JP2732703B2 - Semiconductor laser device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device used for a data file capable of recording, reproducing, or erasing image information, data information, and the like on an optical recording medium by using a laser beam. It is about.

2. Description of the Related Art 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 optical disks. Focusing control and tracking control by driving the objective lens by narrowing the laser beam emitted from the optical head including the semiconductor laser to a minute spot on the recording surface of the optical disk for recording and reproducing signals on the optical disk, etc. Is going.

 Next, a configuration of a general optical head is shown in FIG.

The beam emitted from the semiconductor 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 optical disk 5 by the objective lens 4. The beam reflected by the optical 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 applied to a tracking signal detector 11.
The transmitted beam is collected by a focusing signal detector 10 and used as tracking control and focusing control signals, respectively. 7 is a focusing coil.

However, lasers have good spectral uniformity,
Since the coherent length is considerably longer than the distance between the semiconductor laser 1 of the optical head and the optical disk 5, if there is feedback light to the laser emission surface after reflection on the optical disk 5, the noise of the semiconductor laser emission light is remarkable due to the interference effect. Increase.

As a method for reducing the noise, as shown in FIG. 4, the semiconductor laser 1 is modulated by a high-frequency (for example, about 700 MHz) oscillation circuit 22 (hereinafter, abbreviated as a high-frequency module) to multiplex the laser spectrum and transmit the data from the optical disc 5 There is a method of preventing interference with the feedback light of the semiconductor laser and preventing an increase in noise of the semiconductor laser light, and is most commonly used.

As shown in FIG. 5, the output bias light is stabilized by detecting a light 33 emitted from a rear surface of the laser chip 31 with a light-receiving element 34 and passing the laser light through an amplifier 35 to a laser 32 as shown in FIG. Feedback is applied to the drive circuit 21 to perform stabilization.

If the amount of feedback light to the semiconductor laser 1 is large and the noise cannot be sufficiently reduced only by modulating the semiconductor laser 1 at a high frequency, as shown in FIG. There is also a method of detecting a portion by the light receiving element 12 and feeding it back to the laser drive circuit 21 through the amplifier 35 to reduce noise.

On the other hand, the laser drive circuit 21 is frequently used in digital recording because switching by transistors, for example, a circuit as shown in FIG. 7 is advantageous in terms of speeding up (e.g., 20 nsec) of rise and fall of a light emission waveform. ing. Here, 41 is a power supply, 42 is a constant current source, 43 and 44 are transistors, 45 is a two-phase comparator, 46 is a semiconductor laser, 47
Is a resistor, and 48 is a recording signal. For analog recording, current modulation, for example, a circuit as shown in FIG. 9 is often used. Here, 51 is a semiconductor laser, 52 is a transistor, 53 is a resistor, 54 is a power supply, 55 is an operational amplifier, and 56 is a recording signal.

Problems to be Solved by the Invention However, in the conventional method, for example, in the method shown in FIG. 4, the high-frequency module 22 is used. It is necessary to take measures to reduce unwanted radiation (FCC, VCCI) of the laser. 2. There is variation in the impedance between the laser and the high-frequency module 22, making it difficult to match them. 3. High-frequency module 22 at high output such as recording and erasing. It is necessary to stop the operation of the optical head, which causes problems such as a reduction in S / N, 4. a great restriction on miniaturization of the optical head, and 5. an increase in cost. Also in the case where the bias light is stabilized by the method shown in FIG. 5, if there is feedback light from the optical disk 5 or the like to the semiconductor laser 1, the output of the front emission light 32 and the output of the rear emission light 33 are different, so that the rear emission light 33 is stable. Front emission light that is essentially required
32 has a problem that it fluctuates.

As a method for further solving these problems, as shown in FIG. 6, a part of the front emission light is detected to stabilize the bias light, and the noise in the servo band and the signal band is reduced by the high frequency module 22. Although there is a method, the above-described problem still occurs because the high-frequency module 22 is used.

A method of detecting a part of the light emitted from the front surface and feeding it back to the semiconductor laser has already been filed (for example, Japanese Patent Application Laid-Open No. 56-1455).
34, JP-A-57-154658, JP-A-60-93649, etc.) Since these are used for reproduction-only optical discs such as compact discs, recording and erasing of wideband signals as in the present case is performed. However, there is a problem that a wideband from DC to several tens of MHz, a high-gain amplifier is very expensive and has a narrow operating range, or a signal to be recorded on an optical disk is fed back to a semiconductor laser during recording. Those applications cannot be used.

On the other hand, the light emission waveform of the semiconductor laser 46 can emit only a rectangular wave in the case of the switching method using the transistor 43 as shown in FIG. For this reason, when the optimum recording light emission waveform for the optical disk 5 is not rectangular, for example, in the case of a trapezoidal wave as shown in FIG. Where 49
Denotes an optimum recording waveform, and 50 denotes a laser output waveform.

If the current modulation circuit as shown in FIG. 9 performs analog modulation, the recording light emission waveform can be changed as shown in FIG. 10, but the frequency component of the recording light emission waveform, for example, up to several tens of MHz, can be controlled. Since the band is not extended, there is a problem that the waveform control is open and unstable.

SUMMARY OF THE INVENTION The present invention provides a semiconductor laser device capable of solving such problems without using a high-frequency module, reducing noise during reproduction, recording, and erasing, and easily realizing a laser emission waveform optimal for recording on an optical disk. It is intended to be.

Means for Solving the Problems The present invention relates to a semiconductor laser device comprising a semiconductor laser and a semiconductor laser driving means for driving the semiconductor laser, wherein the semiconductor laser device is used for reproducing, erasing, and recording on an optical recording medium. An optical system for separating a part of the light emitted from the front of the optical signal, a photodetector for detecting the separated beam and converting an electric signal, and a low-frequency amplifier for amplifying a low-frequency component including a DC component of the electric signal Means, high-frequency amplification means for amplifying high-frequency components of the electric signal, addition means for adding outputs from these low-frequency amplification means and high-frequency amplification means, and output of a reference signal according to reproduction, erasure, and recording signals A reference signal generating means for comparing the signal output from the adding means with the reference signal. The laser driving device is a semiconductor laser device that drives a semiconductor laser using a result of comparison by the comparing device.

Function The present invention separates a part of light emitted from the front surface of a semiconductor laser by an optical system, detects the separated beam by its photodetector, converts the beam into an electric signal, and converts the electric signal into a low-frequency amplifier. A low-frequency component including a DC component is amplified, a high-frequency amplifier amplifies a high-frequency component of the electric signal, an adder adds the outputs from the low-frequency amplifier and the high-frequency amplifier, and reproduces the signal by a reference signal generator. A reference signal is output in accordance with a signal for erasing or recording, and a comparison unit compares the signal output from the adding unit with the reference signal, and reproduces, erases, or records the optical recording medium. The driving means drives the semiconductor laser using the result of comparison by the comparing means. This makes it possible to stabilize the bias light, reduce the noise in each of the servo band and the signal band without using a high-frequency module.In addition, since control can be performed up to several tens of MHz, the same waveform as the reference voltage waveform can be obtained. , And a laser emission waveform optimal for recording on an optical recording medium can be easily realized. In addition, a servo band from DC is hereinafter referred to as a low frequency component, and up to several tens of MHz is hereinafter referred to as a high frequency component.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a view showing one embodiment of a semiconductor laser device according to the present invention. Description of the same components as in FIG. 6 will be omitted.

Reference numeral 3 denotes a beam splitter as an example of an optical system that separates a part of light emitted from the front surface of the semiconductor laser 1. Reference numeral 12 denotes a light receiving element as an example of a photodetector that detects the separated beam and converts it into an electric signal. Reference numeral 13 denotes a DC amplifier as an example of a low frequency amplifying unit that amplifies a low frequency component including a DC component of the current output from the light receiving element 12. Reference numeral 14 denotes a coupling capacitor, and reference numeral 15 denotes an AC amplifier, which is an example of a high-frequency amplifier for amplifying a high-frequency component of the electric signal. 16 is
An adder is an example of an adder that adds outputs from the low-frequency amplifier 13 and the high-frequency amplifiers 14 and 15. Reference numeral 17 denotes a recording signal input terminal, reference numeral 18 denotes a reproduction / recording / erasure switching signal input terminal, and reference numeral 19 denotes a reference voltage generator as an example of reference signal generating means for outputting a reference signal in accordance with reproduction, erasure, and recording signals. Reference numeral 20 denotes a comparison circuit as an example of a comparison unit that compares the signal output from the addition unit 16 with the reference signal. The laser drive circuit 21 is a circuit that drives the semiconductor laser 1 according to the comparison result of the comparison circuit 20.

 Next, the operation of the above embodiment will be described.

When the light emitted from the front of the semiconductor laser 1 passes through the beam splitter 3, a part of the reflected light is detected by the light receiving element 12, the low frequency component from DC to the servo band is amplified by the DC amplifier 13, and the high frequency of the signal band is increased. The components are amplified by a coupling capacitor 14 and an AC amplifier 15 to separate bands. Both signals are added to adder 16
Add with The output of the adder 16 is compared with the output of the reference voltage generator 19 by a comparison circuit 20, and the comparison amount is compared with the laser drive circuit 21.
To stabilize the laser and reduce noise. The output of the reference voltage generator 19 changes according to the mode signal 16 for reproduction, erasure, and recording.

FIG. 2 shows a reference voltage generator 19 which changes according to each mode.
Of FIG. That is, during reproduction and erasure, only a DC component corresponding to the laser output is output, but at the time of recording, a reference voltage, such as a trapezoid, is output according to the recording signal 17 so as to have a recording light emission waveform optimal for an optical disk. Since the recording signal is several MHz, a laser emission waveform requires several tens of MHz to become a trapezoidal waveform.However, a trapezoidal laser emission waveform equal to the reference voltage must be obtained because the control band extends to several tens of MHz. And optimum recording can be performed. Of course, if the reference voltage is output as a rectangular wave, the laser emission waveform will be a rectangular wave.

As described above, according to the semiconductor laser device of the embodiment of the present invention, a general-purpose inexpensive operational amplifier and AC amplifier are used without using a high-frequency module for an optical head capable of recording and erasing data on an optical disk by using a high-power semiconductor laser. Thus, the low frequency component and the high frequency component of the laser output can be stabilized and the noise can be reduced, and a reproduced signal having good characteristics can be obtained.

Furthermore, since control is performed up to several tens of MHz, the same waveform as the waveform of the reference voltage can be output from the semiconductor laser,
A laser emission waveform optimal for recording on an optical disk can be easily realized, and since there is no need to perform switching by a laser drive circuit, the number of circuits can be reduced and the cost can be reduced.

In the above embodiment, an optical disk is used as an optical recording medium. However, any other optical recording medium may be used, and it is apparent that the optical recording medium can be used for an optical card or a laser beam printer.

Effects of the Invention As is clear from the above embodiments, according to the present invention,
Detects a part of the light emitted from the front of the semiconductor laser, separates the signal into low-frequency components and high-frequency components, and compares the output of these signals with a reference voltage that changes according to each of the playback, recording, and erasing modes. Is fed back to the semiconductor laser, so that the configuration of inexpensive components can stabilize the laser and reduce noise over a wide range from the DC component to the high signal band.
Further, it is possible to provide a semiconductor laser device capable of easily realizing a laser emission waveform optimal for recording on an optical disk.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an optical system and a laser noise reduction circuit of a semiconductor laser device according to one embodiment of the present invention, and FIG. 2 is a diagram showing a reference voltage reproducing, erasing and recording mode in the embodiment. FIG. 3 is a configuration diagram of an optical system of a conventional general semiconductor laser device, FIG. 4 is a configuration showing an example of conventional noise reduction, and FIG. 5 is a conventional laser output stabilization. FIG. 6 is a block diagram showing another example of a conventional noise reduction method, FIG. 7 is a circuit diagram showing an example of a conventional digital modulation laser drive circuit, and FIG. FIG. 9 is a graph showing an example of a recording light emission waveform, FIG. 9 is a circuit diagram showing an example of a conventional analog modulation laser driving circuit, and FIG. 10 is a graph showing an example of a recording light emission waveform of the analog modulation laser driving circuit. 1 ... Semiconductor laser, 3 ... Beam splitter, 5 ...
Optical disk, 12 ... Light receiving element, 13 ... DC amplifier, 14 ...
... Coupling capacitors, 15 ... AC amplifiers, 16 ... Adders,
17: Recording signal, 18: Playback / record / erase switching signal, 19
…… Laser drive circuit, 20 …… Comparison circuit, 21 …… Laser drive circuit, 31 …… Laser chip, 32 …… Front outgoing light, 33…
... Light emitted from the rear surface.

Claims (1)

(57) [Claims] 1. A semiconductor laser device comprising: a semiconductor laser; and a semiconductor laser driving means for driving the semiconductor laser, wherein the semiconductor laser device is used for reproducing, erasing, and recording on an optical recording medium. An optical system that separates the components, a photodetector that detects the separated beam and converts it into an electric signal, a low-frequency amplifier that amplifies a low-frequency component including a DC component of the electric signal, and the electric signal. High-frequency amplifying means for amplifying the high-frequency component, adding means for adding outputs from these low-frequency amplifying means and high-frequency amplifying means, and reference signal generating means for outputting a reference signal in accordance with reproduction, erasure, and recording signals. And a comparing means for comparing the signal output from the adding means with the reference signal, and when reproducing, erasing, or recording on the optical recording medium, the semiconductor laser driving means The semiconductor laser device, characterized in that for driving the semiconductor laser by utilizing the comparison result by the means.