JPS63164035A - Optical guide type optical pickup - Google Patents

Abstract

PURPOSE:To detect the change in the distance of a disk as the change in the light collecting spot at the light receiving face by transmitting the light beam of light collection and divergence of the reflected return light from a disk through a transparent base used in common for the optical guide path and the diffraction grating in common obliquely. CONSTITUTION:The light emitted from the semiconductor laser 4 is coupled with the optical guide path 2 and propagated. The propagated light is radiated as a divergent beam in a direction deviated from the perpendicular direction of the base into space from the grating coupler 3 and collected onto the surface of an optical disk 6 by the focusing lens 5. The light reflected in the surface is changed for the intensity in response to the information recorded on the disk and reaches the base 1 through reverse path and a part is coupled to the path 2 by the grating 3. Then the light is transmitted through the transparent base 1 and the transmitted light is formed directly near the center of the photodetector 7 divided into four.

Description

Detailed Description of the Invention Field of the Invention The present invention relates to an optical waveguide type optical pickup, and more particularly to an optical pickup device for reading out information recorded on an optical recording medium such as an optical disk. The present invention relates to an optical waveguide-type optical beam guide using an optical waveguide with a built-in grating.

Conventional technology Optical pickups are basically semiconductor lasers.

It consists of an optical system light receiving element. FIG. 2 shows an example of a conventional read-only optical pickup on a practical level. Light emitted from a semiconductor laser 11 is reflected by a half mirror 12 and its direction is changed by a 46° mirror 13. The optical disc 1 is then squeezed by the focusing lens 14.
The light is focused on 5.

The light reflected on the surface of the optical disk travels the optical path backwards and reaches the half mirror 12, and a part of it passes through the half mirror.
An image is formed on a photodetector 14 through a concave lens 13, and information recorded on the disk is read out.

In this optical pickup, the optical system is arranged spatially, so there is a limit to how small and light it can be made.

In response, an integrated optical pickup was proposed to reduce the weight of the prototype. (References, Back, Journal of the Institute of Electronics and Communication Engineers, Volj68-c, 803.

86) Figure 3 shows a schematic diagram of an integrated optical pickup. Light emitted from a semiconductor laser 23 propagates through a dielectric optical waveguide 22 formed on a Si substrate 21 and is focused by a focusing grating coupler 24. A photonic light beam is emitted to the outside and irradiated onto the optical disc 25. The light reflected by the surface of the disk returns to the grating focusing lens 24 and propagates through the optical waveguide toward the light source again. Then, the propagation direction is changed by a focusing beam splitter 26 installed on the surface of the optical waveguide, and the light is focused on two pairs of light receiving elements 26.

The problem that the invention seeks to solve This integrated optical pickup has a miniaturized optical system.

Although it is possible to have a significant effect on weight reduction, in actual operation, the entire board must be moved to control focusing and tracking, and the disadvantage is that the device cannot necessarily be made smaller and lighter. have.

In addition, in this integrated optical pickup, since the arrangement of the optical system is completely fixed, changes in the effective refractive index of the waveguide layer due to manufacturing variations in waveguide film thickness and material composition, etc. The range of variation in the focusing position of the laser beam causes an increase in the spot diameter and is also a factor in the deterioration of performance. Furthermore, since the light containing information reflected from the disk is converted into guided light by the grating coupler 24 and then incident on the light receiving element by the focusing beam splitter, the light utilization efficiency is poor and the S/N will only deteriorate. First, as described above, the light receiving sensitivity is likely to deteriorate due to variations in the effective refractive index of the waveguide. Therefore, it has been extremely difficult to realize an integrated pickup with excellent productivity.

The present invention overcomes the problems of conventional optical pickups and integrated optical pickups as described above, and provides an optical pickup device that is small and lightweight, has high performance, and is easy to manufacture.

Means for Solving the Problems The present invention provides a transparent substrate having an optical waveguide layer disposed on a part or the entire surface thereof, and a diffraction grating having a specific shape formed on a part of the optical waveguide layer. Emitted light from a semiconductor laser is introduced into the optical waveguide layer, and the light propagating through the optical waveguide layer is emitted by the diffraction grating in a converging or diverging shape in a certain direction outside the substrate, and this beam is focused on the information recording medium directly or through a light-concentrating optical medium such as a lens, and the light reflected by the information recording medium is directed to the transparent substrate through the optical medium or directly in a direction perpendicular to the transparent substrate. The light is transmitted as a diverging or condensing light beam from different directions, and is focused on a condensing optical medium or directly on a light-receiving element divided into four or more regions, and detects information on the information recording medium. This is an optical waveguide type optical pickup with the following characteristics.

Function The present invention allows a converging or diverging light beam that is reflected and returned from an optical disk to pass obliquely through a transparent substrate that serves as both an optical waveguide and a diffraction grating, thereby reducing convergence in the vicinity of a light-receiving element. By changing the image position in the vertical and horizontal directions, it is possible to detect changes in the distance of the optical disc as changes in the shape of the focused spot on the light receiving surface.

EXAMPLE An example of the present invention is shown in FIG. 1 is a transparent glass substrate, 2 is an optical waveguide made of silicon nitride, and 3 is a grating coupler made of silicon dioxide film.

Now, the light emitted from the semiconductor laser 4 is coupled to the optical waveguide 2 and propagated. The grating coupler 3 emits the propagating light into space as a diverging beam in a direction deviated from the perpendicular direction of the substrate, and then the focusing lens 5 focuses the light onto the surface of the optical disk 6 . The intensity of the light reflected by this surface changes depending on the information recorded on the disk, and the light travels back along the optical path to reach the substrate 1. Some of the light is coupled to the optical waveguide 2 by the grating 3, but part of it is coupled to the optical waveguide 2 by the grating 3. The light is transmitted through the transparent substrate 1, and the transmitted light is directly imaged near the center of the light-receiving element 7, which is divided into four regions. The principles of focusing and tracking control in this case are exactly the same as those of the conventional optical pickup shown in FIG.

The characteristics of the optical pickup according to the present invention were in no way inferior to those using an ordinary optical system.

In this example, a glass substrate was used as the substrate 1, but it is not necessarily limited to glass substrates, and any material that is transparent to the oscillation wavelength of the laser used, such as lithium niobate or sapphire, can be used. is possible.

In addition, although a silicon nitride dielectric optical waveguide is used as the optical waveguide, it is not limited to this material.
Other dielectric or semiconductor materials may also be used. Further, a layer having a high refractive index may be formed as a waveguide layer on the surface of the substrate using an ion exchange waveguide or the like.

Furthermore, in this embodiment, a light-diverging grating coupler 3 is used, but it does not necessarily have to be light-divergent, and if a light-converging grating coupler is used, the surface of the optical disc 6 can be removed without the need for a focusing lens 6. The light is focused on. However, in this case, the reflected light toward the substrate becomes divergent, so it is converted into a condensing light beam using a convex lens or the like before or after passing through the substrate, and the light is condensed onto the light receiving element. That's fine.

As described above with reference to the embodiments, the effects of the invention are as follows.
As can be seen from the comparison with the figure, the present invention makes it possible to achieve smaller size and lighter weight while maintaining performance compared to conventional optical pickups, and the present invention has great industrial value. It is.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of an optical waveguide type optical pickup according to an embodiment of the present invention, FIG. 2 is a schematic perspective view of a conventional optical pickup at a practical level, and FIG. 3 is a schematic perspective view of a conventional integrated optical pickup. FIG. 1... Glass substrate, 2... Optical waveguide,
3... Grating, 4... Semiconductor laser, 6... Focusing lens, 6...
...Optical disk, 1o... Light receiving element. Name of agent: Patent attorney Toshio Nakao and 1 other person1-
Glass 1 Fu2 - Optical 4 Remaining path 3 - Grating cover 6 - Optical converter 7 - 4 split view Itector 1 Figure 11 - Razor 1 Diode 12 - Half mirror 13 - Concave lens I3 - Mirror - 14 - Fold Nullens (CCF Lens) Fig. 2 14-Photograph 15--Disk 21-S &''No ξ 24-Four 1 Singing Relay One Plaster 25-Single Isk No. 3 Fig. 25-Four One Single Singing Lens Splitter 26- Light receiving element

Claims (1)

[Claims] Emitted light from a semiconductor laser is introduced into the optical waveguide layer of a transparent substrate, in which an optical waveguide layer is disposed on a part or the entire surface of the transparent substrate, and a diffraction grating having a specific shape is formed on a part of the optical waveguide layer, The light propagating through the optical waveguide layer is emitted by the diffraction grating in a converging or diverging shape in a certain direction outside the substrate, and the light beam is emitted directly or through a condensing optical medium. Light that is focused on an information recording medium and reflected by the information recording medium is applied to the transparent substrate through an optical medium or directly as a diverging or converging light beam from a direction different from the perpendicular direction thereof. An optical waveguide type optical pickup configured to allow light to pass through and be directly focused on a light-concentrating optical medium or a light-receiving element divided into four or more regions, and detect information on the information recording medium.