JPH0836778A - Optical head - Google Patents

Abstract

PURPOSE:To reduce in size and weight an optical head, to delete the number of optical components, to facilitate an optical adjustment and to decrease the cost by providing a diffraction grating structure in an optical branching filter. CONSTITUTION:The reflected light of an information carrier 5 is reflected and diffracted by a diffraction grating structure 7 provided at the part of the second surface 6 via an objective lens 4 and the first surface 3 of an optical branching filter 2, reflected on the first surface 3 and the second surface 6 and made incident on a photodetector 8. Since the structure 7 is divided into areas 8-10 so that the grating directions of the structures are different from each other, the lights diffracted in the areas are divided by the photodetectors 8 into photoreceivers 11-14. In this case, when the distance between the lens 4 and the carrier 5 is varied, the incident angle and diameter of the incident luminous flux from the carrier 5 to the filter 2 are altered. The diffracted light in the area 8 is deflected in the direction of arrow B, the difference of the detection signals of the photoreceivers 11, 12 is obtained and a focus error signal can be obtained. The dividing lines of the areas 9, 10 are photoelectrically detected by the photodetectors 13, 14, and a tracing error signal can be obtained by the difference.

Description

Detailed Description of the Invention

[0001]

The present invention relates to irradiating an information carrier with light,
The present invention relates to an optical head device that optically records or reproduces information.

[0002]

2. Description of the Related Art In recent years, compact discs on which digitized audio is recorded with unevenness on the surface and video discs on which TV images are recorded have become remarkably popular.

In particular, compact disc players are greatly expected to advance from a stationary type to a portable type that can be freely carried or a player mounted on a vehicle.

These optical information recording / reproducing apparatuses are required to be thin, small and inexpensive as demands from the user side. Therefore, the optical head apparatus for recording / reproducing information on / from the information carrier as described above is also the same. The demand for is increasing.

FIG. 9 is a block diagram showing an example of a conventional optical head device.

In the figure, the divergent light beam emitted from the laser light source 41 enters the collimator lens 42 to become a parallel light beam, and enters the polarization beam splitter 43. Here, the polarization beam splitter 43 has a characteristic of transmitting almost 100% of linearly polarized light having an oscillating surface in a specific direction and reflecting almost 100% of linearly polarized light having an oscillating surface in a direction orthogonal thereto. .

The linearly polarized light that has passed through the polarization beam splitter 43 passes through the λ / 4 plate 44 to become circularly polarized light, which is condensed by the objective lens 45 onto the information recording surface 47 provided on the substrate 46 of the information carrier. A spot having a spot diameter of about 1 μm is formed.

The light beam reflected by the information recording surface 47 passes through the objective lens 45 to become a parallel light beam,
After passing through the four plates 44, it becomes a linearly polarized light whose vibrating surface is orthogonal to that at the time of incidence, and re-enters the polarization beam splitter 43. Here, the polarization beam splitter 43 functions as a light splitter due to the characteristics as described above, reflects the reflected light from the information recording surface 47 and separates it from the incident light, and focuses it via the sensor lens 48 and the cylindrical lens 49. The light beam is guided to the photodetector 50.

When information is recorded using such an optical head device, the laser light source 41 is driven in accordance with the information signal to modulate the intensity of light incident on the information recording surface 47. When detecting information, unmodulated light is applied to the information recording surface 47 on which information is recorded due to uneven pits or changes in reflectance, and the reflected light modulated by this recorded information is applied. Detected by the photo detector 50,
Play the information. Further, the photodetector 50 has its light-receiving surface divided into four parts, and in combination with the cylindrical lens 49, the focus error signal is detected by a known method (so-called astigmatism method).

[0010]

However, in the above-mentioned conventional optical head device, it is necessary to arrange many optical components of the polarization beam splitter and the photodetector in the space, and mutual position adjustment for that purpose is required. It was complicated.

Further, since the number of parts is large, it is difficult to downsize the device, and many manufacturing processes are required, resulting in high cost.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an optical head device suitable for miniaturization and weight reduction and capable of working at low cost.

[0013]

The above object of the present invention is to provide a light source and light emitted from the light source which is reflected by a first surface to be guided to an information carrier and which transmits the light from the information carrier on the first surface. In an optical head device comprising a light splitting device and a photodetector that detects light from the information carrier, the first surface is transmitted to a second surface parallel to the first surface of the light splitter. This is accomplished by providing a diffraction grating structure that diffracts the light and directs it to the photodetector.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings.

1A and 1B show an outline of a first embodiment of an optical head device according to the present invention. FIG. 1A is a schematic sectional view, and FIG.
FIG. 3 is a plan view of the light splitter 2.

In FIG. 1, a light source 1 such as a semiconductor laser
The light flux emitted from is reflected by the first surface 3 of the light splitter 2 and is condensed by the objective lens 4 as a minute spot on the information recording surface of the information carrier 5. The reflected light from the information carrier 5 again passes through the objective lens 4 and the first surface 3 of the light splitter 2, and is diffracted on a part of the second surface 6 parallel to the first surface 3. The light is reflected and diffracted by the grating structure 7 to change its direction, and is incident on the photodetector 8 while being totally reflected between the first surface and the second surface. The diffraction grating structure 7 provided on the first surface and the second surface of the light splitter may be provided with a reflection film so that a desired reflectance or diffraction efficiency can be obtained, if necessary.

The diffraction grating structure 7 is divided into three regions of 8, 9, and 10 as shown in (B), and the directions of the gratings of the respective diffraction grating structures are different. As a result, the light diffracted in these regions is guided to the divided light receiving portions 11 and 12, 13 and 14 of the photodetector 8, respectively. Here, when the distance between the objective lens 4 and the information carrier 5 is changed, it is well known that the light splitter 2 moves from the information carrier 5 to the information carrier 5.
The incident angle and the incident diameter of the light beam incident on are changed.
Then, the light diffracted by the region 8 deviated from the optical axis sways in the direction of arrow B according to the above fluctuation. Therefore, the focus error signal can be obtained by subtracting the detection signals of the light receiving units 11 and 12.

On the other hand, the regions 9 and 10 of the diffraction grating structure 7 are
The dividing lines are provided in parallel with the information tracks on the information carrier 5, and the light receiving units 13 and 14 photoelectrically detect the light intensity distributions in the far field patterns obtained by dividing the information tracks. Then, a tracking error signal is obtained by using the so-called push-pull method by subtracting these detection signals. Further, when reproducing the information on the information carrier, the reproduction signal can be obtained from the sum signal of all or a part of the light receiving units 13, 14, 15, 16.

The focus error signal and the tracking error signal are fed back to a lens driving mechanism (generally called an actuator) not shown in FIG. 1 to move the objective lens 4 in the optical axis direction and the direction perpendicular to the optical axis. Focusing and tracking are performed by. The optical head device of FIG. 1 uses a thin optical splitter and can be configured integrally with a photodetector by sticking or the like. Therefore, the optical head device is suitable for downsizing and weight reduction, and since the number of optical parts is small, optical adjustment is easy and reliable. It has high properties and can be manufactured at low cost.

Next, a method of manufacturing the optical splitter used in the present invention will be described.

FIGS. 2A, 2B, and 2C are schematic cross-sectional views sequentially showing an example of a manufacturing process of the optical splitter. First, a material such as phosphorus-purified copper is cut by a diamond cutting tool to form a plurality of bridge gratings corresponding to the respective areas of the diffraction grating structure 7. Then, these piece lattices are combined and put into a die that holds the whole to form the forming die 15. Each of the above-mentioned piece lattices may be created by dividing a lattice that is integrally machined. Next, as shown in FIG. 2 (A), this mold is pressed against a molding material such as acrylic resin, polycarbonate, or glass, and the grating mold is transferred to obtain a diffraction grating structure as shown in FIG. 2 (B). A light splitter 16 having a body is obtained. Also, if necessary, FIG. 2 (C)
As shown in, the reflection film 17 may be formed on the diffraction grating structure by vapor deposition or sputtering to improve the reflectance and the diffraction efficiency. In FIG. 2C, at the grating angle α of the diffraction grating structure formed on the second surface of the light splitter 16, the light beam 18 incident from the first surface 23 is reflected and diffracted, and this diffracted light 19 is It is desirable to set the light so that the light is totally reflected by the first surface 23 and is guided to the photodetector with a small light amount loss.

FIGS. 3A, 3B, and 3C are schematic cross-sectional views sequentially showing the steps of another method for manufacturing the optical splitter. First, a resin (epoxy resin, photopolymer resin, etc.) is poured between the molding die 20 and the molding material 21 in which a lattice is formed as in 15 of FIG. Apply energy such as to cure. And the molding die 20
When is removed, the diffraction grating structure is formed as shown in FIG. Next, as shown in FIG. 3C, a reflective film 24 is formed on the diffraction grating structure as required,
The light splitter 25 is produced.

In the above manufacturing method, when the lattice formed on the molding die is a simple linear shape or a conical shape as in the embodiment described later, it can be easily processed by a ruling engine or a precision lathe. . Also, when a complicated shape such as an ellipse, a parabola or a hyperbola is required as the shape of the grating, a resist grating can be formed by hologram exposure or electron beam drawing, and a blazed grating can be produced by a processing method such as ion beam etching. Further, various well-known methods such as a method of machining a lattice with an NC machine tool may be used.

4 to 8 respectively show other embodiments of the optical head device to which the present invention is applied. In the drawings, the same members as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. .

FIG. 4 shows an example in which the photodetector 8 arranged on the objective lens 4 side in FIG. 1 is arranged on the light source side. In this example,
There is an advantage that the photodetector 8 is less susceptible to the electromagnetic noise generated by the actuator for moving the objective lens 4.

FIG. 5 shows an example in which the dividing line AA ′ of the diffraction grating structure 7 of the optical splitter 2 is inclined by θ with respect to the surface of the information carrier 5, where (A) is a schematic sectional view and (B) is. The top view of the light splitter 2 is shown. The configuration of this example has an advantage that the entire optical pickup can be made thinner than the example of FIG. 1 because the waveguide direction of light in the optical splitter is substantially parallel to the surface of the information carrier 5.

Up to this point, an example using a so-called finite imaging system has been shown. However, this system is conspicuous when the surface of the record carrier is large and the objective lens must follow a long stroke. There is a problem that the image magnification changes and the spot diameter on the record carrier changes. An example of solving such a problem is shown below.

FIG. 6 shows an example in which a collimator lens 26 is arranged between the light splitter 2 and the objective lens 27. Since the light incident on the objective lens 27 is parallel light, the above-mentioned problem occurs. Absent.

FIG. 7 shows an example in which a collimator lens 28 is arranged between the light source 1 and the light splitter 29. FIG. 7A is a schematic sectional view and FIG. 7B is a plan view of the light splitter 29. Light splitter 2
The light flux reflected by 9 is focused on the information carrier 5 by the objective lens 30. In this example, the reflected light from the information carrier 5 is the light splitter 2
Since the parallel light beam is mainly incident on 9, the grating portion of the diffraction grating structure 31 preferably has a curvature as shown in (B), and the light beam is condensed by the grating having the curvature,
It is guided to the photodetector 8.

The embodiment shown in FIG. 8 is an example in which an optical path conversion mirror 32 is arranged between the light splitter 2 and the objective lens 4. In the case of this example, the optical path conversion mirror 32 has a feature that the effective area of the reflection part is slightly larger than the spread of the light flux, and therefore the optical head device can be made thinner than other examples.

The present invention is not limited to the embodiment described above,
Various applications are possible. For example, the direction in which the diffracted light is generated can be arbitrarily determined according to the design of the focus error and tracking error detection system.

Further, in the above-mentioned embodiments, the optical medium in the optical path leading to the photodetector is shown as a substance having a single refractive index, but in the implementation, the optical path leading to the photodetector is shown. It is also possible to dispose a transparent plastic such as acrylic or epoxy, or an air layer therein.

[0033]

As described above, according to the present invention, in the conventional optical head device, since the diffraction grating structure is provided in the optical splitter, the size and weight of the device can be reduced and the number of optical parts can be reduced. As a result, the effect of facilitating the optical adjustment and reducing the manufacturing cost can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of an optical head device of the present invention.

2A to 2D are schematic cross-sectional views illustrating a manufacturing process of an optical splitter used in the present invention.

3A to 3D are schematic cross-sectional views illustrating a manufacturing process of an optical splitter used in the present invention.

FIG. 4 is a schematic view showing another embodiment of the optical head device of the present invention.

FIG. 5 is a schematic view showing another embodiment of the optical head device of the present invention.

FIG. 6 is a schematic view showing another embodiment of the optical head device of the present invention.

FIG. 7 is a schematic view showing another embodiment of the optical head device of the present invention.

FIG. 8 is a schematic view showing another embodiment of the optical head device of the present invention.

FIG. 9 is a schematic view showing an example of a conventional optical head device.

[Explanation of symbols]

 1 light source 2 light splitter 4 objective lens 5 information carrier 7 diffraction grating structure

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroaki Hoshi Inventor Hiroaki Hoshi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Dai Ozawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Mitsuhiro Hasegawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masakuni Yamamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (1)

[Claims] 1. A light source, a light splitter that reflects light emitted from the light source on a first surface and guides it to an information carrier, and transmits light from the information carrier on the first surface, and an optical splitter from the information carrier. An optical head device comprising a photodetector for detecting light, wherein the first surface is provided on a second surface of the light splitter parallel to the first surface.
An optical head device comprising a diffraction grating structure that diffracts light transmitted through a surface and guides the light to the photodetector.