JP2008117488A - Optical disk device and laser power control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further stabilize recording/reproducing characteristics by correcting temperature characteristics of an optical component or an electronic component in controlling laser power. <P>SOLUTION: An optical disk device is provided with a power detector 26 for detecting the recording power of a laser beam generated by a pickup 3, a temperature detector 27 for detecting a temperature in the pickup, and a cycle detection part 63 for instructing to execute recording power optimizing process (Walking-OPC) at a predetermined cycle. A calculation part 6 calculates the correction amount of laser beam recording power according to a detected temperature, and evaluates the quality of recorded data to calculate the correction amount of recording power in the recording power optimizing process. A recording power control unit 62 newly sets laser beam recording power based on each calculated correction amount. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus and a laser power control method for controlling laser power applied to an optical disc with high accuracy.

  In an optical disc apparatus, when irradiating a laser beam to an optical disc during recording / reproduction, the laser beam power is controlled to be a constant value in order to stabilize the recording / reproduction quality. For this reason, feedback control (APC = Automatic Power Control) is used so that the power of light emitted from the laser light source is detected and the intensity is constant.

  Japanese Patent Application Laid-Open No. H10-228561 describes a measure that the characteristics of the amplifier circuit of the monitor signal (power detection signal) vary depending on the ambient temperature. That is, in a light emission power control device that controls the light emission power of a laser light source based on a target value of light emission power and a monitor signal that detects the actual light emission power, an amplification circuit that amplifies the monitor signal, and the vicinity of the amplification circuit A configuration is disclosed that includes temperature detection means for detecting temperature, and means for giving a signal for removing the offset component to the amplifier circuit based on a temperature detection signal from the temperature detection means.

JP 2005-228433 A

  As the recording density is increased, the optimum margin of laser power at the time of recording / reproducing has been narrowed, and in order to ensure the recording / reproducing quality, the irradiation power must be controlled with higher accuracy.

  For this purpose, it is necessary to accurately correct the ambient temperature fluctuation in consideration of the temperature characteristics of the optical components and electronic components constituting the optical pickup. For example, the transmittance of the objective lens changes depending on the ambient temperature, and the detection sensitivity of a front monitor detector (FMD) that is a power detector also has temperature characteristics. As a result, even if the APC control operates normally, the power actually irradiated onto the optical disk surface may deviate from the optimum value when the ambient temperature changes. However, this problem has not been taken into consideration in the above-mentioned Patent Document 1 and the prior art.

  An object of the present invention is to correct the temperature characteristics of optical components and electronic components in the control of laser power, thereby further stabilizing the recording / reproducing characteristics.

  An optical disc apparatus of the present invention records a pickup that generates laser light and irradiates the optical disc, a power detector that detects the recording power of the laser light generated by the pickup, a temperature detector that detects the temperature in the pickup, and recording A recording signal processing unit that converts data into a signal of a predetermined format and supplies it to the pickup, a cycle detection unit that instructs execution of a recording power optimization process at a predetermined cycle, and generated by the pickup according to the detected temperature And calculating the correction amount of the recording power of the laser light, and calculating the recording power correction amount by evaluating the quality of the recorded data in the recording power optimization step, and each of the calculation units calculated by the calculation unit A recording power control unit for newly setting the recording power of the laser beam generated by the pickup based on the correction amount.

  Here, in the recording power optimization step, the calculation unit holds a target value of quality for each recording position of the optical disc in advance, compares the quality of the recorded data with the target value, and calculates a correction amount of the recording power. calculate. The period detector sets a period for performing the recording power optimization process according to the allowable recording power width of the optical disc.

  The laser power control method of the present invention detects the temperature in the pickup that irradiates the optical disc with the laser beam, detects the recording power of the laser beam generated by the pickup, and the correction amount of the recording power detected according to the detected temperature As a process for optimizing the recording power, the recording operation is temporarily stopped and the recorded data is reproduced, the quality of the reproduced data is compared with the target quality, and the correction amount of the recording power is calculated and calculated. The recording power of the laser beam is newly set based on each correction amount.

  When the optimization process is performed here, immediately after that, the optimization process is performed again on the data recorded with the newly set recording power.

  According to the present invention, stable recording and reproduction characteristics can be realized even when the ambient temperature changes.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of an optical disc apparatus according to the present invention. In the apparatus of this embodiment, the mounted optical disk 1 is rotated by a spindle motor 2, and the pickup 3 irradiates the recording surface of the optical disk 1 with laser light generated by a semiconductor laser, and records or reproduces data. The pickup 3 is moved to a desired track position on the optical disk by a thread mechanism (not shown). The motor driver 4 supplies a rotation drive signal to the spindle motor 2.

  A laser diode driver (LDD) 5 supplies a laser emission drive signal to the pickup 3. The pickup 3 detects the power of the generated laser light and sends it to the system control microcomputer 6. Further, the temperature in the pickup 3 is detected and sent to the system control microcomputer 6. The system control microcomputer (arithmetic unit) 6 calculates a target value for recording / reproducing laser power generated by the pickup 3 in accordance with the temperature in the pickup 3. The automatic power control (APC) circuit 7 compares the power target value received from the system control microcomputer 6 with the power detection value detected by the pickup 3 so that the laser beam power generated by the pickup 3 becomes the target value. Send a control signal to.

  The reproduction signal processing circuit 8 processes the signal read from the optical disc 1 to reproduce data. The reproduced data is processed by the system control microcomputer 6 and transferred to the host device 11 such as a PC via the interface 10. On the other hand, the recording data transferred from the host device 11 is converted into a predetermined recording signal and recorded on the optical disc 1 with the power set by the APC circuit 7. The servo controller 9 performs control such as motor rotation, tracking, and focusing based on the reproduction signal.

  FIG. 2 is a diagram showing an example of the internal configuration of the pickup 3. The light beam generated from the laser diode (LD) 21 at the time of recording / reproducing is converted into parallel light by the collimator lens 22, and two linearly polarized lights whose polarization directions are orthogonal to each other (polarization beam splitter (PBS) 23). p-polarized light and s-polarized light). The p-polarized light goes straight and is condensed on the disk surface by the objective lens 24. On the other hand, the reflected light read from the disk is reflected by the PBS 23, enters the optoelectronic integrated circuit (OEIC) 25, and is converted into an electric signal.

  The pickup 3 further includes a front monitor detector (FMD) 26 that is a power detector, and detects the laser power when the recording / reproducing light beam generated by the LD 21 is directed from the PBS 23 toward the objective lens 24. A temperature sensor (temperature detector) 27 is installed in the pickup to detect the ambient temperature. The apparatus of the present embodiment has a function of correcting the characteristics of the objective lens 24 and the FMD 26 in the pickup when the characteristics fluctuate depending on the ambient temperature.

  FIG. 3 is a diagram for explaining the temperature characteristic of the objective lens 24 and the correction for the temperature characteristic. The transmittance of the objective lens decreases with increasing temperature (reference numeral 31). For example, when the temperature rises from 25 ° C. to 30 ° C., the transmittance decreases by about 5%. As a result, the laser power applied to the disk surface is reduced, and the recording / reproducing performance is deteriorated.

  In an actual pickup configuration, the mounting position of the FMD 26 for detecting the power must be a position in front of the objective lens 24. Therefore, it is impossible to directly detect a change in the laser power applied to the disk surface. Therefore, the ambient temperature is detected by the temperature sensor 27 incorporated in the pickup, and the fluctuation due to the temperature change of the transmittance of the objective lens is corrected. Specifically, the system control microcomputer (arithmetic unit) 6 changes the PMAX value that is a coefficient indicating the dynamic range of the light emission power for determining the light emission power of the laser diode with respect to the change in transmittance of the objective lens. That is, the PMAX value is corrected so as to cancel the change in transmittance (reference numeral 32), and the power target value (recording target value: WRDA, reproduction target value: REDA) of the APC circuit 7 is calculated and set. Thus, the irradiation power on the disk surface is controlled to be kept constant.

  FIG. 4 is a diagram for explaining the temperature characteristics of the front monitor detector (FMD) 24 and corrections thereto. The detection sensitivity of FMD decreases with increasing temperature (reference numeral 41). As a result, the laser power applied to the disk surface increases and the recording / reproducing performance is deteriorated. Therefore, the ambient temperature is detected by the temperature sensor 27 incorporated in the pickup, and the fluctuation due to the temperature change of the FMD detection sensitivity is corrected. Specifically, the system control microcomputer (arithmetic unit) 6 changes the FMD sensitivity coefficient for determining the target value with respect to the change in the detection sensitivity of the FMD. In this case, the FMD sensitivity coefficient is corrected in the same direction as the change direction of the FMD detection sensitivity (reference numeral 42), and the power target values (WRDA for recording, REDA for reproduction) of the APC circuit 7 are calculated and set. Thus, the irradiation power on the disk surface is controlled to be kept constant.

  The temperature correction data (PMAX value, FMD sensitivity coefficient) described above is obtained in advance based on the temperature characteristics of the objective lens 24 and the FMD 26, and is stored in a memory as firmware, for example. In this case, correction data for each temperature is stored in a table format, and a target value at a desired temperature is calculated by referring to the data. Further, by correcting the target value for APC control when the ambient temperature changes by a predetermined width (threshold value) or more, for example, 5 ° C. or more, the time during which the recording / reproducing operation is interrupted to correct the target value is reduced. Can be reduced. Note that an arithmetic expression for obtaining temperature correction data by calculation can be stored in the firmware, and the target value can be determined by calculation using this.

  When the power target value (recording WRDA, reproduction REDA) is set in the APC circuit 7, the value obtained by calculation is not set as the target value as it is (reflects 100%), but the calculated value is set to a predetermined value. The target value may be set by multiplying by a coefficient (less than 100%). By adding the damping coefficient in this way, it is possible to stabilize the power control operation without overshoot even for a pickup having a large FMD sensitivity coefficient due to component variations.

  FIG. 5 is a flowchart showing an embodiment of the laser power control method according to the present invention. In step S101, the initial temperature T0 in the pickup 3 is detected by the temperature sensor 27 at the start of recording / reproduction. In step S102, the system control microcomputer 6 stores the detected temperature T0 in a memory (SRAM) in the microcomputer. Then, correction data (PMAX value, FMD sensitivity coefficient) of the objective lens 24 and FMD 26 at the detection temperature T0 is read with reference to the firmware, and target values of laser power (recording WRDA, reproduction REDA) are calculated. In step S103, the target power of the APC circuit 7 is set with the calculated target value. In step S104, a data recording / reproducing operation is started.

  In step S105, the temperature T1 in the pickup 3 during the recording / reproducing operation is detected. In step S106, the system control microcomputer 6 determines whether or not the temperature change | T1-T0 | from the initial temperature T0 is greater than or equal to a threshold value (for example, 5 ° C.). If it is less than the threshold value (No in S106), the recording / reproducing operation is continued as it is.

  If the temperature change is equal to or greater than the threshold (Yes in S106), the recording / reproducing operation is interrupted in Step S107. In step S108, the correction data (PMAX value, FMD sensitivity coefficient) of the objective lens 24 and FMD 26 with respect to the detected temperature T1 is read with reference to the firmware, and the laser power target values (recording WRDA, reproducing REDA) are calculated again. . In step S109, the target power of the APC circuit 7 is reset with the calculated target value. In step S110, the data recording / reproducing operation is resumed.

  According to the above control, even if the temperature in the pickup 3 changes, the power of the laser beam applied to the disk can be kept constant, and the recording / reproducing characteristics are stabilized.

  In this embodiment, the power target value of the APC circuit 7 is changed according to the temperature change. As another method, the power target value may be constant and the power detection value may be corrected. That is, the amplifier gain of the FMD signal amplifier circuit (not shown) is changed according to the temperature change of the objective lens and FMD sensitivity according to the temperature change. Specifically, as the correction of the amplifier gain, correction in the direction opposite to the correction curve of the PMAX value and the FMD sensitivity coefficient in FIG. 3 and FIG. 4 may be performed.

  In this embodiment, the objective lens and the FMD in the pickup are taken up as components having temperature characteristics to be corrected, but temperature correction may be applied to only one of them. Also, other optical components and electronic components can be similarly applied when the irradiation power to the disk is affected by the temperature characteristics.

  By combining the temperature correction control described in the first embodiment with a recording power optimization step (hereinafter referred to as “Walking-OPC”), more accurate power control can be realized. This will be described below.

  In the conventional walking-OPC, the quality of the data recorded immediately before is evaluated, and the optimum recording power is obtained and corrected so as to obtain the target quality for the data to be recorded next. Here, as an index for obtaining the target quality, the amplitude (degree of modulation) of the reproduction signal, asymmetry, the relationship between the amplitude of the shortest mark and the longest mark, and the like are used. In Walking-OPC, recording is continued at a predetermined recording power target value within a certain interval. Therefore, when the recording power applied to the disk surface fluctuates due to factors such as temperature fluctuation in the section, the recording power is set by the Walking-OPC including the result of reflecting the correction, so that the Walking-OPC is performed. The optimum power value obtained as a result of (1) can be controlled so as not to deviate from the true optimum value.

  FIG. 6 is a block diagram showing another embodiment of the optical disk apparatus according to the present invention. In the present embodiment, a recording signal processing circuit 61, a recording power control circuit 62, and a period detection circuit 63 are newly added to the configuration diagram of FIG. 1 as components for carrying out Walking-OPC. The same reference numerals as those in FIG. 1 denote the same constituent elements, and here, only the elements related to the recording operation are shown.

  Since the laser light applied to the optical disc 1 has a higher recording power during recording than during reproduction, the temperature rise of the pickup 3 due to laser emission is large. As the temperature rises, the influence on the change in lens transmittance is large, and fluctuation (deterioration) in recording performance is expected. The system control microcomputer (arithmetic unit) 6 calculates the correction amount of the recording power (target value) corresponding to the temperature change by using the power detection signal and the temperature detection signal from the pickup 3. Further, the quality of the reproduction data is evaluated in the Walking-OPC, and the correction amount of the recording power is calculated by comparing with the quality target value. Then, these correction amounts are transmitted to the recording power control circuit 62. The recording power control circuit 62 controls the LDD 5 to set a new recording power based on the correction amount received from the system control microcomputer 6. The recording signal processing circuit 61 converts recording data input from the host device 11 via the interface 10 into a signal of a predetermined format and supplies the signal to the pickup 3 via the LDD 5. The period detection circuit 63 instructs execution of Walking-OPC at a predetermined period (timing).

  When there is an instruction for Walking-OPC, the system control microcomputer 6 temporarily stops the recording operation and confirms the recording power by the Walking-OPC. In the Walking-OPC, the data recorded immediately before by the pickup 3 is reproduced. If the quality of the reproduced data deviates from the target quality, a recording power correction amount for correcting the deviation is transmitted to the recording power control circuit 62. The recording power control circuit 62 sets a new recording power for the data to be recorded next and instructs the LDD 5. Then, the recording of the next data is resumed with a new recording power.

  FIG. 7 is a diagram illustrating an example of a target value that serves as a reference when evaluating the quality of recorded data. Here, the modulation degree is used as an index of quality, and the target value is changed and set as shown by a curve 71 according to the radial position of the disk. Information on the target value is stored in advance in the system control microcomputer 6, and the recording power is confirmed by referring to the target value according to the radial position on the disk. Alternatively, the disk area shown in FIG. 7 may be divided into zones a to e in the radial direction, and the target values for each zone may be tabulated and stored.

  FIG. 8 is a diagram illustrating an example of the execution timing of the Walking-OPC. Here, a case where data is recorded from the inner periphery to the outer periphery of the optical disc is shown. Arrows 81, 83, and 85 indicate continuous recording operations, and circles 82 and 84 indicate the timing of Walking-OPC. For example, recording is started from zone a (arrow 81), recording is temporarily stopped at the boundary with zone b, and Walking-OPC (◯ mark 82) is performed. At this time, it is assumed that the recording power is corrected. In order to confirm the correction result in the Walking-OPC (◯ mark 82), data is recorded for a short time with the corrected recording power (arrow 83), and immediately after that, the Walking-OPC (◯ mark 84) is performed again. . Thereby, the accuracy of the recording power correction can be improved by checking the corrected recording power.

  The execution period of the Walking-OPC can be arbitrarily set by the period detection circuit 63 in FIG. At that time, it is possible to perform recording with a more appropriate recording power by appropriately setting the execution period according to the characteristics of the optical disc and the state of temperature change. For example, in a multilayer disc, the margin (allowable width) for the recording power may be different for each layer. If the first layer is less affected by fluctuations in recording power (large margin) and the second layer is greatly affected by fluctuations in recording power (small margin), the Walking-OPC execution cycle for the first layer is set as follows. The execution cycle of Walking-OPC for the second layer is set to be short. Accordingly, it is possible to efficiently correct the recording power while reducing the number of times of performing Walking-OPC, and to prevent the recording power from deviating from the allowable range in each layer.

  Moreover, you may make it implement the implementation period of Walking-OPC when a temperature change exceeds a predetermined range (allowable width). For example, when the margin for the recording power is different for each layer as in the above-described multi-layer disc, the allowable range of temperature change for the first layer is increased and the allowable range of temperature change for the second layer is decreased. Thereby, it is possible to efficiently correct the recording power for each layer and prevent the recording power from deviating from the allowable range.

  As described above, by combining the temperature correction control of the first embodiment and the control by the recording power optimization process (Walking-OPC), it is possible not only to suppress the power fluctuation applied to the disc due to the temperature change during recording. Further, as a result of Walking-OPC, the recording power can be corrected and set. As a result, the quality of the recording data can be further improved by controlling the recording power value with higher accuracy.

1 is a block diagram showing an embodiment of an optical disc apparatus according to the present invention. FIG. 3 is a diagram illustrating an example of an internal configuration of a pickup 3. The figure explaining the temperature characteristic of the objective lens 24, and correction | amendment with respect to it. The figure explaining the temperature characteristic of the front monitor detector (FMD) 24, and the correction | amendment with respect to it. 3 is a flowchart showing an embodiment of a laser power control method according to the present invention. The block diagram which shows the other Example of the optical disk apparatus by this invention. The figure which shows an example of the target value at the time of evaluating the quality of the recorded data. The figure which shows an example of the implementation timing of Walking-OPC.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical disk, 2 ... Spindle motor, 3 ... Pickup, 4 ... Motor driver, 5 ... Laser driver drive circuit (LDD), 6 ... System control microcomputer (arithmetic unit), 7 ... Automatic power control (APC) circuit, 8 ... Reproduction signal processing circuit, 9 ... servo controller, 10 ... interface, 11 ... host device, 21 ... laser diode (LD), 24 ... objective lens, 25 ... optoelectronic integrated circuit (OEIC), 26 ... front monitor detector (FMD), 27: Temperature sensor, 61: Recording signal processing circuit, 62: Recording power control circuit, 63: Period detection circuit.

Claims (5)

In an optical disc apparatus that records data by irradiating an optical disc with a laser beam,
A pickup that generates laser light and irradiates the optical disc;
A power detector for detecting the recording power of the laser beam generated by the pickup;
A temperature detector for detecting the temperature in the pickup;
A recording signal processing unit that converts data to be recorded into a signal of a predetermined format and supplies the signal to the pickup;
A cycle detector for instructing execution of a recording power optimization process at a predetermined cycle;
In addition to calculating the correction amount of the recording power of the laser beam generated by the pickup according to the detected temperature, the recording power correction amount is evaluated by evaluating the quality of the recorded data in the recording power optimization step. A computing unit to calculate,
A recording power control unit for newly setting a recording power of the laser beam generated by the pickup based on each correction amount calculated by the calculation unit;
An optical disc apparatus comprising: The optical disc apparatus according to claim 1,
In the recording power optimization step, the calculation unit holds a target value of quality for each recording position of the optical disc in advance, and compares the quality of the recorded data with the target value to correct the recording power. An optical disc apparatus characterized by calculating a quantity. The optical disc apparatus according to claim 1,
The optical disk apparatus according to claim 1, wherein the period detection unit sets a period for performing the recording power optimization process according to a recording power allowable width of the optical disk. A laser power control method for recording data on an optical disc,
Detect the temperature in the pickup that irradiates the optical disk with laser light,
Detecting the recording power of the laser beam generated by the pickup;
While calculating the correction amount of the detected recording power according to the detected temperature,
As a process for optimizing the recording power, the recording operation is temporarily stopped and the recorded data is reproduced,
Comparing the quality of the reproduced data with the target quality to calculate the recording power correction amount,
A laser power control method, wherein a recording power of the laser beam is newly set based on the calculated correction amounts. The laser power control method according to claim 4,
A laser power control method characterized in that, immediately after the optimization step, the optimization step is performed again on the data recorded with the newly set recording power.

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