made constant, and the type of optical recording medium to be reproduced is small in the optimum reproducing light amount. In the case of an optical recording medium, a predetermined optimum reproduction light quantity can be obtained by inserting an optical attenuating element in the first optical system, and the first optical system is reflected from the optical recording medium. The return light returning to the semiconductor laser through the light attenuation element can be attenuated by the light attenuating element.

  In order to achieve the above object, an optical recording / reproducing apparatus according to a second aspect of the invention is a type of optical recording medium for reproducing the laser driving means according to the first aspect of the invention selected from a plurality of types of optical recording media. Regardless of the above, the present invention is characterized in that it is means for generating a drive signal on which a high-frequency signal of a certain level is superimposed. In the present invention, a laser beam with a certain average amount of light can be emitted from a semiconductor laser by a drive signal on which a high-frequency signal of a certain level is superimposed regardless of the type of optical recording medium to be reproduced.

  In order to achieve the above object, according to a third aspect of the present invention, there are provided a plurality of types of optical recording media in which two recording layers are laminated, and any one of the two recording layers from one side of the medium. At least a single-layer two-layer optical recording medium that performs recording and reproduction by irradiating a laser beam, and a single-layer optical recording medium having a single recording layer. The optical attenuating element is held outside the first optical system during reproduction, and the optical attenuating element is inserted into the first optical system when reproducing a single-layer optical recording medium. . According to the present invention, when reproducing a single-layer optical recording medium, an optical attenuating element is inserted into the first optical system, so that the same average amount of light from the semiconductor laser as when reproducing a single-sided two-layer optical recording medium is obtained. Even if the laser beam is emitted, it is possible to obtain the optimum reproduction light amount of the single-layer optical recording medium, and attenuate the return light reflected from the single-layer optical recording medium and returning to the semiconductor laser by the light attenuating element. be able to.

  In order to achieve the above object, the fourth invention records information by irradiating a recording laser beam to an optical recording medium having an optimum reproduction light quantity. In an optical pickup that irradiates a laser beam for reproduction, receives the reflected light from the optical recording medium at that time, converts it into an electrical signal and outputs it, as a light source for emitting the recording laser beam or the reproduction laser beam A semiconductor laser, an objective lens for condensing a recording laser beam or a reproducing laser beam on an optical recording medium and transmitting reflected light from the optical recording medium, and a photoelectric conversion means for photoelectrically converting the reflected light transmitted through the objective lens Regardless of the type of optical recording medium to be reproduced selected from a plurality of types of optical recording media for which the optimum amount of reproduction light is determined, a drive signal on which high frequency is superimposed is generated, and the drive signal is transmitted to the semiconductor laser. Applied to A driving means for emitting laser light having a substantially constant average light amount from a semiconductor laser at all times, a light attenuating element in which a light amount attenuation ratio is set, and an optical recording medium for reproduction selected from a plurality of types of optical recording media In the case of the first optical recording medium of the kind whose optimum reproduction light quantity is small, the above optical attenuation element is inserted into the optical path from the semiconductor laser to the objective lens, and the optical recording medium to be reproduced is the optimum reproduction medium. And a light attenuating element moving means for moving the light attenuating element out of the optical path when the second optical recording medium is of a kind whose amount of light is larger than that of the first optical recording medium.

  In this invention, regardless of the type of optical recording medium for which the optimum reproduction light quantity is determined, the average light quantity of the laser light emitted from the semiconductor laser is made constant, and the type of optical recording medium to be reproduced is the optimum reproduction light quantity. When the optical recording medium is small, a predetermined optimum reproduction light quantity can be obtained by inserting an optical attenuating element in the first optical system, and the first recording light is reflected from the optical recording medium. The return light that returns to the semiconductor laser through the optical system can be attenuated by the light attenuating element.

  According to the present invention, a semiconductor device can be driven by a drive signal on which a high frequency of a certain amplitude level is superimposed, regardless of the type of optical recording medium to be reproduced, selected from a plurality of types of optical recording media for which the optimum reproduction light quantity is determined. Since the laser is driven to emit laser light with a substantially constant average amount of light from the semiconductor laser at all times, the effect of high frequency superposition can always be kept in an optimal state and a good reproduction life can be obtained. Deterioration of the recording layer of the optical recording medium and erroneous erasure of data can be prevented.

  Further, according to the present invention, when the type of the optical recording medium to be reproduced is an optical recording medium having an optimal reproduction light amount, the optical attenuating element is inserted into the first optical system, thereby The optimum reproduction light quantity can be obtained, and the return light reflected from the optical recording medium and returning to the semiconductor laser through the first optical system can be attenuated by the optical attenuating element. The laser light with the same high average light amount as that when reproducing an optical recording medium with a large amount of light is emitted. Therefore, the higher the laser power, the lower the laser noise, and the attenuation of the return light. Laser noise can be reduced, reproduction C / N can be improved, and deterioration of the recording layer and erroneous erasure of data can be prevented.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an embodiment of an optical pickup of an optical recording / reproducing apparatus according to the present invention. In the figure, the same components as those in FIG. In the present embodiment, a density filter (ND filter; Neutral Density Filter) 20 is provided in the optical path between the diffraction grating 19 and the polarization beam splitter 16 during reproduction of a single-layer disc for the reason described later. It is characterized in that an ND filter driving unit 21 for moving and controlling the position is provided. When recording on an optical disc or when two recording layers are stacked, reproduction of a single-sided dual-layer optical disc that performs recording and reproduction by irradiating laser light to any one of these two recording layers from one side of the disc In some cases, the ND filter 20 is not provided in the optical path between the diffraction grating 19 and the polarization beam splitter 16.

  When the ND filter 20 is not provided in the optical path between the diffraction grating 19 and the polarization beam splitter 16, the linearly polarized light (for example, P) set to a predetermined power from the LD 2 driven by the LD drive circuit 14 is used. Divergence light having a wavelength of 405 nm is emitted by the wave), and the emitted light is converted into substantially parallel light by the collimator lens 18 and divided by the diffraction grating 19 into three light beams (beams) of 0th order diffracted light and ± 1st order diffracted light It is used for tracking error signal detection using a known differential push-pull (DPP) system. Most of the light emitted from the diffraction grating 19 is reflected by the polarization beam splitter 16, converted into parallel light by the collimator lens 3, passes through the beam splitter 4, and enters the quarter-wave plate 5. The light incident on the quarter-wave plate 5 is converted from linearly polarized light to circularly polarized light and is incident on the objective lens 6.

  The light incident on the objective lens 6 is collected and irradiated as a beam spot onto a desired track of the optical disc 1. When the optical disc 1 is a single-sided dual-layer optical disc, spherical aberration occurs in the objective lens 6 due to the difference in substrate thickness up to the recording surface, so that the spherical aberration can be obtained by driving the motor 17 to move the position of the collimator lens 3. Is corrected.

  As is well known, the objective lens 6 is held by an actuator (not shown) having a focus coil and a tracking coil, and a current is passed from a servo circuit (not shown) to the focus coil in the actuator, thereby changing the position of the objective lens 6 to the optical disk. The beam spot is focused on a desired track of the optical disc 1 to form an image by moving it in a focusing direction perpendicular to the recording surface of one recording current, and a current is supplied from a servo circuit (not shown) to a tracking coil in the actuator. , The optical axis direction of the objective lens 6 is slightly displaced in the radial direction of the optical disc 1 so that the beam spot can follow the track of the optical disc.

  A part of the linearly polarized light incident on the beam splitter 4 is reflected and incident on the condenser lens 7, where it is condensed and received by the photodetector 9. The light received by the photodetector 9 is converted into an electric signal having a level corresponding to the average amount of received light, is photoelectrically converted by the amplifier 11, and is fed back to the LD drive circuit 14 via the APC circuit 13. In the LD drive circuit 14, the output current is adjusted by controlling the drive current of the LD 2 based on the input electric signal. Thereby, a laser beam with stabilized power is emitted from the LD 2. In order to suppress laser noise due to a part of light returning to the LD 2, the high-frequency current from the high-frequency superposition oscillator 15 is superimposed on the drive current to the LD 2.

  Further, the spot light irradiated on the optical disc 1 is reflected on the optical disc 1. This reflected light is incident on the quarter-wave plate 5 through the objective lens 6. The reflected light incident on the quarter-wave plate 5 is converted into a linearly polarized S wave whose polarization plane is orthogonal to the P wave at the time of irradiation, and then transmitted through the beam splitter 4 and further through the collimator lens 3. The light enters the polarization beam splitter 16. The linearly polarized light that has entered the polarization beam splitter 16 is an S wave, so that it is transmitted, is incident on the condenser lens 8, is condensed here, and is received by the photodetector 10. The light received by the photodetector 10 is converted into an electric signal having a level corresponding to the received light level, and the recording signal is detected by the reproduction signal processing system or servo control system (not shown) via the amplifier 12 and This is used for detecting a focus error signal and a tracking error signal.

  FIG. 2 is a diagram showing a laser power characteristic with respect to a drive current when laser light is emitted, a waveform of a laser drive current on which a high frequency component of about 400 MHz is superimposed, and a waveform of emitted light. LD2 emits little light below a threshold current (hereinafter referred to as Ith). As shown in FIG. 2, the current-light output characteristic A is maintained almost linearly from Ith, and the linearity is lost at a rated current (not shown).

  As shown in FIG. 2, the LD 2 is driven by a laser driving current B having a positive and negative high-frequency superimposed current amplitude centered on the current value of Ib, and the LD 2 emits light when the laser driving current exceeds Ith. Since LD2 is extinguished with respect to the laser drive current, a laser emission waveform as shown by C in FIG. 2 is formed.

  In this example, the average value Pr of the disk surface laser power is set to 0.8 mW as the reproduction power of the recording type dual layer disk. The disk surface peak power of the high-frequency superimposed component is about 2.6 mW. In this case, the peak power is not too high, so that the recording layer is not deteriorated and the data is not erased erroneously.

  FIG. 3 is a diagram showing a laser power characteristic with respect to a driving current when laser light is emitted, a laser driving current waveform on which a high frequency component of about 400 MHz is superimposed, and a waveform of the emitted light. The same reference numerals are given. In FIG. 3, the laser power characteristic A with respect to the drive current at the time of laser beam emission is the same as in FIG. 2, but the average value Pr of the disk surface laser power is set to 0.4 mW as the reproduction power of the recording type single layer disk. 2 shows an example in which the base current Ib is lowered from 30 mA in FIG. 2 to about 25 mA without changing the amplitude of the high frequency superimposed current of about 400 MHz.

  As shown in FIG. 3, the LD 2 is driven by a laser driving current D having a positive and negative high-frequency superimposed current amplitude centering on the current value of Ib, and the LD 2 emits light for a laser driving current exceeding Ith, and is less than or equal to Ith. Since LD2 is extinguished with respect to the laser drive current, a laser emission waveform as shown by E in FIG. 3 is formed.

  The high frequency superimposed pulse width of the laser emission waveform E shown in FIG. 3 is narrower than that of the laser emission waveform C of FIG. 2, and the peak power ratio with respect to the average power is high. As a result, the disk surface peak power of the high frequency superimposed component is about 2 mW, and the recording sensitivity of the single-layer disk is about twice better than that of the recording type single-sided dual-layer disk. In this case, the peak power is too high. Therefore, there is a risk that the recording layer is deteriorated or data is erroneously erased.

  In order to solve this problem, the laser emission power is the same during single-sided dual-layer disk reproduction and single-layer disk reproduction, and the average value of the disk surface laser power is set to 0.4 mW, instead of lowering Ib. An example in which the light emitted from the light is attenuated will be described below.

  In the present embodiment, the ND filter 20 shown in FIG. 1 has a transmittance set to, for example, 50%, and the laser light between the LD 2 and the polarization beam splitter 16 by the ND filter driving unit 21 during reproduction of a single-layer disc. The light output from the LD 2 and the reflected return light from the optical disc 1 are attenuated. As shown in the output power vs. noise characteristic diagram of the LD of FIG. 6, the laser noise increases as the laser power is lower, so that the reproduction power on the board cannot be increased in order to prevent reproduction deterioration and erroneous erasure. If the output of LD2 is increased and the board power is made the same with an optical attenuating element such as ND filter 20, the laser noise will be reduced.

  Next, the operation according to the above configuration will be described. First, when recording or reproducing a single-sided dual-layer disc, a control signal from a control system (not shown) is not input to the ND filter driving unit 21. Therefore, the ND filter 20 is held outside the laser beam path by the ND filter driving unit 21.

  In this state, laser light that is linearly polarized light (for example, P wave) is emitted from the LD 2 that is driven with a power of 7.0 mW by a laser driving current that is a 40 mA high-frequency superimposed current, and a collimator lens 18, a diffraction grating 18, The light enters the beam splitter 4 via the optical system of the polarization beam splitter 16 and the collimator lens 3. Most of the light incident on the beam splitter 4 is transmitted and incident on the quarter-wave plate 5. The light incident on the quarter-wave plate 5 is converted from linearly polarized light to circularly polarized light and is incident on the objective lens 6. The light incident on the objective lens 6 is condensed and irradiated onto the optical disc 1 as a beam spot. Thereby, information is recorded or reproduced on a desired track.

  Further, a part of the linearly polarized light incident on the beam splitter 4 is reflected and incident on the condenser lens 7, where it is condensed and received by the photodetector 9. The light received by the photodetector 9 is converted into an electrical signal having a level corresponding to the received light level, and is fed back to the LD drive circuit 14 via the amplifier 11 and the APC circuit 13. In the LD drive circuit 14, the output current is adjusted by controlling the drive current of the LD 2 based on the input electric signal. As a result, laser light with stabilized power is emitted from the LD 2.

  Next, the operation at the time of reproducing a single-layer disc will be described. In this case, a control signal from a control system (not shown) is input to the ND filter driving unit 21. Thereby, the ND filter 20 is held in the laser light path by a slide mechanism (not shown) of the ND filter driving unit 21. In this state, the linearly polarized light (for example, P2) is output from the LD 2 driven at a power of 7.0 mW by the laser driving current, which is a high-frequency superimposed current of 40 mA, in the same manner as when recording by the LD driving circuit 14 or reproducing a single-sided dual-layer disc. Is converted into substantially parallel light by the collimator lens 18, converted into three laser lights by the diffraction grating 19, and then incident on the ND filter 20. The ND filter 20 transmits the incident laser light with a transmittance of 50% and enters the polarization beam splitter 16, most of which is reflected to be collimated by the collimator lens 3 and enters the beam splitter 4.

  Most of the light incident on the beam splitter 4 is transmitted and incident on the quarter-wave plate 5. The light incident on the quarter-wave plate 5 is converted from linearly polarized light to circularly polarized light and is incident on the objective lens 6. The light incident on the objective lens 6 is condensed and irradiated as a reproduction beam spot onto a desired track on which information on the optical disk 1 is recorded. At the time of reproduction, the LD 2 is driven with the same power of 7.0 mW as that at the time of recording. However, since the transmitted light amount is attenuated by 50% by the ND filter 20, the surface power of the laser light on the optical disc 1 (disc (Surface laser power) is the same as 0.4 mW at the time of conventional reproduction.

  The spot light irradiated on the optical disc 1 is reflected on the optical disc 1. This reflected light is incident on the quarter-wave plate 5 through the objective lens 6. The reflected light incident on the quarter-wave plate 5 is converted into linearly polarized S waves whose polarization plane is orthogonal to the P wave at the time of irradiation, and most of the light is transmitted by the beam splitter 4 and further transmitted through the collimator lens 3. Then, the light enters the polarization beam splitter 16. The linearly polarized light that has entered the polarization beam splitter 16 is an S wave, so it is transmitted, is incident on the condenser lens 8, is condensed here, and is received by the photodetector 10. The light received by the photodetector 10 is converted into an electric signal having a level corresponding to the received light level, and is output to a reproduction signal processing system and servo control system (not shown) via the amplifier 12.

  As described above, the light reflected by the optical disk 1 is led to an optical path different from the laser light irradiation optical path by the optical isolator composed of the polarization beam splitter 16 and the quarter wavelength plate 5, but in practice, 1 / Due to the deviation of the four-wave plate 5 from the ideal state and the birefringence of the optical disk 1, some light is transmitted through the beam splitter 4 and the collimator lens 23 as return light including the P-polarized component instead of the original S-polarized light. The light enters the beam splitter 16, is reflected here, and enters the ND filter 20. The return light incident on the ND filter 20 is attenuated and enters the LD 2 through the diffraction grating 19 and the collimator lens 18.

  Here, the return light to the LD 2 increases the laser noise. However, in this embodiment, the amount of the return light is reduced by the ND filter 20, and as a result, the laser noise is reduced compared to the conventional case. The Further, since the output laser beam power of the LD 2 is high at the same time as recording and a single-sided dual-layer optical disc, the laser noise is further reduced. Thereby, in this embodiment, the reproduction C / N can be improved when reproducing a single-layer disc as compared with the conventional one, and the deterioration of the recording layer and the erroneous erasure of data can be prevented.

  As described above, according to the present embodiment, as shown in FIG. 4, the ND filter 20 is removed from the optical path between the diffraction grating 19 and the polarization beam splitter 16 (off) when reproducing a single-sided, dual-layer optical disc. As in the conventional case, the LD 2 is driven with a power of 7.0 mW by a laser driving current that is a high-frequency superimposed current of 40 mA to set the laser power of the disk surface to a predetermined 0.8 mW. Unlike the conventional case, the ND filter 20 is inserted (turned on) in the optical path between the diffraction grating 19 and the polarizing beam splitter 16, so that the LD 2 is driven by a laser driving current that is a high-frequency superimposed current of 40 mA. Double the power of 7.0 mW so that the laser power on the disk surface is the same as the conventional 0.4 mW and the laser output is The laser noise is reduced more than that of the prior art, and the laser noise is also reduced by attenuating the return light to the LD 2 by the ND filter 20.

  Note that the present invention is not limited to the above-described embodiment. For example, the LD output power, the laser power of the disk surface, and the LD high-frequency superimposed current value are examples. It is also possible to use an optical attenuating element other than the ND filter instead of the ND filter 20. Further, the insertion (ON) and the removal (OFF) of the light attenuating element into the optical path are not only when the light attenuating element itself is mechanically moved, but also when the light attenuating element is electrically connected like a liquid crystal element. In the case of an element that is controlled to be in a damped operation state or a non-attenuated operation state, it includes a case where the attenuation operation is turned on and off electrically without moving the light attenuating element mechanically.

It is a block diagram of an embodiment of an optical pickup of the optical recording / reproducing apparatus of the present invention. FIG. 6 is a diagram (part 1) illustrating a relationship between an LD driving current versus a disk surface laser power characteristic, and a relationship between a high frequency superimposed current amplitude and a laser emission waveform. FIG. 6 is an explanatory diagram (No. 2) showing the relationship between the LD driving current versus the disk surface laser power characteristic, and the relationship between the high-frequency superimposed current amplitude and the laser emission waveform. It is a figure which shows an example of each value of the presence or absence of use of the ND filter by embodiment of FIG. 1, a disk surface laser power, LD output power, and LD high frequency superimposed current. It is a block diagram of an example of the optical pick-up of the conventional optical recording / reproducing apparatus. It is a characteristic view which shows the relationship between the output power of LD, and noise.

Explanation of symbols

1 Optical disk 2 Semiconductor laser (LD)
3, 18 Collimator lens 4 Beam splitter 5 1/4 wavelength plate 6 Objective lens 7, 8 Condensing lens 9, 10 Photo detector 11, 12 Amplifier 13 APC circuit 14 LD drive circuit 15 High frequency superposition oscillator 16 Polarizing beam splitter 17 Collimator Drive motor 19 Diffraction grating 20 Density filter (ND filter)
21 ND filter driver

Claims (4)

When recording, laser light emitted from a semiconductor laser is modulated with recording information, and then the optical recording medium is irradiated through a predetermined first optical system to record the recording information. A laser beam emitted from a semiconductor laser driven by a signal is irradiated to an optical recording medium having an optimum reproduction light amount through the predetermined first optical system, and thereby reflected light reflected from the optical recording medium Is an optical recording / reproducing apparatus for converting information recorded on the optical recording medium from the electrical signal through a predetermined second optical system,
Regardless of the type of optical recording medium that is selected from the plurality of types of optical recording media for which the optimum amount of reproducing light is determined during reproduction, laser light having a substantially constant average amount of light is always emitted from the semiconductor laser. Laser drive means for generating the drive signal for causing
Corresponding to the type of optical recording medium to be reproduced selected from the plurality of types of optical recording media, the light quantity attenuation ratio is set so as to obtain the optimum reproduction light quantity determined for the type of optical recording medium An optical recording / reproducing apparatus comprising: an optical attenuating means for inserting the optical attenuating element into the first optical system or holding the optical attenuating element outside the first optical system.   The laser driving unit is a unit that generates a driving signal on which a high-frequency signal of a certain level is superimposed regardless of the type of the optical recording medium to be reproduced selected from the plurality of types of optical recording media. The optical recording / reproducing apparatus according to claim 1. The plurality of types of optical recording media have two recording layers stacked, and recording and reproduction are performed by irradiating any one of the two recording layers with the laser light from one side of the optical recording medium. At least a single-layer two-layer optical recording medium and a single-layer optical recording medium having one recording layer,
The optical attenuating means holds the optical attenuating element outside the first optical system when reproducing the single-sided two-layer optical recording medium, and when reproducing the single-layer optical recording medium, 2. The optical recording / reproducing apparatus according to claim 1, wherein an optical attenuating element is inserted into the first optical system. When recording, information is recorded by irradiating a recording laser beam onto an optical recording medium with an optimum reproduction light amount. At the time of reproduction, the optical recording medium is irradiated with a reproducing laser beam. In an optical pickup that receives the reflected light from the optical recording medium and converts it into an electrical signal and outputs it,
A semiconductor laser as a light source for emitting the recording laser beam or the reproducing laser beam;
An objective lens for condensing the recording laser light or the reproducing laser light on the optical recording medium and transmitting reflected light from the optical recording medium;
Photoelectric conversion means for photoelectrically converting reflected light transmitted through the objective lens;
Regardless of the type of optical recording medium to be reproduced selected from a plurality of types of optical recording media for which the optimum reproduction light quantity is determined, a drive signal on which a high frequency is superimposed is generated, and the drive signal is transmitted to the semiconductor laser. Driving means for emitting laser light having a substantially constant average light amount from the semiconductor laser at all times,
A light attenuating element in which a light attenuation ratio is set;
When the optical recording medium to be reproduced selected from the plurality of types of optical recording media is the first optical recording medium of the type having the small optimal reproduction light quantity, the optical attenuating element is separated from the semiconductor laser. When the optical recording medium that is inserted into the optical path to the objective lens and is to be reproduced is the second optical recording medium of the type in which the optimum reproduction light quantity is larger than that of the first optical recording medium, the light An optical pickup comprising: the optical attenuation element moving means for moving the attenuation element out of the optical path.

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