JPH05144062A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To properly control the laser light output without using a temperature detecting thermistor neither an AD converter. CONSTITUTION:The temperature change of a laser diode 1 is detected in a CPU 3 by a laser drive current for lighting a prescribed read light output (for reproducing output) of the laser diode 1; and if the detection result exceeds a prescribed value, the laser drive current is obtained by the CPU 3 so that a prescribed output of the laser diode 1 for write and erase can be obtained.

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 / reproducing apparatus, and more particularly to an optical information recording / reproducing apparatus characterized by a light output control method of a laser diode used as a light source.

[0002]

2. Description of the Related Art Conventionally, an optical output control circuit of a laser diode of an optical information recording / reproducing apparatus is constructed as shown in FIG. First, the configuration will be described. In the figure, 1 is a laser diode as a light source, 2 is a photodiode for monitoring the optical output of the laser diode 1, 3 is a CPU, 4, 7
Is a register whose value can be rewritten by the CPU 3,
Reference numerals 5 and 8 are DA converters that convert the values of the registers 4 and 7 into analog values, and reference numerals 6 and 9 are the DA converters 5 and 8.
A current source controlled by the output voltage of 10; a high-speed switch for generating write pulse light and erase light;
Reference numeral 11 is a gain adjustment circuit that adjusts the output current of the photodiode 2 into a voltage by adjusting the gain, 12 is an AD converter that converts the output voltage of the gain adjustment circuit 11 into a digital value, and 13 to 15 are the registers and the like. Is a memory for temporarily storing the value of, the numeral 16 is a thermistor for detecting the temperature of the laser diode 1, and 17 is an AD converter for converting the output voltage of the thermistor 16 into a digital value.

Structures other than the optical output control circuit, such as a spindle motor and an actuator servo system, which compose the optical information recording / reproducing apparatus, will not be described because they do not interfere with the description of the present invention.

Next, the operation will be described, but before that, the characteristics of the laser diode will be described in order to help understanding of the operation. FIG. 3 is a diagram showing a relationship between forward current and light output of the laser diode. As shown in the figure, the laser diode does not emit laser light up to a current of a certain value (Ith), and thereafter the optical output increases linearly. In the figure, a is a typical thing, but there are things like b and c due to individual variations, and the thing of a also has characteristics like d at high temperature and e and f due to high temperature and deterioration. Change. Therefore, when it is necessary to accurately obtain a predetermined light output as in an optical information recording / reproducing apparatus, the light output is monitored and the forward current for driving the laser diode is adjusted so that the light output reaches a predetermined value. A possible light output control circuit is required. In the figure, IB is a forward current required to obtain a reading optical output, and IP is a forward current required to obtain a writing and erasing optical output in addition to IB. The reason for using two current sources in this way will be described later. Returning to FIG. 2 again, the explanation will be continued.

In the figure, the output current of the photodiode 2 and the optical output of the laser diode 1 are in a proportional relationship, but since some optical parts pass from the laser diode to the recording medium, the optical efficiency of this optical part is increased. And the variation of the photodiode 2 cause variation in the proportional coefficient between the laser power on the recording medium and the output current of the photodiode. The gain adjusting circuit 11 is adjusted so that the CPU 3 can correct this variation and detect the absolute value of the laser power on the recording medium via the AD converter 12. The procedure for lighting the laser diode 1 with the reading light output is as follows. First, the register B is cleared and the switch 10 is off.

Therefore, the current value of the current source (B) 9 is 0, and the laser diode 1 does not emit light. Next, the CPU 3 gradually increases the value of the register (B) 7 and increases the drive current of the laser diode 1. Then, when it is detected via the AD converter 12 that the predetermined optical power is obtained, the increase of the register (B) 7 is stopped. As described above, the laser diode changes its emission output even when a constant current is supplied due to temperature change or deterioration due to energization. Therefore, the CPU 3 constantly monitors the output of the laser 1 via the AD converter 12. However, when it becomes larger than a predetermined value, the value of the register (B) 7 is decreased, and when it becomes smaller than the predetermined value, the value of the register (B) 7 is increased so that the output of the laser 1 becomes a predetermined value. Control to maintain.

As described above, the current corresponding to IB in FIG. 3 is supplied by adjusting the current source (B) 9 and the light is read by the optical output for reading. After that, such automatic control was performed by APC (A
utoPower Control).

The procedure for lighting the laser diode 1 with the writing and erasing light outputs is as follows.
The register (B) 7 holds a value that gives a read optical output immediately before the start of writing and erasing. The register (A) 4 is preset with a value such that a predetermined optical output for writing and erasing can be obtained by a method described later. Then, the high-speed switch 10 is turned on / off in accordance with the write pulse and the erase timing.
Thus, the current corresponding to IP in FIG.
Is adjusted and added to the current corresponding to IB and applied to the laser diode 1 to obtain the writing and erasing optical outputs. Since the current sources (A) 6 and (B) 9 cannot change the current value at high speed, in order to perform high-speed pulse lighting, such a configuration of "two current sources and one high-speed switch" is used. To take.

Even when the optical output for writing and erasing is turned on (hereinafter, when high output is turned on), it is necessary to control the current for keeping the optical output at a predetermined value in consideration of the temperature characteristics of the laser diode. This is performed by adjusting the value of the register (A) 4 so that the optical output (the average value of the portion where the duty is constant is often used during writing) becomes a predetermined value.
Rather than APC performed during high output lighting, it is important to control the setting of a value that can give a predetermined light output in the register A in advance before the high output lighting described above. This is due to the following two reasons.

Since the response speed of the APC is slow, if the APC is started after the high output lighting is started, there is a possibility that a predetermined light output is not obtained for a long time.

Since the high output lighting time is relatively short, the light output fluctuation during that period is small even if APC is not performed.

The value for high output lighting is registered in the register (A).
A comparatively easy and typical conventional method of presetting to 4 is as follows.

1. An erasable test track is provided on the recording medium in advance.

2. After the power is turned on and the laser spot is focused on the recording medium, the laser spot is sought on the test track described in 1 above.

3. After setting an appropriate value in the register (A) 4, high output lighting is started and APC is performed so as to obtain the first laser power.

4. When the APC is performed with the first laser power, the CPU 3 stores the value of the register (A) 4 in the memory (A).
Save to 13.

5. Then, the CPU 3 performs APC so as to obtain the second laser power.

6. When the APC is performed with the second laser power, the CPU 3 stores the value of the register (A) 4 in the memory (B).
Save to 14.

7. End high output lighting.

8. The CPU 3 measures the temperature of the laser diode 1 at this time through the thermistor 16 and the AD converter 17, and stores the value in the memory (C) 15.

As described above, a series of the steps of seeking the laser spot on the test track, obtaining the value of the register (A) 4 capable of emitting light with the first and second laser powers by the APC, and storing it in the memory. The operation is hereinafter referred to as a write test.

9. At the next high output lighting, the CPU 3 first measures the temperature of the laser diode 1 via the thermistor 16 and the AD converter 17, and compares it with the value stored in the memory (C) 15.

10. If the difference between the two is greater than a specified value,
The write test is performed again, and the memories (A) 13 and (B) 1
4 and (C) 15 is updated.

11. The value of the register (A) 4 corresponding to the desired high output emission power is set to the value of the memory (A) 13 corresponding to the first laser power and the value of the memory (B) 14 corresponding to the second laser power. It is obtained from the relationship of the above and is set in the register (A) 4. As shown in FIG. 3, the IP current and the laser emission power have a linear relationship. Generally, the relationship between the resistor (A) 4 and the current source (A) 6 is made linear to correspond to the above desired power. When obtaining the value of the register (A) 4, the linear interpolation (or external measurement) is performed from the values of the memory (A) 13 and the memory (B) 14.

As described above, the laser diode 1
When the temperature of the laser diode 1 changes by a predetermined value or more, a write test is performed and the value of the register (A) 4 is set in advance, so that even if the temperature of the laser diode 1 changes, high output can be relatively easily performed with a minimum loss time. The desired laser power can be accurately obtained from the start of lighting.

This completes the description of the entire operation of the light output control circuit of the laser diode.

[0027]

The method of presetting the value of the register A of the conventional example has the following drawbacks.

That is, conventionally, a thermistor and an AD converter for measuring the temperature of the laser diode are required, which is disadvantageous in cost and mounting area. In particular, regarding the thermistor, simplification and miniaturization around the laser diode for miniaturization of mechatronics have been extremely difficult.

Therefore, an object of the present invention is to provide an optical information recording / reproducing apparatus which solves the above problems.

[0030]

In order to achieve the above object, the present invention provides a drive current calculating means for obtaining a laser drive current required to obtain a predetermined output of a laser diode for writing and erasing, and a laser. A reproduction output control means for maintaining the diode at a predetermined reproduction output, a current detection means for detecting a forward current of the laser diode during operation of the reproduction output control means, and a detection result of the current detection means are predetermined. Means for activating the drive current calculation means when the value changes by more than a value.

[0031]

According to the present invention, the temperature change of the laser diode is detected by the laser driving current when the reading optical output is turned on (when reproducing is output), and when the result is a predetermined value or more, writing and erasing are performed. The drive current calculating means for obtaining the laser drive current required to obtain the predetermined laser power of is activated. This allows you to
Thermistor and A for temperature detection of laser diode
Appropriate control of the laser diode light output can be performed without the need for a D converter.

[0032]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a thermistor for measuring the temperature of the laser diode 1 and an AD converter are deleted from the circuit of FIG. Since the other structure is the same as that of FIG. 1, the operation of detecting the temperature change of the laser diode 1, which is a feature of the present invention, will be mainly described below.

As described above, the current-light output characteristic of the laser diode 1 changes as shown in FIG. 3, and the IB current at this time approximately follows the following equation.

[0035] _{IB (T1) = IB (T0} ) exp {(T 1 -T 0) / T k} IB (T1): IB IB at the temperature T _{1 (T0):} IB T at the temperature T _{0 k} : Characteristic temperature (constant) For laser diodes of the same type, the individual variations in the values of IB _(T0) and T _k are within a certain value. Therefore, the laser can be detected by detecting this change in IB. The temperature change of the diode 1 can be known. T _k is generally 1
Since it is 30 ° K to 160 ° K, which is a sufficiently large value with respect to the temperature change of the laser diode 1, the change of the IB current with respect to the temperature change may be regarded as substantially linear.

The write test in the present invention is performed as follows.

1. After the power is turned on, the first write test is the same as the conventional one, but the memory (C) 15 has the register (B) 7 immediately before the write test, not the temperature of the laser diode 1 via the thermistor and the AD converter. The value is saved.

2. When the high output is turned on, the CPU 3 first compares the value of the register (B) 7 at that time with the previous value of the register (B) 7 stored in the memory (C) 15.

3. When the difference between the two is greater than or equal to the predetermined value, the write test is performed again and the values in the memories (A) 13, (B) 14 and (C) 15 are updated. If not, go to the next 4 as it is.

4. The value is set in the register (A) 4 in the same manner as in the conventional case, and high output lighting is started.

(Other Embodiments) In order to simplify the explanation,
In the description of the conventional example, the CPU is configured to perform a series of APC operations, but the present invention can be applied in the same manner even if it is configured by a comparator and an up / down counter. Further, normally, a high-frequency current is superposed on the applied current in order to reduce the laser noise during lighting by using the output for reading, but the present invention can be applied even in such a case within a range in which the high-frequency current does not largely change.

[0042]

As described above, according to the present invention, the laser light output can be appropriately controlled without the need for the temperature detecting thermistor and the AD converter, and further, the cost can be reduced, especially, the laser diode output can be reduced. It has a great effect on downsizing.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional example.

FIG. 3 is a diagram showing characteristics of a laser diode.

[Explanation of symbols]

 1 Laser Diode 2 Photodiode 3 CPU 4 Register A 5 DA Converter A 6 Current Source A 7 Register B 8 DA Converter B 9 Current Source B 10 High Speed Switch 11 Gain Adjusting Circuit 12 AD Converter 13 Memory A 14 Memory B 15 Memory C

Claims (1)

[Claims] 1. A drive current calculation means for obtaining a laser drive current required to obtain a predetermined output of a laser diode for writing and erasing, and a reproduction output for maintaining the laser diode at a predetermined reproduction output. Control means, current detection means for detecting a forward current of the laser diode during operation of the reproduction output control means, and starting the drive current calculation means when the detection result of the current detection means changes by a predetermined value or more. An optical information recording / reproducing apparatus characterized by comprising: