JPH06290482A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To arbitrarily set the angle of a reflected light beam being polarized/ splitted from an optical information recording medium by utilizing a prism on which a grating is formed and a photodetector. CONSTITUTION:The device is provided with an objective lens 9 converging a light beam emitted from a semiconductor laser light source 1 on an optical information recording medium 20 and a half mirror 5a having a light beam splitting surface for separating the reflected beam by the recording medium 20 from the optical path started from the light source 1. The device is also provided with a grating prism 12 splitting the reflected light beam splitted by the mirror 5a into mutually orthogonal polarization components by means of a transmission type grating surface formed on an entrance end surface and having periodicity and transmitting the components from an exit end surface not parallel to the entrance end surface and a photodetector 13 having two light receiving areas receiving two light beams splitted by the prism 12. respectively. Consequently, an angle between the separated light beams is made small and a distance between the grating surface and the light receiving area and the angle of the photodetector 13 in reference to an optical axis are arbitrarily set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for recording or reproducing information on a recording medium such as a magneto-optical disk, and more particularly to an apparatus using a grating for polarization separation of a light receiving system. .

[0002]

2. Description of the Related Art An optical information recording / reproducing apparatus for separating polarized light using a grating of this type is disclosed in, for example, Japanese Patent Laid-Open No. 3-15.
No. 2428, etc. This publication discloses a polarization detecting device in which a grating and a light receiving element are integrally configured.

[0003]

However, since the above-mentioned conventional optical information recording / reproducing apparatus uses the flat plate-shaped grating element, the angle between the separated light beams is large, and the light receiving area is formed on the same plane. The distance between the grating surface and the light-receiving region is set to be quite small in order to secure the distance, which makes it difficult to perform alignment during manufacturing or assembly.

In addition, it is necessary to incline the light receiving element with respect to the optical axis by a certain angle, which makes positioning difficult.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and it is possible to reduce the angle between the separated light fluxes, the distance between the grating surface and the light receiving region, and An object of the present invention is to provide an optical information recording / reproducing apparatus capable of arbitrarily setting the angle of the light receiving element with respect to the optical axis.

Another object of the present invention is to provide an apparatus capable of detecting an information signal and an error signal recorded on a medium by using a common light receiving area.

[0007]

In order to achieve the above object, an optical information recording / reproducing apparatus according to the present invention has a light source, an objective lens for converging a light beam emitted from the light source onto an optical information recording medium, and an optical information. The light beam splitting surface that separates the reflected light from the recording medium from the optical path from the light source, and the reflected light that is separated by the light beam splitting surface are polarized orthogonally to each other by the periodic transmission type grating surface formed on the incident end surface. A grating prism that separates the light into components and emits the light from an emission end surface that is not parallel to the incident end surface, and receives two light beams separated by the grating prism 2
And a light receiving element having one light receiving region.

[0008]

EXAMPLES Examples of the optical information recording / reproducing apparatus will be described below. FIG. 1 shows an optical system of a magneto-optical disk device as an optical information recording / reproducing device according to an embodiment of the present invention.

A divergent light beam emitted from a semiconductor laser 1 as a light source is made into a parallel light beam by a collimator lens 2 and shaped into a circular cross section by two anamorphic prisms 3 and 4. A rectangular prism 5 is joined to the anamorphic prism 4, and the joining surface is a half mirror surface 5a. The light flux reflected by the half mirror surface 5 a is condensed by the condenser lens 6 on the light receiving element 7 for automatic output adjustment of the semiconductor laser 1.

The light flux transmitted through the half mirror surface 5a is reflected by the mirror 8 and is converged on the signal recording surface of the magneto-optical disk 20 as an optical information recording medium via the objective lens 9. The objective lens 9 and the mirror 8 are provided in a head (not shown) that slides in the radial direction x of the magneto-optical disk 20. The objective lens 9 is provided on an actuator provided in the head, and is driven in the optical axis direction z and the radial direction x of the disk.

On the other hand, the light beam reflected from the magneto-optical disk 20 is reflected by the half mirror surface 5a as a light beam separating surface, the polarization direction is rotated by 45 ° by the λ / 2 plate 10, and is converged by the condenser lens 11. The light is made incident on the grating prism 12. The light beam incident on the grating prism 12 is separated into 0th-order diffracted light and 1st-order diffracted light by the grating surface formed on the incident end face, and reaches two light-receiving regions formed on the light-receiving element 13. The light receiving element 13 is provided perpendicularly to the optical axis of the reflected light from the disk, and its positioning is easier than that of the conventional device.

In the signal detection optical system of the optical information recording / reproducing apparatus of the embodiment, as shown in FIG. 2, the light beam incident through the λ / 2 plate 10 and the condenser lens 11 is divided into first-order diffracted light and zero-order diffracted light. And a light receiving element 13 having two light receiving regions 13a and 13b for receiving the light beams separated by the grating prism 12 are integrally formed. 2, (a) is an explanatory view in the xy plane in FIG. 1, (b) is an explanatory view in the yz plane, and (c) is an explanatory view in the xz plane.

The grating prism 12 is shown in FIG.
As shown in, the grating surface formed on the incident end face separates the vibration component parallel to the groove of the grating of the light beam incident at the Bragg angle and the vibration component as the 0th-order diffracted light and the 1st-order diffracted light, and separates them. One of the 0th-order diffracted lights is emitted from the exit end face as it is, and the other 1st-order diffracted light is internally reflected and then emitted from the exit end face in parallel with the 0th-order diffracted light.

The specific numerical configuration of the grating prism 12 is as shown in Table 1 (a). In the table,
The angle of the apex facing the grating surface of the prism is θ
c, the angles of the remaining vertices are θa and θb, the refractive index of the prism is n, and the incident angle of the light beam on the grating surface is θ.
in, the pitch of the grating pattern is p, and the wavelength used is λ. Both the incident angle and the exit angle are angles with respect to the normal line of the surface.

[0015]

[Table 1] Working wavelength λ 0.780 (μm) Grating pitch p 0.4875 (μm) λ / p 1.600 Refractive index n 1.51072 Incident angle θ in 53.13 (deg.) First-order light diffraction angle 31.98 (deg.) Zero-order light diffraction angle 31.97 (deg.) Primary light exit angle 20.59 (deg.) Zero order light exit angle 20.59 (deg.) Prism apex angle θa 53.13 (deg.) Prism apex angle θb 90.00 (deg.) Prism apex angle θc 36.87 (deg. )

When the incident angle of the light beam on the grating is set to the Bragg angle and the ratio λ / p between the wavelength λ and the grating pitch p is set to about 1.6, the vibration component parallel to the groove of the grating is parallel. The oscillating component is distributed to the 0th-order diffracted light and the 1st-order diffracted light, and the polarization separation characteristic by the grating becomes the best. By satisfying this condition, the grating prism 12 separates the incident light flux into two polarized light components of P component and S component and emits them.

Since the polarization direction of the laser light reflected by the magneto-optical disk 20 is rotated by the magnetic Kerr effect in accordance with the magnetization direction of the disk at the position where the spot is imaged, it is rotated by 45 ° to be 2 °. The magneto-optical recording signal can be read out by separating the two linearly polarized light components, detecting them by respective light receiving regions, and taking the difference.

The light receiving areas 13a and 13b are arranged at positions which are optically equidistant from the focal position of the reflected light when the objective lens 9 is focused on the magneto-optical disk 20, By comparing the spot sizes on both the light receiving areas, the focus state (focusing error) of the objective lens 9 with respect to the magneto-optical disk 20 can be detected.

Light receiving regions 13a, 13b of the light receiving element 13
3 are parallel to the direction corresponding to the tangential direction of the magneto-optical disk 20 as shown in FIG.
It is divided into four strip-shaped areas divided by one division line. Then, the P-polarized light flux (0th-order diffracted light) and the S-polarized light flux (first-order diffracted light) separated by the grating prism 12 enter the light receiving regions 13a and 13b, respectively.

The signals from the respective light receiving areas are calculated by a calculation circuit (not shown) and recorded on the disk as a magneto-optical recording signal MO, a preformat signal RO recorded by physical unevenness, a focus error signal FE, The track error signal TE is output to a reproducing circuit and a servo circuit (not shown).

Each signal can be obtained by the following equations when the output of each light receiving area is represented by the same symbol as the light receiving area.

[0022]

## EQU1 ## MO = (A + B + C + D)-(E + F + G + H) RO = (A + B + C + D) + (E + F + G + H) FE = (A + D-B-C)-(E + H-F-G) TE = (B-C) + (G-) F)

According to this embodiment, the information signal and the error signal can be detected by using the common light-receiving region, the structure of the light-receiving element can be simplified and the cost can be reduced, and other later-described Compared to the embodiment, the single condensed light path makes it possible to occupy a small space and downsize the entire apparatus.

[0024]

As described above, according to the present invention, the angle of the reflected light from the polarization separated optical information recording medium can be arbitrarily set by using the prism having the grating and the light receiving element. The distance from the light receiving element and the angle of the light receiving element with respect to the optical axis can be set arbitrarily. Particularly, when the light receiving element is set perpendicularly to the optical axis, the positioning and adjustment of the light receiving element become easy.

Further, according to the present invention, the reflected light from the medium is separated into two components and is received by at least two light receiving regions on the light receiving element, so that the common region is used for recording on the medium. The signal and the error signal can be detected, the cost of the light receiving element can be reduced, and the optical system can be simplified.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a magneto-optical disk device that uses the optical information recording / reproducing device according to a first embodiment.

2A and 2B are explanatory views of a light receiving system of the apparatus of FIG. 1, where FIG. 2A is an explanatory view in the xy plane in FIG. 1, FIG. 2B is an explanatory view in the yz plane, and FIG. Is an explanatory diagram in the xz plane.

FIG. 3 is an explanatory diagram of a single grating prism used in an example.

FIG. 4 is a plan view showing a light receiving region of the light receiving element of the first embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 5a ... Half mirror surface 9 ... Objective lens 10 ... λ / 2 plate 11 ... Condensing lens 12 ... Grating prism 13 ... Light receiving element 13a, 13b ... Light receiving area 20 ... Magneto-optical disk

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Maruyama 2-36 Maeno-cho, Itabashi-ku, Tokyo Inside Asahi Optical Co., Ltd. (72) Masahiro Ohno 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Asahi Optical Co., Ltd.

Claims (3)

[Claims] 1. A light source, an objective lens for converging a light beam emitted from the light source onto an optical information recording medium, a light beam separating surface for separating reflected light from the optical information recording medium from an optical path from the light source, and the light beam. A grating prism that separates the reflected light separated by the separation surface into polarized light components orthogonal to each other by a transmission type grating surface having periodicity formed on the incident end surface and emits the light from an exit end surface that is not parallel to the incident end surface. And an optical information recording / reproducing apparatus comprising: a light receiving element having two light receiving regions for respectively receiving the two light beams separated by the grating prism. 2. The grating prism is arranged so that an incident angle of the reflected light with respect to the grating surface becomes a Bragg angle, and any one of a 0th order diffracted light and a 1st order diffracted light separated into each polarization component by the grating surface. 2. The optical information recording / reproducing according to claim 1, wherein either one of the light fluxes is internally reflected by a reflecting surface that is not parallel to the incident end face, and then both light fluxes are emitted from the emission end face in a substantially parallel state. apparatus. 3. The grating prism and the light receiving element are integrally joined together.
The optical information recording / reproducing apparatus described in 1.