JPH05315687A - Apparatus for controlling semiconductor laser output - Google Patents

Abstract

PURPOSE:To provide a device for reducing laser noise by allowing high-frequency current in a laser diode, so as to reduce the power consumption of the laser diode, decrease the undesirable radiation level due to a disc and eliminate the level adjustment of high-frequency current. CONSTITUTION:A photodetector 6 and a converter 7 cooperate to produce a first control signal depending on the level of the output from a semiconductor laser 1, and the ac component of the first control signal is extracted by a capacitor 9. The ac component contains the fluctuation due to laser noises. A detector circuit 10 detects the amplitude of the ac component, and produces a second control signal depending on the detected amplitude. The second control signal is fed back to a high-frequency current source 3 for the amplitude control of the source current. As a result, the high-frequency current source is so controlled that the ac component in the first control signal may become constant; therefore, laser noises are sufficiently suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser emission light control device for controlling the power of a laser beam in an optical information reader such as a video disc player or a compact disc player.

[0002]

2. Description of the Related Art Optical discs such as video discs and compact discs have pits formed on the discs. When a laser beam is irradiated onto the pits, the reflected light is optically modulated depending on the presence or absence of the pits. receive. A conventional optical player converts a modulated laser beam into an electric signal, converts the electric signal into a rectangular wave, and then supplies the electric wave to a demodulation stage to reproduce information recorded on a disc.

Incidentally, a semiconductor laser is often used as a light source of a laser beam in a conventional optical player. The laser power of this semiconductor laser has temperature dependence, and it is known that the laser power decreases as the external temperature rises. When the laser power fluctuates due to the external temperature, the S / N ratio of the read signal read from the disk deteriorates. Therefore, in order to suppress the fluctuation of the laser power in a relatively low frequency band, the emitted light of the semiconductor laser is monitored by the light receiving element so that the monitored laser power becomes constant (APC
Servo: Automatic Power Controller
ol servo) is used.

When the semiconductor laser is driven by a single direct current, it oscillates in a so-called single mode, but when the reflected light from the disk returns to the semiconductor laser, the laser power fluctuates due to this return light component. Is known to do. In addition to the optical resonator formed by the two cleavage planes of the semiconductor crystal constituting the semiconductor laser, a second optical resonator formed by the side surface of the semiconductor laser disk and the disk surface is formed. This is because if the distance between the disk and the semiconductor laser changes due to surface wobbling of the disk or the like, high-frequency laser noise is observed.

In order to reduce the occurrence of such high-frequency laser noise, it is known to superimpose a high-frequency current on a driving current for driving a semiconductor laser, and the outline of such a device is disclosed in Japanese Patent Publication No. 59-9085. It is also described in.

FIG. 4 is a block diagram showing a configuration of an example of a conventional semiconductor laser emission light control device using such an APC servo and a device for suppressing laser noise caused by superposition of a high frequency current. In the figure, a semiconductor laser 1 is connected to a current source 2 for supplying a bias current and a high frequency current source 3 for supplying a high frequency current via a DC cutting capacitor 4, and a power source for determining a bias current value. 5
Are connected to the current source 2. Further, for the APC servo, a light receiving element 6 for receiving a laser beam emitted from the semiconductor laser 1 and a converter (IV) 7 for converting a current value photoelectrically converted by the light receiving element 6 into a voltage are provided. The output of the converter 7 is supplied to the APC circuit 8. AP
The C circuit 8 detects the DC level of the output of the converter 7, and controls the bias current value supplied from the current source 2 so that this DC level becomes constant.

FIG. 5 is a block diagram showing the configuration of another example of the conventional emitted light control device. Unlike the conventional example of FIG. 4, the output of the APC circuit 8 is connected to the high frequency current source 3,
It is configured to control the amplitude of the output of the high frequency current source 3.

[0008]

A conventional semiconductor laser emission light control apparatus controls the output level of the emission light monitored by the light receiving element 6 by controlling the current value of the current source 2 or the amplitude of the high frequency current source 3. I try to keep it constant. Therefore, it is possible to suppress the fluctuation of the average laser power of the semiconductor laser 1. However, 19
Article entitled "Reduction of laser noise in semiconductor laser mounted video disc player by high frequency current superposition method", published in October 1985, "Optics" Vol. 14, No. 5, pp. 53 to 60. It is known that the amplitude of the high frequency current source 3 has a dependency on the laser noise, but even in the conventional example of FIG.
The circuit 8 detects only the average value of the laser power of the semiconductor laser 1 received by the light receiving element 6, and does not directly control the amplitude of the high frequency current source 3 according to the laser noise. Therefore, it is conceivable to widen the band of the APC circuit 8 to form an APC servo that feeds back an AC component, but malfunction due to noise cannot be avoided.

Further, it is entitled "Reduction of Laser Noise in Optical Disc System by Negative Feedback Method", which is published in "Laser Research" Vol. 18, No. 5, pp. 348 to 354, published in May 1990. According to the article, only the AC component of the laser power fluctuation detected by the light receiving element 6 is supplied to the current source 2
Although a method of returning to the above is also considered, it is not practical because it requires the speedup of the entire loop, high S / N ratio, and miniaturization.

Therefore, the high-frequency current generated by the conventional high-frequency current source 3 is adjusted to have a relatively large amplitude in order to withstand the differences in the optical system, the semiconductor laser 1, the temperature characteristics, etc., and is unnecessary. This causes power consumption, a burden on the semiconductor laser 1, and an increase in unnecessary radiation.

Further, a standard concerning a recording / reproducing apparatus capable of recording / reproducing both an aluminum disk having a high reflectance as a disk and a magneto-optical disk having a low reflectance has been proposed. If the high-frequency current possessed by the semiconductor laser 1 is supplied to the semiconductor laser 1, the magneto-optical disk will be over-specified, and the above-mentioned unnecessary power consumption, increase in unnecessary radiation, shortening of life due to increase in load on the semiconductor laser 1, etc. The problem becomes more prominent.

According to the present invention, in a device for reducing laser noise by superposing a high frequency current on the semiconductor laser 1, the power consumption of the semiconductor laser 1 is reduced, the unwanted radiation level by the disk is reduced, and the level of the high frequency current is reduced. It is an object of the present invention to provide a semiconductor laser emission light control device that can be adjusted.

[0013]

An emission light control device for a semiconductor laser according to the present invention is a device for reducing a laser noise by superposing a high frequency current on the semiconductor laser 1, and it is suitable for the emission light amount of the semiconductor laser 1. First to generate a first control signal
A light receiving element 6, a converter 7 as a signal generating means of
According to the capacitor 9 as the second control signal generating means for generating the second control signal according to the amplitude of the AC component of the control signal, the detection circuit 10, and the second control signal output from the detection circuit 10. And a high frequency current source 3 as a high frequency current generating means for generating a high frequency current whose amplitude is controlled.

[0014]

In the emitted light control device for a semiconductor laser having the above structure, the semiconductor laser 1 includes the light receiving element 6 and the converter 7.
The first control signal is generated according to the level of the outgoing light emitted by, and the AC component included in the first control signal is extracted by the capacitor 9. This AC component contains fluctuations due to laser noise. The amplitude of the AC component extracted by the capacitor 9 is detected by the detection circuit 10, and the second control signal corresponding to the amplitude is fed back to the high frequency current source 3. The amplitude of the high frequency current source 3 is controlled according to the second control signal.

Accordingly, the light is received by the light receiving element 6, and the converter 7
Since the high-frequency current source 3 is controlled so that the AC component included in the first control signal converted in step 1 is constant, the generation of laser noise is suppressed under favorable conditions.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. The same parts as those in the conventional case are designated by the same reference numerals, and the description thereof will be omitted as appropriate. FIG. 1 is a block diagram showing the configuration of an embodiment of a semiconductor laser emission light control apparatus of the present invention. In the figure, the outputs of the light receiving element 6 as the first signal generating means and the converter 7 are supplied to the APC circuit 8 as the first control signal and also to the DC cut capacitor 9. The AC component included in the first control signal output from the converter 7 is extracted by the capacitor 9. The amplitude of the AC component signal extracted by the capacitor 9 is detected by the detection circuit 10 and is fed back to the high frequency current source 3 (high frequency current generating means) as the second control signal. On the other hand, the output of the APC circuit 8 is fed back to the current source 2 as in the conventional example of FIG.

The operation of the above configuration will be described.
The average fluctuation of the laser power of the semiconductor laser 1 is AP
By controlling the current source 2 by the C circuit 8, the current is suppressed as in the conventional case. In the present embodiment, the detection circuit 10 further detects the amplitude of the relatively high frequency fluctuation component (AC component) of the first control signal output from the converter 7. Since the amplitude of the AC component detected by the detection circuit 10 is changed by the laser noise, the influence of the laser noise is reduced by controlling the amplitude of the high frequency current source so that the amplitude becomes constant. ..

FIG. 3 is a graph showing the relationship between the bias current supplied to the semiconductor laser 1 and the laser power.
The graph (a) is a current-power characteristic diagram of the semiconductor laser 1, the graph (b) is a waveform of the high frequency current generated by the high frequency current source 3, and the graph (c) is a case where the high frequency current of the graph (b) is supplied. The characteristics of the emitted light of the semiconductor laser 1 are shown.

In the graph (a), the horizontal axis represents the intensity of the bias current and the vertical axis represents the laser power. When the threshold current A is supplied, the laser power is substantially linear with a slope B for a larger current. Increase to. Therefore, a current having a current value F slightly lower than the threshold current A is supplied from the current source 2 to the semiconductor laser 1, and the high frequency current source 3 supplies a high frequency current whose amplitude is larger than twice (A-F). Is supplied to the semiconductor laser 1, a current whose amplitude changes with time is supplied to the semiconductor laser 1, as shown in the graph (b). The graph (b) shows current on the horizontal axis and time on the vertical axis.

When the bias current shown in the graph (b) is supplied to the semiconductor laser 1, the laser power of the semiconductor laser 1 becomes 0 in the period in which a current lower than the threshold current A is supplied, and exceeds the threshold current A. A predetermined laser power is output during the period in which the current is supplied, and the peak power D depends on the amplitude of the high frequency current generated by the high frequency current source 3. Graph (c) shows the change over time in the laser power. In graph (c), the horizontal axis indicates time,
The vertical axis shows the laser power. In the graph (C), the average laser power is shown by C.

In the embodiment shown in FIG. 1, the APC circuit 10 supplies the current source 2 so that the average laser power C becomes constant.
Current value (F in graph (b)) is controlled, and the amplitude of the high-frequency current generated by the high-frequency current source 2 in the detection circuit 10 (E in graph (b)) is controlled so that the peak power D becomes constant. To be done.

In the conventional apparatus shown in FIGS. 4 and 5, only one of E and F in the graph (b) is controlled, but in the present embodiment, the laser power is changed. Is controlled by the current level (F) of the current source 2 by the APC circuit 10, and a high frequency fluctuation caused by laser noise is controlled by the amplitude (E) of the high frequency current source 3 by the detection circuit 10. Therefore, the fluctuation of the laser power is suppressed from the low range to the high range.

FIG. 2 is a block diagram showing the configuration of another embodiment of the emitted light control apparatus for a semiconductor laser of the present invention. The difference from the embodiment of FIG. 1 is that the output of the APC circuit 8 is a high frequency current source. As the control signal for controlling the amplitude of 3, the adder 11
Is added to the output of the detection circuit 10. That is, the average laser power of the semiconductor laser 1 (C in the graph (c) of FIG. 3) not only affects the current value of the current generated by the current source 2 but also the amplitude of the high frequency current generated by the high frequency current source 3. Therefore, the current source 2 and the high frequency current source 3 may be controlled together by the output of the APC circuit 8 in order to suppress the average fluctuation of the laser power as in the embodiment of FIG. ..

In the graph (c) of FIG. 3, the waveform of the emitted light itself fluctuates periodically, but if the frequency of the high frequency current is sufficiently higher than the carrier frequency read from the disk, Readability is hardly affected. For example, in the case of a video disc, the maximum frequency of the read RF signal is about 10 MHz, so the frequency of the high frequency current may be set to about 50 MHz, for example.

[0025]

As described above, according to the emitted light control apparatus for a semiconductor laser of the present invention, the AC component contained in the first control signal corresponding to the power of the emitted light of the semiconductor laser is detected and its amplitude is detected. A means for generating a second control signal according to the second control signal is provided, and the amplitude of the high-frequency current supplied to the semiconductor laser is set to the second value.
Since it is controlled by the control signal of, the relatively high frequency fluctuation of the laser power due to the laser noise can be suppressed.

In other words, since the laser noise can be reduced without unnecessarily increasing the amplitude of the high frequency current, unnecessary power consumption is not required and the load on the semiconductor laser can be reduced, so that the life of the semiconductor laser can be reduced. In addition to being able to extend the length, it is possible to reduce the unwanted radiation level from the disk.

Furthermore, the initial adjustment of the amplitude of the high-frequency current can be eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a semiconductor laser emission light control apparatus of the present invention.

FIG. 2 is a block diagram showing the configuration of another embodiment of the emitted light control device for a semiconductor laser of the present invention.

FIG. 3 is a graph showing a relationship between a semiconductor laser, a bias current, and a laser power.

FIG. 4 is a block diagram showing a configuration of an example of a conventional emission control device for a semiconductor laser.

FIG. 5 is a block diagram showing a configuration of another example of a conventional emitted light control device for a semiconductor laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 semiconductor laser 2 current source 3 high frequency current source (high frequency current generating means) 4 capacitor 5 power source 6 light receiving element 7 converter (first signal generating means) 8 APC circuit 9 capacitor 10 detection circuit (second signal generating means)

Claims (1)

[Claims] 1. A device for reducing laser noise by superimposing a high-frequency current on a semiconductor laser, comprising: first signal generating means for generating a first control signal according to the amount of light emitted from the semiconductor laser; Second signal generating means for generating a second control signal according to the amplitude of the AC component of the first control signal; and a high-frequency current for generating a high-frequency current whose amplitude is controlled according to the second control signal. An emission light control device for a semiconductor laser, comprising: a generation unit.