JPH052761A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain an optical recording and reproducing device equipped with as table control system by detecting the fluctuation of the waveform of a semiconductor laser and operating a feed-back to the push-pull signal even when the amplitude of the push-pull signal is changed according to the fluctuation of the pertinent waveform. CONSTITUTION:A light flux 14 reflected by a beam splitter 5 among the light flux outgoing from a semiconductor laser 1, is made incident to a diffracting grating 15 with a waveform selectivity and the transmitting diffracted light flux 16 is received by a light detector 17 and current/voltage converted by amplifiers 18 and 19, and inputted to a subtracter 20. A signal obtained by current/voltage converting a signal from a light detector 11 which receives a reflected light flux from a disk 8 and the signal from the above-mentioned subtracter 20 are inputted to a subtracter 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing device, and more particularly to a tracking sensor in an optical disc device for optically recording / reproducing information.

[0002]

2. Description of the Related Art FIG. 8 shows an optical system of a conventional optical information reproducing apparatus. In the figure, 1 is a semiconductor laser which is a light source, 2 is a light flux emitted from the semiconductor laser 1,
Reference numeral 3 is a collimator lens for converting the light beam 2 into a parallel light beam, and 4 is a parallel light beam. Reference numeral 5 is a beam splitter for separating a light beam, 6 is an objective lens, and 7 is a light beam condensed by the objective lens 6, which is applied to an information recording medium (hereinafter referred to as a disk) 8. Reference numeral 9 is a focusing lens that collects the reflected light flux from the disk 8, and 11 is a first photodetector that converts the focused light flux 10 into an electric signal. Reference numeral 12 is an amplifier for converting the signal from the first photodetector into current / voltage. Also, 13
Is a drive circuit for adjusting the output of the semiconductor laser 1.

Next, the operation will be described. The light beam 2 emitted from the semiconductor laser 1 is converted into a parallel light beam 4 by the collimator lens 3, passes through the beam splitter 5, and is irradiated onto the disk 8 as a minute spot by the objective lens 6. The light beam reflected from the disk 8 is reflected by the beam splitter 5
The direction is changed by and the light is incident on the first photodetector 11 through the focusing lens 9. From the first photodetector 11, a focus error signal for always keeping the spot on the disc,
A track error signal for tracking on the track and an information signal are obtained. Here, the focus error signal and the information signal are not directly related to the present invention, and therefore omitted. Although various types of track error signals have been proposed, the push-pull method is generally used in the recording / reproducing apparatus as in the present invention. This is a method of detecting the deviation from the center of the track by using the reflected light diffracted by the track (hereinafter, this error signal is referred to as a push-pull signal).

[0004]

By the way, a compact disc (hereinafter referred to as a CD), which has been used only for reproduction, has been proposed as a recordable standard, and discs conforming to this standard have become available. . The write-once CD standard requires that the recorded disc can be played back by a conventional CD player, so it is necessary to secure the reflectance of the disc at about 80%, which is the same as that of the read-only CD disc. For this reason, a pigment-based material is used as the material of the disc. However, this dye-based disk has a dependency on the wavelength of light, and in particular, the amplitude of the push-pull signal described above greatly changes depending on the difference in wavelength. This situation will be described with reference to FIG. FIG. 3 shows an example of the relationship between the wavelength of the light source and the push-pull signal, and when it is large, the push-pull signal amplitude may change over several dB with respect to the wavelength difference of several nm. on the other hand,
The semiconductor laser, which is a light source, has a different wavelength in each semiconductor laser, and at the same time, its own wavelength also fluctuates. Therefore, in the conventional optical system, even if the gain of the servo loop is adjusted at the initial stage, there is a problem in that the gain varies and stable servo cannot be obtained.

The present invention has been made to solve the above problems, and provides a stable control system by suppressing the fluctuation of the gain of the servo loop even if the wavelength of the semiconductor laser as the light source fluctuates. It is an object.

[0006]

An optical recording / reproducing apparatus according to the present invention is provided with a second photodetector for monitoring a light beam from a light source, and a diffraction grating having wavelength selectivity is arranged in its optical path. It was done.

According to the present invention, a divider is provided for normalizing the push-pull signal obtained from the first photodetector which receives the reflected light from the disk at the output of the second photodetector of the monitor. It is a thing.

Further, in order to control the power of the semiconductor laser which is the light source by the output of the second photodetector of the monitor, the drive circuit of the light source is provided with the comparison circuit corresponding to the divider.

[0009]

By providing a divider for normalizing the push-pull signal obtained from the first photodetector, the push-pull signal is normalized by this signal even if the wavelength of the semiconductor laser changes. Therefore, even if the push-pull signal changes, the gain of the servo loop does not change, and a stable control system can be obtained.

Further, in order to control the power of the semiconductor laser which is the light source by the output of the second photodetector, the drive circuit of the light source is provided with the comparison circuit corresponding to the divider,
Even if the wavelength of the semiconductor laser fluctuates, the semiconductor laser is controlled by this signal. Therefore, the optimum semiconductor laser power that does not cause the fluctuation of the gain of the servo loop even if the push-pull signal changes can be obtained. .

[0011]

【Example】

Example 1. FIG. 1 is an optical system and signal connection diagram showing an embodiment of the present invention. In the figure, 1 to 13 are exactly the same as the conventional device. Reference numeral 14 is a light beam which is incident on and reflected by the beam splitter 5, 15 is a diffraction grating, and 16 is a diffraction grating 1.
5, 17 is a diffracted light beam transmitted through 5, 17 is a second split photodetector for monitoring the diffracted light beam 16, and 18 and 19 are second split photodetectors.
It is an amplifier for converting the signal from the photodetector 17 of FIG. Reference numerals 20 and 21 are dividers.

Next, the operation will be described. The light beam emitted from the semiconductor laser 1 is applied to the disk 8, the reflected light is detected by the first photodetector 11, and the push-pull signal is obtained from the amplifier 12, as in the conventional device. Of the light beam 4 entering the beam splitter 5, the light beam 14 reflected by the beam splitter 5 enters the diffraction grating 15. The diffraction grating 15 has wavelength selectivity, which will be described with reference to FIG. FIG. 2 shows the diffraction angle with respect to the wavelength, and the diffraction grating 15 has the same wavelength selectivity as the push-pull signal shown in FIG. Therefore, if the two-divided second photodetector 17 is arranged so as to receive the diffracted light beam other than the 0th order light, the diffracted light beam 16 transmitted through the diffraction grating 15 has a different diffraction angle depending on the wavelength. Positional deviation occurs in the spot irradiated on the divided second photodetector 17. Therefore, the signal obtained from the two-divided second photodetector 17 is obtained by converting the wavelength into the spot position shift, and this is an electric signal which is current / voltage converted by the amplifiers 18 and 19. The signal obtained as described above is input to the divider 20, and the output signal from the divider 20 (hereinafter referred to as a wavelength monitor signal) and the push-pull signal are input to the divider 21.

In the divider 20, the signal B from the amplifier 18
Division is performed using 1 as the numerator and the signal B2 from the amplifier 19 as the denominator, and a wavelength monitor signal is obtained. The wavelength monitor signal is divided by the divider 21 using the push-pull signal as the numerator and the wavelength monitor signal as the denominator, so that a track error signal normalized by the wavelength monitor signal is obtained. These will be described with reference to FIGS. 2, 3, and 4. Now the wavelength is λ
Assuming that the electrical signals adjusted by 0 and obtained from the amplifiers 18, 19 are B1 = B2, the wavelength monitor signal is: wavelength monitor signal = B1 / B2 = 1 (= T0). Assuming that the push-pull signal at this time is A0, the track error signal is: track error signal = A0 / T0. Next, assume that the wavelength changes from λ0 to λ1.
At this time, since the push-pull signal changes from A0 to A1 as shown in FIG. 3, the gain of the servo loop increases as it is, but the wavelength monitor signal also changes from T0 to T1 as shown in FIG. The track error signal = A1 / T1. Here, if the rate of change of the wavelength monitor signal with respect to the change of wavelength is set to be the same as the rate of change of the push-pull signal, A0 / T0 = A1 / T1, that is, the gain of the track error signal does not change and is stable. You can get a servo. Further, the two-divided second photodetector 17 is arranged so as to be displaced from the vertical with respect to the diffracted light beam 16 incident on the two-divided second photodetector 17, thereby detecting the two-divided second photodetector The reflected light from the container 17 is prevented from returning to the semiconductor laser 1 which is the light source. Therefore, the semiconductor laser 1 which is the light source is prevented from generating noise.

Example 2. In FIG. 5, a similar effect can be obtained by providing a focusing lens 22 between the diffraction grating 15 and the two-divided second photodetector 17 to focus the diffracted light. This method can shorten the distance between the focusing lens 22 and the second photodetector 17 divided into two. Moreover, since the spot on the second photodetector 17 divided into two becomes smaller, the light receiving sensitivity can be increased, and the second photodetector 17 divided into two can be made smaller.

Example 3. In FIG. 6, the transmissive diffraction grating 15 used as the wavelength selective element in the first embodiment is replaced with a concave mirror 23 with a reflective diffraction grating. This method can also obtain the same effects as those shown in the first and second embodiments.

Example 4. FIG. 7 shows another embodiment of the optical recording / reproducing apparatus for stabilizing the control system by using the wavelength monitor signal. The push-pull signal normalized in the first embodiment is used for the semiconductor laser 1 as the light source. It controls the power of. In the figure, the wavelength monitor signal is obtained in the same manner as in the first embodiment, but this wavelength monitor signal is input to the drive circuit 13. Although not shown in the drawing, the drive circuit 13 has a comparison circuit corresponding to a divider similar to that of the first embodiment, and the power of the semiconductor laser 1 is adjusted so that the amplitude of the push-pull signal obtained from the amplifier 12 becomes constant. Controlled. Needless to say, the same effect can be obtained by using the methods shown in the second and third embodiments as means for obtaining the wavelength monitor signal.

[0017]

Since the present invention is constructed as described above, even if the wavelength of the semiconductor laser, which is the light source, changes, the change in the push-pull signal caused by it can be suppressed, so that it is stable. A control system can be obtained.

Further, even for semiconductor lasers having different wavelengths, it is possible to obtain the optimum power of the semiconductor laser which can suppress the change in the push-pull signal caused by that.

[Brief description of drawings]

FIG. 1 is a connection diagram of an optical system and signals according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of a diffraction grating used in Examples 1 and 2 of the present invention.

FIG. 3 is a diagram showing wavelength dependence of a push-pull signal of a write-once CD disc.

FIG. 4 is a diagram showing wavelength dependence of a wavelength monitor signal obtained by the present invention.

5 is an optical system and signal connection diagram of Example 2 of the present invention. FIG.

FIG. 6 is a connection diagram of an optical system and signals of Example 3 of the present invention.

FIG. 7 is an optical system and signal connection diagram of Example 4 of the present invention.

FIG. 8 is a diagram showing an optical system of a conventional optical recording / reproducing apparatus.

[Explanation of symbols]

1 Semiconductor laser 5 Beam splitter 6 Objective lens 8 Information recording medium 11 First photodetector 14 luminous flux 15 diffraction grating 17 Second photodetector 20, 21 Divider

Claims (2)

[Claims] 1. An objective lens which collects a light beam from a light source, emits the light beam to an information recording medium, and enters a reflected light beam from the information recording medium, and a beam which separates the light beam emitted from the light source and the reflected light beam. In an optical recording / reproducing apparatus having a splitter and a first photodetector for detecting a track error signal for receiving the light beam separated by the beam splitter, a light beam reflected by the beam splitter among the light beams from the light source is A second photodetector for receiving light is provided, a diffraction grating having wavelength selectivity is provided between the beam splitter and the second photodetector, and a signal obtained from the second photodetector
An optical recording / reproducing apparatus characterized in that the gain of a track servo loop is controlled. 2. The optical recording / reproducing apparatus according to claim 1, wherein the intensity of the light source is controlled by a signal obtained from the second photodetector.