JP2008234732A - Optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress recording quality deterioration caused by wavelength shift due to the temperature increase of a semiconductor laser element. <P>SOLUTION: The APC 24 of an optical disk device controls the increase of a driving current to compensate for a reduction in light emission amount due to the temperature increase of a semiconductor laser element. A system controller 32 detects the temperature increase of the semiconductor laser element and wavelength shift caused by the temperature increase based on the change of a driving current output from the APC 24, and suppresses recording quality deterioration caused by wavelength shift by updating the target level of the APC 24 to compensate for the wavelength shift. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus, and more particularly to adjustment of recording power.

  In an optical disc apparatus for recording data, it is indispensable to control the recording power of laser light during recording in order to maintain the recording quality at a constant level. Normally, data recording is performed on an optical disk on which data is to be recorded with a recording power optimized by an OPC (Optimum Power Control) operation and while calibrating a laser light amount by an APC (Auto Power Control) operation. When recording is performed for a long time, the recording quality deteriorates due to a change in temperature inside the apparatus or variations in the in-plane recording sensitivity of the optical disk.

  It is considered that the recording quality deteriorates when the recording takes a long time despite the APC operation during recording because the wavelength of the laser beam shifts due to the temperature rise of the semiconductor laser. However, since the wavelength measuring device is relatively large and cannot be mounted on an optical disk device, and the temperature inside the device is greatly different from the element temperature of the semiconductor laser, the wavelength is estimated based on the temperature inside the device. I can't do that either.

  Therefore, recording quality has been maintained by using ROPC (Running OPC) or retrospective OPC methods, but ROPC has been difficult to detect the pit state during recording. There is a risk of quality loss. Further, although the retrospective OPC is relatively easy to implement, there is a problem in that the recording time must be increased because the recording must be interrupted each time.

  In Patent Document 1 below, a provisional optimum recording power is calculated by OPC using a test area of an optical disc, and the length of the wavelength of the laser light is evaluated based on the calculated provisional optimum recording power. It is disclosed that the recording strategy is changed according to the length of the wavelength.

  Patent Document 2 below discloses that a light wavelength change detecting means for detecting a change in the light wavelength emitted from the light source is provided, and the recording power is corrected in accordance with the output of the light wavelength change detecting means. .

JP 2003-67927 A JP-A-8-315400

  In Patent Document 1, the length of the wavelength is evaluated according to the provisional optimum recording power, but the optimum recording power is not adjusted according to the length of the wavelength. Further, in Patent Document 2, it is necessary to newly provide a wavelength variation detection circuit, resulting in an increase in complexity and size of the apparatus.

  An object of the present invention is to provide an apparatus that can suppress a decrease in recording quality due to fluctuations in the element temperature of a semiconductor laser with a simple configuration without separately providing a temperature sensor.

  The present invention includes a semiconductor laser that records data by irradiating a laser beam onto an optical disc, a power control circuit that feedback-controls a driving current of the semiconductor laser so that the power of the laser beam matches a target power, and the driving And an adjustment circuit that adjusts the target power to compensate for a decrease in recording quality caused by a wavelength shift due to a temperature variation of the semiconductor laser in accordance with a change in current.

  In one embodiment of the present invention, the adjustment circuit includes the relationship between the drive current and the element temperature of the semiconductor laser, the relationship between the element temperature and the wavelength, the relationship between the wavelength and the recording quality, and the power and the recording quality. The target power is adjusted in accordance with the change in the drive current using the relationship of.

  In another embodiment of the present invention, the adjustment circuit uses the relationship between the drive current and the element temperature of the semiconductor laser, the relationship between the element temperature and the wavelength, and the relationship between the wavelength and the target power. The target power is adjusted according to the change in the drive current.

  According to the present invention, it is possible to suppress deterioration in recording quality due to fluctuations in the element temperature of a semiconductor laser without providing a temperature sensor or the like separately.

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

  FIG. 1 shows the overall configuration of the optical disc apparatus according to this embodiment. An optical disc 10 such as a CD, DVD, HD-DVD, or Blu-ray is driven by a spindle motor (SPM) 12. The spindle motor SPM 12 is driven by a driver 14, and the driver 14 is servo-controlled by a servo processor 30 so as to have a desired rotation speed.

  The optical pickup 16 includes a laser diode (LD), which is a semiconductor laser element for irradiating the optical disk 10 with laser light, and a photodetector (PD) that receives reflected light from the optical disk 10 and converts it into an electrical signal. Are arranged opposite to each other. The optical pickup 16 is driven in the radial direction of the optical disk 10 by a sled motor 18 constituted by a stepping motor, and the sled motor 18 is driven by a driver 20. The driver 20 is servo-controlled by the servo processor 30 similarly to the driver 14. The semiconductor laser element of the optical pickup 16 is driven by a driver 22, and the driver 22 is controlled by an auto power control circuit (APC) 24 so that the drive current becomes a desired value. The APC 24 and the driver 22 control the light emission amount of the semiconductor laser element according to a command from the system controller 32. In FIG. 1, the driver 22 is provided separately from the optical pickup 16, but the driver 22 may be mounted on the optical pickup 16.

  The recording / reproducing operation with respect to the optical disc 10 is as follows. When data recorded on the optical disk 10 is reproduced, a laser beam of reproduction power is irradiated from the semiconductor laser element of the optical pickup 16, and the reflected light is converted into an electric signal by the PD and output. A reproduction signal from the optical pickup 16 is supplied to the RF circuit 26. The RF circuit 26 generates a focus error signal and a tracking error signal from the reproduction signal and supplies them to the servo processor 30. The servo processor 30 servo-controls the optical pickup 16 based on these error signals, and maintains the optical pickup 16 in an on-focus state and an on-track state. Further, the RF circuit 26 supplies an address signal included in the reproduction signal to the address decoding circuit 28. The address decoding circuit 28 demodulates the address data of the optical disk 10 from the address signal and supplies it to the servo processor 30 and the system controller 32. Further, the RF circuit 26 supplies the reproduction RF signal to the binarization circuit 34. The binarization circuit 34 binarizes the reproduction signal and supplies the obtained signal to the encoding / decoding circuit 36. The encode / decode circuit 36 demodulates the binary signal and corrects errors to obtain reproduction data, and outputs the reproduction data to a host device such as a personal computer via the interface I / F 40. When the reproduction data is output to the host device, the encoding / decoding circuit 36 temporarily stores the reproduction data in the buffer memory 38 and outputs it.

  When recording data on the optical disk 10, data to be recorded from the host device is supplied to the encode / decode circuit 36 via the interface I / F 40. The encode / decode circuit 36 stores data to be recorded in the buffer memory 38, encodes the data to be recorded, and supplies the data to the write strategy circuit 42 as modulated data. The write strategy circuit 42 converts the modulation data into a multi-pulse (pulse train) or the like according to a predetermined recording strategy, and supplies it to the driver 22 as a recording pulse. Since the recording strategy affects recording quality, optimization is performed prior to data recording. The laser light power-modulated by the recording pulse is irradiated from the semiconductor laser element of the optical pickup 16 and data is recorded on the optical disk 10. The recording power at the time of data recording is optimized by trial writing test data using a PCA (Power Calibration Area) formed on the inner circumference side of the optical disc 10 by OPC (Optimum Power Control). . After recording the data, the optical pickup 16 reproduces the recorded data by irradiating a laser beam with a reproduction power, and supplies it to the RF circuit 26. The RF circuit 26 supplies the reproduction signal to the binarization circuit 34, and the binarized data is supplied to the encode / decode circuit 36. The encoding / decoding circuit 36 decodes the modulated data and collates it with the recording data stored in the buffer memory 38. The result of the verification is supplied to the system controller 32. The system controller 32 determines whether to continue recording data or execute a replacement process according to the result of verification. The system controller 32 controls the operation of the entire system, drives the sled motor 18 via the servo processor 30, and controls the position of the optical pickup 16.

  FIG. 2 shows a circuit configuration of the APC 24 in FIG. The front monitor PD arranged in the vicinity of the semiconductor laser element (LD) receives the laser beam and outputs a current corresponding to the laser beam power. The detection current is supplied to the current / voltage converter I / V 24a after only a signal of a predetermined period is sampled by a sampling circuit (not shown). The current-voltage converter I / V 24a converts the input current value into a voltage value, and outputs it to the inverting input terminal (−) of the differential amplifier 24c. On the other hand, the system controller 32 supplies a target level (target voltage value) corresponding to the optimum recording power set by OPC to the non-inverting input terminal (+) of the differential amplifier 24c. The differential amplifier 24c compares the signal voltage value with the target voltage value, amplifies the error value, and outputs the amplified error value to the voltage / current converter V / I 24d. The voltage-current converter 24d supplies the amplified current (drive current) to the driver 22 and performs feedback control so that the recording power of the semiconductor laser element always becomes the optimum recording power determined by OPC. In FIG. 2, an A / D may be provided after the current / voltage converter I / V 24a and a D / A may be provided before the voltage / current converter V / I 24d.

  As described above, the recording power is optimized by using both the OPC operation and the APC operation. However, if the recording takes a long time despite the APC operation being performed during recording, the recording quality is improved. It may deteriorate. The reason is that not only the temperature of the semiconductor laser element rises and the recording power of the semiconductor laser element, that is, the amount of light emission decreases, but also the wavelength of the laser beam shifts to the longer wavelength side. This is because even if the decrease in the light emission amount of the semiconductor element can be compensated, it cannot be compensated until the decrease in the light absorption rate of the optical disk 10 due to the wavelength shift. When the recording film of the optical disk 10 is an organic dye system (for example, CD-R, DVD-R, etc.), the recording sensitivity is deteriorated because the light absorption rate of the recording film changes depending on the wavelength of the laser beam.

  FIG. 3 shows the relationship between the wavelength of the laser beam and the light absorption rate of the recording film when the recording film is an organic dye. When the wavelength of the laser light is shifted from λ1 to λ2 toward the longer wavelength side, the light absorption rate of the recording film is significantly reduced. Since the light absorptance of the recording film affects the degree of pit formation, a decrease in the light absorptivity causes a deterioration in recording quality. Therefore, in addition to the power adjustment by the APC 24, it is necessary to accurately evaluate the wavelength shift accompanying the temperature rise of the semiconductor laser element, and to adjust the recording power so as to compensate for the decrease in the light absorption rate of the recording film according to the evaluation result. There is. On the other hand, the configuration for directly detecting the temperature of the semiconductor laser element or the configuration for directly detecting the shift of the laser light wavelength leads to a complicated or large configuration. Therefore, in the present embodiment, attention is paid to the drive current that is the output of the APC 24, the temperature rise of the semiconductor laser element is detected by the change of the drive current, and the shift of the laser light wavelength is further detected. The APC 24 sequentially increases the drive current so as to compensate for the decrease in the light emission amount accompanying the temperature rise of the semiconductor laser element. Therefore, the increase in the temperature of the semiconductor laser element can be quantitatively evaluated from the increase in the drive current that is the output of the APC 24. In FIG. 2, the drive current from the V / I 24d is supplied to the driver 22 and also to the system controller 32 for this reason. The system controller 32 constantly monitors the drive current to monitor the temperature of the semiconductor laser element. Detect rise.

  FIG. 4 shows the relationship between the drive current, which is the output of the APC 24, and the light emission amount, with the temperature of the semiconductor laser element as a parameter. As the temperature T of the semiconductor laser element increases to 20 ° C., 50 ° C., and 80 ° C., the drive current necessary to obtain the same light emission amount increases sequentially. Now, when the temperature of the semiconductor laser element is 20 ° C. and 50 ° C. and the driving currents for obtaining the light emission amount Pa are I1 and I2, respectively, conversely, when the driving current increases from I1 to I2, the semiconductor laser It means that the temperature of the device has increased from 20 ° C. to 50 ° C. The relationship of FIG. 4 (temperature characteristics of drive current and light emission amount) is a characteristic unique to the semiconductor laser element.

  FIG. 5 shows the relationship between the element temperature of the semiconductor laser and the emission wavelength. Generally, when the element temperature of a semiconductor laser rises, the emission wavelength is monotonously shifted to the long wavelength side. The temperature and the emission wavelength are uniquely determined. When the element temperature is T1 and T2, the emission wavelengths are λ1 and λ2, respectively. It will be understood from the relationship between FIGS. 4 and 5 that the change in the wavelength of the laser light can be detected from the change in the drive current.

  As described above, the shift of the laser light wavelength from the change in the driving current of the APC 24 to the longer wavelength side can be evaluated. The shift to the longer wavelength side of the laser light wavelength appears as a deterioration of the recording film sensitivity when the recording film is an organic dye-based material, particularly a change in the β value. Therefore, the optimum recording power is set so that the β value becomes a desired value. By further adjusting the recording quality, the recording quality can be maintained.

  FIG. 6 shows the relationship between the emission wavelength and the recorded β value. Here, the β value is a value defined as β = (A + B) / (A−B), where A is the peak level of the reproduction RF signal that is AC-coupled, and B is the bottom level. Is the parameter used for. In OPC, the recording power is adjusted so that this β value matches the target β value. If the obtained β value is constant, it can be evaluated that the recording quality is constant. As shown in the figure, when the emission wavelength shifts to the longer wavelength side, the β value also decreases due to a decrease in the absorption rate of the recording film. If the β value at the wavelength λ1 is β1, the β value at the wavelength λ2 is lowered to β2. Therefore, when the wavelength is shifted from λ1 to λ2, the recording power may be increased in order to increase β2, which is the β value at the wavelength λ2, to β1, which is the original β value.

  FIG. 7 shows the relationship between the recording power and the β value. This relationship is well known when executing OPC. In OPC, the recording power is changed in a plurality of stages, the β value is measured, and the recording power at which the target β value is obtained is set to the optimum recording power. As can be seen from FIG. 7, the recording power and the β value uniquely correspond to each other. If β1 is obtained when the recording power P1 and β2 is obtained when the recording power P2, the current β2 is set to β1. It can be seen that the required power increment ΔP is ΔP = P1−P2.

  When the relationship between the recording power P and the β value is expressed as a function β = f (P), strictly speaking, the function β = f (P) at the wavelength λ1 of the laser beam and the function β = f (P at the wavelength λ2). ) Is slightly different. Specifically, the function β = a1P + b1 at the wavelength λ1 is different from the function β = a2P + b2 at the wavelength λ2. However, the applicant has confirmed that almost all of the temperature rise of the semiconductor laser element during data recording can be regarded as a1 = a2 and b1 = b2. Therefore, the relationship β = f (P) acquired at the time of OPC execution (the relationship at the time of wavelength λ1 because it is performed prior to recording) is used as it is, and the relationship β = f (P) at the wavelength λ2 is established. From the above, it is possible to calculate the recording power increment ΔP for setting β2 to β1.

  FIG. 8 shows the recording power adjustment process of this embodiment. First, prior to recording, OPC is executed to set the optimum recording power Po (S101). That is, test data is test-written in the test area of the optical disc 10 by changing the recording power into a plurality of stages, the test data is reproduced, the β value is measured, and the measured β value is stored in the memory of the system controller 32 in advance. The stored target β value is compared, and the recording power at which the target β value is obtained is set as the optimum recording power Po. During OPC execution, the value of the drive current Io necessary for obtaining the optimum recording power Po and the relationship between the recording power and the β value are acquired and stored in the memory of the system controller 32 (S102, S103). The drive current Io is an output of the APC 24 for obtaining the initial optimum recording power Po, and is a current value serving as a reference for detecting a temperature rise of the semiconductor laser element. Further, the relationship between the recording power and the β value when executing OPC corresponds to the relationship shown in FIG. The relationship between the recording power and the β value may be stored in the memory as a set of numerical values, or may be stored in the memory as a function obtained by linear approximation or higher-order approximation.

  The optimum recording power Po is set by OPC, the drive current Io and the relationship between the recording power and the β value are acquired and stored, and then data is recorded in the data area of the optical disc 10 (S104). During data recording, the APC 24 always adjusts the drive current so that the recording power matches the optimum recording power Po. As the temperature of the semiconductor laser element rises, the amount of light emission decreases, so that the drive current is sequentially increased from Io so as to compensate for this decrease.

  The system controller 32 always monitors the drive current (at a predetermined time interval) during recording, and determines whether or not the increment from the drive current Io has reached a predetermined value ΔIp (S105). This predetermined value is a value for determining that the temperature of the semiconductor laser element has risen to such an extent that the recording quality deteriorates, and is stored in the memory of the system controller 32 in advance. When the drive current increment reaches ΔIp, it is assumed that the temperature of the semiconductor laser element has risen to a degree that cannot be ignored (to the extent that the recording quality deteriorates), and the current β value associated with the temperature rise is estimated ( S106). Specifically, the current β value is estimated as follows. That is, the current temperature of the semiconductor laser element can be detected from the increment of the drive current as shown in FIG. 4, and the current emission wavelength can be detected from the temperature of the semiconductor laser element as shown in FIG. Then, the current β value can be estimated from the current emission wavelength using the relationship of FIG. The memory of the system controller 32 may store the correspondence relationships of FIGS. 4, 5, and 6, and obtain the relationship between the drive current and β from the relationships of FIGS. Relationships may be stored. The system controller 32 can estimate the current β value using these relationships stored in the memory.

  After estimating the current β value, the system controller 32 uses the estimated β value to record the target β value based on the relationship between the recording power and the β value acquired at the time of OPC execution and stored in the memory. The power is calculated and supplied to the APC 24 as a new target level (S107). As shown in FIG. 2, when APC is executed, the system controller 32 supplies a new target level to the differential amplifier 24c of the APC 24 so that a new optimum recording power can be obtained. The system controller 32 supplies the new target level to the APC 24 instead of the initial target level, thereby updating the light emission amount that is the optimum recording power of the semiconductor laser element from Po to Po + ΔP. Thereby, the target β value can be obtained even at the current wavelength, and the recording quality can be maintained.

  As described above, in the present embodiment, the temperature rise of the semiconductor laser element, the wavelength shift accompanying the temperature rise, and the β value change accompanying the wavelength shift are detected based on the change (increase) in the drive current of the APC 24, and recording is performed. Since the optimum recording power Po is adjusted by calculating the recording power necessary to return the current β value to the original target β value using the relationship between the power and the β value, a temperature sensor or a wavelength detection sensor Etc., and it is possible to suppress deterioration in recording quality due to temperature rise of the semiconductor laser device using the existing APC 24.

  In the present embodiment, the recording power necessary for returning the current β value to the target β value is calculated using the relationship between the recording power and the β value. The relationship between the emission wavelength and the β value shown in FIG. From the relationship and the relationship between the recording power and β value shown in FIG. 7, the relationship between the emission wavelength and the optimum recording power is calculated and stored in the memory as shown in FIG. 9, and based on the change in the drive current of the APC 24 After detecting the wavelength shift, the optimum recording power at the current wavelength may be obtained and updated. Specifically, the element temperature of the semiconductor laser is first detected using the relationship shown in FIG. 4 in accordance with the change in drive current, and the emission wavelength at the detected element temperature is detected using the relationship shown in FIG. Then, the target level supplied to the APC 24 may be updated by obtaining the optimum recording power at the current emission wavelength using the relationship shown in FIG.

  Further, as shown in FIG. 10, the relationship between the drive current and the optimum recording power is calculated and stored in the memory using the relationship shown in FIGS. The optimum recording power may be obtained directly from the drive current and updated.

  In the present embodiment, the function β = a1P + b1 at the wavelength λ1 and the function β = a2P + b2 at the wavelength λ2 are substantially the same. It may be used to calculate the optimum recording power. That is, the wavelength of the laser beam is calculated from the change in the drive current, the optimum recording power for obtaining the target β value is calculated using the function at the calculated wavelength, and a new target level is supplied to the APC 24.

  In this embodiment, the β value is used as the recording quality, but a γ value, an error rate, a modulation degree, and the like can also be used.

  Further, in the present embodiment, it can be used together with the retrospect OPC. The look-back OPC is interrupted in the middle of data recording, reproduces the previous recorded portion, calculates the recording quality (β value, etc.), and continues to add according to the deviation from the target quality (target β value). The recording power is corrected. By using the method of the present embodiment together with the retrospective OPC, the number of executions of the retrospective OPC can be reduced, so that the recording time can be shortened.

Furthermore, in the present embodiment, the temperature increase is described as an example of the temperature variation of the semiconductor laser element, but the present invention is not limited to the temperature increase, and can be applied to a temperature decrease. When the temperature decreases, the emission wavelength shifts to the short wavelength side, thereby increasing the light absorption rate of the optical disc 10 and improving the recording film sensitivity. Then, it can be estimated that the β value is increasing, and the recording power is updated (the optimum recording power is reduced) so as to decrease to the target β value. By thus adjusting the recording power to be reduced, it is possible to prevent thermal distortion of the reproduced signal waveform due to excessive recording power (so-called over-baking). The case where the temperature decreases is, for example, the case where the recording is resumed after the recording is interrupted, and the recording power at the time of the interruption is stored in the memory when the recording is resumed, and is used as it is at the time of the resume (thereby This eliminates the need to re-execute OPC).

1 is a block diagram illustrating a configuration of an optical disc device. It is a block diagram of APC in FIG. It is a figure which shows the relationship between the light emission wavelength and the light absorption rate of a recording film. It is a figure which shows the relationship between a drive current, light emission amount, and element temperature. It is a figure which shows the relationship between element temperature and light emission wavelength. It is a figure which shows the relationship between a light emission wavelength and recording beta value. It is a figure which shows the relationship between recording power and recording (beta) value. It is a processing flowchart of an embodiment. It is a figure which shows the relationship between light emission wavelength and optimal recording power. It is a figure which shows the relationship between a drive current and optimal recording power.

Explanation of symbols

  10 Optical disk, 24 APC (auto power control circuit) 24, 32 System controller.

Claims (6)

A semiconductor laser that records data by irradiating an optical disk with laser light; and
A power control circuit that feedback-controls the drive current of the semiconductor laser so that the power of the laser beam matches a target power;
An adjustment circuit that adjusts the target power to compensate for a recording quality degradation caused by a wavelength shift due to a temperature variation of the semiconductor laser in accordance with a change in the drive current;
An optical disc apparatus comprising: The apparatus of claim 1.
The adjustment circuit uses the relationship between the drive current and the element temperature of the semiconductor laser, the relationship between the element temperature and the wavelength, the relationship between the wavelength and the recording quality, and the relationship between the power and the recording quality. An optical disc apparatus, wherein the target power is adjusted according to a change in current. The apparatus of claim 2.
The adjustment circuit includes:
A memory for storing the relationship between the drive current and the element temperature of the semiconductor laser, the relationship between the element temperature and the wavelength, the relationship between the wavelength and the recording quality, and the relationship between the power and the recording quality; Is calculated using the relationship between the drive current and the element temperature of the semiconductor laser, and the wavelength of the laser light is calculated using the relationship between the element temperature and the wavelength. Calculating the recording quality at the wavelength of the laser beam using the relationship between the wavelength and the recording quality, and obtaining the target recording quality at the wavelength of the laser beam using the relationship between the power and the recording quality. An optical disc apparatus characterized by calculating The apparatus of claim 3.
An optical disc apparatus characterized in that the recording quality is a β value. The apparatus of claim 1.
The adjustment circuit uses the relationship between the drive current and the element temperature of the semiconductor laser, the relationship between the element temperature and the wavelength, and the relationship between the wavelength and the target power, according to a change in the drive current. An optical disc apparatus characterized by adjusting power. The apparatus of claim 5.
The adjustment circuit includes:
A memory for storing a relationship between the drive current and an element temperature of the semiconductor laser, a relationship between the element temperature and a wavelength, and a relationship between the wavelength and a target power, and the drive according to a change in the drive current; The element temperature of the semiconductor laser is calculated using the relationship between the current and the element temperature of the semiconductor laser, the wavelength of the laser beam is calculated using the relationship between the element temperature and the wavelength, and the wavelength and the target power The target power at the wavelength of the laser light is calculated using the relationship.

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