JP2005191264A - Light emitting device control unit, and optical information recording/reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To implement a light emitting device control unit emitting laser beams by a predetermined light amount, and an optical information recording/reproducing apparatus reliably and stably recording/reproducing optical information. <P>SOLUTION: The optical information recording/reproducing apparatus 1 comprises a light emitting device control unit 14. The light emitting device control unit 14 is structured to comprise a pulse generation circuit 18 for generating pulse signals, and to modulate the current supplied to a semiconductor laser 4 using the pulse signal and cause the semiconductor laser 4 to emit pulsed light. The light emitting device control unit 14 further comprises a controller 17 for detecting threshold current, which is a light emission starting current value of the semiconductor laser 4, and a duty adjustment circuit 19 for adjusting the pulse width of the pulse signals based on the detection result of the controller 17. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light emitting element control apparatus and an optical information recording / reproducing apparatus for controlling the amount of light emitted from a light emitting element such as a semiconductor laser used as a light source of an optical information recording / reproducing apparatus such as a magneto-optical disk apparatus. The present invention relates to control when a light emitting element such as a semiconductor laser emits pulses.

  Conventionally, magneto-optical disk devices such as MD (Mini Disk) are known as large-capacity optical information recording / reproducing devices. With the spread of such portable devices, the demand for further downsizing and low power consumption of the device is increasing. Further, as the capacity of information increases, the density and speed of magneto-optical disks increase, and an apparatus capable of recording and reproducing information with high reliability is desired.

  In a magneto-optical disk apparatus, a semiconductor laser is used as a light emitting element used for recording and reproducing information. Since a semiconductor laser is generally greatly affected by temperature drift, a light intensity of laser light applied to a magneto-optical disk is held at a predetermined value by using a control device that controls the amount of emitted light.

  When reproducing information recorded on the magneto-optical disk, the laser light emitted from the semiconductor laser is emitted as a direct current with a constant output. On the other hand, when recording information on a magneto-optical disk medium, a method based on laser pulse emission magnetic field modulation has been proposed as a method suitable for recording information on a magneto-optical disk at high density. This modulates the magnetic field according to the information data to be recorded and causes the laser beam to emit light at a channel clock frequency (see, for example, Patent Documents 1 to 3).

  In Patent Document 1, a data clock output from a data PPL circuit is supplied to a laser control circuit, and irradiation of a light beam onto a disk from an optical head is intermittently performed in synchronization with the data clock. In this way, by intermittently irradiating the light beam, the temperature change in the surrounding area where the bit is formed can be reduced compared to the case of irradiating the light beam continuously. A technique is disclosed that can prevent the displacement of the formation position.

  In Patent Document 2, in the laser diode drive circuit, a constant current circuit is connected between the switching transistor and the laser diode so that a current that is n times larger than the current flowing in the switching transistor flows in the laser diode. The power consumption can be reduced, and the laser diode is switched at a high frequency without being limited by the frequency characteristics of the constant current circuit. That is, a technique for emitting laser light with low power consumption is disclosed.

  In Patent Document 3, an accurate delay phase is given to a data clock by using a delay device capable of obtaining a plurality of delay phases, the light emission / extinction position of laser light that emits pulses is accurately set, and magnetic field modulation is performed. The phase of the data is also set separately according to the timing of laser light pulse emission. Thus, a technique capable of obtaining a laser driving pulse and a magnetic head driving pulse suitable for a magneto-optical disk device is disclosed.

  Here, the relationship between the laser drive current of the semiconductor laser and the laser light emission amount will be described. FIG. 6 is a graph showing the relationship between the driving current (forward current) of the semiconductor laser and the amount of emitted light, generally called an IP curve. As shown in FIG. 6, the semiconductor laser does not emit laser light below the threshold current Ith, which is the current at which the semiconductor laser starts to emit light. On the other hand, when the threshold current Ith is exceeded, the semiconductor laser emits laser light, and the amount of emitted light increases substantially in proportion to the drive current.

  The semiconductor laser is greatly affected by temperature drift, and the threshold current greatly changes depending on the temperature. In FIG. 6, the threshold current at 20 ° C. is illustrated as Ith20, and the threshold current at 50 ° C. is illustrated as Ith50. Although the threshold current is not a linear change with respect to the temperature, the average rate of change ranges from 0 ° C. to 50 ° C., and as high as 1% / ° C. Further, the value of the threshold current also changes with the aging of the semiconductor laser.

  When the semiconductor laser emits pulses, the drive current is pulse-driven to a current value that emits light with a predetermined light amount. FIG. 7 shows a pulse waveform when the semiconductor laser emits pulses. FIG. 7A shows a pulse waveform of the drive current, where the horizontal axis represents time and the vertical axis represents the drive current amount. FIG. 7B shows the pulse waveform of the semiconductor laser in FIG. 7A, where the horizontal axis represents time and the vertical axis represents the amount of emitted light.

  As shown in FIGS. 7A and 7B, when the drive current is less than or equal to the threshold current Ith of the semiconductor laser, the amount of light emitted from the semiconductor laser becomes almost zero. In addition, during the non-light emitting period Td, it is desirable that the drive current is zero in order to suppress current consumption.

  However, it takes some time for the drive current to rise / fall when the semiconductor laser emits pulses. The frequency of pulsed light emission has become a frequency exceeding 10 MHz (with a period of 100 ns or less) as recording / reproduction of the magneto-optical disk is accelerated. On the other hand, the drive current of the semiconductor laser requires several tens of mA, and even when a switching circuit that switches at high speed is used, it takes several ns for the rising Tr / falling Tf of the drive current. Sometimes.

  When the threshold current Ith of the semiconductor laser changes, the pulse emission duty changes. That is, the time during which the semiconductor laser emits light changes, and the ratio between the light emission time and the quenching time changes. Specifically, the semiconductor laser emits pulses from the time when the drive current exceeds the threshold current, and enters a non-emission state when the drive current becomes lower than the threshold current. Therefore, when the threshold current is Ith20, the semiconductor laser emits light for the period T20. When the threshold current is Ith50, light is emitted for the period T50.

  Such a change in duty of the pulsed emission changes the amount of laser light emitted by the pulsed light, and the magneto-optical disk cannot be irradiated with the appropriate amount of light. In addition, there will be a shift in timing between the magnetic field modulation data and the pulse emission of the laser beam. For this reason, in a magneto-optical disk apparatus that requires high reliability for information recording, a change in duty of pulsed light emission accompanying a change in the threshold current of the semiconductor laser is a problem that cannot be ignored.

  Several methods have been proposed for solving the problem that the pulse emission duty changes when laser light is pulsed (see, for example, Patent Documents 4 to 7).

Japanese Patent Application Laid-Open No. 2004-228867 discloses a technique for maintaining a constant optical output duty by detecting the operating temperature of a laser using a temperature sensor and changing the duty of a pulse signal for driving the laser in accordance with the detected temperature. It is disclosed. Patent Documents 5 and 6 disclose techniques for monitoring laser light that emits pulses with a photodetector, detecting the pulse width (duty), and controlling the laser light so as to have a predetermined duty. In Patent Document 7, in a drive circuit that drives a laser using a pulse current and a DC bias current, the drive current is controlled so that the ratio of the emission current (current in the region exceeding the threshold) to the pulse current is kept constant. Thus, a technique for keeping the duty of light output constant has been disclosed.
Japanese Patent Laid-Open No. 5-225638 (published on September 3, 1993) JP-A-6-349097 (published December 22, 1994) Japanese Patent Laid-Open No. 7-264023 (published October 13, 1995) JP 3-192784 A (published August 22, 1991) Japanese Patent Laid-Open No. 3-91277 (published on April 16, 1991) JP-A-5-63272 (published on March 12, 1993) JP-A-6-85362 (published on March 25, 1994)

  However, since the technique described in Patent Document 4 corrects the pulse emission duty in accordance with the operating temperature of the laser, the pulse emission duty change caused by the change in the threshold current accompanying the change over time of the semiconductor laser is reduced. There is a problem that it cannot be corrected. In addition, the configuration in which a temperature sensor is disposed in the vicinity of the laser to detect the temperature has a problem that the apparatus cannot be reduced in size.

  Further, in the techniques described in Patent Documents 5 and 6, the pulse emission duty is detected by the photodetector, but it is difficult to accurately detect the pulse emission duty in a device that is increasing in speed. Has the problem.

  Furthermore, in the technique described in Patent Document 7, a laser is driven by a pulse current and a DC bias current, and in order to control the drive current so that the ratio of the light emission current to the pulse current is kept constant, a bias is used. The current cannot be made zero. For this reason, the technique described in Patent Document 7 has a problem that it is difficult to suppress power consumption.

  In addition, Patent Documents 1 to 3 do not provide any specific proposals for solving the above problems. That is, in any of the above-described patent documents, it is impossible to control the duty change of pulsed light emission accompanying the change of the threshold current of the semiconductor laser.

  The present invention has been made in view of the above-described problems, and its purpose is to control the pulse emission duty so as to be a predetermined value even when the threshold current changes, so that it is always desired. It is to realize a light emitting element control device capable of emitting laser light with a sufficient amount of light and an optical information recording / reproducing device capable of always recording / reproducing with high reliability and stability.

  In order to solve the above-described problem, a light emitting element control device according to the present invention includes pulse generation means for generating a pulse signal, and uses the pulse signal to pulse-modulate a current supplied to the light emitting element, thereby pulsing the light emitting element. A light emitting element control device for emitting light, wherein a threshold value detecting means for detecting a threshold current which is a light emission start current value of the light emitting element, and a pulse for adjusting a pulse width of a pulse signal based on a detection result of the threshold value detecting means And width adjusting means.

  According to the above configuration, the light emitting element control device performs pulse modulation on the current using the pulse signal generated by the pulse generation unit, and controls the light emitting element to emit light in pulses. The threshold detection means detects the threshold current, and the pulse width adjustment means adjusts the pulse width of the pulse signal based on the detection result. As a result, even when the threshold current of the light emitting element changes, the light emitting element can be controlled to emit a desired pulsed light, so that the light emitting element can always emit pulses with a desired light amount. There is an effect.

  In the light emitting element control device according to the present invention, it is preferable that the threshold value detection means outputs a pulse width adjustment signal for adjusting the pulse width of the pulse signal. Since the threshold detection means outputs the pulse width adjustment signal, the pulse width adjustment means can adjust the pulse width of the pulse signal based on the pulse width adjustment signal, so that the stable pulse There is an additional effect that the width can be adjusted.

  In the light emitting element control device according to the present invention, it is preferable that the pulse width adjusting means adjusts the pulse width so that the duty of pulse light emission of the light emitting element is 50%. By adjusting the pulse width so that the duty of pulse light emission of the light emitting element is 50%, even when the threshold current of the light emitting element changes, pulse light emission can always be performed with a constant light amount. There is a further effect.

  In order to solve the above-described problem, a light emitting element control device according to the present invention includes pulse generation means for generating a pulse signal, and uses the pulse signal to pulse-modulate a current supplied to the light emitting element, thereby pulsing the light emitting element. A light-emitting element control device that emits light, detects a threshold current that is a light emission start current value of the light-emitting element, and outputs a light amount adjustment signal that adjusts the maximum emitted light amount of the light-emitting element based on the detection result It is characterized by comprising adjusting means.

  According to the above configuration, the light emitting element control device performs pulse modulation on the current using the pulse signal generated by the pulse generation unit, and controls the light emitting element to emit light in pulses. The light amount adjusting means detects the threshold current and outputs a light amount adjustment signal for adjusting the maximum emitted light amount of the light emitting element based on the detection result. Accordingly, even when the threshold current of the light emitting element changes, the maximum emitted light amount of the light emitting element can be controlled to a desired value, so that the light emitting element always emits light with a desired light amount. There is an effect that can be.

  In the light emitting element control device according to the present invention, it is preferable that the light amount adjusting means adjusts the maximum emitted light amount of the light emitting element to a constant value. Thereby, even if it is a case where a threshold current changes, a light emitting element has the further effect that the largest emitted light quantity can perform pulse light emission with fixed constant.

  In order to solve the above problems, an optical information recording / reproducing apparatus according to the present invention comprises: a light emitting element that emits light when supplied with a current; and a pulse generation unit that generates a pulse signal for pulse-modulating the current. The light-emitting element is an optical information recording / reproducing apparatus configured to emit pulsed light when recording information on a recording medium, and detects light quantity of light emitted from the light-emitting element. A detection unit; a current control unit that outputs a current control signal that controls a current value based on a detection result of the light detection unit; and a threshold that is a light emission start current value of the light emitting element based on the current control signal. Threshold detection means for detecting current and pulse width adjustment means for adjusting the pulse width of the pulse signal based on the detection result of the threshold detection means are provided.

  According to the above configuration, in the optical information recording / reproducing apparatus, when information is recorded on the recording medium, the current is pulse-modulated by the pulse signal, and the light emitting element emits pulse light. Further, the light detection means detects the amount of light emitted from the light emitting element, and the current control means outputs a current control signal based on the detection result. Further, based on the current control signal, the threshold detection means detects the threshold current. Based on the detection result, the pulse width adjusting means adjusts the pulse width of the pulse signal.

  That is, it is controlled so as to obtain a desired light amount by detecting the light amount of light emitted from the light emitting element. Further, since the threshold current is detected by the threshold detection means and the pulse width is adjusted based on the detection result, the amount of light emitted from the light emitting element is always set to a desired value even when the threshold current changes. It can be controlled so as to obtain a light amount. Thereby, there is an effect that information can be recorded on the recording medium with high accuracy.

  In the optical information recording / reproducing apparatus according to the present invention, it is preferable that the threshold value detection means outputs a pulse width adjustment signal for adjusting the pulse width of the pulse signal. Since the threshold detection means outputs the pulse width adjustment signal, the pulse width adjustment means can adjust the pulse width of the pulse signal based on the pulse width adjustment signal, so that the stable pulse The width can be adjusted, and there is an additional effect that information can be recorded more stably on the recording medium.

  In the optical information recording / reproducing apparatus according to the present invention, it is preferable that the pulse width adjusting means adjusts the pulse width so that the duty of pulse light emission of the light emitting element is 50%. By adjusting the pulse width so that the duty of pulse light emission of the light emitting element is 50%, even when the threshold current of the light emitting element changes, pulse light emission can always be performed with a constant light amount. Further, there is an additional effect that information can be recorded on the recording medium with higher accuracy.

  In order to solve the above problems, an optical information recording / reproducing apparatus according to the present invention comprises: a light emitting element that emits light when supplied with a current; and a pulse generation unit that generates a pulse signal for pulse-modulating the current. The light-emitting element is an optical information recording / reproducing apparatus configured to emit pulsed light when recording information on a recording medium, and detects light quantity of light emitted from the light-emitting element. A detection unit; a current control unit that outputs a current control signal that controls a current value based on a detection result of the light detection unit; and a threshold that is a light emission start current value of the light emitting element based on the current control signal. And a light amount adjusting means for detecting a current and outputting a light amount adjustment signal for adjusting the maximum emitted light amount of the light emitting element based on the detection result.

  According to the above configuration, in the optical information recording / reproducing apparatus, when information is recorded on the recording medium, the current is pulse-modulated by the pulse signal, and the light emitting element emits pulse light. Further, the light detection means detects the amount of light emitted from the light emitting element, and the current control means outputs a current control signal based on the detection result. Further, based on the current control signal, the light amount adjusting means detects a threshold current and outputs a light amount adjustment signal.

  That is, it is controlled so as to obtain a desired light amount by detecting the light amount of light emitted from the light emitting element. Further, since the threshold current is detected by the threshold detection means and the maximum emitted light amount is adjusted based on the detection result, the maximum emitted light amount emitted from the light emitting element is always desired even when the threshold current changes. It is possible to control so that the light quantity becomes. Thereby, there is an effect that information can be recorded on the recording medium with high accuracy.

  In the optical information recording / reproducing apparatus according to the present invention, it is preferable that the light amount adjusting means adjusts the maximum emitted light amount of the light emitting element to a constant value. The light amount adjusting means adjusts the maximum emitted light amount of the light emitting element to a constant value, so that even when the threshold current changes, it is possible to control the maximum emitted light amount irradiated to the recording medium. There is an additional effect that the information can be recorded with higher accuracy.

  As described above, the light emitting element control device according to the present invention is configured to detect a threshold current that is a light emission start current value of a light emitting element, and a pulse width of a pulse signal based on the detection result of the threshold value detecting means. And pulse width adjusting means for adjusting. In addition, as described above, the light emitting element control device according to the present invention detects the threshold current that is the light emission start current value of the light emitting element, and adjusts the maximum emitted light quantity of the light emitting element based on the detection result. A light amount adjusting means for outputting an adjustment signal is provided. Thereby, there is an effect that the light emitting element can always emit pulses with a desired light amount.

  As described above, the optical information recording / reproducing apparatus according to the present invention controls the value of the current based on the light detection means for detecting the amount of light emitted from the light emitting element and the detection result of the light detection means. A current control means for outputting a current control signal; a threshold detection means for detecting a threshold current which is a light emission start current value of the light emitting element based on the current control signal; and a pulse based on a detection result of the threshold detection means. Pulse width adjusting means for adjusting the pulse width of the signal. Further, as described above, the optical information recording / reproducing apparatus according to the present invention detects the amount of light emitted from the light emitting element, and the current value based on the detection result of the light detection unit. A current control unit that outputs a current control signal to be controlled; and a threshold current that is a light emission start current value of the light emitting element based on the current control signal; and a maximum emission light amount of the light emitting element based on the detection result Light amount adjusting means for outputting a light amount adjustment signal for adjusting the light amount. Thereby, there is an effect that information can be recorded on the recording medium with high accuracy.

[Embodiment 1]
The first embodiment of the present invention will be described with reference to FIGS. 1 to 3 as follows. In this embodiment, the amount of light emitted from the light emitting element is controlled, and the amount of light emitted from the light emitting element is controlled using a light emitting element control device. Accordingly, even when the threshold current of the light emitting element changes, the light emitting element can always emit a desired amount of light, so that the reproduction accuracy of the recording medium is reduced, and information is recorded on the recording medium. It is possible to prevent a deterioration in the quality of the recording signal for recording the image. Here, the threshold current is a current value at which the light emitting element starts light emission (oscillation).

  In this embodiment, the optical information recording / reproducing apparatus will be specifically described by taking a magneto-optical disk recording / reproducing apparatus as an example, but the present invention is not limited to this, and a light emitting element is used. The present invention can be applied to an optical information recording / reproducing apparatus that emits pulses.

  FIG. 1 is a block diagram showing a schematic configuration of an optical disc recording / reproducing apparatus (optical information recording / reproducing apparatus) according to the present embodiment. As shown in FIG. 1, an optical disc recording / reproducing apparatus 1 according to the present embodiment includes a current source 2, a switch circuit 3, a semiconductor laser (light emitting element) 4, a photodetector (light detecting means) 5, and a current-voltage conversion circuit. 6, differential amplifier 7, reproduction mode reference voltage source 8, recording mode reference voltage source 9, changeover switch 10, low pass filter 11, drive current control circuit (current control means) 12, analog / digital conversion circuit 13, light emitting element control It has a device 14, a gate circuit 15, and a memory 16.

  The current source 2 outputs a current for driving the light emitting element of the magneto-optical disk recording / reproducing apparatus 1 in the present embodiment. For example, a semiconductor laser is driven by the drive current output from the current source 2. The switch circuit switches whether to supply the drive current output from the current source to the semiconductor laser 4.

  The semiconductor laser 4 records information on a magneto-optical disk (not shown), which is an optical information recording medium, or reproduces information recorded on the magneto-optical disk (hereinafter simply referred to as “recording / reproducing of a magneto-optical disk”). A laser beam for performing (described). The semiconductor laser 4 emits laser light having a light amount corresponding to the value of the drive current supplied from the current source 2.

  The photodetector 5 detects the amount of laser light emitted from the semiconductor laser 4. The photodetector 5 outputs a current signal S1 corresponding to the detected light amount. The current-voltage conversion circuit 6 receives the current signal S1 output from the photodetector 5, and converts it into a voltage signal S2. The current-voltage conversion circuit 6 outputs the voltage signal S2 to the differential amplifier 7.

  The differential amplifier 7 has two input terminals. One input terminal is a terminal for inputting the voltage signal S2 output from the current-voltage conversion circuit 6, and the other input terminal is the reproduction mode reference voltage source 8 or the recording mode reference voltage via the changeover switch 10 described later. This is a terminal for inputting the reference voltage signal S3 output from the source 9. The differential amplifier 7 computes and amplifies the difference between the voltage signals S2 and S3 input from these different input terminals, and outputs the computed and amplified signal to the low-pass filter 11.

  The reproduction mode reference voltage source 8 outputs a reference voltage signal S3 when reproducing the magneto-optical disk, and the recording mode reference voltage source 9 outputs the reference voltage signal S3 when recording information on the magneto-optical disk. Output. This reference voltage signal S3 is a signal indicating a drive current that is a reference when reproducing or recording the magneto-optical disk, and the amount of laser light emitted from the semiconductor laser 4 is set to a preset value. It is a signal for.

  The changeover switch 10 switches the reference voltage source connected to the differential amplifier 7 to either the reproduction mode reference voltage source 8 or the recording mode reference voltage source 9. Switching by the changeover switch 10 is performed according to a mode signal S7 output from a controller 17 described later.

  The low pass filter 11 removes a high frequency component of the signal output from the differential amplifier 7. This stabilizes the feedback control described later and prevents the semiconductor laser 4 from deteriorating due to a sudden change such as a surge generated in any of the circuits provided in the magneto-optical disk recording / reproducing apparatus 1. it can.

  The drive current control circuit 12 outputs a drive current control signal S4 according to the signal output from the low pass filter 11. The drive current control signal S4 is a signal for controlling the output current of the current source 2. The drive current control signal S4 is generated by performing gain adjustment or offset adjustment on the signal output from the low-pass filter 11, and the current source 2 And output to the analog / digital conversion circuit 13. The analog / digital conversion circuit 13 converts the drive current control signal S4 input from the drive current control circuit 12 into a digital signal and outputs it to the light emitting element control device 14.

  The light emitting element control device 14 controls the amount of light emitted from the semiconductor laser 4, and includes a controller (threshold detection means) 17, a pulse generation circuit (pulse generation means) 18, and a duty adjustment circuit (pulse width adjustment means). 19 is provided.

  The controller 17 receives the drive current control signal S5 output from the analog / digital conversion circuit 13, and outputs a duty adjustment signal S6 to the duty adjustment circuit 19 based on the drive current control signal S5. Further, the controller 17 outputs a mode signal S7 for setting to a reproduction mode for reproducing information recorded on the magneto-optical disk or a recording mode for recording information on the magneto-optical disk, to the gate circuit 15 and the changeover switch 10. It is like that. The duty adjustment signal S6 is a signal for adjusting the pulse width of the modulation pulse signal S8 output from the pulse generation circuit 18.

  The pulse generation circuit 18 generates and outputs a data clock signal using a PLL from a signal (wobble signal) recorded as a meandering groove on the magneto-optical disk. The frequency of the modulated pulse signal S8 output from the pulse generation circuit 18 is the same as the channel frequency of the recording data. The pulse signal is adjusted to have a specific phase in synchronization with a recording data signal for driving a magnetic head (not shown).

  The duty adjustment circuit 19 adjusts the pulse width of the modulation pulse signal S8 output from the pulse generation circuit 18. The modulated pulse signal S9 whose pulse width is adjusted by the duty adjustment circuit 19 is output to the gate circuit 15. The duty indicates the ratio of the operation time to the sum of the operation time and the subsequent rest time, and the duty adjustment circuit 19 adjusts the pulse width of the modulation pulse signal S8, thereby adjusting the duty. The pulse signal S9 is obtained.

  The gate circuit 15 has two terminals. One terminal is a terminal for inputting the modulation pulse signal S9 output from the duty adjustment circuit 19, and the other terminal is a terminal for inputting the mode signal S7 output from the controller 17. The gate circuit 15 outputs a gate signal for switching the switch circuit 3 based on the mode signal S7 and the modulation pulse signal S9.

  The memory 16 stores the result of previously measuring the value of the duty adjustment signal S6 with respect to the value of the drive current control signal S5.

  A method for controlling the amount of laser light emitted from the semiconductor laser 4 when recording / reproducing the magneto-optical disk using the magneto-optical disk recording / reproducing apparatus 1 having the above-described configuration will be described.

  The mode signal S7 output from the controller 17 has a reproduction mode and a recording mode. In the present embodiment, when the mode signal is “H” level, the recording mode is selected, and when the mode signal is “L” level, the reproduction mode is selected. These mode signals S7 are input to the changeover switch 10 and the gate circuit 15.

  The changeover switch 10 switches the switch based on the input mode signal and is connected to either the reproduction mode reference voltage source 8 or the recording mode reference voltage source 9. That is, when the input mode signal is “L” level, it is connected to the reproduction mode reference voltage source 8, and when it is “H” level, it is connected to the recording mode reference voltage source 9.

  On the other hand, the gate circuit 15 outputs a gate signal based on the input mode signal S7 and modulation pulse signal S9. When the mode signal S7 is at “L” level, the gate circuit 15 outputs an “L” level gate signal to the switch circuit 3 regardless of the modulation pulse signal S9. When the mode signal S7 is at the “H” level, the gate circuit 15 outputs an “H” level gate signal or an “L” level gate signal to the switch circuit according to the modulation pulse signal S9.

  Therefore, in the reproduction mode (when the mode signal is at “L” level), the gate signal output from the gate circuit 15 is fixed at “L” level regardless of the modulation pulse signal S9, and the switch circuit 3 Is always on. The changeover switch 10 is connected to the reproduction mode reference voltage source 8, and the semiconductor laser 4 emits a laser beam having a light amount corresponding to the drive current controlled based on the reference voltage signal S3. That is, in the reproduction mode, the semiconductor laser 4 emits direct current.

  On the other hand, in the recording mode (when the mode signal is “H” level), the gate signal output from the gate circuit 15 becomes “H” level or “L” level according to the modulation pulse signal S9. When the output of the gate circuit 15 is “L” level, the switch circuit 3 is turned on, and the drive current output from the current source 1 flows to the semiconductor laser 4. When the output of the gate circuit 15 is at “H” level, the switch circuit 3 is turned off and no drive current flows through the semiconductor laser 4. That is, the semiconductor laser 4 emits pulses according to the modulation pulse signal S9.

  As described above, when the switch circuit 3 is on, the drive current output from the current source 1 is input to the semiconductor laser 4 via the switch circuit 3. The semiconductor laser 4 is driven by an input of a drive current, and emits a laser beam having a light amount corresponding to the value of the input drive current.

  Laser light emitted from the semiconductor laser 4 is applied to the magneto-optical disk, and a part of the laser light enters the photodetector 5. As a result, recording / reproduction of the magneto-optical disk is performed, and the light amount of the laser light emitted from the semiconductor laser 4 is detected by the photodetector 5.

  The photodetector 5 outputs a current signal S1 corresponding to the detected light amount, and this current signal S1 is input to the current-voltage conversion circuit 6. The current-voltage conversion circuit 6 converts the input current signal S 1 into a voltage signal S 2 and outputs the voltage signal S 2 to the differential amplifier 7. The output voltage signal S2 is input to one input terminal of the differential amplifier 7. When the mode signal S7 is in the reproduction mode, the reproduction mode reference voltage source 8 is connected to the other input terminal of the differential amplifier 7 via the changeover switch 10, and the reference voltage signal S3 corresponding to the reproduction mode is connected. Is entered. When the mode signal S7 is in the recording mode, the recording mode reference voltage source 9 is connected to the other input terminal of the differential amplifier 7, and the reference voltage signal S3 corresponding to the recording mode is input. . In the differential amplifier circuit 7, the difference between the voltage signal S2 output from the current-voltage conversion circuit 6 and the reference voltage signal S3 corresponding to the mode signal S7 is calculated and amplified. Is output.

  The low pass filter 11 removes the high frequency component of the input signal and then outputs it to the drive current control circuit 12. The drive current control circuit 12 performs gain adjustment, offset adjustment, etc. on the input signal, and compares the value of the reference voltage signal S3 output from the reference voltage source and the voltage signal S2 output from the current-voltage conversion circuit 6. A drive current control signal S4 for controlling the values to be equal is generated. The drive current control circuit 12 outputs (feeds back) the drive current control signal S4 to the current source 1 and outputs it to the analog / digital conversion circuit 13. The current source 1 outputs a drive current corresponding to the fed back drive current control signal S4. A series of controls for feeding back the drive current control signal S4 to the current source 1 is referred to as feedback control.

  Here, a method of controlling the amount of laser light emitted from the semiconductor laser 4 when the threshold current of the semiconductor laser 4 changes will be described more specifically with reference to FIG. FIG. 2 is a graph showing the relationship (IP curve) between the amount of light emitted from the semiconductor laser 4 and the drive current.

  As shown in FIG. 2, when the threshold current of the semiconductor laser 4 is Itha, when the drive current supplied to the semiconductor laser 4 is I1, the semiconductor laser 4 emits light with the emitted light amount P1. However, when the threshold current changes to Ithb due to a temperature change or the like, the amount of light emitted from the semiconductor laser 4 is reduced to P2 by the drive current I1 supplied to the semiconductor laser 4.

  In this case, the difference between the voltage signal S2 corresponding to the detected light amount and the reference voltage signal S3 becomes large. For this reason, in order to make these signals equal, the value of the drive current control signal S4 is increased. As a result, the current source 1 to which the drive current control signal S4 is input is controlled so that the output drive current has a value of I2. Since the semiconductor laser 4 is driven by the drive current I2, the semiconductor laser 4 emits light with the emitted light quantity P1, and the emitted light quantity is controlled.

  When the semiconductor laser 4 emits DC light in the reproduction mode, the drive current is controlled so that the emitted light quantity becomes the light quantity set by the reproduction mode reference voltage source 8. Note that the amount of light emitted from the semiconductor laser 4 in the reproduction mode is a relatively low light amount of about several mW.

  FIG. 2 is a graph in the case where the drive current is DC driven, that is, in the reproduction mode, but the emitted light amount can be controlled in the same manner even in the case of pulse driving in the recording mode. .

  When the semiconductor laser 4 emits pulses in the recording mode, the frequency of the modulated pulse signal S9 is a relatively high frequency of several MHz to several tens of MHz, so that the detection signal by pulse emission is smoothed. For this reason, the voltage signal S2 output from the current-voltage conversion circuit 6 indicates the average light amount of the pulsed light. Therefore, the drive current is controlled so that the average light amount becomes the light amount set by the recording mode reference voltage source 9.

  In the recording mode, information is recorded by lowering the coercive force by raising the recording film of the magneto-optical disk to near the Curie temperature by laser light. For this reason, it is necessary to increase the peak value of the amount of laser light emitted from the semiconductor laser 4. Specifically, the amount of emitted light is preferably several tens of mW.

  As described above, in either case of the recording mode or the reproduction mode, the amount of light emitted from the semiconductor laser 4 is detected, and the voltage signal S2 based on the detection result is compared with the reference voltage signal S3 to drive current. The amount of light emitted from the semiconductor laser 4 can be controlled by generating the control signal S4 and feeding it back to the current source 1. Thereby, even if the threshold current of the semiconductor laser 4 changes, the light quantity of the laser beam emitted from the semiconductor laser 4 can always be kept at a predetermined value.

  In the present embodiment, the emission time of the semiconductor laser 4 is controlled in addition to suppressing the change in the emitted light amount by controlling the light amount of the semiconductor laser 4 as described above. In other words, the pulse emission duty is also controlled. Thereby, even when the threshold current of the semiconductor laser 4 changes, the amount of laser light emitted from the semiconductor laser 4 can be controlled and the amount of laser light can be controlled.

  The above control is performed by detecting a change in the threshold current by the controller 17 and adjusting the duty of the modulation pulse signal S8 output from the pulse generation circuit 18 by the duty adjustment circuit 19 based on the detection result. Hereinafter, a specific description will be given based on FIGS. 2 and 3.

  FIG. 3A shows the waveform of the modulation pulse signal S9 output from the duty adjustment circuit 19, where the horizontal axis represents time and the vertical axis represents the voltage value. FIG. 3B shows the pulse waveform of the drive current in FIG. 3A, where the horizontal axis represents time and the vertical axis represents the drive current amount. FIG. 3 (c) shows the pulse emission waveform of the semiconductor laser 4 in FIG. 3 (a), where the horizontal axis represents time and the vertical axis represents the amount of emitted light.

  The analog / digital conversion circuit 13 converts the drive current control signal S4 input from the drive current control circuit 12 into a digital signal and outputs the digital signal to the controller 17. The controller 17 can detect a change in the threshold current of the semiconductor laser 4 based on a change in the voltage value of the input drive current control signal S5.

  That is, as shown in FIG. 2, even when the value of the threshold current changes, the light amount of the laser light emitted from the semiconductor laser 4 is detected by the photodetector 5, and the voltage signal S2 based on the detection result. The threshold current change can be detected based on the drive current control signal S4 generated by comparing the value of the reference voltage signal S3 with the value of the reference voltage signal S3.

  A change in the threshold current of the semiconductor laser 4 is detected by a change in the voltage value of the drive current control signal S4 not only in the reproduction mode as shown in FIG. 2 but also in the case of pulse driving in the recording mode. The same can be done.

  Further, the controller 17 outputs a duty adjustment signal S6 for adjusting the pulse width of the modulation pulse signal S8 to the duty adjustment circuit 19 in accordance with the detected change in threshold current. The relationship between the value of the drive current control signal S5 indicating the threshold current of the semiconductor laser 4 and the value of the duty adjustment signal S6 to be sent from the controller 17 is measured in advance and stored in the memory 16 connected to the controller 17. Yes. The controller 17 inputs the drive current control signal S5 output from the analog / digital conversion circuit 13 prior to the recording mode or during the recording mode, and compares it with the value stored in the memory 16 to thereby generate a pulse. A control value for keeping the light emission duty at a predetermined value is selected, and a duty adjustment signal S 6 is generated and output to the duty adjustment circuit 19.

  When the duty adjustment circuit 19 receives the duty adjustment signal S6 output from the controller 17, the duty adjustment circuit 19 adjusts the pulse width of the modulation pulse signal S8 output from the pulse generation circuit 18, and generates a modulation pulse signal S9 having a predetermined pulse width. Output. Thereby, the emission time of the laser beam emitted from the semiconductor laser 4 can be adjusted. That is, the duty of the modulation pulse signal S8 is adjusted, and as a result, the duty of the laser light emitted from the semiconductor laser 4 can be adjusted. For example, the duty of the modulation pulse signal S8 is adjusted so that the duty of the pulsed light emitted from the semiconductor laser 4 is 50%.

  Specifically, as shown in FIGS. 3A to 3C, when the threshold current of the semiconductor laser 4 is Ita, when the pulse width of the modulation pulse signal S9 indicated by the solid line is Wa, the laser beam 4 is emitted from the semiconductor laser 4. The duty of the emitted pulse light is 50%. On the other hand, when the threshold current of the semiconductor laser 4 changes to Ithb, the drive current rises due to the feedback of the drive current control signal S4 to the current source 1 and the duty adjustment signal from the controller 17 as shown by the broken line. Based on S6, the duty adjustment circuit 19 adjusts the pulse width of the modulation pulse signal S8 to Wb.

  As a result, the duty of the pulse emission emitted from the semiconductor laser 4 is maintained at 50%, and the emitted light quantity of the laser light can be controlled to a predetermined value, and the fluctuation of the light quantity of the laser light is suppressed. can do.

  As described above, even when the threshold current of the semiconductor laser 4 changes, the light amount of the laser light emitted from the semiconductor laser 4 is detected, and the voltage signal S2 and the reference voltage signal S3 based on the detection result are obtained. By comparing and generating the drive voltage control signal S4, the emitted light quantity of the laser light emitted from the laser light can be controlled to be a predetermined value. Further, the threshold current of the semiconductor laser 4 can be detected based on the drive voltage control signal S4, and the pulse emission duty is controlled to be a predetermined value by adjusting the pulse width of the modulation pulse signal S8. can do. As a result, the peak value of the emitted light amount (maximum emitted light amount) can be controlled to a predetermined value, and the laser light can always be emitted with a desired light amount. Therefore, recording / reproducing of the magneto-optical disk can be performed with high accuracy.

  In an optical information recording / reproducing apparatus such as a magneto-optical disk apparatus, so-called high-frequency superposition is generally performed such that a high-frequency current of several hundred MHz is superimposed on a drive current in order to suppress noise due to feedback light of a semiconductor laser. ing. In the present embodiment, high-frequency superposition is omitted for the sake of simplicity, but the present invention can be similarly applied to high-frequency superposition.

  In addition to adjusting the duty of the modulated pulse signal and adjusting the phase of the magnetic field modulation data that modulates the recording magnetic field with the information data and the pulse emission of the laser beam, the timing deviation between the magnetic field modulation data and the pulse emission of the laser beam Can also be suppressed.

  In this embodiment, the optical information recording / reproducing apparatus for recording / reproducing information on the magneto-optical disk has been described. However, the present invention can also be applied to an optical information recording apparatus for recording information on the magneto-optical disk. .

[Embodiment 2]
A second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the peak value (maximum emitted light amount) of the light emitted from the light emitting element is controlled using the light emitting element control device, so that the laser light emitted from the light emitting element has a predetermined light amount. It controls to become. Thereby, even when the threshold current of the light emitting element changes, it is possible to prevent the reproduction accuracy of the recording medium from being lowered and the quality of the recording signal for recording information on the recording medium from being lowered.

  In this embodiment, the optical information recording / reproducing apparatus will be specifically described by taking a magneto-optical disk recording / reproducing apparatus as an example. However, the present invention is not limited to this, and a light emitting element is used. The present invention can be applied to an optical information recording / reproducing apparatus that emits pulses.

  FIG. 4 is a block diagram showing a schematic configuration of an optical disc recording / reproducing apparatus (optical information recording / reproducing apparatus) 20 according to the present embodiment. As shown in FIG. 4, the magneto-optical disk recording / reproducing apparatus 20 according to the present embodiment is different from the magneto-optical disk recording / reproducing apparatus 1 shown in FIG. The configuration is the same.

  The light emitting element control device 21 in the present embodiment includes a pulse generation circuit (pulse generation means) 18 and a controller (light quantity adjustment means) 22. The pulse generation circuit 18 is the same as that in the first embodiment. The controller 22 outputs a voltage adjustment signal S10 to the recording mode reference voltage source 9 in addition to outputting the mode signal S7 in the reproduction mode or the recording mode. The voltage adjustment signal S10 is a signal for adjusting the reference voltage signal S3 output from the recording mode reference voltage source 9 based on a change in the threshold current of the semiconductor laser 4.

  A method for controlling the amount of light emitted from the semiconductor laser 4 in the recording mode will be described with reference to FIG. FIG. 5A shows the waveform of the modulation pulse signal S8, where the horizontal axis represents time and the vertical axis represents the voltage value. FIG. 5B shows a pulse waveform of the drive current in FIG. 5A, where the horizontal axis represents time and the vertical axis represents the drive current amount. FIG. 5C shows the pulse emission waveform of the semiconductor laser 4 in FIG. 5A, where the horizontal axis represents time and the vertical axis represents the amount of emitted light.

  As shown in FIG. 5B, when the threshold current of the semiconductor laser 4 is Itha, when the pulse width of the modulated pulse signal S8 indicated by the solid line is Wa, the duty of the pulse emission emitted from the semiconductor laser 4 is 50%. It becomes. The average amount of light emitted from the semiconductor laser 4 is Pa and the peak value is Pp. Since the duty of the pulse emission is 50%, the peak light amount Pp is twice the average light amount Pa.

  When the threshold current of the semiconductor laser 4 changes to Ithb, the drive current rises by feedback (feedback control) of the drive current control signal S4 to the current source 1 as shown by the broken line. However, since the pulse width of the modulation pulse signal S8 is not adjusted, the duty of the pulse emission emitted from the semiconductor laser 4 becomes smaller than 50%. For this reason, when the average emitted light amount is controlled to the predetermined light amount Pa by feedback control, the peak light amount Ppb becomes a value higher than the predetermined peak light amount Pp.

  Therefore, the value of the voltage adjustment signal S10 output from the controller 22 is changed to adjust the reference voltage signal S3 corresponding to the recording mode output from the recording mode reference voltage source 9. For example, when the recording mode reference voltage source 9 is composed of an analog / digital converter, the adjustment is performed by inputting a voltage adjustment signal S10 that is a digital signal and outputting an analog voltage signal according to the value. Done. As a result, the value of the peak light quantity of pulsed light emitted from the semiconductor laser 4 is maintained at the predetermined value Pp.

  Here, the value of the voltage adjustment signal S10 to be sent from the controller 22 with respect to the drive current control signal S5 indicating the threshold current of the semiconductor laser 4 is measured in advance and stored in the memory 16 connected to the controller 22. Prior to the recording mode or during the recording mode, the controller 22 inputs the drive current control signal S5 output from the analog / digital conversion circuit 13 to detect the threshold current, and the value stored in the memory 16 By comparison, a control value for keeping the peak light amount of the pulse emission at a predetermined value Pp is selected, and the voltage adjustment signal S10 is generated and output to the recording mode reference voltage source 9.

  Since the magneto-optical disk recording / reproducing apparatus 20 in this embodiment is not configured to adjust the duty of the modulation pulse signal S8, the duty of pulse emission changes with the change of the threshold current of the semiconductor laser 4. However, since the peak light intensity of the pulse emission is kept at the predetermined value Pp, it is possible to suppress the quality deterioration of the recording signal. Although the average light amount Pa changes in order to keep the peak light amount of pulsed light emission at a predetermined value Pp, it is mainly the peak light amount that determines the information recording quality of the magneto-optical disk, and the effect of the change in the average light amount Pa. Because it is small.

  Further, the magneto-optical disk recording / reproducing apparatus 20 in the present embodiment does not require a duty adjustment circuit for controlling the duty of the modulation pulse signal S8 in units of several ns, so that the circuits constituting the magneto-optical disk recording / reproducing apparatus are greatly increased. It becomes possible to simplify.

  Note that the present invention can be applied in the same manner to the above-described high-frequency superposition. The present invention can also be applied to an optical information recording apparatus that records information on a magneto-optical disk.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  As described above, by using the light emitting element control apparatus according to the present invention, the obtained optical information recording / reproducing apparatus can perform recording and reproduction with high reliability. Further, the light emitting element control device according to the present invention can be particularly suitably used as an optical information recording / reproducing device with reduced size, higher density, higher speed, and lower power consumption.

  Accordingly, the present invention is not only applied to the industrial field of manufacturing optical information recording / reproducing apparatuses, but also to the industrial field of manufacturing light emitting elements, and other industrial fields of manufacturing various electronic / electrical parts related to optical information recording / reproducing apparatuses. It can be used suitably.

1 is a block diagram showing a schematic configuration of a magneto-optical disk recording / reproducing apparatus in an embodiment of the present invention. It is a graph which shows the relationship between the emitted light quantity and drive current in one Embodiment of this invention. 3A is a diagram illustrating a waveform of a modulated pulse signal output from the duty adjustment circuit, FIG. 3B is a diagram illustrating a pulse waveform of a drive current, and FIG. It is a figure which shows the waveform of the pulse light emission of a semiconductor laser. It is a block diagram which shows schematic structure of the magneto-optical disc recording / reproducing apparatus in other embodiment of this invention. It is a graph which shows the relationship between the emitted light quantity and drive current in other embodiment of this invention. It is a graph which shows the relationship between the emitted light quantity and the drive current in the conventional optical information recording / reproducing apparatus. FIG. 7A is a diagram showing a pulse waveform of a conventional semiconductor laser driving current, and FIG. 7B is a diagram showing a pulse emission waveform of a conventional semiconductor laser.

Explanation of symbols

1 Magneto-optical disk recording / reproducing device (optical information recording / reproducing device)
4 Semiconductor laser (light emitting device)
5 Light detector (light detection means)
12 Drive current control circuit (current control means)
14 Light Emitting Element Control Device 17 Controller (Threshold Detection Means)
18 Pulse generation circuit (pulse generation means)
19 Duty adjustment circuit (pulse width adjustment means)
20 Magneto-optical disk recording / reproducing apparatus (optical information recording / reproducing apparatus)
21 Light-Emitting Element Control Device 22 Controller (Light intensity adjustment means)

Claims (10)

A light emitting element control device comprising pulse generating means for generating a pulse signal, pulse-modulating a current supplied to the light emitting element using the pulse signal, and causing the light emitting element to emit light in a pulse;
Threshold detection means for detecting a threshold current which is a light emission start current value of the light emitting element;
A light emitting element control device comprising: pulse width adjusting means for adjusting a pulse width of a pulse signal based on a detection result of the threshold value detecting means.   2. The light emitting element control device according to claim 1, wherein the threshold value detection means outputs a pulse width adjustment signal for adjusting the pulse width of the pulse signal.   3. The light emitting element control device according to claim 1, wherein the pulse width adjusting means adjusts the pulse width so that the duty of pulse light emission of the light emitting element is 50%. A light emitting element control device comprising pulse generating means for generating a pulse signal, pulse-modulating a current supplied to the light emitting element using the pulse signal, and causing the light emitting element to emit light in a pulse;
A light amount adjusting means for detecting a threshold current which is a light emission start current value of the light emitting element and outputting a light amount adjustment signal for adjusting the maximum emitted light amount of the light emitting element based on the detection result is provided. A light emitting element control device.   5. The light emitting element control device according to claim 4, wherein the light amount adjusting means adjusts the maximum emitted light amount of the light emitting element to a constant value. A light-emitting element that emits light when supplied with a current; and pulse generation means that generates a pulse signal for pulse-modulating the current. The light-emitting element emits pulsed light when recording information on a recording medium. An optical information recording / reproducing apparatus adapted to emit light,
Light detection means for detecting the amount of light emitted from the light emitting element;
Current control means for outputting a current control signal for controlling the value of the current based on the detection result of the light detection means;
Based on the current control signal, threshold detection means for detecting a threshold current which is a light emission start current value of the light emitting element;
An optical information recording / reproducing apparatus comprising: pulse width adjusting means for adjusting a pulse width of a pulse signal based on a detection result of the threshold value detecting means.   7. The optical information recording / reproducing apparatus according to claim 6, wherein the threshold detection means outputs a pulse width adjustment signal for adjusting the pulse width of the pulse signal.   8. The optical information recording / reproducing apparatus according to claim 6, wherein the pulse width adjusting means adjusts the pulse width so that the duty of pulse light emission of the light emitting element is 50%. A light-emitting element that emits light when supplied with a current; and pulse generation means that generates a pulse signal for pulse-modulating the current. The light-emitting element emits pulsed light when recording information on a recording medium. An optical information recording / reproducing apparatus adapted to emit light,
Light detection means for detecting the amount of light emitted from the light emitting element;
Current control means for outputting a current control signal for controlling the value of the current based on the detection result of the light detection means;
A light amount adjusting means for detecting a threshold current which is a light emission start current value of the light emitting element based on the current control signal and outputting a light amount adjustment signal for adjusting the maximum emitted light amount of the light emitting element based on the detection result; An optical information recording / reproducing apparatus comprising:   The optical information recording / reproducing apparatus according to claim 9, wherein the light amount adjusting means adjusts the maximum emitted light amount of the light emitting element to a constant value.

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