JPH0258737A - Semiconductor laser writing control device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a write power control device for an optical recording/reproducing device.

[Prior Art] An optical recording/reproducing device focuses a beam from a light source onto a disk-shaped or quad-shaped recording medium using an objective lens (this focused point is called a spot), and this spot is called a spot on the recording medium. Scans the surface to record and reproduce information. In many cases, a semiconductor laser is used as this light source.

Information is recorded thermally by irradiating the recording medium with a high-power beam. The write signal is usually in the form of a pulse, and the recording medium undergoes thermal changes due to the write pulse. The part that has undergone this change is called the recording domain. In other words, the recording pulse forms a recording domain on the surface of the recording medium.

The characteristics of the reproduced signal are determined by the laser power at the time of recording (hereinafter referred to as
It is greatly influenced by the write power (abbreviated as write power). For example, if you write with a strong power, the recording domain will become larger compared to the size of the spot, but if you write with a weaker power, the recording domain will become smaller compared to the size of the spot. Naturally, if the size of the recording domain differs, the state of the reproduced signal will also differ. That is, control of write power is important if stable signal recording and reproduction is to be performed.

In contrast, in the past, the writing power was controlled in accordance with the linear velocity at which the recording beam scans the recording medium.

FIG. 5 shows a conventional semiconductor laser writing control circuit.

Power control of a semiconductor laser is performed by controlling the current flowing through the semiconductor laser. Therefore, the semiconductor laser write control circuit is a write current control circuit. The amplifier 10 controls the transistor 11 and sets the value of current flowing through the semiconductor laser during writing. Setting is variable resistor 19
However, in an actual optical recording/reproducing device, it is set by a control device such as a microcomputer using, for example, a D/A converter. Transistors 12 and 13 are operated complementarily by inverter 14 to switch the current from transistor 11 according to write data pulse U.

[Intelligence BE to be Solved by the Invention However, in the conventional technology, when writing is performed continuously, heat accumulates in the scanning direction of the beam, and the recording characteristics change over time even under the same recording conditions.

This is generally called a residual heat effect and may cause distortion in the reproduced waveform. Figure 6 shows this situation. u 4i
There is a write pulse, and the laser beam is switched in accordance with this pulse to thermally write data onto the recording medium. DR is a recording domain formed on the medium, and S is a reproduction signal when recorded data is read. When pulses are written continuously, the recording domain DR is small at the beginning of writing, and then gradually becomes larger. Furthermore, if the pulse width is long, the width of the recording domain changes in the recording direction, resulting in a blurry appearance. In this case, there is a problem in that the pulse width of the reproduction signal S is different from the width of the recording pulse U. If this problem exists, it is not possible to give meaning to the width of the recording domain in the recording direction (bi-width recording), and the recording density cannot be increased.

The present invention aims to solve these problems by estimating the residual heat effect by integrating the write signal, and using the output thereof to control the write power.

[Means for Solving the Problems] A semiconductor laser writing control device of the present invention is a semiconductor laser writing control device that writes onto a recording medium using a semiconductor laser. (b) A write power setting circuit that sets the current value to flow through the semiconductor laser during writing; (c) Detects the write pulse emitted from the semiconductor laser. (d) a pulse integrator circuit that integrates the output of this write pulse detection circuit; and (e) negative feedback of the output of this pulse integrator circuit to the write power setting circuit. .

[Embodiment] FIG. 1 shows a block diagram of a semiconductor laser writing control device of the present invention. 1 is a write power setting circuit, 2 is a write signal generation circuit, 3 is a write pulse detection circuit, 4
is a pulse integration circuit.

In the write operation, the write signal generation circuit 2 switches the write current set by the write power setting circuit 1 in accordance with the write data pulse U to generate a write pulse current.

The write pulse detection circuit No. 3 detects the write pulse, and the method for doing so may be to optically detect the actual write pulse emitted from the semiconductor laser, or to detect the current flowing through the semiconductor laser and generate a pseudo pulse. The write pulse may be detected automatically.

The output of the write pulse detection circuit No. 3 is integrated by the pulse integration circuit No. 4, and is negatively fed back to the write power setting port No. 1. That is, as the pulse integration circuit output increases, the write power set at 1 acts in the direction of decreasing.

FIG. 2 shows the first part of the semiconductor laser writing control device of the present invention.
An example of the circuit is shown below. In this case, the write pulse detection circuit actually detects the laser beam emitted from the semiconductor laser using an optical sensor (in this case, a photodiode is used). The pulse integrator circuit does not integrate in the mathematical sense, but is configured as a low-pass filter with a certain time constant. This is due to the following reason. The pulse integration circuit 4 estimates the residual heat effect of the recording medium during writing. Since the beam scans the recording surface of the recording medium, the temperature of the recording point changes exponentially in accordance with the thermal time constant of the recording medium. Therefore, in order to estimate this behavior, it is appropriate to use a low-pass filter configuration as shown in the figure and to match its time constant to the thermal time constant of the recording medium.

In this embodiment, the detection time constant of the write pulse detection circuit must be at least shorter than the thermal time constant of the recording medium.

FIG. 3 shows a second embodiment. In this case, the write pulse detection circuit detects the write pulse current flowing through the semiconductor laser and performs pseudo pulse detection. Further, the pulse detection circuit itself is a low-pass filter, and also serves as a pulse integration circuit.

FIG. 4 shows waveforms of various parts in the semiconductor laser writing pulse control device of the present invention. The signal names should be as shown in Figure 1. U is a write data pulse, r2 is a pulse integration circuit output, and iLD is a write current that drives the semiconductor laser.

When the pulse width of the write data pulse is short and the pulse interval is wide, the output of the pulse integrator circuit is close to 0 and the write power is approximately equal to the initial value set by the variable resistor 19 in FIG. Even if the pulse width is short, as the interval becomes narrower, the output r2 of the pulse integration circuit increases and the current value set by the write power setting circuit decreases. However, once the interval between the pulses becomes wider, the power setting value (setting current value) recovers. Furthermore, when the pulse width is long, the write power gradually decreases and converges to a certain constant value. By controlling the recording power in this manner, stable recording domains can be formed.

[Effects of the Invention] As described above, stable recording domains can be formed by controlling the write power using the output of the write pulse integration circuit, and pit width recording, which has conventionally been considered difficult due to residual heat effects, is possible. Became.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a semiconductor laser writing control device of the present invention. FIG. 2 is a circuit diagram showing a first embodiment of the present invention. FIG. 3 is a circuit diagram showing a second embodiment of the present invention. FIG. 4 is a signal waveform diagram of each part of the semiconductor laser writing control device of the present invention. FIG. 5 shows a conventional semiconductor laser writing control circuit. FIG. 6 shows recording and reproduction waveform diagrams according to the conventional method, and
Recording domain shape diagram. 1 ・ ・ 2 ・ ・ 3 ・ ・ 4 ・ ・ 10 ・ 11 ・ 12 ・ 13 ・ 14 ・ 15 ・ 16 ・ 17 ・ 18 ・ 19 ・ 20 ・ 21 ・ u L - iLD ・ Write power setting circuit, ・ Write signal Generation circuit, ・Write pulse detection circuit, ・Pulse integrator circuit, amplifier, transistor, transistor, transistor, inverter, semiconductor laser, photoelectric converter, amplifier (current-voltage converter), ・amplifier (low-pass filter), ・variable resistor, differential Amplifier (low-pass filter) ・Current detection resistor ・Write data pulse ・Power setting circuit output current ・Write pulse current ・Write power setting voltage r2 Pulse integration circuit output R ・Record domain ・Write pulse detection circuit output ・More than reproduction signal

Claims (1)

[Claims] (1) In a semiconductor laser writing control device that writes onto a recording medium using a semiconductor laser, (a) a write signal generation circuit that switches current to the semiconductor laser at a predetermined timing when writing information onto the recording medium; (b) ) a write power setting circuit that sets the current value to flow through the semiconductor laser during writing; (c) a write pulse detection circuit that detects the write pulse emitted from the semiconductor laser; and (d) an integrated output of the write pulse detection circuit. A semiconductor laser writing control device comprising: (e) a pulse integrating circuit; and (e) negative feedback of the output of the pulse integrating circuit to a writing power setting circuit.