JPH04263130A - Radiation power controller of laser diode - Google Patents

Abstract

PURPOSE:To always maintain radiation power to the optimum value by detecting temperature of a laser diode and correcting deviation from the optimum value of the radiation power based on the temperature dependency of laser diode using such detected signal. CONSTITUTION:A controller 16 fetches a current temperature T of a laser diode. Next, the controller 16 obtains a difference between the current temperature input and a predetermined reference temperature and calculates a correction value of the optimum recording laser power value by multiplying such difference with a correction coefficient. The correction coefficient can be obtained from laser waveform varying characteristic for laser diode temperature and optimum recording laser power value varying characteristic for the waveform. The obtained correction value of the optimum recording laser power value is outputted to a recording amplifier 4 as a recording laser power control signal (m) from the controller 16. As a result, the recording amplifier 4 outputs a recording signal (EFM)C having the amplitude depending on the recording laser power control signal m to a pickup 6 via a playback/record selection switch 8.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation power control device for a laser diode, and more particularly to a radiation power control device for a laser diode.
The present invention relates to a device that temperature-corrects the radiation power of a laser diode used to record information on a recordable optical disk such as a double compact disk to an optimum value.

0002

[Prior Art] Conventionally known CD (compact)
R-CD is known as an optical disc that can be recorded by the user. When recording information on an R-CD by an R-CD recorder, a recording laser diode is used. Since the quality of recording depends on the physical characteristics and optical characteristics of the R-CD, the wavelength of the laser used, etc., it is necessary to calibrate to the optimum recording laser power value.

[0003] In the conventional calibration method, first,
As shown in FIG. 4(a), the recording signal c shown in FIG. 4(c) is recorded on the dedicated track 2 provided on the R-CD 1 in FIG.
)'s ATIP (Absolute Time In P)
Recording is performed while changing the recording signal c at predetermined time intervals (hereinafter referred to as STEP) as shown in FIG. 4C based on the sync (synchronizing signal) a. After that, track 2 on the R-CD 1 is read and reproduced, and the DC component of the obtained FEM RF signal is removed (using an AC coupling capacitor), resulting in a signal like the AC coupled reproduction signal d in Fig. 4(e). Calibration was performed using the value of the recording laser power b at which the amplitude center of the AC coupled reproduction signal d becomes approximately zero as the optimum recording laser power value. The eye patterns of sections A, B, and C in FIG. 4(e) are shown in FIG. As can be seen from FIG. 5, part B can be said to be the power value.

For reference, PREC for calibration and its reproduced waveform are shown in FIG. 9, and an explanatory diagram of an eye pattern is shown in FIG. Here, a recordable and reproducible R-
The main parts of the CD player are shown in FIG. During calibration recording, the R-CD 1 is rotated by a spindle motor 7, and its rotation is controlled by a servo circuit 10. At this time, the pickup 6 is controlled by the servo circuit 10 to a position corresponding to the track 2. The recording signal c is input to the recording amplifier 4 to drive the laser diode of the pickup 6. At this time, the recording laser power b is controlled by the controller (servo/mechanical control/microcomputer) 1.
6. The recording amplifier is controlled by the recording laser power control signal m given via the D/A converter 14 in step S1 of FIG.
- Shown in S7.

During calibration playback, the recording/playback switch 8 is switched to the PB side, the read signal from the pickup 6 is amplified by the playback amplifier 9, and then the RF
Output the signal to the EFM decoder. On the other hand, playback amplifier 9
The RF signal output from the RF signal is DC-cut by an AC coupling capacitor 11, and sent through a peak detection circuit 12 and a bottom detection circuit 13 to detect the amplitude center voltage. The detected amplitude center voltage is input to the controller 16 via the A/D converter 15, and is used to calculate the optimum power value. This control calculation algorithm is performed in steps S10 to S in FIG.
17.

By the way, the above-mentioned calibration is specifically performed by dividing the range of approximately 4 to 10 mw of the recording laser power value into 0.5 to 2 mw increments, and measuring the recording laser power value at each division point. Then, the recording laser power values between the dividing points are interpolated by a method such as linear approximation, and the accuracy is adjusted to about 0.1 mw.

[0007]

[Problems to be Solved by the Invention] However, the optimum recording laser power value obtained by the above-mentioned calibration varies depending on the wavelength of the output laser beam, and has a wavelength dependence that changes by a coefficient of about 0.1 mw/nm. have. Furthermore, this wavelength changes depending on the chip temperature of the laser diode, and also has a temperature dependence that changes by a coefficient of about 0.33 nm/°C. As a result, the optimum recording laser power value will change by a factor of about 0.033 mw/°C.

[0008] For this reason, even if the above-mentioned calibration is performed, within the guaranteed performance range of laser diodes (5 to 35°C), the temperature change of 30°C is approximately 1%.
An optimum value deviation of about mw will occur. Further, when the laser diode is operated continuously, the temperature may rise to about 60°C. Therefore, it is expected that the true optimum recording laser power value will vary greatly between calibration and actual operation, and the recording operation will not necessarily be performed at the optimum value.

SUMMARY OF THE INVENTION An object of the present invention is to provide a radiation power control device for a laser diode that can compensate for changes in the optimum power value of a laser beam due to temperature changes and can always maintain the optimum power value.

0010

Means for Solving the Problems In order to solve the above problems, the invention as set forth in claim 1 provides an apparatus for controlling the radiation power of a laser beam emitted from a laser diode to an optimum value. temperature detection means for detecting the ambient temperature of the laser diode and outputting a temperature detection signal; and temperature correction means for always correcting the radiation power of the laser diode to an optimum value based on the temperature detection signal and the temperature characteristics of the laser diode. and,
It is composed of:

According to a second aspect of the invention, in the laser diode radiation power control device according to the first aspect, the temperature correction means adjusts the change characteristics of the output laser wavelength with respect to temperature changes of the laser diode and the optimum radiation for the laser wavelength. It is configured to include a correction calculation means for calculating a correction value of the optimum radiation power based on the power change characteristics.

0012

According to the present invention, the temperature detection means directly or indirectly detects the temperature of the laser diode and outputs a temperature detection signal. The temperature correction means uses the temperature detection signal to correct a deviation in the optimum value of the radiation power due to the temperature dependence of the laser diode. In this way, the radiation power is always maintained at an optimum value.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the invention. FIG. 1 shows a recordable and reproducible R-C including a radiation power control device according to the present invention.
FIG. 2 is a block diagram of main parts of the D player. 1, the parts that are different from FIG. 6 (conventional example) are a temperature detector 18, an A/D
The point is that the converter 17 and the controller 16 include temperature correction means. Since the other parts have substantially the same configuration as in FIG. 6, they will be described below using the same reference numerals.

The temperature detector 18 is attached to or near the laser diode chip (not shown) in the pickup 6, and outputs a temperature detection signal T having a voltage corresponding to the temperature of the laser diode. As the temperature detector 18, a thermistor or the like can be used, for example, and a lightweight one that does not interfere with the operation of the pickup 6 is preferable.

The A/D converter 17 converts the temperature detection signal T into digital data. The temperature correction means is embodied in a control program stored in a ROM within the controller 16. The algorithm of the control program is shown in Figure 2.
This is shown in steps S20 to S25. That is, as shown in FIG. 2, the controller 16 takes in the current temperature of the laser diode T (step S20). Next, find the difference between the input current temperature and a predetermined reference temperature,
The difference value is multiplied by a correction coefficient to calculate a correction value for the optimum recording laser power value (step S21). Note that the reference temperature is stored in advance in storage means such as RAM or ROM within the controller 16. The correction coefficient is based on the change characteristics of the laser wavelength with respect to the temperature of the laser diode (see Figure 3 (a)) and the change characteristics of the optimum recording laser power value with respect to the wavelength (see Figure 3 (a)).
(b)). The correction coefficient is "0.033 mw/°C" in the example of FIG. The correction value of the optimal recording laser power value calculated in this way is output from the controller 16 to the recording amplifier 4 as a recording laser power control signal m (step S22). the result,
The recording amplifier 4 outputs a recording signal (EFM) c having a magnitude corresponding to the recording laser power control signal m to the pickup 6 via the recording/reproducing switch 8 (step S23). The above processing is repeatedly executed at each sampling period by sampling the temperature detection signal T at appropriate time intervals. Next, the presence or absence of a recording end request is confirmed (step S24),
If YES, the recording operation ends (step S25).

[0016]

[Effects of the Invention] As described above, according to the present invention, the temperature of the laser diode is detected and the detected signal is used to correct the deviation in the optimum value of the radiation power due to the temperature dependence of the laser diode. , the radiation power can always be maintained at an optimal value.

[Brief explanation of the drawing]

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

FIG. 2 is a flowchart showing the operation of temperature correction means in the present invention.

FIG. 3(a) is a characteristic diagram of changes in laser wavelength with respect to temperature, and (b) is a characteristic diagram of changes in optimum recording laser power value with respect to laser wavelength.

FIG. 4 is a time chart of a conventional recording laser power value calibration operation.

FIG. 5 is an explanatory diagram showing an eye pattern of each part of the reproduced RF signal in FIG. 4(e).

FIG. 6 is a block diagram of main parts of a conventional R-CD player.

FIG. 7 is a time chart of a conventional calibration operation during recording.

FIG. 8 is a time chart of a conventional calibration operation during playback.

FIG. 9 is a diagram of recording power and reproduction waveforms in a conventional recording laser power calibration method.

FIG. 10 is a general explanatory diagram of an eye pattern.

[Explanation of symbols] 1...R-CD 2...Truck 3...Calibration area 4...Recording amplifier 6...Pickup 7...Spindle motor 8...Recording/playback switch 9...Reproduction amplifier 10...Servo circuit 11...AC coupling capacitor 12...Peak detection circuit 13...Bottom detection circuit 14...D/A converter 15...A/D converter 16...Controller 17...A/D converter 17 18...Temperature detector a...ATIP sink b...Recording laser power c... Recording signal (EFM) d...AC coupled reproduction signal m...Recording laser power control signal n... Recording/playback switching signal T...Temperature detection signal

Claims (2)

[Claims] 1. A device for controlling the radiation power of a laser beam emitted from a laser diode to an optimum value, comprising: temperature detection means for detecting the temperature of the laser diode or the ambient temperature of the laser diode and outputting a temperature detection signal; A radiation power control device for a laser diode, comprising: temperature correction means for always correcting the radiation power of the laser diode to an optimum value based on the temperature detection signal and the temperature characteristics of the laser diode. 2. The laser diode radiation power control device according to claim 1, wherein the temperature correction means is configured based on a change characteristic of the output laser wavelength with respect to a temperature change of the laser diode and a change characteristic of the optimum radiation power with respect to the laser wavelength. A radiation power control device for a laser diode, comprising a correction calculation means for calculating a correction value of the optimum radiation power.