JPH0246536A - Optical pickup device - Google Patents

Abstract

PURPOSE:To miniaturize and lighten an optical pickup by guiding a reflecting light from an optical disk to a light waveguide path by plural diffraction gratings and after the light is propagated to a constant distance or above in plural directions in the light waveguide path, radiating to the external part of the light waveguide path and making it incident on plural light receiving elements different from the light waveguide path. CONSTITUTION:The light radiated from a semiconductor laser 1 transmits a transparent substrate 2, diffused and converged to the surface of an optical disk 4 by a condensing lens 3. A reflecting light from the optical disk 4 transmits the condensing lens 3 again and returns to the semiconductor laser 1, a part is guided to a light waveguide path 6 by an input grating coupler 5, propagated toward an output grating coupler 7, radiated by the grating coupler 7, arrives at a light receiving element 8 of another body and the signal is detected. At this time, since the light is propagated into the waveguide path 6 by the grating coupler 5, even when the light receiving element 8 is away from the laser 1, the laser 1 and a transparent substrate 2 can be made close to about several mum. Thus, the pickup can be miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical information processing device for recording and reading out information stored in an optical storage medium such as an optical disk or a magneto-optical disk using a laser beam. An optical pickup that uses laser light to record and read information stored in an optical storage medium uses a semiconductor laser as a light source, the semiconductor laser, and a device for converging the light emitted from the semiconductor laser onto the optical storage medium. Optical lens, beam splitter that guides the laser beam reflected by the optical storage medium to the light receiving element, adds astigmatism to the reflected light, makes it possible to detect the defocus of the light converged on the optical storage medium, and receives the light. It is configured to include a cylindrical lens for forming an image on the element, and a light receiving element for receiving reflected light and detecting focal deviation, tracking deviation, and information stored in the optical storage medium.

Normal optical pickups use a beam splitter to guide the laser light reflected by the optical storage medium to the light receiving element, and apply astigmatism to the reflected light to correct the focal shift of the light converged on the optical storage medium. Since a cylindrical lens or the like is required to enable detection and form an image on the light-receiving element, the number of optical components increases, making it difficult to align the optical axis and making the manufacturing cost expensive.In addition, the optical pickup can be made smaller. It was a big problem in doing so.

Therefore, in order to achieve miniaturization, an optical pickup was announced in which a hologram element was used to replace the conventional optical pickup with a hologram element that can simultaneously function as both a beam splitter and a cylindrical lens. [References, Moku et al., 22nd Micro-Optics Research Kanawa Bun, vol.
14.228 ('86)] A schematic diagram of this hologram type optical pickup is shown in FIG. semiconductor laser 61
The emitted light passes through a hologram lens 62 and is focused on the surface of an optical disk 64 by an imaging lens 63. The light that is reflected and spread by the surface of the optical disk 64 with an intensity corresponding to the recorded information is converged again by the imaging lens 63, and
A part returns to the semiconductor laser 61, but a part returns to the two regions (
The hologram element 62 is divided into two parts (R1, R2), and the image is focused on the four-divided light receiving element 65, and the focus shift is detected by the so-called Naifezi method, and the tracking shift and the optical memory are detected. A signal of information stored on the medium is detected.

There have also been proposals to integrate a hologram element and a light-receiving element on a glass substrate. [Part 6 Heh.

References, Sunagawa et al., 1985 National Conference of the Optical and Radio Division of the Institute of Electronics and Communication Engineers] The outline of this optical pickup is shown in Figure 6. Light emitted from a semiconductor laser (LD) 71 passes through a collimation lens 72 and an objective lens 73, and is focused onto an optical disk 74. The reflected light from the optical disc is
An optical waveguide 75 on a substrate 70 installed between the two lenses is guided by a condensing grating coupler 76, 77, and two sets of light receiving elements 78, 79 are formed.

80.81. Focus error is detected using the Foucault method.

Problems to be Solved by the Invention However, in the above-mentioned hologram type optical pickup, the light receiving element cannot be installed unless the distance between the hologram element and the semiconductor laser is at least a certain distance (several meters). Furthermore, it was extremely difficult to adjust the positional relationship between the hologram and the light receiving element. Although optical waveguide-type optical pickups still have the potential to be miniaturized, they still require a light-receiving element to be formed on the optical waveguide, which increases costs and requires an element that operates at high sensitivity and high speed as a light-receiving element. It is difficult to form. For example, using amorphous silicon.

Although it is relatively easy to form a light-receiving element on a substrate such as glass, the response speed is slow at several hundred kbit/s, and the information stored on an optical disk cannot be processed at a speed of several tens of Mbit/s, which is required for practical use. It is difficult to read at a speed of

The present invention overcomes these problems and provides a small, lightweight, and high-performance optical pickup.

Means for Solving the Problems The present invention provides a semiconductor laser for emitting light, an optical lens for converging the light emitted from the laser onto an optical storage medium, and an optical path of the light reflected by the optical storage medium. an optical waveguide in which a grating coupler is formed, and the reflected light is coupled to the optical waveguide.

an optical coupler that emits the light propagating through this optical waveguide to the outside;
and an optical pickup including an optical waveguide and a separate light receiving element for detecting emitted light. Divergent lens means may still be used to widen the divergence angle of the light emitted from the laser.

Effects of the present invention The reflected light from an optical disk is guided to an optical waveguide by a plurality of diffraction gratings, propagated in a plurality of directions within the optical guide for a certain distance or more, and then radiated to the outside of the optical waveguide and transmitted to a plurality of optical waveguides separate from the optical waveguide. By making the light incident on the light-receiving element, the optical pickup can be made smaller and lighter, and a high-speed, high-sensitivity light-receiving element can be used, resulting in a high-performance optical pickup.

Examples Details of the optical pickup of the present invention will be explained using examples. FIG. 1 schematically shows the pickup of the present invention, with arrows indicating light propagation conditions. Light emitted from the semiconductor laser 1 is transmitted through the transparent substrate 2 and diverged, and is focused onto the surface of the optical disk 40 by the condenser lens 3. The reflected light from the optical disk 4 passes through the condenser lens 3 again and tries to return to the semiconductor laser 1, but a part of it is guided to the optical waveguide 6 by the input grating coupler 5 and propagates toward the output grating coupler 7. The signal is radiated to the grating coupler 9 at one output, reaches the separate light receiving element 8, and the signal is detected.

FIG. 2 schematically shows the surface of a substrate on which the optical waveguide of the present invention is formed. A grating coupler 5 (sa, 5b, 50.5d) divided into four parts is formed on the surface of a transparent substrate. This grating coupler is a diverging grating coupler that couples guided light and diverging light. Conversely, when convergent light is incident on the grating coupler, it is converted into guided light.

The convergent light incident on the couplers sa, sb, sc, and 5d becomes almost parallel light and travels through the waveguide.

The output grating couplers γ (γa) propagate in the directions of arrows 9a, 9b, 9c, and 9d and have a parallel shape.

7b, 7C, 7d) and is radiated into space.

Four separate light receiving elements 5 (sa, sb, sc.

8d).

Incidentally, a divergent grating coupler has a characteristic that the coupling efficiency deteriorates if the set focal point position and the actual convergence point of light differ. Therefore, the set focal length of couplers 5a and 5d is f. +Δf is set to 107, -7, and the focal length of coupler sc and 5b is set to f. -Δf. Here f. is the focal length when the semiconductor laser is focused to the minimum on the surface of the optical disk.

Then, when the optical disk approaches the converging lens, the convergence distance becomes longer, and the coupling efficiency between grating couplers 5a and 6d becomes better than the coupling efficiency between grating couplers 5b and 50. Therefore, the outputs of the light receiving elements sa and sd are also larger than the outputs of the elements 8b and 80. Therefore, Motoko Ba
, sb, 8c.

If the output of 8d is person, B, C, D, (A+D)>
(B+C). On the other hand, when the optical disk moves away from the converging lens, a focused signal with (A+D)<(B-1) is obtained. Also, if the track direction of the optical disk is perpendicular to the propagation direction of the guided light in Figure 2, (Jinshi G)
A tracking signal is obtained by -(B+D). Further, the signal stored on the optical disk is obtained as (A+B+C+D).

According to the pickup shown in FIG. 1, it is possible to use grating couplers 5 and 7 for input and output, and to use something similar to single crystal S1 as the light receiving element 8, and the response speed is several tens of Mbit. /s ~ number 100
Mbit/s can be obtained and it can be put to practical use.

In addition, in FIG. 1, since the grating coupler 5 propagates through the waveguide 6, even if the light receiving element 8 is separated from the laser 1, the laser 1 and the transparent substrate 2 can be brought close to each other within several μm, making the pickup compact. can be achieved.

Note that the laser 1 is preferably a DFB (distributed feedback) laser. The wavelength of a typical semiconductor laser varies depending on current, temperature, etc., and the amount of light guided into an optical waveguide varies greatly.

Therefore, a DFB laser with little wavelength fluctuation is suitable.

A second embodiment of the invention is shown in FIG.

The light emitted from the semiconductor laser 1 is transmitted through the concave lens 1° to the transparent substrate 2 as a highly divergent beam, and is focused onto the surface of the optical disk 4 by the condensing lens 3. The reflected light from the optical disk tries to return to the semiconductor laser 1 through the condensing lens 3 again, but a part of it is guided to the optical waveguide 6 by the input grating coupler 5, propagates toward the output grating coupler 7, is emitted, and passes through the concave lens. 1
It reaches the light receiving element 8 through o.

The principle of signal detection is exactly the same as the embodiment shown in Fig. 1, but compared to Fig. 1, by using the concave lens 1o,
For example, the distance between the semiconductor laser 1 and the condensing lens 3 is set to 6rr.
It can be shortened to less than a.

In FIG. 1, approximately I Cm is required. Furthermore, the feature of the optical pickup shown in FIG. 3 is that the distance between the semiconductor laser 1 and the converging lens 3 can be shortened in this way, which has been difficult to achieve with conventional hologram-type optical pickups.

Another embodiment of a semiconductor laser device that can be used in the optical pickup of the present invention is shown in FIG. As shown in Figure 4,
The same functional parts as in FIG. 3 are given the same numbers, and the condenser lens 3 and optical disk 4 are omitted from the figure. This laser device includes a semiconductor laser 1, a light receiving element 8, an optical waveguide 6. The concave lens and grating couplers 5, 7 are mounted on the same mount. 41 is a cap, and 42 is a Si sub-13K'.

A laser 1 is mounted on a mount, and a plurality of divided light receiving elements 8 are installed on a mount 9.

Concave lens 10. optical waveguide 6 and grating coupler 5,
7 is installed on a transparent substrate 2, the transparent substrate 2 also serves as a top cap, the inside is sealed with this and a side cap 41, and an inert gas is sealed inside.

By using the semiconductor laser device of this embodiment, the optical pickup can be made smaller.

In this embodiment, a concave lens 10 is installed.

It is not necessary to install the concave lens 10, and in this case, the optical pickup is similar to the optical pickup of the first embodiment.

According to FIG. 4, the light receiving element 8 and the laser 1 are integrated and sealed in the same mount, making it easy to align the element 8 and the laser 1, easy to assemble, and high reliability. structure can be realized.

In a detailed embodiment of the present invention, the grating coupler is simply formed on a transparent substrate, but the transparent substrate or the medium for forming the grating is an anisotropic refractive index material such as lithium niobate or liquid crystal.

It is possible to increase the efficiency of light utilization by using an optical medium that has the properties of light and combining it with a VL wave plate or the like.

Effects of the Invention As shown above, the present invention overcomes the problems of conventional optical pickups and provides a small, lightweight, and high-performance optical pickup, which is of great value for optical information processing devices. .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical pickup according to an embodiment of the present invention;
FIG. 2 is a plan view of a substrate on which an optical waveguide used in the same embodiment is installed, FIG. 3 is a schematic diagram of an optical pickup according to another embodiment of the present invention, and FIG. 4 is a semiconductor laser device used in the present invention. FIGS. 5 and 6 are schematic diagrams of an example of a conventional optical integrated pickup and a conventional hologram type optical pickup. 1... Semiconductor laser, 2... Transparent substrate, 3
...Focusing lens, 4. River... Optical disk, 5.
River/input grating, 6... Optical waveguide, 7
...Output grating, 8,8...
Light receiving element. ward eagle r 澾 ward U) castle a) O- toi 8mi

Claims (9)

[Claims] (1) A semiconductor laser that emits light, an optical lens that focuses the light emitted from the laser onto an optical storage medium, and is arranged in the optical path of the light reflected by the optical storage medium so that the reflected light is combined. An optical pickup device comprising an optical waveguide on which a grating coupler is formed, an optical coupler for emitting light propagating through the optical waveguide to the outside, and a light receiving element for detecting the emitted light. (2) a semiconductor laser that emits light; a diverging optical lens for expanding the divergence angle of the light emitted from the laser;
an optical lens for converging the diverging light onto an optical storage medium, an optical waveguide formed with a grating coupler disposed in the optical path of the light reflected by the optical storage medium and to which the reflected light is coupled; An optical pickup device comprising: an optical coupler that emits light propagating through a wave path to the outside; and a light receiving element that detects the emitted light. (3) The optical pickup device according to claim 1 or 2, wherein the grating coupler is a plurality of divergent grating couplers. (4) The optical pickup device according to claim 3, wherein a plurality of light receiving elements are installed corresponding to the plurality of grating couplers. (5) The optical pickup device according to claim 1 or 2, wherein the divergent grating coupler has two or more focal lengths. (6) The optical pickup device according to claim 1 or 2, wherein the optical coupler that emits the light propagating through the optical waveguide to the outside is a grating coupler. (7) The optical pickup device according to claim 1 or 2, wherein the diffraction grating is formed of an optical medium having refractive index anisotropy. (8) A semiconductor laser and a plurality of light receiving elements are arranged on the same mount, and the laser is sealed with a transparent substrate on which the grating coupler, optical coupler, and optical waveguide are formed. The optical pickup device according to scope 1 or 2. (9) The optical pickup device according to claim 8, characterized in that a concave lens is interposed between the transparent substrate on which the optical waveguide is formed and the semiconductor laser.