JPH0810848Y2 - Laser oscillation output controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used in an optical disk drive,
The present invention relates to a laser oscillation output control device that controls intermittent oscillation laser output light.

[Prior Art] Conventionally, in an optical disk drive, a laser beam is used for writing on an optical disk or reading optical disk information. In order to improve the reliability of writing and reading of information, it is necessary to stabilize the laser output light, and there is a device that controls the laser output conventionally.

However, such a control device usually controls the average value of the laser output, and the peak value (maximum value) or bottom (minimum value) of the output of a laser that intermittently oscillates in a pulsed manner such as when driving an optical disk. There was no such device that could accurately control.

The object of the present invention is made in view of such a point, and in a semiconductor laser drive circuit of an optical disk drive, the maximum and minimum values of the intensity of modulated (intermittent) laser light output are accurately determined. The present invention is intended to realize a laser oscillation output control device that can be controlled so as to maintain a constant value.

[Means for Solving the Problem] In order to achieve such an object, in the present invention, a laser current interrupting device controlled by an external signal to turn on / off a current given to a laser and a part of a laser output are provided. An optical / electrical conversion unit that outputs an electric signal corresponding to the intensity of its output, one envelope detector that obtains a voltage waveform corresponding to the maximum value of the output waveform of the optical / electrical conversion unit, and the optical / electrical conversion unit Another envelope detection device that obtains a voltage waveform corresponding to the minimum value of the output waveform of the electric conversion means, and a signal that amplifies the difference between the output of the one envelope detection device and a predetermined reference voltage to drive the laser. As a difference between the output of one of the differential amplifiers, which is given to the laser through the voltage / current converter for converting the voltage to the current and the laser current interrupting device, and the output of the other envelope detection device, and the predetermined reference voltage. Amplifies As a signal for driving the laser, there is provided another differential amplifier which gives the laser through a voltage / current converter for converting a voltage into a current, and the maximum value and the minimum value of the oscillation output of the laser are the respective reference values. It is characterized in that it is controlled so as to be maintained at a constant value corresponding to the set value of the voltage.

[Operation] Since the present invention feeds back a part of the oscillation output of the laser that is turned on and off by the laser current interrupting device, amplifies the difference between this and the set value, and drives the laser with that output. The maximum and minimum values of the laser oscillation output are controlled to be maintained at certain constant values corresponding to the set values.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a main part configuration diagram showing an embodiment of a laser oscillation output control device according to the present invention, and is a configuration diagram of a circuit relating to maximum value control of laser oscillation output. In the figure, 1 is a reference voltage generator, 2 is a differential amplifier, 3 is a voltage / current converter, 4 is a laser current interrupting device, 5 is a semiconductor laser, 6 is a photodiode, 7 is a current / voltage converter, and 8 Is an envelope detection circuit.

The reference voltage generator 1 is for setting a control target value, and can set an output reference voltage value appropriately. The differential amplifier 2 amplifies and outputs the difference between this reference voltage output and the output of the envelope detection circuit 8. The output voltage of the amplifier 2 is input to the voltage / current converter 3. The output current of the voltage / current converter 3 is supplied to the semiconductor laser 5 via the laser current interrupting device 4. The laser current interrupting device 4 is driven on / off by a control signal given from the outside.

When the output light of the semiconductor laser 5 is applied to the photodiode 6, a current corresponding to the intensity of the laser light flows, and the current / voltage converter 7 converts the current into a voltage. The part consisting of the photodiode 6 and the current / voltage converter 7 is referred to as an optical / electrical converting means here.

The envelope detection circuit 8 is composed of a diode 9, a capacitor 10 and a resistor 11, and detects the envelope of the pulse voltage waveform given by the current / voltage converter 7, that is, the voltage waveform corresponding to the laser oscillation output.

The operation in such a configuration will be described below. The output of the differential amplifier 2 having the reference voltage applied to one input terminal is input to the voltage / current converter 3. The output current of this converter flows through the semiconductor laser 5, and this current can be interrupted by the laser current interrupting device 4.

On the other hand, a part of the light output from the laser is guided to the photodiode 6. The photocurrent of the photodiode 6 is converted into a voltage by the current / voltage converter 7 and input to the envelope detection circuit 8. The output of the envelope detection circuit thus obtained is input to the other input end of the differential amplifier 2.

The laser oscillation output output from the semiconductor laser 5 driven by the current interrupted by the laser current interrupting device 4 is
Increase / decrease corresponding to increase / decrease in the current output from the voltage / current converter 3.

A part of the oscillation output light of the laser is guided to the photodiode 6. Therefore, as the intensity of the laser light increases, a larger photocurrent flows through the photodiode 6. This photocurrent is converted into a voltage by the current / voltage converter 7 and is input to the envelope detection circuit 8. The output of the envelope detection circuit 8 has a larger voltage as the intensity of the laser output light increases.

The differential amplifier 2 amplifies the difference between the output of the envelope detection circuit 8 and the reference voltage. Then, the output is converted into a current and then given to the semiconductor laser, and a signal corresponding to the output intensity enters the envelope detection circuit 8 again via the photodiode 6 and the current / voltage converter 7. ,
Eventually, the output of the envelope detection circuit 8 is automatically controlled so that it becomes equal to the reference voltage. Therefore, the intensity of the laser oscillation output can be maintained at a desired constant value by setting the reference voltage.

Next, an operation when the laser current interrupting device 4 is turned on / off by an external signal in the above operation will be described. When a laser output modulation pulse is given to the laser current interrupting device 4, the laser current interrupting device 4 is turned on / off according to this voltage signal, and the semiconductor laser 5 is pulsed on / off driven. The photodiode 6 captures the laser output light that is pulsed on and off and converts it into a pulse current. The pulse current input to the current / voltage converter 7 becomes a pulse voltage and enters the envelope detection circuit 8.

By the way, the pulse voltage has a waveform as shown by the solid line in FIG. 2, whereas the output of the envelope detection circuit 8 has a waveform as shown by the broken line, creating the envelope of the original waveform. As a result, for a pulse group with a time interval narrower than the time constant determined by the capacitor 10 and the resistor 11, the oscillation output is controlled as if the peak values were continuously output from the laser. The peak value of the oscillation output can be controlled to a desired output value as in the case where the laser current is always on.

What is shown in FIG. 3 is such that not only the maximum value of the pulse oscillation output but also the minimum value can be controlled. In the figure, what is different from FIG. 1 is an additional portion of a reference voltage generator 31, an envelope detection circuit 38, a differential amplifier 32, and a voltage / current converter 33. This part is for controlling the minimum value of pulse oscillation output.
The laser oscillation output is controlled to the value set in.

In the envelope detection circuit 38, the diode 39 is reversely connected to the diode connection of the envelope detection circuit 8 and a battery 42 is further added to make the envelope of the negative polarity, that is, the minimum value of the laser oscillation output waveform. To get.

According to such a configuration, the sum of the output current of the voltage / current converter 3 on the maximum value side and the output current of the voltage / current converter 33 on the minimum value side flows in the semiconductor laser 5 as a result. . In this case, when the laser current interrupting device 4 is on, the current controlled as the maximum value flows through the laser, and when it is off, the current controlled to the minimum value flows. Therefore, the maximum value and the minimum value of the output light intensity of the semiconductor laser are controlled to a certain fixed value (set value) in accordance with the on / off of the laser current interrupting device 4.

In the embodiment, the semiconductor laser is targeted for control, but the invention is not limited to this, and lasers other than semiconductor lasers, such as solid-state lasers and gas lasers, can be targeted, and the laser output intensity is controlled similarly. can do.

[Effects of the Invention] As described above, according to the present invention, not only the average value control as in the past but also the maximum value (and the minimum value) of the pulse oscillation output can be controlled, and it can be used in the industrial field. Is very effective.

[Brief description of drawings]

FIG. 1 is a partial configuration diagram of a laser oscillation output control device according to the present invention, FIG. 2 is a diagram showing input / output voltage waveforms of an envelope detection circuit, and FIG. 3 is a laser oscillation output control device according to the present invention. It is a figure which shows an example. 1 ... Reference voltage generator, 2 ... Differential amplifier, 3 ... Voltage / current converter, 4 ... Laser current interrupting device, 5 ... Semiconductor laser, 6 ... Photodiode, 7 ... Current / voltage Converter, 8 ... Envelope detection circuit, 9 ... Diode, 10
…… Capacitor, 11 …… Resistor.

Claims (1)

[Scope of utility model registration request] 1. A laser current interrupting device controlled by an external signal to turn on / off a current applied to a laser, and an optical / electrical converting means for receiving a part of a laser output and outputting an electric signal corresponding to the intensity of the output. And one envelope detector that obtains a voltage waveform corresponding to the maximum value of the output waveform of the optical-electrical converting means, and the other of the envelope detecting devices that obtains a voltage waveform corresponding to the minimum value of the output waveform of the optical-electrical converting means. An envelope detection device, a voltage-current converter for converting a voltage into a current and the laser current interruption as a signal for driving the laser by amplifying a difference between the output of the one envelope detection device and a predetermined reference voltage. One differential amplifier that is given to the laser through the device, a signal that amplifies a difference between the output of the other envelope detection device and a predetermined reference voltage, and drives the laser, and a voltage that converts a voltage into a current. The other differential amplifier for giving to the laser through a current converter is provided so that the maximum value and the minimum value of the oscillation output of the laser are maintained at constant values corresponding to the set values of the reference voltages. A laser oscillation output control device characterized by controlling.