JPS59119547A - Semiconductor laser driver for optical disk device - Google Patents

Abstract

PURPOSE:To avoid the noises generated by the mode transition, etc. by detecting the generation of noises with use of a filter circuit that transmits the frequency component containing no video FM signal, etc. with the reproduction output and switching the optical output of laser among >=2 set levels. CONSTITUTION:The reflected light of an optical disk 15 that emits a semiconductor laser 1 is led to a polarizing surface 12a, a photodetector 17 and a demodulating circuit 18 and converted into video and sound signals respectively. If a mode transition and then noises and generated to the laser 1 at a certain temperature, the noise component is extracted through a filter circuit 22 and compared with the prescribed reference voltage 26 through a comparator 27 after amplification and rectification. A monostable multivibrator 27 is actuated by the output of a comparator 25, and a comparison arithmetic circuit 3 is switched to the reference voltage 30a or 30b by an FF28 and a changeover switch 29 and every actuation of the vibrator 27 and then compared with the output signal of a photodetector 2. Then two levels can be selected with control for the optical output of the laser 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a device for reducing noise contained in the optical output of a semiconductor laser capable of single-mode oscillation used as a light source for optical disk devices and the like.

[Prior art]

The noise of a semiconductor laser used as a light source for an optical disk device such as a video disk device or an optical audio disk device varies depending on the operating temperature and drive current (light output) K. In particular, semiconductor lasers that can detect a single mode When using a constant drive current, there is usually almost no noise, but at a certain temperature mode transition occurs and noise is generated, for example in video mode.

This was a cause of deterioration in the quality of the reproduced images in the Sufu device.

Conventionally, the device shown in FIG. 1 is known as a semiconductor laser drive device for an optical disk device ηI. In Figure 1, 1
is a semiconductor laser, 2 is a photodetector, 5 is a comparison calculation circuit, 4
5 is a reference rotation pressure, and 5 is an amplifier circuit. The backward light 1 h emitted from one end face of the semiconductor laser 1 is incident on the photodetector 2 .

The output signal of the photodetector 2 is compared with the reference rotation voltage 4 by the comparison calculation circuit 3, and the output signal of the comparison calculation circuit 5 is amplified by the amplifier circuit 5, which changes the drive current of the semiconductor laser 1 and changes the optical output. Control is performed to cancel out the fluctuations.

According to the conventional semiconductor laser drive device described above, optical detection/
The optical output of the semiconductor laser 1 is maintained in a band below the cutoff frequency of the l'l device 2.

However, since the rear light 1h spreads radially and is emitted, the photodetector 2 must have a sufficiently large light-receiving area.
It has been difficult to suppress noise over a band of several tens of Mllz that is generated during mode transition of the semiconductor laser 1 while remaining at Ez.

Further, the noise level and phase of the forward light 1α and the backward light 1h of the semiconductor laser 1 are generally not necessarily -i. In the semiconductor laser drive device shown in Fig. 1, the /ize detection is performed using the backward light 1h, and the information reading from the optical disk is performed once using the forward light 1α. If the noise level and phase were different between the front light beam 1b and the front light beam 1b, it was not possible to suppress the noise of the forward light beam 1α actually used.

[Purpose of the invention]

The purpose of the present invention is to solve the problems of the prior art described above,
An object of the present invention is to provide a semiconductor laser driving device for an optical disk device that can avoid noise caused by mode transition of a semiconductor laser.

[Summary of the invention]

The semiconductor laser drive device according to the present invention utilizes the property that the noise generation characteristics with respect to the operating temperature of the semiconductor laser differ depending on the optical output of the semiconductor laser. The generation of noise is detected from the output signal of a filter circuit that passes components in a frequency band where no frequency band exists, and if noise is detected, the optical output of the semiconductor laser is adjusted between at least two preset values. The key point is to hold this set value between switching and the next time noise is detected.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to the drawings.

Figure 2 shows noise generated by mode transition in a semiconductor laser that can oscillate in a single mode.

FIG. The solid line is the characteristic when the optical output is P1, and the dotted line is the characteristic when the optical output is P2, and there is a relationship of pz/p+'':: 1.1 to 1.3. From FIG. 2, the output of the semiconductor laser.

When the temperature is increased, the temperature at which noise occurs becomes lower.

It can be seen that the temperature range in which noise is generated is narrow, and noise generation can be avoided by shifting the optical output by 10 to 50%. The present invention takes this noise generation characteristic into consideration and attempts to control the optical output so as to avoid noise. For example, in a video disk device using a semiconductor laser as a light source, when the noise of the semiconductor laser reaches level N shown in the figure, it appears as noise in the reproduced image. Therefore, it is sufficient to operate the semiconductor laser under conditions such that the noise level is always below N. Generally, it is difficult to control the operating temperature, so if the optical output of the semiconductor laser can be controlled as soon as the occurrence of noise is detected, it will be possible to operate the semiconductor laser at a noise level N or lower over the required temperature range.

FIG. 5 is a block diagram showing an embodiment of a semiconductor laser driving device according to the present invention together with a pickup device of an optical disk device. First, the pick amplifier device will be explained. The forward light 1α emitted from the semiconductor laser 1 is made into parallel light by the collimating lens 11, and then the polarizing prism 1
2. Wavelength plate 13. Objective lens drive device 140 objective lens! 4 (Z) and is converged onto the information surface of the optical disc 15. The reflected light modulated by the optical information of the optical disc 15 is incident on the polarizing prism 12 via the objective lens 14α and the '/4 wavelength plate 13. The reflected light incident on the polarizing prism 12 is reflected by the polarization plane 12α of the polarizing prism 12 by the action of the quarter-wave plate 150, condensed by the lens 16, and incident on the photodetector 17. The optical information on the optical disc 15 is converted into a drowsiness signal by a photodetector 17.The output of the photodetector 17 is converted by a preamplifier 20 into a pRF output 21.This RF output 21 is sent to a demodulation circuit 18. Guided by.

For example, in a video disk device, the signal is converted into a video signal and a -B voice.

Here, the pickup device used in the present invention is not limited to the above-mentioned pickup device, but may have any structure as long as it has a function of converting the optical information of the optical disc 15 into a drowsiness signal.

Next, the semiconductor laser drive circuit according to the present invention will be explained. 22 is a filter circuit), which has the characteristic of passing only the frequency band in which no signal exists in order to extract the noise component from the RF output 21 (the setting of the frequency band to be passed will be explained in detail later). ).

Now, when a mode transition occurs in the semiconductor laser 1 at a certain temperature and generates noise, the noise generated by the laser usually includes a wide range of frequency components, so the components in the above-mentioned band also increase.

A filter circuit 22 extracts noise components.

This noise is amplified by 23 high frequency amplifier circuits and rectified by 24 full wave rectifier circuits to obtain a noise level signal. After that, the noise level signal is input to the comparator 25,
It is compared with a reference voltage 26 set in advance using the level N explained in FIG. 2, and a high level or low level signal is obtained at the output of the comparator 25 depending on the voltage level of the noise level signal. Then, by the output of the comparator 25, the monostable multibar, fBV
- Operate the controller 27.

For example, if the output of the comparator 25 is configured to change from a low level to a high level when the semiconductor radar 1 generates noise, the monostable multivibrator 27 will generate a high level output for a preset time. Configure.

The purpose of providing the monostable multi-pipe break 27 is to stabilize the switching of the optical output of the semiconductor laser 1 when the noise level takes a value near level N, and the output of the monostable multi-pipe break 27 is at a high level. During this period, even if the output of the comparator 25 changes, this change is not reflected in the receiver. 2nd is a flip-flop, and the output is inverted by 1° every time the monostable multivibrator 27 operates 1-. The output of this flip-flop 28 causes the changeover switch 2
Switch 9. By switching the changeover switch 29, the voltage at the middle terminal of the comparator circuit 6 can be changed to 1 standard (city voltage 50α).
It can be switched to stop or standard squirt pressure 6ob. The output signal of the photodetector 2 is compared with the reference pressure 30α or the basic arsenal pressure 50b by the comparison calculation circuit 5. The power signal from the comparison calculation circuit 60 is inputted to the amplifier circuit 5, and the output signal from the semiconductor laser 1
The light output of is controlled to select between two values. Note that it is also possible to switch the optical output to a value of two or more values without using the flip-flop 28, using a pulse counter or the like.

With the above configuration and dynamic f', the semiconductor laser 1 can always be operated in a single-e-mode oscillation state with a low noise level.

Next, regarding the characteristics of the filter circuit 22 shown in FIG.
This will be explained in detail by taking the case of a bitemed disk device as an example.

As an example of the recording spectrum of an optical videotask, the one shown in Figure 4 is widely known.
FJlffM and two channels of audio FM signals are recorded in the frequency band shown in Figure 1. dC above
RF during playback of original disk 15 with C spectrum
In the output 21, the reproduced video FM No. 4 and the reproduced audio P'M signal for channel 2 are in the same frequency band as in FIG. 4, and noise components are present in the frequency range ゛υ where there is no signal. Noise generated by the mode transition of the semiconductor laser 1 exists over several bands L (several fiz to tens of watts) over a wide range, as mentioned above.

In addition, the level of the noise is almost uniform in the frequency range shown in FIG. 4. When the semiconductor laser generates noise, 'C/°C/rail changes significantly at frequencies where there is no sound FM signal or audio FM signal. Therefore, K for detecting noise generation in the semiconductor laser 1 is a video FM-signal and a shout F, 5f4-
Prefectural areas where no number exists, such as A and H shown in Figure 4.
It is sufficient to extract the change in the noise level in the frequency band. In other words, the filter circuit 22 has a special filter that passes either one of the wave number bands A and H or both bands. may be configured as a low-pass filter or band-pass filter, and when passing through B, a bypass filter or band-pass filter may be configured.Also, in optical disc devices other than video disc device y1, , the filter circuit 22 has an RF output 21
It is sufficient to pass a frequency band in which no signal exists.

[Effect between lights]

As explained above, the semiconductor laser drive device of the optical disk device according to the present invention generates noise from the output signal of the filter circuit that passes noise components in the frequency band where no video signal etc. are present in the optical disk playback output by the pickup device. Since the optical output of the semiconductor laser is detected and the optical output of the semiconductor laser is switched, it is possible to reliably detect and avoid the occurrence of nozzles in the forward light used to actually read information from the optical disk. Furthermore, since the generation of noise itself is avoided, a noise suppression effect can be obtained over all frequency bands.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional semiconductor laser driving device, Fig. 2 is a diagram illustrating the power generation characteristics due to the mode transition of a semiconductor laser using the operating 1NA degree as a parameter, Fig. 6
The figure is a block diagram showing an embodiment of the semiconductor laser driving device according to the present invention together with a pickup device, and FIG. 4 is a diagram showing the 18-tsuba spectrum of the optical video gusset along with an example of each pass frequency band in the filter circuit. It is. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 5... Comparison calculation circuit, 5
...Amplification circuit, 15...Optical disk, 17.
...Photodetector, 22...Filter circuit. 24...Double wave rectifier circuit, 25...Comparator. 27... Monostable multivibrator. 28... Flip-flop, 29... Changeover switch, 50α, 50h... Reference voltage. sheep once

Claims (1)

[Claims] 1. Optical means for reading optical information on an optical disc;
- A pickup device comprising a first photodetector that converts the optical information into an electrical signal, a semiconductor laser capable of single mode oscillation, and a second photodetector that detects the optical output of the semiconductor laser. and a comparison calculation circuit that generates a control signal according to the output of the second photodetector. a semiconductor laser driving device comprising an amplifier circuit that supplies current to the semiconductor laser; and a filter circuit that passes only a frequency band in which no signal component exists in the output of the first photodetector. , comprising a double-wave rectifier circuit for double-wave rectifying the output of the filter circuit, detects the occurrence of noise from the output of the double-wave rectifier circuit, and when the output of the double-wave rectifier circuit exceeds a preset value, the semiconductor : A semiconductor laser for an optical disk device, characterized in that the optical output of the laser is switched between at least two preset values and the set value is maintained until the occurrence of primary noise is detected. Drive device.