JPS619844A - Optical information device - Google Patents

Abstract

PURPOSE:To suppress the variance of the optical output of a semconductor laser due to return light with a very simple constitution by flickering the optical output of the semiconductor laser and selecting the frequency of this flickering so that the return light does not overlap lighting of the semiconductor laser with respect to time. CONSTITUTION:A driving current of a semiconductor laser 1 is subjected to AC modulation to flicker the optical output. This modulating frequency is selected to be c/4l where l is the optical length between the semiconductor laser 1 and a recording plate 5 such as an optical disc or the like and (c) is the velocity of light. Since the optical output of the semiconductor laser (indicated by solid lines) and the light returned to the recording plate (indicated by broken lines) are shifted from each other with respect to time as shown in the figure, the variance of the optical output dut to the interaction between the output light and the return light is prevented. If overlap between the output light and the return light is not completely eliminated, that is, if the overlap time is shortened by modulation of a lower frequency, the variance of the optical output can be reduced to a level where the variance is not a problem practically.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an optical information device using a recording plate such as an optical disk.

<Background of the Invention> In an optical information device using a recording plate such as an optical disk, it is inevitable that light reflected from the recording plate returns to the semiconductor laser as a light source. If there is light returned to the semiconductor laser, the optical output will increase even if the semiconductor laser ('LD) is operated with a constant current. This situation is shown in FIG. In addition, constant output power (APC;
Even if the Auto Power Control (Auto Power Control) operation is performed, the reflected light output changes due to the returned light.

In this case, the rate of increase in output due to returned light is the opposite of that in constant current operation, since the back side optical output of the semiconductor laser, which is received by the built-in photodiode, is greater than the front side optical output. , as shown in Figure 4.

The above phenomenon is particularly noticeable in high-output semiconductor lasers in which the reflectance of the front resonant surface is reduced.

<Object of the Invention> The present invention has been made in view of the above points, and an object of the present invention is to provide an optical information device having a completely new configuration for suppressing fluctuations in optical output due to returned light. It is.

<Structure of the Invention> The optical information device of the present invention blinks the optical output of a semiconductor laser, and converts the frequency of the blinking into either the light reflected by a recording plate such as an optical disk and returned to the semiconductor laser, or the light output from the semiconductor laser. The present invention is characterized by suppressing fluctuations in the optical output of the semiconductor laser due to the return light by selecting the light so that it does not overlap in time with the lighting or so that the overlap is small.

<Example> Fig. 2 shows an example of an optical system. In the figure, ■ is a semiconductor laser, 2 is a collimator lens, 3 is a beam splitter,
4 is an objective lens, and 5 is a recording plate. Further, l is the optical length.

AC modulation is applied to the drive current of the semiconductor laser 1 to blink the optical output. This modulation frequency is selected to be c/41, where l is the optical length of the semiconductor laser 1 and the recording plate 5 such as an optical disk, and C is the speed of light. In this way,
As shown in Figure 1, there is a time lag between the optical output of the semiconductor laser (shown by the solid line) and the light returning from the recording plate (shown by the broken line), resulting in an interaction between the output light and the returning light. No light output fluctuation occurs.

The above explanation is for when the duty ratio of optical output is 50%, but if the duty ratio is smaller than C
Even by modulating a frequency lower than /41, the overlap between the output light and the returned light can be eliminated, and the same effect can be obtained.

In addition, even if the overlap between the output light and the return light is not completely eliminated, in other words, by modulating a lower frequency, by reducing the overlap time, fluctuations in the optical output can be reduced to a level that does not pose a practical problem. Is possible.

<Effects of the Invention> As explained in detail above, the optical information device of the present invention blinks the optical output of the semiconductor laser, and adjusts the frequency of the blinking to
By selecting the light reflected by a recording plate such as an optical disk and returning to the semiconductor laser so that it does not temporally overlap with the lighting of the semiconductor laser, or so that the overlap is small, the The present invention is characterized by suppressing fluctuations in the optical output of a semiconductor laser, and the present invention is an extremely useful method that can suppress fluctuations in the optical output of a semiconductor laser due to returned light with a very simple configuration. It is possible to provide an optical information device.

[Brief explanation of the drawing]

FIG. 1 shows the time relationship (duty ratio 50%) between the semiconductor laser light output (solid line) and the returned light (broken line) when the present invention is implemented.
2 is a diagram showing an example of the optical system. FIG. 3 is a diagram showing the dependence of optical output on the amount of returned light during constant current operation. The figure is a diagram showing the dependence of optical output on the amount of returned light during APC operation. Explanation of symbols]: Semiconductor laser, 2: Collimator lens, 3: Beam splitter, 4: Objective lens, 5: Recording plate, l: Optical length. Agent Patent attorney Aihiko Fuku (and 2 others) Figure 1 Figure 2

Claims (1)

[Claims] 1. The light output of the semiconductor laser is blinked, and the frequency of the blinking is set so that the light reflected by a recording plate such as an optical disk and returned to the semiconductor laser does not overlap in time with the lighting of the semiconductor laser, or . An optical information device characterized in that optical output fluctuations of the semiconductor laser due to the returned light are suppressed by selecting such that the overlap is small.