JP2769376B2 - Semiconductor laser device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a semiconductor laser optical head used for an optical disk file capable of recording, reproducing, or erasing image information, data information, and the like on a disk using a laser beam. And a noise removal method.

[Related Art] A semiconductor laser is used as a light source of an optical disk file that can be recorded, reproduced, or erased as a processing unit for image information, data information, and the like.

In recent years, higher output and higher reliability of semiconductor lasers have been advanced,
Due to cost reduction, semiconductor lasers have become popular as light sources used for optical disk files capable of recording, reproducing, or erasing image information, data information, and the like on a disk. Focusing control and tracking control by driving the objective lens by narrowing down the laser beam emitted from the optical head including the semiconductor laser to a minute spot on the disk recording surface for recording and reproducing signals on the disk, etc. ing.

 FIG. 2 shows the configuration of a general optical head.

The beam emitted from the laser 1 becomes parallel light by the collimator lens 2, passes through the beam splitter 3, and converges on the signal surface 6 of the disk 5 by the objective lens 4. The beam reflected by the disk 5 is reflected by the beam splitter 3, passes through the detection lens 8, and enters the parallel plate 9. The beam reflected by the parallel plate 9 is collected by a tracking signal detector 11, and the transmitted beam is collected by a focusing signal detector 10, and used as tracking control and focusing control signals, respectively.

However, lasers have good spectral uniformity,
The coherent length is the laser 1 of the optical head and the disk 5
Because it is considerably longer than the distance between, after reflection on the disc,
If there is feedback light to the laser emission end face, the noise of the semiconductor laser emission light increases significantly due to the interference effect.

As a method of reducing the noise, as shown in FIG. 3, a laser high-frequency (for example, about 700 MHz) oscillation circuit (21:
Hereafter, there is a method of modulating with a high frequency module, multiplying the spectrum of the laser so as not to interfere with the feedback light from the disk, and preventing an increase in the noise of the semiconductor laser light, which is most commonly used.

As shown in FIG. 4, the output bias light is stabilized by detecting the light 32 emitted from the front surface of the laser chip 30 by the light receiving element 33 and the light emitted from the rear surface by the light receiving element 33. Apply feedback to 19 for stabilization.

If the amount of feedback light to the laser 1 is large and noise cannot be sufficiently reduced by merely modulating the laser at a high frequency, a part of the light emitted from the front of the laser is further converted to a light receiving element as shown in FIG. There is also a method of detecting noise at 12 and feeding it back to the laser drive circuit 19 via the amplifier 13 to reduce noise.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional method, for example, in the method shown in FIG. 3, a high-frequency module is used.
Problems when using a high-frequency module include the following.

It is necessary to take measures to reduce unnecessary radiation (FCC, VCCI) of high-frequency radiation power.

There is variation in the impedance between the laser and the high-frequency module, and it is difficult to ensure consistency between the two.

 This is a major constraint on miniaturization of the optical head.

 Increases cost.

Also in the case where the bias light is stabilized by the method shown in FIG. 4, the output of the front emission light 31 and the output of the rear emission light 32 are different if there is feedback light to the laser from a disk or the like. However, there is a problem that the front emission light 31 originally required fluctuates.

As a method for further solving these problems, as shown in FIG. 5, a method of detecting a part of the front emission light, stabilizing the bias light, and reducing the noise in the servo band and the signal band by the high-frequency module. However, the use of a high-frequency module causes the same problem as described above.

Methods for detecting a part of the light emitted from the front and returning the light to the laser have already been proposed (for example, Japanese Patent Application Laid-Open Nos. 56-145534, 57-154658, 60-93949). Because it is used for a read-only optical disk such as a compact disk, when recording and erasing a wide-band signal such as a video signal targeted by the present invention, a wide-band amplifier from DC to tens of MHz is practically used. However, there is a problem that the method is very expensive and the operating range is narrow, or a signal to be recorded on a disk is fed back to a laser during recording, and the method disclosed in the above-mentioned publication cannot be used.

An object of the present invention is to provide an apparatus capable of reducing noise during reproduction, recording, and erasing without using a high-frequency module in order to solve the above-mentioned problems of the related art.

Means for Solving the Problems In order to achieve the above object, the present invention provides a semiconductor laser,
An optical system that separates a part of the beam of the semiconductor laser that is emitted toward the disk toward the disk, and detects the separated beam,
A photodetector that converts the electric signal, an amplifier of a low-frequency component including a DC component of the electric signal, an amplifier of a high-frequency component,
A circuit for adding outputs from both amplifiers, a switch for switching the addition of the high-frequency component according to a signal for reproduction, recording, and erasing; and a semiconductor laser driving circuit, and a low-frequency component of the output of the photodetector. While the semiconductor laser is being driven, it returns to the semiconductor laser and reproduces the high-frequency component from the optical disc,
A semiconductor laser device provided with means for returning to a semiconductor laser at the time of erasing.

A characteristic requirement of the present invention is that a part of the front emission light is detected and its signal is converted from a direct current to a servo band (hereinafter, abbreviated as a low frequency component) and several tens of MHz (hereinafter, abbreviated as a high frequency component).
The combination for returning to the laser is switched according to the mode of reproduction, recording, and erasing.

[Operation] According to the configuration of the present invention described above, the means for feeding back the low-frequency component of the output of the photodetector to the semiconductor laser during driving of the semiconductor laser and returning the high-frequency component to the semiconductor laser when reproducing and erasing the optical disk is provided. A part of the light emitted from the front is detected, and its signal is converted from a direct current to a servo band (hereinafter abbreviated as a low frequency component) and several tens of MHz (hereinafter abbreviated as a high frequency component).
The combination of feedback to the laser is switched according to the mode of reproduction, recording, and erasing. Therefore, in the optical disk head capable of recording, reproducing, and erasing, stabilization of bias light without using a high-frequency module, Noise in each of the servo band and the signal band can be reduced.

Embodiment An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a view of one embodiment of the present invention, but the description of the conventional optical system will be omitted because it has already been described in the section of the prior art.

In FIG. 1, when a front emission light of a laser 1 passes through a beam splitter 3, a part of reflected light is detected by a monitor diode 12, and a low frequency component from a direct current to a servo band is amplified by a direct current amplifier 13, By feeding back to the laser, it stabilizes the laser and reduces noise, and amplifies the high-frequency components of the signal band with the coupling capacitor 14 and the AC amplifier 15,
Similarly, the band is separated so as to reduce noise by returning to the laser. The two signals are added by an adder 18. The addition of the high-frequency component is switched by a switch 17 in accordance with a reproduction, recording, and erasing mode signal 16.

Table 1 below shows a state in which two types of frequency components are added according to each mode. That is,
At the time of reproduction and erasing, both the low frequency component and the high frequency component of the detection output of the front emission light are fed back to the laser, and at the time of recording, only the low frequency component is fed back to the laser.

As described above, according to the semiconductor laser device of the embodiment of the present invention, a high-power laser is used, an optical head capable of recording and erasing data on an optical disk is not used with a high-frequency module, and a general-purpose inexpensive operational amplifier and AC amplifier are used. It is possible to stabilize the low-frequency component and the high-frequency component of the laser output and reduce noise, and it is possible to obtain a reproduced signal having good characteristics.

[Effects of the Invention] As is clear from the above embodiments, according to the present invention,
A part of the light emitted from the front surface of the laser is detected, its signal is separated into a low-frequency component and a high-frequency component, and the addition state of both components is switched according to the mode of reproduction, recording, and erasing, so that the cost is low. The remarkable effect of providing a semiconductor laser device that stabilizes a laser and reduces noise in a wide range from a DC component to a high-frequency signal band can be achieved by the component configuration.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an optical system and a laser noise reduction circuit of a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a conventional general optical system, and FIG. FIG. 4 is a circuit diagram of one embodiment of a conventional laser output stabilization, and FIG. 5 is a circuit diagram of another embodiment of the conventional noise reduction. DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Collimating lens, 3 ... Beam splitter, 5 ... Disk, 12 ... Monitor diode,
13 ... DC amplifier, 15 ... AC amplifier, 19 ... Laser drive circuit.

Claims (1)

(57) [Claims] A semiconductor laser; an optical system for separating a part of a beam of light emitted from a front surface of the semiconductor laser toward a disk; a photodetector for detecting the separated beam and converting the beam into an electric signal; A low-frequency component amplifier including a DC component of a signal, a high-frequency component amplifier, a circuit for adding outputs from both amplifiers, a switch for switching the addition of the high-frequency component according to reproduction, recording, and erasing signals; and a semiconductor. A laser driving circuit, and feeds back the low-frequency component of the output of the photodetector to the semiconductor laser while driving the semiconductor laser,
A semiconductor laser device comprising a means for returning a high frequency component to a semiconductor laser when reproducing or erasing an optical disk.