JP4359125B2 - Semiconductor laser measuring device - Google Patents

Description

  The present invention relates to a semiconductor laser measuring apparatus for measuring a semiconductor laser used in an optical recording apparatus for recording data on a recording medium by driving a semiconductor laser of an optical head by a laser driving signal having a pulse waveform output from a laser driver. In particular, the present invention relates to a semiconductor laser measuring device that detects the stability of the emission amount of a semiconductor laser.

  As an optical disk recording apparatus for recording a digital data signal on a disk using a light beam from an optical head, CD-R (Recordable) and CD-RW (ReWritable) of CD (Compact Disc) family, or DVD (Digital Versatile) Drive devices corresponding to minus (−) and plus (+) R (Recordable), − and + RW (ReWritable), and RAM of the Disc family are well known. In this case, the recording speed is increased.

  By the way, in the optical head used in such an optical recording apparatus, the semiconductor laser (laser diode) serving as a light source is initially defective or deteriorates, so that the characteristics of the semiconductor laser become out of specification, and the semiconductor laser is defective. If so, the laser output emitted from the optical head does not become the intended value, and a recording failure occurs.

  Therefore, the characteristics of the semiconductor laser of the optical head are measured, and when the characteristics of the semiconductor laser are out of specification, the use of the optical recording apparatus is stopped, or the recording operation is prohibited and the recording medium such as a defective recording disk Needs to be created.

For this reason, it is detected that the semiconductor laser is defective and the recording operation is prohibited in that case. (See Patent Document 1)
JP-A-5-342594

  By the way, it is known that when the laser light reflected by the recording medium is returned to the laser diode of the optical head, the return light interferes with the laser light emitted from the laser diode, and the light emission output of the laser diode becomes unstable. It has been. This phenomenon becomes prominent in an optical head adapted to high-speed recording in which the intensity of the laser emitted from the laser diode is increased.

  Therefore, in order to prevent the light emission output of the laser diode from becoming unstable, an optical head having a polarization optical system is provided so that the laser light reflected by the recording medium is polarized by a half wavelength and is not returned to the laser diode. In many cases, the optical head of a non-polarizing optical system that does not include this polarizing optical system is inevitably adopted due to cost limitations.

  If an optical head of such a non-polarization optical system is adopted, the light emission output of the laser diode becomes unstable as described above, so that servo failure is likely to occur during recording, and the recording quality is deteriorated. invited.

  In the semiconductor laser measuring apparatus disclosed in Patent Document 1, it is not measured that the light emission output of the laser diode is unstable.

  In addition, since the recording speed is increased in the optical recording apparatus, and the pulse width of the pulse waveform of the laser drive signal is narrowed by the write strategy, the laser based on the pulse width of the pulse waveform corresponding to the recording speed. Unless the stability of the light emission output of the diode is measured, the stability of the light emission output of the laser diode in accordance with actual use cannot be measured.

  The present invention measures the amplitude value of the write power value generation period of the monitor output obtained by the monitor light receiving element at the timing corresponding to the period of generating the write power value in the pulse waveform for performing mark recording of the laser drive signal by the signal generation circuit. Measuring means for comparing the amplitude value measured by the measuring means with a standard value set in advance corresponding to the amplitude value for each predetermined write power value of the laser drive signal from the laser driver on the recording medium. And a determination means for determining the stability of the light emission output from the semiconductor laser based on the comparison, and when the determination means determines the stability of the light emission output from the semiconductor laser, the focus is obtained using a read-only recording medium. While the servo is turned on and the tracking servo is turned off, the laser driver And so as to generate a laser driving signal when recording.

  The semiconductor laser measuring apparatus of the present invention measures the amplitude value of the monitor output obtained by the monitor light receiving element during the generation period of the write power value in the pulse waveform of the laser drive signal by the measuring means, and this amplitude value and the predetermined write power value By comparing with a standard value set in advance corresponding to the amplitude value every time, it can be determined whether or not the fluctuation amount of the monitor output in the write power value is larger than the standard value, and the emission output of the semiconductor laser can be determined. Stability can be measured.

  In this case, the amount of fluctuation of the monitor output at the write power value of the pulse waveform of the laser drive signal is measured, so the characteristics of the semiconductor laser can be measured according to actual use, and the recording speed can be increased. Correspondingly, it is possible to measure the stability of the emission output of the semiconductor laser in a state where the semiconductor laser is driven by a laser drive signal having a pulse waveform with a narrow pulse width.

  In particular, since the focus servo is turned on using a read-only recording medium and the laser drive signal is generated when data is recorded from the laser driver with the tracking servo turned off, recording on the recording medium is performed. The stability of the emission output of the semiconductor laser can be measured without performing the above.

  In addition, the stability of the light emission output of the semiconductor laser is measured by using an existing circuit in the optical recording apparatus, and the circuit configuration is simplified.

  In addition, the tolerance of the standard value for determining that the light emission output from the semiconductor laser is normal is widened by the judging means in response to the increase of the write power value of the laser drive signal. The ratio of the width is set to be constant or nearly constant, and the determination of the stability of the light output of the semiconductor laser by the change of the write power value can be made equal.

  In addition, it is possible to determine the stability of the emission output of the semiconductor laser for each output level that changes the laser drive signal generated from the laser driver, so that the region where the semiconductor laser becomes unstable beyond the tolerance can be understood, It is possible to perform a recording operation in an area where it does not become unstable.

  FIG. 1 is a circuit block diagram showing an embodiment of an optical disk recording / reproducing apparatus provided with a semiconductor laser measuring apparatus according to the present invention. This optical disk recording / reproducing apparatus employs an optical head of a non-polarization optical system.

  A laser diode 1 serving as a light source of the optical head is driven by a laser driver 2 and emits a laser beam for recording and reproduction on a disk (not shown).

  The optical head is provided with a front monitor diode 3 for receiving a laser beam emitted from the laser diode 1 and separated in the middle of the optical path guided to the disk. The front monitor diode 3 has a light intensity of the received laser beam. In response, a light receiving current flows, and a monitor output of a voltage signal corresponding to the light receiving current is generated.

  The laser driver 2 is supplied with a signal selected by the switch circuits 5 and 6 that is switched at a timing associated with the operation of the encoder / decoder 4, and the read power generated from the read power signal generation circuit 8 at the time of disk reproduction. A signal is supplied, and a pulse waveform signal generated by the read power signal generated from the read power signal generation circuit 8 and the write power signal generated from the write power signal generation circuit 9 is supplied during recording of the write-once disk. Is done.

  The APC output from an APC (Automatic Power Control) circuit 11 is input to the read power signal generation circuit 8. In this APC circuit 11, the monitor output corresponding to the light quantity of the laser beam received by the front monitor diode 3 is related to the processing operation by the encoder / decoder 4 by the sample / hold circuit (S / H circuit) 12 and the read power The S / H voltage sampled and held at the timing when the laser diode 1 is driven by the value and the data acquired and stored in advance in correspondence with the recording condition and reproduction condition by the CPU 13 are converted into a digital / analog conversion circuit (D / A reference voltage obtained by digital / analog conversion is applied by the A circuit) 14, and the APC circuit 11 corrects the APC output corresponding to the differential voltage of the S / H voltage with respect to the reference voltage.

  Therefore, the read power signal generation circuit 8 generates a control signal for controlling the laser driver 2 so as to control the monitor output from the front monitor diode 3 to be constant corresponding to the read power value by the APC output from the APC circuit 11. To do.

  During disk reproduction, the data supplied from the CPU 13 to the D / A circuit 14 is set so that the laser diode 1 is driven so that the laser output is suitable for reproduction conditions such as the disk type and recording speed. Therefore, the read power signal generation circuit 8 generates a read power signal for controlling the laser driver 2 so as to control the laser output from the laser diode 1 to a certain level suitable for disk reproduction that meets the reproduction conditions.

  On the other hand, at the time of recording on a write-once disk, the data supplied from the CPU 13 to the D / A circuit 14 is such that the drive of the laser diode 1 has a laser output appropriate for the read power value suitable for the recording conditions such as the disk type and recording speed. It is set to be. Therefore, the read power signal generation circuit 8 generates a read power signal for controlling the laser driver 2 to control the laser output from the laser diode 1 to a certain level of the read power value suitable for disk recording that meets the recording conditions. .

  Either the APC output from the APC circuit 16 or the ACC output from the ACC (Automatic Current Control) circuit 17 is selectively input to the write power signal generation circuit 9 by switching the switch circuit 15.

  The APC circuit 16 outputs a monitor output corresponding to the amount of the laser beam received by the front monitor diode 3 at a timing when the laser diode 1 is driven by the sample / hold circuit (S / H circuit) 18 by the write power value. The S / H voltage (WSHO voltage) sampled and held during the write power value generation period and the data acquired and stored in advance by the CPU 13 corresponding to the recording conditions are output by a digital / analog conversion circuit (D / A circuit) 19. A digital / analog converted reference voltage is applied. Note that the sample period of the S / H circuit 18 is set by the WAPC signal of the timing signal for generating the write power value of the encoder / decoder 4, whereby the sample period becomes the timing at which the laser diode 1 is driven by the write power value. ing.

  Therefore, the APC circuit 16 corrects the APC output corresponding to the differential voltage of the S / H voltage (WSHO voltage) with respect to the reference voltage.

  When the APC output from the APC circuit 16 is selected by switching the switch circuit 15, the write power signal generation circuit 9 changes the monitor output from the front monitor diode 3 to the write power value by the APC output from the APC circuit 16. A write power signal for controlling the laser driver 2 is generated to control the corresponding constant. In this case, the write power signal generation circuit 9 generates a write power signal for controlling the laser driver 2 to control the laser output from the laser diode 1 to a certain level of the write power value suitable for disk recording that meets the recording conditions. .

  On the other hand, the ACC circuit 17 is applied with an ACC voltage generated by digital / analog conversion of data stored in the CPU 13 by a digital / analog conversion circuit (D / A circuit) 20, and the ACC circuit 17 uses the ACC voltage. Based on this, an ACC signal having a constant current is generated.

  Therefore, when the ACC output from the ACC circuit 17 is selected by switching the switch circuit 15, the write power signal generation circuit 9 responds to the write power value by the ACC output from the ACC circuit 17. A write power signal for controlling the is generated. In this case, the write power signal generation circuit 9 generates a write power signal for controlling the laser driver 2 so as to control the laser output from the laser diode 1 to a write power value suitable for disk recording that meets the recording conditions.

  The switching control circuit 21 controls switching of the switch circuit 15 based on the operation of the encoder / decoder 4, whereby the switch circuit 15 selects the ACC output from the ACC circuit 17 immediately before recording at the time of disk recording, and starts recording. At the same time, the APC output from the APC circuit 16 is selected.

  That is, the ACC circuit 17 is a first-out setting circuit for setting a control output to be generated by the write power signal generation circuit 9 until immediately before recording at the time of recording on the disc.

  The peak value of the S / H voltage (WSHO voltage) obtained by sampling and holding the monitor output from the front monitor diode 3 by the S / H circuit 18 during the write power value generation period is extracted by the peak hold circuit (PH circuit) 22. At the same time, the bottom value is extracted by the bottom hold circuit (BH circuit) 23.

The peak value of the S / H voltage (WSHO voltage) extracted during the write power value generation period extracted by the peak hold circuit 22 is converted into digital data by an analog / digital conversion circuit (A / D circuit) 24 and then supplied to the CPU 13. On the other hand, after the bottom value of the S / H voltage (WSHO voltage) extracted during the write power value generation period extracted by the bottom hold circuit 23 is converted into digital data by the analog / digital conversion circuit (A / D circuit) 25, the CPU 13
To be supplied.

  The CPU 13 measures the amplitude value of the WSHO by calculating the difference between the peak value of the WSHO voltage of the digital data via the A / D circuit 24 and the bottom value of the WSHO of the digital data via the A / D circuit 25. Means 26 and determination means 27 for determining the stability of the light emission output from the laser diode 1 based on the amplitude value of the WSHO voltage measured by the measuring means 26 are provided.

  In the circuit shown in FIG. 1 configured as described above, when measuring the stability of the light emission output of the laser diode 1, it is generally measured by setting a read-only stamp disk on which a signal surface is formed by aluminum vapor deposition. Perform the start operation.

  When this measurement start operation is performed, the disk is driven at a predetermined constant angular velocity (CAV) using, for example, a rotary encoder, regardless of whether the disk is of a constant linear velocity type. Then, the focus servo of the optical head is set to the on state, and the tracking servo is set to the off state.

  Further, the laser driver 2 is controlled by a recording signal generated from a signal generating circuit composed of a read power signal generating circuit 8 and a write power signal generating circuit 9, and a light emission output corresponding to the time of disk recording is generated from the laser diode 1. Become so. In this case, the write strategy is set by the CPU 13 so as to correspond to the maximum recording speed that can be recorded or a recording state at a predetermined speed close to this maximum speed, and the APC output from the APC circuit 16 is switched by the switching of the switch circuit 15. The APC to be selected is turned on.

  Then, the switch circuits 5 and 6 are switched so that random recording is performed, and a pulse waveform test signal generated by the read power signal and the write power signal is supplied to the laser driver 2.

  Here, the write power setting value set in the D / A circuit 19 by the CPU 13 is a laser at a predetermined output step within a measurement range of a write power value for driving the laser diode 1, for example, 25 mW to 60 mW, for example, 5 mW step. Write power is output from the diode 1.

  The laser driver 2 is controlled by a test signal corresponding to the read power setting value set by the D / A circuit 14 and the write power setting value set by the D / A circuit 19, and the laser diode 1 is driven by the laser driver 2. Then, the monitor output from the front monitor diode 3 is sampled and held by the S / H circuit 18 at the timing when the laser diode 1 is driven by the write power value to obtain the WSHO voltage. The peak value and the bottom value are extracted by the PH circuit 22 and the BH circuit 23, respectively.

  The peak value and the bottom value of the WSHO voltage are respectively taken into the CPU 13 after A / D conversion, and the measuring means 26 calculates the difference between the peak value and the bottom value of the WSHO voltage to measure the amplitude value of the WSHO voltage.

Here, a recording signal having a pulse waveform is generated in accordance with the encoding operation of the encoder / decoder 4, and the monitor output from the front monitor diode 3 (minus from Vref is inverted in polarity with respect to the recording signal to have a negative polarity. 2) is generated as shown in FIG. 2B, the WAPC signal is generated as shown in FIG. 2B to synchronize with the timing of the period corresponding to the write power of the monitor output. By this WAPC signal, the S / H circuit 1
The timing at which the sample is held by 8 is determined. For this reason, the amplitude value of the WSHO voltage of the monitor output measured by the measuring means 26 in the CPU 13 is based on the write power value of the recording signal.

  The amplitude value of the WSHO voltage measured by the measuring unit 26 is compared with a standard value for each write power value set in advance by the determining unit 27. As shown by the shaded portion in FIG. 3, the standard value S has a wider allowable range corresponding to the increase in the write power value centered on the reference value indicated by the solid line. The determination means 27 determines the amplitude of the WSHO voltage. It is determined whether or not the value is within the standard value for each corresponding write power value, and when the amplitude value of the WSHO voltage is within the standard value, it is determined that the light emission output from the laser diode 1 is stable.

  The above-described measurement of the amplitude value of the WSHO voltage by the measuring unit 26 and the determination of whether the amplitude value of the WSHO voltage by the determination unit 27 is within the standard value are the write power setting values set in the D / A circuit 19. Is performed every time the write power value for driving the laser diode 1 is switched.

  Incidentally, since the optical disk recording apparatus shown in FIG. 1 employs an optical head of a non-polarization optical system, the laser light reflected by the disk is returned to the laser diode 1 and the return light is emitted from the laser diode 1. The light emission output of the laser diode 1 becomes unstable due to interference with the laser light, but if the amplitude value of the WSHO voltage is within the standard value, it is determined that the degree of instability is within an allowable range for practical use. I can do it.

  In this way, the amplitude value of the WSHO voltage is measured for each write power value changed in predetermined increments, and each time it is determined whether or not the amplitude value of the WSHO voltage is within the standard value, the laser diode 1 The stability of the light output is determined. This determination is stored in the RAM 28 in the CPU 13 in association with each write power value.

  When it is determined that the amplitude value of the WSHO voltage is outside the standard value and it is determined that the stability of the light emission output of the laser diode 1 is outside the allowable range, the determination of instability is performed. The recording operation using the specified write power value is prohibited.

  That is, it is possible to allow only a recording operation using a write power value in which the light emission output of the laser diode 1 is stable according to the determination data stored in the RAM 28 in the CPU 13.

  The present invention can be applied to a semiconductor laser measuring apparatus that measures the stability of the emission output of a semiconductor laser when the return light interferes when the quality inspection of the semiconductor laser is performed.

It is a circuit block diagram which shows one Example of an optical disk recording device provided with the semiconductor laser measuring apparatus which concerns on this invention. 4 is a timing chart showing the timing at which a WSHO voltage, which is a monitor voltage during a write power value generation period, obtained from the front monitor diode 3 is sampled and held by the S / H circuit 18; It is explanatory drawing which shows the standard value for every write power value compared with the amplitude value of a WSHO voltage by the determination means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser diode 2 Laser driver 3 Front monitor diode 4 Encoder / decoder 8 Read power signal generation circuit 9 Write power signal generation circuit 13 CPU
16 APC circuit 17 ACC circuit 18 S / H circuit 19, 20 D / A circuit 22 Peak hold circuit 23 Bottom hold circuit 26 Measuring means 27 Determination means

Claims (4)

Oite the semiconductor laser measuring device for measuring a semiconductor laser used in an optical recording apparatus for recording data to the semiconductor laser of the optical head to the recording medium by driving a laser drive signal pulse waveform outputted from the laser driver, wherein A signal generation circuit for generating a control signal for controlling the laser driver to generate a laser drive signal having a pulse waveform from the laser driver, and an encoder for generating a control signal from the signal generation circuit corresponding to the recording data to be recorded on the recording medium And a monitor light receiving element for receiving light emitted from the semiconductor laser of the optical head, and the monitor light receiving at a timing corresponding to a period for generating a write power value in a pulse waveform for performing mark recording of a laser drive signal by the signal generating circuit. Light of monitor output obtained by the element Measuring means for measuring the amplitude value of the word value generation period, the amplitude value measured by this measuring means and a predetermined write power value of the laser drive signal from the laser driver on the recording medium in advance corresponding to the amplitude value A determination means for determining the stability of the light emission output of the semiconductor laser based on the comparison with a set standard value, and when determining the stability of the light emission output of the semiconductor laser by the determination means, A semiconductor laser measuring apparatus, wherein a focus servo is turned on using a recording medium, and a laser drive signal for performing data recording is generated from the laser driver in a state where the tracking servo is turned off. The signal generation circuit includes an APC circuit that corrects a control signal generated in response to a monitor voltage obtained by sampling and holding a monitor output from the monitor light receiving element by a sample and hold circuit, and a measuring unit includes the sample and hold circuit 2. The semiconductor laser measuring apparatus according to claim 1, wherein the amplitude value is measured by detecting a peak value and a bottom value of the monitor voltage from the first to fourth. The standard value that is a criterion for comparison with the amplitude value of the write power value generation period of the monitor output by the determination unit is the light emission output of the semiconductor laser by the determination unit in response to an increase in the write power value of the laser drive signal. 2. The semiconductor laser measuring apparatus according to claim 1, wherein an allowable range for determining that the laser beam is stable is widened. The control signal generated from the signal generation circuit is changed in order to sequentially change the output level of the laser drive signal generated from the laser driver, and the amplitude value of the monitor output write power value generation period is measured by the measuring means each time. The semiconductor laser measuring apparatus according to claim 1, wherein the determination means determines the stability of the emission output of the semiconductor laser.

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