JPH02223029A - Optical head device - Google Patents

Abstract

PURPOSE:To monitor the oscillation wavelength of a laser diode with a simple optical system by arranging a wavelength filter on an optical path, where the emission light of the laser diode is reflected with a beam splitter, and detecting the light transmitting through the wavelength filter. CONSTITUTION:A wavelength filter 14 is arranged on the optical path of the parallel light reflected with a beam splitter 3 from the beam splitter 3. The emission light of a laser diode 1 is shaped to the parallel light with a collimator lens 2, transmitted through the beam splitter 3 and guided to a reflection mirror 4. Then, a part of the light is reflected with the beam splitter 4, passes through the wavelength filter 14 and arrives at the light receiving surface of an optical detector 15. The longer the wavelength of the light is, the more the transmissivity of the wavelength filter 14 is increased. Accordingly, when the oscillation wavelength of the laser diode 1 is changed with a temperature change or degradation with the lapse of time, the received light quantity of the optical detector 15 is changed. Thus, the oscillation wavelength of the laser diode 1 can be monitored.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical head device used in an optical disk device or the like.

BACKGROUND ART FIG. 3 shows the configuration of a conventional magneto-optical disk device.

In FIG. 3, 1 is a laser diode serving as a light source;
2 is a collimating lens that shapes the emitted light from the laser diode I into parallel light; 3 is a collimating lens that transmits the parallel light from the collimating lens 2 and guides it to the reflecting mirror 4, and reflects the light from the reflecting mirror 4 to This is a beam splitter that guides the beam to the /2 wavelength plate 7.

5 is an objective lens that focuses the parallel light from the beam splitter 3 reflected by the reflection mirror 4 onto the magneto-optical disk 6; the light reflected by the magneto-optical disk 6 is converted into parallel light by the objective lens 5; Shaped reflective mirror 4
, is reflected by the beam splitter 3, and is reflected by the 1/2 wavelength plate 7.
As a result, the direction of vibration is rotated by 45°.

8 transmits the y-axis component of the light from the 1/2 wavelength plate 7,
A polarizing beam splitter that reflects the X-axis component; 9, a condensing lens that condenses the light transmitted through the polarizing beam splitter 8; 10, a condensing lens that condenses the light reflected by the polarizing beam splitter 8; 11; .12 is a photodetector that detects the amount of light condensed by the condenser lenses 9 and 10, and 13 is a differential amplifier that compares the amounts of light detected by the photodetectors 11 and 12.

Next, the above-mentioned conventional operation will be described for the case where information recorded on the magneto-optical disk 6 is read.

In FIG. 3, when laser diode light linearly polarized by the laser diode 1 or the like is focused on the magnetic material on the magneto-optical disk 6, the vibration axis of the reflected light is directed in the magnetization direction of the focused part due to the Kerr effect. Rotates ±00 relative to

The reflected light whose vibration axis has rotated ±00 degrees is reflected by the beam splitter 3, and the vibration direction is rotated by 45 degrees by the 1/2 wavelength plate 7 (Fig. 4), and then as shown in Figs. 5 and 6.
As shown in the figures, the y-axis component and the X-axis component of light transmitted and reflected by the polarizing beam splitter 8 are compared by a differential amplifier 13, and outputted as a read signal as shown in FIG. 7.

Problems to be Solved by the Invention However, in the conventional optical head device described above, the oscillation wavelength of the laser diode 1 changes due to temperature changes and deterioration over time, so there is a problem that reading and writing information cannot be performed stably. There is a point.

In addition, in order to solve the above problem, the laser diode 1
A beam splitter may be separately arranged in the optical path of the laser diode 1 to take out the emitted light of the laser diode 1 and monitor the oscillation wavelength of the laser diode l. However, in this case, since the beam splitter is separately arranged, the optical system The problem is that it becomes complicated.

SUMMARY OF THE INVENTION In view of the above conventional problems, an object of the present invention is to provide an optical head device that can monitor the oscillation wavelength of a laser diode with a simple optical system.

Means for Solving the Problems In order to achieve the above object, the present invention has a device that transmits the emitted light of a laser diode and guides it to a recording medium, and also reflects the light reflected by the recording medium and guides it to a reading system. By utilizing the fact that the beam splitter reflects the emitted light from the laser diode, by placing a wavelength filter in the optical path where the emitted light from the laser diode is reflected by this beam splitter, and by detecting the light that has passed through this wavelength filter. It is designed to detect the oscillation wavelength of a laser diode.

Effect of the Invention With the above configuration, the present invention can detect the oscillation wavelength of the laser diode without separately arranging a beam splitter for extracting the emitted light from the laser diode. Therefore, the oscillation wavelength of the laser diode can be detected with a simple optical system. can be monitored.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of an optical head device according to the present invention, and FIG. 2 is an explanatory diagram showing the spectral characteristics of the wavelength filter shown in FIG. 1, and the constituent members shown in FIG. Identical items are given the same reference numerals.

In FIG. 1, 1 is a laser diode serving as a light source;
2 is a collimating lens that shapes the emitted light from the laser diode 1 into parallel light, and 3 is a collimating lens that transmits the parallel light from the collimating lens 2 and guides it to the reflecting mirror 4, and also reflects the light from the reflecting mirror 4. This is a beam splitter that guides the beam to the wavelength plate 7, and due to its structure, the beam splitter 3 reflects the parallel light from the collimating lens 2.

14 is a wavelength filter disposed on the optical path of the parallel light from the beam splitter 3 reflected by the beam splitter 3; 15 is a photodetector that detects the amount of light transmitted through the wavelength filter 14; Transmittance increases as the wavelength of light increases, as shown in FIG.

5 is an objective lens that focuses the parallel light from the beam splitter 3 reflected by the reflection mirror 4 onto the magneto-optical disk 6; the light reflected by the magneto-optical disk 6 is converted into parallel light by the objective lens 5; Shaped reflective mirror 4
, is reflected by the beam splitter 3, and is reflected by the 1/2 wavelength plate 7.
The vibration direction is rotated by 45 degrees (see Figure 4).
.

8 transmits the y-axis component of the light from the 1/2 wavelength plate 7,
A polarizing beam splitter that reflects the X-axis component (see FIGS. 5 and 6), 9 a condensing lens that condenses the light transmitted through the polarizing beam splitter 8, and 10 a polarizing beam splitter that reflects the light reflected by the polarizing beam splitter 8. a condensing lens that condenses light; 11.
12 is a photodetector that detects the amount of light condensed by the condensing lens 9.10, and 13 is a photodetector 11.12.
This is a differential amplifier that outputs a read signal as shown in FIG. 7 based on the difference in the amount of light detected.

Next, the operation of the above embodiment will be explained.

In FIG. 1, the emitted light from a laser diode 1 is shaped into parallel light by a collimating lens 2, and this parallel light is
The beam passes through the beam sinter 3 and is guided to the reflection mirror 4,
Further, a part of the light is reflected by the beam splitter 3 and reaches the light receiving surface of the photodetector 15 via the wavelength filter 14 .

Here, as shown in FIG. 2, the transmittance of the wavelength filter 14 increases as the wavelength of the light becomes longer. Therefore, when the oscillation wavelength of the laser diode 1 changes due to temperature change or deterioration over time, the photodetector 15 The amount of light received by the laser diode 1 changes, and therefore the oscillation wavelength of the laser diode 1 can be monitored.

Further, in the above embodiment, the collimating lens 2 transmits the parallel light and guides it to the reflecting mirror 4, and the beam splitter 3 reflects the light from the reflecting mirror 4 and guides it to the 1/2 wavelength plate 7. Since the laser beam for monitoring the oscillation wavelength of the laser diode 1 is extracted using the optical system, the optical system does not become complicated.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, the present invention allows light emitted from a laser diode to pass through and guide it to a recording medium, and also allows light reflected by the recording medium to be transmitted. Taking advantage of the fact that the beam splitter reflects the emitted light from the laser diode to guide it to the reflected reading system, a wavelength filter is placed in the optical path where the emitted light from the laser diode is reflected by the beam splitter. Since the oscillation wavelength of the laser diode is detected by detecting the light transmitted through the laser diode, it is possible to detect the oscillation wavelength of the laser diode without installing a separate beam splitter to extract the light emitted from the laser diode. Therefore, the oscillation wavelength of the laser diode can be monitored with a simple optical system.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of an optical head device according to the present invention, FIG. 2 is an explanatory diagram showing spectral characteristics of the wavelength filter of FIG. 1, and FIG. 3 is a conventional optical head device. FIG. 4 is an explanatory diagram of the operation of the 1/2 wavelength plate, FIGS. 5 and 6 are explanatory diagrams of the operation of the polarizing beam splitter, and FIG. 7 is a waveform diagram showing the read signal. . DESCRIPTION OF SYMBOLS 1... Laser diode, 3... Beam splitter 6... Magneto-optical disk, 14... Wavelength filter, 1
5...Photodetector. Name of agent: Patent attorney Shigetaka Awano and one other person

Claims (1)

[Claims] a beam splitter that transmits the emitted light of the laser diode and guides it to the recording medium, and reflects the light reflected by the recording medium and guides it to the reading system; and an optical path through which the emitted light of the laser diode is reflected by the beam splitter. An optical head device comprising: a wavelength filter disposed in the wavelength filter; and means for detecting the oscillation wavelength of the laser diode by detecting light transmitted through the wavelength filter.