JPS63146243A - Optical head device - Google Patents

Abstract

PURPOSE:To miniaturize an optical head device without deteriorating its characteristics by arranging a thin film wave guide element into a converging optical system so that the light beam is made incident on a grating coupler and receiving the light emitted from the end face of a thin film waveguide by a photodetector. CONSTITUTION:The light emitted from a semiconductor laser 1 is converged on a recording medium 5 via a collimator lens 2 and a convergent lens 3. The reflected light sent from the medium 5 is partly led into a thin film waveguide 8 as a converging beam by a grating coupler 9. Then this converging beam is demultiplexed into two pieces by a splitter 1 and made incident on a photodetector 7 provided on the end face of the waveguide 8. A thin film waveguide element 6 can be obtained by providing a waveguide and a grating element on a glass substrate by a sputtering process, etc., and via the dielectric substance of a high refractive index. Then it is possible to reduce the size of an optical head device without deteriorating its characteristics by converting a detecting optical system for reflected light into a thin film element.

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]

A conventional optical head device used for optical recording of optical discs and the like has a configuration as shown in Figure 5, which includes an optical system that focuses the emitted laser light onto the recording medium as a minute spot, and a system that collects the reflected light from the recording medium. It consists of a detection system that obtains a spot position error signal and an information signal from the spot.

FIG. 5 is a block diagram showing an example of the configuration of a conventional optical head device. In the same figure, the light emitted from the semiconductor laser 1 is transmitted through a collimating lens 2. Beam splitter 4. The light is focused as a minute spot on the recording medium via the condenser lens 3. The reflected light from this spot is separated from the laser output light by a beam splitter 4, and converged by a converging lens 11 and a splitting prism 12 onto two two-split photodetectors 7.

A focus error is detected from the differential output of each photodetector 7 using the principle of the Knifezi method, and a tracking error is detected from the difference between the sum components of the two photodetectors 7 using the principle of the push-pull method.

[Problem that the invention seeks to solve]

The conventional optical head described above is constructed by combining individual parts such as lenses and prisms, so it is large in size and heavy in weight. Therefore, it is possible to downsize the entire optical disk device and reduce the access time when searching for information. I couldn't do it enough.

As a method for downsizing an optical head device, a method using a waveguide element as shown in FIG. 6 has been proposed. FIG. 6 is a perspective view showing an example of the detector shown in FIG. 5, in which the emitted light of the semiconductor laser 1 is coupled to the end face of the thin film waveguide 8, and the condensed beam is directed to the recording medium by a condensing grating coupler 9. irradiate.

The reflected light from the recording medium is guided again to the thin film waveguide 8 by the grating coupler 9, further separated by the demultiplexer 13, and the end-emitted light is received by the photodetector 7.

Although this configuration makes it possible to downsize the optical head device, coupling the laser emitted light to the thin film waveguide 8 at the end face requires precision on the order of 1 μm, which is difficult to manufacture. In addition, in order to condense the light emitted by the grating coupler 9 into a spot of about 1 μm, the grating must be formed with an accuracy of 0.01 μm over an area of several mm2 or more, which has the disadvantage of making it even more difficult to manufacture. .

[Means for solving problems]

The optical head device of the present invention includes an optical head device that has an optical system that focuses the emitted light of a laser light source on a recording medium as a minute spot, and includes a grating that guides a part of the incident light into a thin film waveguide as a focused beam. A thin film waveguide element including a coupler and a splitter that splits the focused beam into two from the beam optical axis is installed in the optical system of the optical head device so that the light beam is incident on the grating coupler, and It is equipped with a photodetector that receives the light emitted from the end face of the thin film waveguide. Further, a photodetector for receiving guided light may be integrated on the thin film waveguide element.

[Effect]

In an optical head device, high utilization efficiency and low aberration are required for an optical system that condenses light emitted from a laser light source onto a recording medium. This is to focus the light on a minute spot. On the other hand, a system that detects reflected light has a large tolerance for aberrations if its characteristics change little due to temperature fluctuations.

Therefore, in the present invention, the reflected light detection optical system, which occupies more than half of the optical system in conventional optical head devices, is made into a thin film element, thereby realizing miniaturization without deteriorating the characteristics of the optical head device. ing.

〔Example〕

Next, the present invention will be explained with reference to FIGS. 1 to 4.

FIG. 1 is a block diagram showing an embodiment of an optical head device of the present invention. In the figure, light emitted from a semiconductor laser 1 is transmitted through a collimating lens 2. Recording medium 5 through condensing lens 3
Focus the light upward. A portion of the reflected light from the recording medium 5 is guided by the grating coupler into the thin film waveguide as a focused beam.

The thin film waveguide element 6 has a structure shown in FIG. 2, for example. FIG. 2 is a perspective view showing an example of the detection system in FIG. The light enters the detector 7.

As with the conventional optical head described above, the error detection signal can be obtained by the principle of the Knifezi method for focus errors, and by the principle of the push-pull method for track errors.

The thin film waveguide element 6 used here may be one in which a waveguide or a grating element is provided on a glass substrate using a dielectric material with a high refractive index by sputtering or the like.

FIG. 3 is a perspective view showing another example of the detection system in FIG. 1. The photodetector 7 may be integrated on a thin film waveguide 8 as shown in FIG. 3. If it is a glass substrate, a Si photodetector can be formed by vapor phase growth or the like.

Furthermore, if a transparent sapphire substrate is used, a detector can be constructed by epitaxially growing Si.

FIG. 4 is a block diagram showing another embodiment of the present invention.
Although the structure is simple without the collimating lens 2 shown in the figure, the same effect as the embodiment shown in FIG. 1 can be obtained.

Note that in these embodiments, coupling is performed from the film surface side to the thin film waveguide, but a configuration may also be adopted in which incident light from the substrate side is coupled to the thin film waveguide.

〔Effect of the invention〕

As explained above, the present invention includes installing a thin film waveguide element in a condensing optical system so that a light beam enters a grating coupler, and receiving light emitted from the end face of the thin film waveguide by a photodetector. This has the effect of making it possible to downsize the optical head device without deteriorating its characteristics.

[Brief explanation of the drawing]

1 and 4 are block diagrams showing one embodiment of the optical head device of the present invention and other embodiments, and FIGS. 2 and 3 show an example of the detection system in FIG. 1 and another example. FIG. 5 is a block diagram showing an example of the configuration of a conventional optical head device, and FIG. 6 is a perspective view showing an example of the detection system in FIG. 5. 1... Semiconductor laser, 2... Collimator lens, 3
... Condensing lens, 4... Beam splitter, 5...
- Recording medium, 6... Thin film waveguide element, 7... Photodetector, 8... Thin film waveguide, 9... Grating coupler, 10... Divider, 11... Converging lens , 12...
・Split prism, 13... splitter. , ( ≧≧r5 Pu 1 ear〈] 6 Kuzu Z diagram

Claims (2)

[Claims] (1) In an optical head device having an optical system that focuses emitted light from a laser light source onto a recording medium as a minute spot,
A thin film waveguide element comprising a grating coupler that guides a part of the incident light as a focused beam into the thin film waveguide and a splitter that splits the focused beam into two from the beam optical axis is included in the optical system of the optical head device. An optical head device comprising: a photodetector installed so that a light beam is incident on the grating coupler; and a photodetector configured to receive light emitted from the end face of the thin film waveguide. (2) An optical head device according to claim (1), in which a photodetector for receiving guided light is integrated on a thin film waveguide element.