JPH0746436B2 - Driving device for semiconductor laser - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving device used in an optical information recording / reproducing device for optically recording and reproducing information on a disc.

Conventional Technology Conventional technology will be described with reference to FIGS. 2 and 3. Second
The figure shows the current vs. light output characteristics of the semiconductor laser, but the temperature dependence is high, and it is difficult to obtain a constant output by constant current drive. Therefore, the semiconductor laser backward light is detected and feedback is given to the drive circuit. On the other hand, the semiconductor laser drive circuit in the optical recording device operates so as to have a constant output of low power at the time of reproduction for reading information,
It is necessary to repeat high-power and low-power light emission at high speed during recording for writing information. However, simply adding a modulation circuit to a constant output circuit having a feedback loop for temperature compensation generally makes it difficult to obtain light emission power proportional to the modulation signal because the time constant of the feedback loop is large.

A conventional example and its problems corresponding to this problem will be described below with reference to FIG.

FIG. 3 shows a block diagram of a conventional semiconductor laser drive circuit. At the time of reproduction, the first switching circuit 5 has the terminal b.
And c are closed and the second switching circuit 13 is open.
Regarding the optical output of the semiconductor laser 7, the rear light is detected by the power detection circuit 1, and the control circuit 3 and the first drive circuit 6
The drive current of the semiconductor laser is controlled by. Therefore, this feedback control stabilizes the reproduction power with respect to the ambient temperature. Next, during recording, the terminals a and b of the first switching circuit 5 are closed and the second switching circuit 13 is closed.

The reproduction value holding circuit 4 holds the control signal 14 at the time of reproduction, and the semiconductor laser drive current corresponding to the signal flows. At this time, the semiconductor laser drive current corresponding to the value of the recording power setting circuit 11 is superimposed to emit light at the recording power. Further, the switching circuit 12 turns on or off the second drive circuit 10 according to the recording data, and the semiconductor laser 7 repeats the recording power and the reproducing power at high speed.

Problems to be Solved by the Invention In the conventional circuit configuration shown in FIG. 3, since power control is not performed during recording, the emission power deviates from the set recording power depending on the ambient temperature and the heat generation state of the circuit. There is.

The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor laser drive circuit capable of performing stable power setting by performing power control not only during reproduction but also during recording.

Means for Solving the Problems In order to solve the above problems, the present invention provides a value for the output signal of the power detection circuit when the recording power is emitted during the recording period, and a recording power immediately before that when the recording power is not emitted. A light emission power holding circuit for holding the value at the time of light emission and a correction amount detection circuit for comparing the value of the recording power setting circuit and the value of the light emission power holding circuit and outputting the drive amount of the semiconductor laser for correcting the difference are added.

Action The present invention, which has the above-described configuration, enables feedback control not only during reproduction but also during recording, and stable light emission power can be obtained.

Embodiment FIG. 1 is a block diagram showing an embodiment of a semiconductor laser drive circuit of the present invention. In FIG. 1, reference numeral 1 is a power detection circuit for detecting the power of the rear light of the semiconductor laser.
During reproduction, the output of the power detection circuit 1 and the output of the reproduction power setting circuit 2 are added to the input of the control circuit 3. The terminals c and b of the first switching circuit 5 are closed, and the control circuit 3 controls so that the two input signals are equal to each other. The semiconductor laser 7 controls the emission power set by the reproduction power setting circuit 2. It emits light stably. At this time, the second switching circuit
13 is open and the second drive circuit is not operating.

FIG. 4 shows an example of the waveform of each circuit during the recording period.
FIG. 4 The recording period A is t ₁ to t ₆ . Also, C ₁ is the reproducing power, C ₂ is the recording power, and the value of the recording power setting circuit is C ₂
Has become. As shown in FIG. 2, the relationship between the light output and the current of the semiconductor laser is approximately (P ₂ −P ₁ ) / (i ₂ −i ₁ ) = K depending on the temperature in the stable laser emission region.
It is (constant).

Figure 1 reproduction value holding circuit 4 between t ₁ ~t ₅ recording period A t ₁
The control signal 14 immediately before is held, and the first switching circuit 5 closes the terminals a and b. Therefore, a driving current for reproduction just before t ₁ flows through the semiconductor laser 7. Also, the second switching circuit 13 is closed. At this time, the drive current which is superposed on the semiconductor laser 7 by the second drive circuit 10 and flows will be described. t _{1 to} t ₂
During this period, the output of the power detection circuit 1 is as shown in FIG.
It is C ₁ . The light emission power holding circuit 8 holds the value of the reproduction power C ₁ until t ₂ . Also, the output of the recording power setting circuit 11 is C ₂ , and the correction amount detection circuit 9 has a current value proportional to (C ₂ −C ₁ ). Is output. Here, since K is a value corresponding to the slope of the relationship of the emitted light amount with respect to the driving current of the semiconductor laser, the correction amount detection circuit 9 stores the value corresponding to the slope and K and (C ₂ -C ₁ ). An arithmetic means for calculating the value of the drive current based on the value is configured.

If the current of (1) is superposed on the semiconductor laser 7 by the second drive circuit 10 and is made to flow, the light emission power is increased by C ₂ -C _{1 and} as a result, light is emitted at the recording power of C ₂ . However, at this time (t _{1 to} t ₂ ), the recording data B shown in FIG. Therefore, at this time, the switching circuit 12 becomes the second drive circuit 10
The operation is turned off and the current does not actually flow in the semiconductor laser 7 due to the superposition. The section from t _{2 to} t _{3 is} a section where light emission should actually be performed with the recording power, and at this time, the switching circuit 12 turns on the operation of the second drive circuit 10. It is assumed that the output of the power detection circuit 1 in the section from t _{2 to} t _{3 is} as shown in FIG. 4c. Originally, the recording power should be C ₂ by the output of the correction amount detection circuit 9, but the recording power is increased by ΔC ₂ due to the influence of temperature and the like. Therefore, the correction amount detection circuit 9 Is output.

The emission power gradually approaches C ₂ due to the time constant of the circuit. In FIG. 4, as an example, it is assumed that the emission power becomes C ₂ at t ₃ . From t _{3 to} t ₄ , since the recording data B in FIG. ₄ is “O” and it is not the interval for emitting light at the recording power,
The hitting circuit 12 turns off the operation of the second drive circuit 10, and the current that has been superimposed and passed on the semiconductor laser 7 stops flowing. Therefore, the emission power is C ₁ during reproduction. At this time, the light emission power holding circuit 8 holds the value immediately before t ₃ (C _{2 in} FIG. 4).

After that, the same operation is repeated for the recording periods t _{1 to} t ₆ , and the recording power becomes stable at the value C ₂ of the recording power setting circuit 11.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to drive a semiconductor laser at a high frequency that cannot be feedback-controlled by the conventional circuit configuration, and perform feedback control with a simple circuit configuration by utilizing the characteristics of the semiconductor laser. This makes it possible to stabilize the recording power and is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a block diagram of a semiconductor laser drive circuit according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of current-optical output of a semiconductor laser, FIG. 3 is a block diagram of a conventional semiconductor laser drive circuit, and FIG. FIG. 6 is a diagram showing a change with time of an output value of each circuit in one embodiment of the present invention. 1 ... power detection circuit, 2 ... reproduction power setting circuit, 3
...... Control circuit, 4 ...... Reproduction value holding circuit, 5 ...... First switching circuit, 6 ...... First driving circuit, 7 ...... Semiconductor laser, 8 ...... Emission power holding circuit, 9 ...... Correction Quantity detection circuit, 10 ... second driving circuit, 11 ... recording power setting circuit, 12 ... switching circuit, 13 ... second switching circuit, 14 ... control signal, a to e ... terminals.

Claims (3)

[Claims] 1. A detecting means for detecting the emitted light quantity of a semiconductor laser, a first setting means for setting the emitted light quantity of a semiconductor laser to a first level, an output value of the detecting means and the first level.
Control means for driving and controlling the semiconductor laser according to the difference in the output value of the setting means, and
Second setting means for setting a level corresponding to the slope of the relationship of the emitted light amount with respect to the drive current of the semiconductor laser, the value set in the second setting means and the detection means. Arithmetic means for calculating a difference between output values and calculating a driving current corresponding to the difference based on a value corresponding to the inclination stored in the storage means, and irradiating the semiconductor laser with the radiated light quantity at the first level. When switching from the second level to the second level, the control means opens the control loop, and supplies a current obtained by adding the current according to the value calculated by the computing means to the drive current of the semiconductor laser immediately before switching to the semiconductor laser. A semiconductor laser drive device characterized by the above. 2. A detecting means for detecting the emitted light quantity of the semiconductor laser, a first setting means for setting the emitted light quantity of the semiconductor laser to a first level, an output value of the detecting means and the first level.
Control means for driving and controlling the semiconductor laser according to the difference in the output value of the setting means, and
Second setting means for setting the level of the radiation intensity of the semiconductor laser, signal generation means for generating a signal for modulating the intensity of the emitted light of the semiconductor laser, and a value corresponding to the slope of the relation of the emitted light intensity with respect to the driving current of the semiconductor laser. Means and the semiconductor laser is pulse-modulated and the detection means outputs a high level signal during a period in which the output value of the detection means is output, and the detection means outputs a low level signal during a period. The detected value holding means for holding and outputting the immediately preceding high level value, and the difference between the value set in the second setting means and the output value of the detected value holding means is obtained, and the drive current corresponding to this difference is obtained. And an arithmetic means for calculating based on a value corresponding to the inclination stored in the storage means, and when the semiconductor laser is strongly modulated from the state of the emitted light amount of the first level, Control loop A semiconductor laser characterized by causing a current obtained by adding a current corresponding to a calculated value of the arithmetic means to a drive current of the semiconductor laser immediately before starting the modulation and starting the modulation to cause the semiconductor laser to emit a high-level light amount. Drive. 3. The semiconductor laser drive device according to claim 1, wherein the control means calculates the output value of the detection value holding means based on the output value when the output value is stable.