JPH0210524A - Optical head device - Google Patents

Abstract

PURPOSE:To easily detect any defect of a recording medium by setting the operating point of a semiconductor laser in a hysteresis loop without using any additional electric circuit. CONSTITUTION:The operating point of the semiconductor laser is set in the hysteresis loop. In case of a defect on the recording medium 4, because of its reflectance change, the light quantity of a return light to the semiconductor laser 2 is increased or decreased. As a result, even when the operating point is shifted, and the light quantity of the return light is restored to the original, this operating point is maintained. In case of increasing the reflectance, an optical output of the semiconductor laser is shifted from a low output to a high output, while in case of decreasing the reflectance, the optical output of the semiconductor laser is shifted from the high output to the low output. Consequently, by monitoring the output of the semiconductor laser 2, a defect of the recording medium 4 can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical head device used for optical recording that records and reproduces information using light.

[Conventional technology]

In optical recording, information is recorded by emitting light from a light source as a minute spot onto an optical recording medium, and an optical head device is used that irradiates weak light and detects information from changes in reflectance. . As a recording medium, one in which a recording layer is formed on the surface of a disk-shaped substrate and a spiral or concentric trunk is provided is mainly used.

To record information on a recording medium using such an optical head device, first play back the recording trunk once to confirm that there are no abnormal changes in reflectance, that is, there are no defects on the recording medium, and then start recording. It is carried out.

Conventional optical head devices use electrical circuits to detect such recording medium defects. FIG. 4 shows an example of its configuration. When the output from the photodetector 1 that detects the amount of reflected light from the recording medium is input to the comparator 9 and an abnormal change in the amount of light is detected, the flip-flop 10 is turned on. do. If the flip-flop 1o is turned on after scanning a recording track, it is known that the track is defective.

[Problem to be solved by the invention]

As described above, in order to detect defects in a recording medium when recording information, conventional methods have a problem in that an electric circuit must be constructed and added.

An object of the present invention is to provide an optical head device that can easily detect track defects without causing such problems.

[Means to solve the problem]

The present invention includes a light source and a light beam emitted from the light source that is focused on a recording medium as a minute spot by a condensing lens.
In an optical head device having an optical system that returns reflected light from the light condensing point to the light source, the light source has a discontinuous change in optical output depending on a certain injection current value, and a discontinuous change in the direction in which the optical output increases. A semiconductor laser exhibits different hysteresis characteristics in which the injection current value changes in the direction of decreasing optical output and the injection current value changes discontinuously in the direction of decreasing optical output, and the injection current value changes depending on the return light from the outside. The operating point of this semiconductor laser is set within the hysteresis loop.

[Effect]

If there is a defect in the recording medium, the amount of light returned to the semiconductor laser increases or decreases due to a change in reflectance. As a result, even if the operating point shifts and the intensity of the returned light returns to its original value, the operating point will be maintained. 0 When the reflectance increases, the optical output of the semiconductor laser will shift from low to high output. , when the reflectance decreases, the optical output of the semiconductor laser shifts from high output to low output. Therefore, by monitoring the output of the semiconductor laser, it is possible to detect defects in the recording medium.

〔Example〕

FIG. 1 shows an embodiment of the present invention. In this optical head device, the optical output changes discontinuously depending on a certain injection current value, and the injection current value changes discontinuously in the direction in which the optical output increases, and the optical output changes discontinuously in the direction in which the optical output decreases. a semiconductor laser 2 that exhibits a hysteresis characteristic in which the injection current value is different from the injection current value, and in which the injection current value changes depending on return light from the outside;
A photodetector 1 is provided on the back side of the semiconductor laser to monitor the output of the semiconductor laser 2, and a photodetector 1 is provided to monitor the output of the semiconductor laser 2, and a photodetector 1 is installed to condense the emitted light beam from the semiconductor laser 2 as a minute spot on the recording medium 4. It has a condenser lens 3 that returns reflected light to the semiconductor laser 2.

As the semiconductor laser 2, a tandem electrode type semiconductor laser is used, for example, as shown in FIG. 2, in which an excitation region 5 and an absorption region 6 are provided by dividing one electrode in the resonator length direction. In this semiconductor laser, as shown in FIG. 3, the relationship between the injection current and the optical output shows hysteresis. That is,
The optical output changes discontinuously depending on a specific injection current value, and exhibits different characteristics depending on whether the specific injection current value increases or decreases the optical output, and hysteresis occurs when the amount of light returned from the outside increases. The loop changes from a solid line to a broken line.

Next, the recording medium defect detection operation in this embodiment will be explained.

The semiconductor laser 2 sets its operating point at P7 in the hysteresis loop shown in FIG. 3, and emits weak light. The light emitted from the semiconductor laser 2 is focused onto the recording medium 4 by the condenser lens 3, and the reflected light from the focus point returns to the semiconductor laser 2 in the opposite path. If there is a defect in the recording medium 4 and there is an abnormal increase in reflectance, the amount of returned light increases, so the state changes to operating point P17, and this state is maintained even if the reflectance returns to its original value.

The photodetector l monitors the output on the back surface of the semiconductor laser 2, and it can be seen that there is a defect in the recording medium 4 that increases the reflectance due to an increase in the optical output.

In addition, when detecting a defect that decreases the reflectance, if the operating point is set to P8, the state will shift to the operating point P1B as the amount of returned light decreases, and even if the reflectance returns to its original state, it will remain in this state. is maintained. The decrease in light output is detected by the photodetector l, indicating that the recording medium 4 is defective.

In the above embodiment, the optical output of the semiconductor laser 2 is changed by a photodetector provided on the back surface of the semiconductor laser 2.
As shown in FIG. 2, the value of the current flowing through the resistor 11 connected to the absorption region 6 of the semiconductor laser 2 may be monitored.

〔Effect of the invention〕

According to the present invention, without using additional electrical circuits,
It becomes possible to easily detect defects in the recording medium using the optical head device itself.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention; FIG. 2 is a diagram showing the configuration of a semiconductor laser used in the present invention; Figure 3 is a diagram showing the hysteresis characteristics of a semiconductor laser. FIG. 4 is a diagram showing a conventional defect detection circuit. 1...Photodetector 2... Semiconductor laser 3...Condensing lens 4...Recording medium 5...Excitation region 6・ 9・ 10・ 11・ ・Absorption area ·comparator ・Flip Flop ·resistance

Claims (1)

[Claims] (1) In an optical head device that includes a light source and an optical system that focuses the emitted light beam from the light source as a minute spot on a recording medium using a condensing lens, and returns reflected light from the condensed point to the light source. As the light source, the light output changes discontinuously depending on a certain injection current value, and the injection current value changes discontinuously in the direction of increasing the optical output and the injection current value changes discontinuously in the direction of decreasing the optical output. A light source characterized by using a semiconductor laser that exhibits a hysteresis characteristic that differs from a current value, and in which the injected current value changes depending on return light from the outside, and the operating point of this semiconductor laser is set within a hysteresis loop. head device.