JPH0737265A - Optical information recorder - Google Patents

Abstract

PURPOSE:To improve the S/N of a reproducing signal in the manner of accurately forming a recording pit by a semiconductor laser and to prevent the semiconductor laser LD from being damaged due to the overshooting of a driving current for the semiconductor laser at the time of recording, by a simple constitution. CONSTITUTION:The current to be supplied to the semiconductor laser LD is switched by a recording signal generating circuit 1 of a recording APC circuit in accordance with the signal of a light emitting pulse (a). When the current is supplied to the semiconductor laser LD by the switching operation, the light is emitted from the semiconductor laser LD. The emitting power of the semiconductor laser LD is detected by a photodiode PD for monitoring. By a high speed current control part 2, the current 12 is controlled so that the detected light emitting power becomes the predetermined value. By a low speed current control part 3, a current I1 controlled with temperature is supplied independently of the detected light emitting power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording device for recording on a recording medium using a semiconductor laser.

[0002]

2. Description of the Related Art An optical card is in the shape of a credit card and is capable of recording about 2.8 MB of data. The recorded data cannot be erased, and this card is used as a medical record in a hospital or for recording medical examination data in a health examination system, for example. It is also used for recording image data.

A conventional example will be described below with reference to the drawings.

In the optical head of the conventional optical recording / reproducing apparatus, at the time of reproduction, as shown in FIG.
The light beam of 00 becomes parallel light by the collimator lens 102 and is condensed on the recording medium 104 by the objective lens 103. The return light from the recording medium 104 passes through the objective lens 103 and the collimator lens 102, and the monitor detector 1
01 is detected and sent to the APC circuit 106. APC
In the circuit 106, the laser drive current is controlled so that the reproduction light power is always constant.

At the time of recording, a pulse current of a certain constant value is superimposed on the laser drive current from the pulse current drive circuit 107, so that the optical power of the semiconductor laser 100 changes in a pulse form. As a result, the recording pit 105 is formed on the recording medium 104 and the information is recorded.

When information is recorded on a recording medium, pits called pits having a reduced reflectance are formed. Since the pits are formed using a semiconductor laser, the amount of return light decreases as the reflectance decreases in the process of forming the pits. Therefore, the emission intensity of the semiconductor laser is not constant when the pulsed drive current is applied. Therefore, as shown in FIG. 8, the emission intensity decreases in the latter half of the pit formation, and the pit shape becomes unstable.

On the other hand, when the optical head having the structure shown in FIG. 7 is used, the current I applied during recording is constant. Therefore, FIG.
As shown in, the differential efficiency changes from A to B when the amount of returning light decreases. Therefore, the recording pulse power is reduced from P2 to P1. As a result, there has been a problem that the recording pulse power fluctuates due to fluctuations in the returning light, and the recording pits are distorted, so that the S / N of the reproduced signal decreases.

Therefore, in order to solve the above problem, an optical head provided with a recording APC circuit 106 dedicated to recording has been proposed. In this optical head, as shown in FIG. 10, the light obtained by the semiconductor laser 100 is emitted from the collimator lens 10
2. Irradiate the recording medium 104 through the objective lens 103.

The output of the semiconductor laser 100 is detected by the monitor photodetector 101, and the reproducing APC circuit 106 and the recording A are detected.
It is sent to the PC circuit 108. APC for playback during playback
The circuit 106 operates to keep the output of the semiconductor laser 100 constant. Further, at the time of recording, a current is applied from the pulse current drive circuit 107, and the output of the semiconductor laser 100 increases. As a result, the recording pit 105 is formed on the recording medium 104.
Is formed. At this time, the recording APC circuit 108 keeps the recording power level of the semiconductor laser 100 constant.

That is, the reproduction output P of the semiconductor laser 100
Since L is controlled by the reproduction APC circuit 106 and the recording output Pn is controlled by the recording APC circuit 108, FIG.
It is always constant, as shown in. Therefore, even if the differential efficiency of the semiconductor laser 100 changes from A to B, the recording light emission intensity Po is always kept constant by changing the current value. As shown in FIG. 11, the recording APC circuit 1 described above is used.
At 08, when the light emission pulse a changes from L to H, T
r1 turns off and Tr2 turns on. As a result, a current flows through the semiconductor laser 101, and the semiconductor laser 101 starts emitting light.

The light emission amount of the semiconductor laser 101 is detected as a current Im by the monitor detector 101. The current generated here produces the potential of Im-R1 at b.

Zener voltage VZ of Zener diode D1
The sum of the base-emitter voltage VBE of d1 and Tr1 is compared with the potential (Im-R1) of b. When Im-R1 is smaller, Tr4 does not operate, but when Im-R1 becomes larger than VZD1 + VBE, Tr4 Operates and the base potential of Tr3 drops, so that the current flowing through the semiconductor laser 100 decreases.

By this negative sweep, the light emission amount of the semiconductor laser 100 is controlled to the light emission amount P0 set by VZD1 and R1.

[0014]

However, when the emission pulse a becomes H and the semiconductor laser 100 emits light, the response speed of the negative feedback is not sufficiently faster than the rising speed of the emission of the semiconductor laser 100. A period in which the amount is not controlled occurs and an overshoot occurs in the light emission pulse.

The maximum light emission power Pmax at the time of this overshoot can be calculated from the current value Imax = (V0-VBEE) / R2 determined by the reference potential V0 and VBE and R2 of Tr3. That is, when the utilization efficiency of the semiconductor laser 100 is η, Pmax = Imax · η.

Therefore, in order to deal with all changes in the amount of light emitted from the semiconductor laser 100 due to return light and temperature changes, Imax
Must be increased. But in that case Imax
May exceed the maximum rating of the semiconductor laser 100 and destroy the LD.

Further, as shown in FIG. 12, the utilization efficiency η of the semiconductor laser 100 has a negative temperature coefficient. Therefore, when the temperature is raised while the semiconductor laser 100 emits light with a constant current, the amount of light emitted from the semiconductor laser 100 decreases. Even if Imax does not change with temperature and is constant current, the control range of the light emission amount of the semiconductor laser 100 becomes narrower as the temperature rises. Therefore, in order to secure a certain control range at all temperatures, it is necessary to prepare an unnecessarily wide control range at low temperatures.

The present invention has been made in view of the above circumstances. The S / N of reproduced signals can be improved by accurately forming recording pits by a semiconductor laser with a simple structure, and the semiconductor at the time of recording can be improved. An object of the present invention is to provide an optical information recording device capable of preventing damage to a semiconductor laser due to overshoot of a laser drive current.

[0019]

An optical information recording apparatus of the present invention is an optical information recording apparatus for recording on a recording medium by using a semiconductor laser LD, and when the information is recorded on the recording medium, the semiconductor laser LD has a predetermined timing. A recording signal generating circuit 1 for switching a current with a semiconductor laser LD
The monitor photodiode PD as a detection circuit for detecting the recording light emission power emitted from the device is compared with the detected recording light emission power and the preset setting power, and the semiconductor is adjusted so that the recording light emission power becomes equal to the setting power. A high-speed current controller 2 as a first current controller that controls the current flowing through the laser LD is provided.

The optical information recording apparatus of the present invention can be constructed by including a low-speed current control unit 3 as a second current control unit for controlling the current supplied to the semiconductor laser LD according to the temperature change.

[0021]

[Operation] In the optical information recording apparatus of the present invention, the recording light emission power detected by the monitor photodiode PD by the high-speed current control unit 2 is compared with the preset power setting, and the recording light emission power becomes the set power. By controlling the currents flowing through the semiconductor lasers so that they are equal to each other, the S / N of the reproduction signal is improved by accurately forming the recording pits by the semiconductor laser LD with a simple configuration, and the semiconductor laser LD at the time of recording is improved. It is possible to prevent the semiconductor laser LD from being damaged by the overshoot of the driving current of the above.

Further, in the optical information recording apparatus of the present invention, the low-speed current controller 3 controls the current supplied to the semiconductor laser LD according to the temperature change, so that the recording pit is formed by the semiconductor laser LD with a simple structure. Accurate formation improves the S / N ratio of the reproduced signal, and prevents damage to the semiconductor laser LD due to overshoot of the drive current of the semiconductor laser LD during recording.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first optical information recording / reproducing apparatus according to the present invention.
FIG. 6 is a circuit diagram showing a configuration of a recording APC circuit of an example, and since it has almost the same configuration as a conventional example including a configuration of an optical information recording / reproducing apparatus, the same portions are denoted by the same reference numerals and description thereof is omitted.

As shown in FIG. 1, the recording signal generating circuit 1 of the recording APC circuit switches the current supplied to the semiconductor laser LD according to the signal of the light emission pulse a. When a current is supplied to the semiconductor laser LD by switching, the semiconductor laser LD emits light. The emission power of the semiconductor laser LD is detected by the monitor photodiode PD. The high-speed current controller 2 controls the current I2 so that the detected light emission power has a preset value. The low-speed current control unit 3 gives a current I1 controlled by the temperature regardless of the detected light emission power.

The fast current controller 2 suppresses fluctuations in the fast emission amount due to fluctuations in the return light, and the slow current controller 3 suppresses fluctuations in the slow emission amount due to temperature changes. .

The detailed operation of the circuit will be described below.

When the light emission pulse a changes from L to H, Tr1
Turns off and Tr2 turns on. As a result, a current flows through the semiconductor laser LD, and the semiconductor laser LD starts emitting light. The light emission amount of the semiconductor laser LD is detected as a current Im by the monitoring photodiode PD. The current generated here produces a potential of Im · R1 at b.

Zener voltage VZ of Zener diode D1
The sum of the base-emitter voltage VBE of D1 and Tr4 is compared with the potential Im.R1 of b. When Im.R1 is smaller, Tr4 does not operate, but when Im.R1 becomes larger than VZD1 + VBE, Tr4 Operates and the base potential of Tr3 decreases, so that the current flowing through the semiconductor laser LD decreases.

By this negative sweep, I2 is set so that the light emission amount of the semiconductor laser LD becomes the light emission amount P0 set by VZD1 and R1.
Is controlled.

I1 is determined by the emitter potential of Tr5 and R3. The emitter potential of Tr5 is R4, R5, TSR and T
Determined by VBE of r5. Since TSR is a temperature-sensitive resistance and its resistance value increases in proportion to the rise in temperature, the emitter potential of Tr5 rises in proportion to temperature. Therefore, I1 increases in proportion to temperature. If this proportional coefficient is matched with the temperature characteristic of the utilization efficiency of the semiconductor laser LD, the variation of the light emission amount due to the temperature does not occur.

As shown in FIG. 2, when the emission pulse a becomes H, the current I1 + I2 flows through the semiconductor laser LD, and the semiconductor laser LD emits light.

I1 changes the electric value by the temperature change,
Its time constant is long (low-speed current control). Further, since I1 is not controlled by the light emission amount of the semiconductor laser LD, the current value of I1 does not change while the light emission pulse is H, and I1 becomes a square wave.

As shown in FIG. 3, regarding the temperature characteristic of I1, the utilization efficiency η of the semiconductor laser LD has a negative temperature coefficient. Therefore, when the temperature is raised while the LD emits light with a constant current, the light emission amount of the semiconductor laser LD decreases. By making I1 have a positive temperature characteristic on the circuit and making the temperature coefficient thereof coincide with the temperature coefficient of η, it is possible to cancel the temperature change of the light emission amount of the semiconductor laser LD due to I1.

Since I2 is controlled by the negative feedback of the light emission amount, if the detection of the light emission amount is delayed, a period in which the current value cannot be controlled occurs. I2 becomes the maximum value (I2max) and overshoot occurs.

As shown in FIG. 4, regarding the temperature characteristic of I2, the utilization efficiency η of the semiconductor laser LD has a negative temperature coefficient. Therefore, if the temperature is raised while the semiconductor laser LD emits light with a constant current, the emission amount of the semiconductor laser LD decreases.

On the circuit, I2max is given a positive temperature characteristic,
By matching the temperature coefficient with the temperature coefficient of η, I
It is possible to cancel the temperature change of the light emission amount of the semiconductor laser LD due to 2max. As a result, the control range of the semiconductor laser LD emission amount becomes constant over the entire temperature range.

In order to give I2max a positive temperature characteristic, the Zener potential VZD2 of the Zener diode D2 of the recording APC circuit of FIG. 1 may be given a positive temperature coefficient.

As described above, in order to cope with the change in the light emission amount of the semiconductor laser LD due to the returning light or the temperature change, I2m
ax must be large (wide dynamic range). In this case, I2max may exceed the maximum rating of the semiconductor laser LD and destroy the semiconductor laser LD.

However, in this embodiment, I1 controls the light emission amount change of the semiconductor laser LD due to temperature change, and I2 which requires high-speed current value control is the semiconductor laser LD light emission change due to the returning light. Since only the control needs to be performed, I2max can be made small (the dynamic range can be made narrow). Therefore, even if the detection of the light emission amount is delayed, the amount of overshoot of the light emission amount of the semiconductor laser LD is small and the semiconductor laser LD is not destroyed.

Next, the second embodiment will be described.

As shown in FIG. 5, the recording APC circuit of the second embodiment is different from the first embodiment only in that C1 and Tr6 are added. Therefore, the added function will be described.

In FIG. 5, an inverted signal c of the light emission pulse is input to Tr6 in synchronization with the light emission pulse a. Tr6 is OFF when the light emission pulse is H, and is ON when the light emission pulse is L. When Tr6 is ON, all the current passing through R6 passes through Tr6, so the potential at point d becomes GND.

The emission pulse a becomes H, and the semiconductor laser LD
At the same time when the current is supplied to Tr6, Tr6 turns off. A current of I1 + I2 is supplied to the semiconductor laser LD, but since the potential at the point d is GND, I2 = 0 in reality.

When Tr6 is turned off, the potential at the point d rises with the time constant of T1 = R6 × C1 to reach the potential determined by the Zener diode D. Along with this, the base potential of Tr3 also rises, so that I2 also increases according to the time constant T1.

The amount of light emitted from the semiconductor laser LD is detected by the monitor photodiode PD and has the potential at point b. The detection speed of the monitor photodiode PD is limited by the junction capacitance of the monitor photodiode PD and the like, and a delay of a certain time constant T2 occurs. If T1 is set so that T2 <T1, a semiconductor laser LD emission pattern without any overshoot can be obtained as shown in FIG. Other functions and effects are the same as those in the first embodiment.

The recording medium of the above embodiments may be an optical card, an optical disc, a magneto-optical disc, or the like. They can also be used to record data for personal computers, workstations, etc.

[0048]

As described above, according to the optical information recording apparatus of the present invention, the recording light emission power detected by the detection circuit by the first current controller is compared with the preset power setting, and the recording light emission is performed. By controlling the current flowing through the semiconductor laser so that the power becomes equal to the set power, the S / N of the reproduction signal can be improved by accurately forming the recording pits by the semiconductor laser with a simple structure, and at the time of recording. The semiconductor laser can be prevented from being damaged by the overshoot of the driving current of the semiconductor laser.

Secondly, by controlling the current supplied to the semiconductor laser by the temperature change in the current controller, the semiconductor laser can accurately form the recording pits with a simple structure, and the S / There is also an effect that N can be improved and damage to the semiconductor laser LD due to overshoot of the driving current of the semiconductor laser at the time of recording can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the configuration of a first embodiment of a recording APC circuit of the present invention.

FIG. 2 is a waveform diagram illustrating the operation of the recording APC circuit of FIG.

3 is a characteristic diagram showing a first temperature characteristic of each signal in FIG.

4 is a characteristic diagram showing a second temperature characteristic of each signal of FIG.

FIG. 5 is a circuit diagram showing the configuration of a second embodiment of the recording APC circuit of the present invention.

FIG. 6 is a waveform diagram illustrating the operation of the recording APC circuit of FIG.

FIG. 7 is a configuration diagram showing a configuration of a first conventional example of an optical head.

8 is a characteristic diagram showing an output characteristic of a light beam of the optical head of FIG.

9 is a waveform diagram showing an output waveform of a light beam of the optical head shown in FIG.

FIG. 10 is a configuration diagram showing a configuration of a second conventional example of the optical head.

11 is a characteristic diagram showing an output characteristic of a light beam of the optical head of FIG.

12 is a circuit diagram showing a configuration of a conventional recording APC circuit of FIG.

FIG. 13 is a waveform diagram illustrating the operation of the recording APC circuit of FIG.

FIG. 14 is a characteristic diagram showing temperature characteristics of each signal in FIG.

[Explanation of symbols]

 1 recording signal generation circuit 2 high speed current control unit 3 low speed current control unit LD semiconductor laser PD monitor photodiode

Claims (6)

[Claims] 1. An optical information recording apparatus for recording on a recording medium using a semiconductor laser, comprising: a recording signal generating circuit for switching a current to the semiconductor laser at a predetermined timing when recording information on the recording medium; The detection circuit that detects the recording light emission power emitted from the laser is compared with the detected recording light emission power and the preset power setting, and the current flowing through the semiconductor laser is adjusted so that the recording light emission power becomes equal to the set power. An optical information recording device comprising: a first current control unit for controlling. 2. The optical information recording apparatus according to claim 1, further comprising a second current control unit which controls a current supplied to the semiconductor laser according to a temperature change. 3. The control band of the first current control unit is sufficiently higher than the recording frequency of the signal, and the control band of the second current control unit is sufficiently lower than the recording frequency of the signal. The optical information recording device according to claim 2. 4. The optical information recording apparatus according to claim 1, wherein the maximum value of the current controlled by the first current controller changes according to the external temperature. 5. The light according to claim 1, wherein the operation of the first current control unit is normally stopped, and the operation is started together with a light emission command. Information recording device. 6. The optical information recording apparatus according to claim 5, wherein a time constant T1 at the time of starting the operation of the first current controller is set longer than a time constant T2 of the detection circuit.