JPH0246537A - Semiconductor laser driving circuit - Google Patents

Abstract

PURPOSE:To obtain a circuit in which the light emitting power at the time of modulation is not fluctuated from an initial set value even when a environmental temperature, etc., are changed by setting the power width of a pulse- shaped light emitting power to execute the modulation based on a sample-and- hold circuit output when the light emitting power of the semiconductor laser is modulated. CONSTITUTION:When the light emitting power of a semiconductor laser is modulated, after the output of a sample-and-hold circuit (S-H circuit) 5 is amplified by a voltage amplifier 7, it is voltage-divided by a voltage divider 8 and impressed to a constant current source 9. The constant current source 9 outputs the current of the level in proportion to the holding output of the S-H circuit 5 and is impressed to a modulating circuit 3. The modulating circuit 3 controls the communication to the next circuit of the impressed current by an information signal. When the output current of the constant current source 9 passes through the modulating circuit 3, the current is superimposed with the output current of an APC circuit 6 and impressed to a semiconductor laser 1. Thus, the circuit without a light emitting power fluctuation due to the environment temperature change or the like can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser drive circuit for a disk drive in which information can be written.

(Prior Art) Conventionally, in a magneto-optical disk drive, information is recorded, reproduced, and erased using laser light from a semiconductor laser, but the light emitting power thereof is easily affected by environmental temperature changes and the like. If the light emission power fluctuates, the S/N of the drive will deteriorate. Therefore, it is essential for a semiconductor laser drive circuit to have a configuration in which the emission power is not easily affected by temperature changes.

FIG. 2 is a block diagram of a conventional semiconductor laser drive circuit. In the figure, reference numeral 11 indicates a semiconductor laser, and reference numeral 12 indicates a detector for detecting emitted light power, which is disposed opposite to the rear surface of the semiconductor laser 11. Reference numeral 13 denotes a constant current source, and 14 a modulation circuit that modulates the emitted light power according to an information signal.Whether or not the output current of the constant current source 13 is applied to the semiconductor laser 11 is controlled by the information signal. 15 is a current-voltage conversion amplifier (hereinafter abbreviated as I-V amplifier) that receives the current signal from the detector 12; 16 is a sample-and-hold circuit (hereinafter referred to as S-V amplifier) that receives the output signal of IV amplifier 15 as input; (abbreviated as H circuit) selects the hold state when the light emission power is modulated by an external control signal, and the sample state when not modulated.

Reference numeral 17 denotes an emission power control circuit (hereinafter abbreviated as APC circuit) that performs feedback control of the emission power of the semiconductor laser 11 using the output signal of the S-H circuit 16 as a reference control signal.
It is.

When the emission power is not modulated, the current to the semiconductor laser 11 is supplied from the APC circuit 17, and when the emission power is modulated, the current is supplied to the semiconductor laser 11 from the APC circuit 17.
The signal is superimposed and supplied from the PC circuit 17 and the modulation circuit 14. The current supply state in each case is shown in FIG.

(Problems to be Solved by the Invention) 1. When the emission power of a conventional semiconductor laser is not modulated, when the emission power of the semiconductor laser fluctuates due to temperature change, the output current signal of the detector changes according to the amount of variation. The amount of current fluctuation is converted into a voltage signal by the I-V amplifier and input to the S-H circuit. Since the S-H circuit is in a sample state, the input signal becomes an output signal and is applied to the APC circuit. A drive current for the semiconductor laser is applied from an APC circuit in a direction that suppresses changes in emission power, thereby suppressing power fluctuations due to temperature changes.

Next, when modulating the emission power of the semiconductor laser, S
-H circuit holds the input signal just before entering the modulation state,
During the modulation state, this hold value is output, and the APC circuit supplies a drive current to the semiconductor laser based on this hold value. Furthermore, the output current of the constant current source is applied to the modulation circuit. The modulation circuit controls the transmission of the applied current to the next stage circuit using an information signal. When the output current of the constant current source passes through the modulation circuit, it is superimposed on the output current of the APC circuit and applied to the semiconductor laser. FIG. 4 shows the light emitting state of the semiconductor laser.

As described above, the emission power of a semiconductor laser is controlled by controlling the semiconductor laser drive current based on the output signal of the detector when not modulating, and when modulating, it is driven in a pulsed manner based on the detector signal immediately before modulation. This is carried out by controlling the low level current value of the current.

However, in the above configuration, the output current of the constant current source is constant regardless of environmental temperature changes, etc., so if a temperature change occurs, the minimum value of the pulse generation power during modulation will change. However, a phenomenon occurred in which the maximum value changed significantly (for example, ±30% of the initial setting value).

As described above, in conventional semiconductor laser drive circuits, if environmental temperature changes occur, the power width of the light emitting power during modulation will vary greatly from the initial setting value, and the S/N of the written information signal will decrease. There was a drawback that the drive performance deteriorated significantly and the drive performance could not be maintained.

An object of the present invention is to eliminate the drawbacks of the conventional technology, and to ensure that even when environmental temperature changes occur, the fluctuation in the maximum light emitting power during modulation is sufficiently small (for example, ±10%) relative to the initial setting value.
It is an object of the present invention to provide a semiconductor laser drive circuit that does not change the S/N of a written information signal and provides stable drive performance.

(Means for Solving the Problems) A semiconductor laser drive circuit of the present invention includes a detector for detecting emission power disposed facing the rear surface of the semiconductor laser,
a current-voltage conversion circuit that converts the current signal from the detector into a voltage signal; a sample-and-hold circuit whose operating state is defined by an external control signal;
A light emission power control circuit inputs the signal from the sample and hold circuit to control the light emission power of the semiconductor laser, a modulation circuit modulates the light emission power of the semiconductor laser according to the information signal, and a signal from the sample and hold circuit. It consists of a current source circuit that determines the magnitude of the current supplied to the modulation circuit based on a reference.

(Function) According to the above-described configuration, when modulating the emission power of a semiconductor laser, the present invention holds the output of the detector for detecting the emission power immediately before modulation in the sample-and-hole circuit 1 and then outputs the modulated pulse. By determining the power width of the optical emission power based on the output of the sample-and-hold circuit, it is possible to obtain a semiconductor laser drive circuit in which the optical emission power during modulation hardly changes from the initial setting value even if the environmental temperature or the like changes.

(Example) An embodiment of the present invention will be described based on FIG.

FIG. 1 is a block diagram of a semiconductor laser drive circuit according to the present invention. In the figure, ] is a semi-semiconductor laser 2 is a detector for detecting emission power, 3 is a modulation circuit, 4 is an I-V amplifier, 5 is an S-H circuit, 6 is an APC circuit, and 7 is an S-T
A voltage amplifier 8 amplifies the output of the -T circuit 5, a voltage divider 8 divides the output of the voltage amplifier 7, and a constant current source 9 whose current value is determined according to the output of the voltage divider 8.

Next, the operation will be explained.

First, a case will be described in which the emission power of the semiconductor laser is not modulated.

When the emission power of the semiconductor laser 1 fluctuates due to a temperature change, the output current signal of the detector 2 fluctuates in accordance with the amount of fluctuation. This current fluctuation amount is converted into a voltage signal by the IV amplifier 4 and input to the S-■-■ circuit 5. S-H
Since the circuit 5 is in the sample state, the input signal becomes the output signal as it is and is applied to the APC circuit 6. A driving current for the semiconductor laser 1 is applied from the APC circuit 6 in a direction that suppresses changes in emission power, thereby suppressing power fluctuations due to temperature changes.

Next, a case will be described in which the emission power of the semiconductor laser is modulated. When performing modulation, the S-H circuit 5 holds the input signal immediately before entering the modulation state, outputs this hold value during the modulation state, and the APC circuit 6 controls the drive current to the semiconductor laser 1 based on this hold value. supply to.

Further, the output of the S-H circuit 5 is amplified by a voltage amplifier 7, divided by a voltage divider 8, and applied to a constant current source 9. The constant current source 9 outputs a current proportional to the holding output of the S-H circuit 5 and applies it to the modulation circuit 3. Modulation circuit 3
controls the transmission of the applied current to the next stage circuit using an information signal.

If the output current of the constant current source passes through the modulation circuit 3, the APC
The current is applied to the semiconductor laser 1 in a superimposed manner with the output current of the circuit 6.

As described above, according to this embodiment, even when modulating the emission power of a semiconductor laser, it is possible to realize a semiconductor laser drive circuit with almost no variation in emission power due to changes in environmental temperature or the like.

(Effects of the Invention) According to the present invention, the light emitting power of the semiconductor laser is not easily affected by environmental temperature changes, etc. even when reading, erasing, or writing information, and the signal quality is extremely high under a wide range of environmental conditions. It is possible to provide a stable magneto-optical disk drive, and its practical effects are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a semiconductor laser drive circuit according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional semiconductor laser drive circuit, and FIG. 3 is a block diagram of a semiconductor laser drive circuit with and without modulation of the emission power. Semiconductor laser drive current. FIG. 4 shows the semiconductor laser emission power with and without modulation of the emission power. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Detector for light emission power detection, 3... Modulation circuit, 4... Knee ■ amplifier, 5... S-I-I circuit, 6... APC
Circuit, 7. Voltage amplifier, 8. Voltage divider, 9. Constant current source. Patent applicant Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] (1) The light emitting power of a semiconductor laser is modulated according to the information signal, the information signal is recorded by irradiating the modulated light emitting power onto the information recording carrier, and then a weak laser beam is irradiated to record the information signal. regenerates the information signal,
Alternatively, a semiconductor laser drive circuit of a device that erases the recorded information signal by irradiating strong laser light,
Also when modulating the semiconductor laser according to an information signal,
A semiconductor laser drive circuit characterized by reducing fluctuations in the light emitting power of the semiconductor laser due to changes in the temperature of the environment in which the device is used. (2) A detector for detecting emission power placed opposite to the rear surface of the semiconductor laser, a current-to-voltage conversion circuit that converts a current signal from the detector into a voltage signal, and an external control signal that defines its operating state. a sample-and-hold circuit that inputs a signal from the sample-and-hold circuit to control the emission power of the semiconductor laser, and a modulation circuit that modulates the emission power of the semiconductor laser according to an information signal. and,
The semiconductor laser drive circuit according to claim 1, comprising a current source circuit that determines the magnitude of the current supplied to the modulation circuit based on the signal from the sample-and-hold circuit.