JPH02143931A - Laser diode drive circuit - Google Patents

Abstract

PURPOSE:To prevent discontinuation of the light emission of a laser diode when the power of the diode is switched from reproducing power to signal recording power by stopping flowing of a high-frequency current when reproducing power is switched to signal recording power and making a DC to flow to the laser diode together with another DC. CONSTITUTION:At the time of recording signals, the current of a DC source 102 is made to flow to a laser diode 106 together with the current of another DC source 101 by closing a switch 109 by means of a control signal 112. Simultaneously, flowing of a high-frequency current from a high-frequency current source 104 to the diode 106 is stopped by opening a switch 111 by means of a recording/reproduction switching control signal 112. By adding the DC to the laser diode 106 a current larger than the threshold current value (Ith2) can be made to flow to the diode 106 when the high-frequency current is not superposed. Therefore, discontinuation of the light emission of the laser diode 106 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a laser diode drive circuit for recording and reproducing signals by irradiating a laser beam onto an optical recording medium. The present invention relates to a laser diode drive circuit characterized by a diode drive current superimposition method.

Optical discs that can record conventional technical information at high density using laser light have recently been developed.

The signal on this optical disk is normally generated by irradiating a laser reproduction power of about 1 [mW1 and using a focus servo on the disk.
It is read by performing tracking servo. Furthermore, recording of signals is performed by irradiating the tracks of the optical disc with a recording power greater than the reproduction power.

Problems to be Solved by the Invention In recording such optical discs, in order to improve the signal-to-noise ratio of the reproduced signal, the reproduction power must be increased by several hundred [M
A high frequency current of Hz is superimposed. Superimposition of this high frequency current is stopped during recording to protect the laser diode.

FIG. 2 shows the driving current vs. light emission output characteristics of the laser diode when high frequency superimposition is performed and when not. As shown in this figure, by stopping the superposition of the high-frequency current when changing from the reproducing power to the recording power, the current vs. emission output characteristic of the laser diode changes depending on the driving amplitude of the high-frequency superimposition, as shown in Figure 2 ( 0) to (b).

Therefore, the laser diode driving DC current is I in Figure 2.
If s is left as is, the threshold current will be 1 when high frequency superimposition is turned off.
th or less, the laser diode's light emission may be interrupted and the focus may be removed, making recording impossible.Also, even if the focus is not removed, the recording current may be superimposed on a current lower than the threshold current of the laser diode. As a result, the rising edge of the recording waveform becomes dull and the recording light emission waveform deteriorates.

In view of the above, the present invention has been developed so that even if the superimposition of the high-frequency current is stopped when switching from the reproducing power to the recording power, defocusing due to interruption of the laser diode's light emission does not occur, and the current is larger than the threshold current of the laser diode. The object of the present invention is to provide a laser diode drive circuit that can drive a good recording light emission waveform by flowing current.

Means for Solving the Problems The present invention provides a means for passing a direct current Is necessary for causing a laser diode to emit a reproduction power PII, a means for supplying a high frequency current Lr, and a means for supplying a high frequency current Lr when switching from reproduction power to signal recording power. A laser diode drive comprising means for stopping the flow of the high frequency current Lr and causing a DC current I+ to flow through the laser diode together with the DC current Is, and means for flowing a recording signal current I2 for emitting recording power to the laser diode. It is a circuit.

Effect of the Invention With the above-described configuration, the present invention can produce a good recording light emission waveform at a threshold current of the laser diode or higher without causing defocus due to interruption of light emission when switching from reproduction to recording.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a laser diode drive circuit in one embodiment of the present invention.

In FIG. 1, 101 and 102 are DC current sources, 103 is a signal current source, 104 is a high frequency current source, 105 is a control circuit, 108 is a laser diode, 107 is a PIN photodiode, 108 is an inverter, 109, 110, 1
11 is a switch, and 112 is a recording/reproduction switching control signal.

The operation of the laser diode drive circuit of this embodiment configured as described above will be explained below.

During signal reproduction, the current ■- from the DC current source 101 and the current Lt from the high-frequency current source 104 are applied to the laser diode 106 by turning on the signal switch 109 by the recording/reproduction switching control 112, and the reproduction power Pl is applied to the laser diode 106.
The laser diode 106 emits light at i. At this time, part of the emitted light power is detected by the PIN photodiode 107 and is applied to the control circuit 105 for keeping the emitted light power of the laser diode constant regardless of the temperature. The output of the control circuit 105 controls the output current value of the DC current source 101 to keep the reproduction laser power constant.

Next, during signal recording, the current of the DC current source 102 is switched to the switch 109 under the control of the recording/reproduction switching control signal 112.
When closed, the DC current ■1 becomes the laser diode 1.
06 flows together with the current IO of the DC current source 101. At the same time, the high frequency current from the high frequency current source 104 stops flowing to the laser diode 106 because the switch 111 is opened by the recording/reproduction switching control signal 112.

At this time, the laser diode lO6 is connected to the DC current source 102.
The current 11 flowing through is indicated by I in FIG. By applying this current I to the laser diode 106, the second
As shown in the figure, a current larger than the current threshold value (I th2) when no high-frequency current is superimposed can flow through the laser diode 106.
It is possible to prevent the light emission of the signal current source 1 from being interrupted.
Since the recording current from 03 is also superimposed at a point larger than the threshold current, a recording light emission waveform with a quick rise can be obtained.

After the recording is completed, the switch 111 is turned on under the control of the recording and reproduction control signal 112, and the switch 109 is turned off, whereby a high frequency current is superimposed on the laser diode and reproduction power is radiated from the laser diode.

As described in detail, according to the present invention, it is possible to prevent interruptions in the light emission of the laser diode that occur when turning on and off the superimposition of high-frequency current on the laser diode, and to reduce the threshold current of the laser diode. The recording signal current can be added to a bias current larger than that of the recording signal current, and a recording signal with a fast rise is emitted from the laser diode, allowing good recording and reproduction.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a laser diode drive circuit according to an embodiment of the present invention, and Fig. 2 is a block diagram showing how the laser diode drive current vs. emission power characteristics change depending on whether high frequency superimposition is applied or not. It is a graph. 101.102...DC current source, 103...Signal current source, 104...High frequency current source, 10...Control circuit, 106
...Laser diode, 107...PIN photodiode, 108...Inverter, 109,110.1
11...Switch, 112... Recording/reproduction switching control signal. Name of agent: Patent attorney Shigetaka Awano and 1 other person 2 Figure (0) Laser power when high-frequency current is superimposed versus electrodynamics vs. light emitting power (b) When high-frequency current is not superimposed

Claims (1)

[Claims] In a laser diode drive circuit for recording and reproducing signals by irradiating a laser beam onto an optical recording medium, there is provided a means for supplying a direct current (I_0) to the laser diode, and a means for supplying a direct current (I_0) to the laser diode in addition to the direct current (I_0) during signal reproduction. a means for superimposing a high frequency current (I_r_f) on the diode; a means for stopping the superposition of the high frequency current (I_r_f) and simultaneously applying a direct current (I_1) in addition to the direct current (I_0) during signal recording; and a recording power to the laser diode. 1. A laser diode drive circuit comprising means for superimposing a recording signal current (I_2) on a laser diode to cause the laser diode to emit light.