JPH06243500A - Optical information reproducer - Google Patents

Abstract

PURPOSE:To perform the drive control of a semicondcutor laser regardless of the impedance variation or the aging deterioration of the semiconductor laser. CONSTITUTION:A high frequency oscillator 11 can optionally set its oscillation frequency and oscillates the output signal X1 of the frequency and the output signal X2 obtained by inverting the polarity of the signal X1 to a laser driving circuit 12. The circuit 12 generates an AC current based on the input of both signals X1 and X2 and also superposes the AC current on the DC current of a laser driving current source 13 to drive a semiconductor laser 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reproducing apparatus for optically reproducing information from a disk medium.

[0002]

2. Description of the Related Art Conventionally, an apparatus of this type has been disclosed in Japanese Patent Laid-Open No. 56-37.
834, and FIG. 6 is a configuration diagram disclosed in that publication. This device includes a semiconductor laser 1, a lens 2 for parallelizing the light from the semiconductor laser 1,
A lens 3 for condensing the laser light passing through the lens 2 on the surface of the optical disc medium 4 into a spot diameter of about the wavelength of light, a photodetector 5 for detecting the amount of reflected feedback light from the optical disc medium 4, a resistor R, and a coil L. The semiconductor laser 1 is provided with a direct current source 6 for supplying a direct current to the semiconductor laser 1, and a high frequency current source 7 for supplying a high frequency current to the semiconductor laser 1 via a capacitor C. Information is reproduced from the optical disc medium 4. At this time, the direct current of the direct current source 6 and the high frequency current of the high frequency current source 7 are superposed and supplied to the semiconductor laser 1 so that multiple longitudinal mode oscillation occurs.

[0003]

In the conventional device as described above, when the high frequency current of the high frequency current source 7 is superimposed on the direct current of the direct current source 6, the impedance of the semiconductor laser 1 may vary. Due to the secular change of the semiconductor laser 1, a frequency mismatch between the capacitor C and the coil L occurs, and in such a case, the oscillation light output of the semiconductor laser 1, the low noise level, the light emission waveform, etc. greatly change. Was there. Furthermore, the output impedance of the high-frequency current source 7 due to the coupling of the high-frequency current source 7 and the semiconductor laser 1
Due to the mismatching of the impedances, the noise characteristics varied depending on the oscillation frequency. Further, when the high frequency current is superposed on the direct current, the emission peak power of the semiconductor laser 1 rapidly increases, so that the semiconductor laser 1 deteriorates.

The present invention has been made to solve the above problems, and an object thereof is to obtain an optical information reproducing apparatus for driving and controlling a semiconductor laser regardless of variations in impedance of the semiconductor laser and aging. .

[0005]

An optical information reproducing apparatus according to the present invention comprises a laser element for irradiating a disk medium with a laser beam, a direct current source for supplying a direct current to the laser element, and an oscillation frequency. Is arbitrarily set, and a high-frequency oscillator that oscillates a first signal of the frequency and a second signal with the polarity of the first signal inverted, and an alternating current based on the inputs of the first and second signals, A laser drive circuit for driving the laser element by superposing the alternating current and the direct current is provided.

[0006]

In the present invention, the high frequency oscillator can set the oscillation frequency arbitrarily, and oscillates the first signal having the frequency based on the setting and the second signal which is the inverted polarity of the first signal to the laser drive circuit. The laser drive circuit generates an alternating current based on the inputs of the first and second signals, and superimposes the alternating current on the direct current of the direct current source to drive the laser element.

[0007]

1 is a circuit diagram showing an embodiment of the present invention, FIG.
Is a correlation diagram between semiconductor laser drive current and time, FIG. 3 is a block diagram showing an example of a high frequency oscillator having a delay circuit, FIG. 4 is a time chart for explaining the operation of the high frequency oscillator, and FIG. 5 is a semiconductor laser. It is a figure which shows the multiple longitudinal mode oscillation spectrum of. Incidentally, the same or corresponding parts as those of the conventional example described in FIG.

In FIG. 1, a high frequency oscillator 11 is provided with an OR gate 11a and a delay circuit (for example, a delay line) 11b connected in parallel to the OR gate 11a as shown in FIG. By changing it, the oscillation frequency can be changed arbitrarily.

For example, when the input signal A becomes low level as shown in FIG. 4, the OR gate 11a operates at time t1 (O
After a delay time due to the characteristics of the R gate), a low level output signal X1 and a high level output signal X2 obtained by inverting the level of the signal are output. On the other hand, the delay circuit 11b receives time t2 after the output signal X2 is input.
After that (the delay time of the delay circuit 11b), the output signal X2 is output to the OR gate 11a as the output signal X21. OR gate 11 to which the high level output signal X21 is input
After the time t1, the a outputs the output signal X1 by inverting the level thereof to the high level and the output signal X2 by inverting the level thereof to the low level. This state is the time t1 after the level of the output signal X21 of the delay circuit 11b becomes low level.
, And then the levels of the output signals X1 and X2 are inverted. This series of operations is repeated while the input signal A is at the low level, and ends when the input signal A becomes at the high level. As can be understood from the above description, the time t
The frequencies of the output signals X1 and X2 can be changed according to the length of 2.

The laser drive circuit 12 comprises a pair of transistors Q1 and Q2, of which the transistor Q1
Has a collector connected to the high voltage side via the semiconductor laser 1, an emitter connected to the auxiliary current source 14, and a base connected to one output end of the high frequency oscillator 11 to output the output signal X2. It is supposed to be entered. The auxiliary current source 14 has a high-frequency current amplitude so that the oscillation of the semiconductor laser 1 is turned on and off at a high frequency.

In the transistor Q2, the collector is directly connected to the high voltage side, the emitter is connected to the connection point between the emitter of the transistor Q1 and the auxiliary current source 14, and the base is the other end of the high frequency oscillator 11. It is connected to the output terminal so that the output signal X1 can be input. The laser drive current source 13 is the semiconductor laser 1
And a collector of the transistor Q1 via a resistor R and a coil L.

In the optical information reproducing apparatus configured as described above, when the input signal A is at high level, the high frequency oscillator 11 is turned off, and the laser drive circuit 1 is accordingly turned off.
Since 2 is also in the stopped state, the current flowing through the semiconductor laser 1 is only the direct current I from the laser driving current source 13 as shown in FIG. At this time, when the input signal A becomes low level, the high frequency oscillator 11 outputs the output signal X1 to the transistor Q2 of the laser amplification circuit 12 and the output signal X2 to the transistor Q1 as described with reference to FIG. Transistor Q of laser amplification circuit 12
When 1 and Q2 are alternately turned on and off based on the inputs of the output signals X1 and X2, a high frequency alternating current is superimposed on the direct current component to drive the semiconductor laser 1 as shown in FIG. 2 (b). To do. The semiconductor laser 1 is a transistor Q
When 1 is on, the current becomes equal to or less than the oscillation threshold value Ith so that the light is extinguished, and when the transistor Q2 is on, light is emitted.
The current I1 shown in FIG. 2 becomes smaller than the current I by the effective value of (I2 + I3) when the input signal A becomes low level, and the current I is the sum of the average of the current I1 and (I2 + I3). Then, while the semiconductor laser 1 is being driven, the oscillation spectrum becomes a multiple longitudinal mode oscillation as shown in FIG.

[0013]

As described above, according to the present invention, the semiconductor laser is driven by superimposing the alternating current generated by driving the laser drive circuit on the direct current. Since stable control is possible and the output of the high-frequency oscillator can be adjusted irrespective of changes over time, the effect of facilitating the circuit design of this type of device is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a correlation diagram between a semiconductor laser drive current and time.

FIG. 3 is a block diagram showing an example of a high-frequency oscillator including a delay circuit.

FIG. 4 is a time chart for explaining the operation of the high frequency oscillator shown in FIG.

FIG. 5 is a diagram showing a multiple longitudinal mode oscillation spectrum of a semiconductor laser.

FIG. 6 is a configuration diagram of an optical information reproducing apparatus disclosed in Japanese Patent Laid-Open No. 56-37834.

[Explanation of symbols]

 1 Semiconductor Laser 11 High Frequency Oscillator Having Delay Circuit 12 Laser Driving Circuit 13 Laser Driving Current Source 14 Auxiliary Current Source

Claims (1)

[Claims] 1. A laser element for irradiating a disk medium with a laser beam, a direct current source for supplying a direct current to the laser element, and an oscillation frequency arbitrarily set, and a first signal and a first signal of the frequency. A high-frequency oscillator that oscillates a second signal with the polarity of the signal inverted, and an alternating current that is generated based on the inputs of the first and second signals, and the laser device that superimposes the alternating current and the direct current. And a laser driving circuit for driving the optical information reproducing apparatus.