JPH0636497Y2 - Optical system device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Use) The present invention relates to an optical system device such as a compact disc reproducing device for optically reading information from a disc.

(Prior Art) One light flux from a conventional light source is caused to generate diffracted light by a diffraction grating, and the 0th order and ± 1st order diffracted light on both sides thereof are extracted, and the three diffracted light fluxes (beams) are extracted. A line connecting the centers of beam spots on a recording medium such as a disk is converged through an objective lens so that it has a minute offset angle with respect to the track direction, and is arranged before and after the 0th-order main light flux for reading out an HF signal. A tracking control method called a three-beam method is known in which the tracking state of the main light beam spot is determined by the difference in the light amount of the sub-light beams of the ± first-order light beams.

The above-mentioned three-beam method is a state in which the sub-beam spots S2 and S3 are positioned before and after the main beam spot S1 converged on the track Tn composed of the recording pit (P) row as shown in FIG. Recorded information Target track Sub spot from center of track Tn
S2 and S3 are in opposite directions (adjacent recording tracks Tn-
1, the direction of approaching Tn + 1) is adjusted so that the spots of the light flux on the recording disk are the target track Tn.
The focal points are aligned in a line so as to have a predetermined offset angle of about 1 degree or less.

However, if a finite converging system (an optical system in which an optical path separating means such as a beam splitter or a half mirror is provided in the divergent optical path from the light source) is used for the purpose of downsizing the optical system, a detector that receives 0th order and ± 1st order respectively There was a drawback that crosstalk was likely to occur between the two.

When using the so-called astigmatism method for focus control,
As proposed in Japanese Patent Application No. 59-166415 by the present applicant, if the peripheral edge is shielded in the direction of the light flux, the light flux is twisted by 90 ° due to astigmatism to prevent crosstalk. You can

However, when the tracking control is not of the optical system integrated drive type and the objective lens alone is driven, the optical axis of the returned light moves according to the tracking (the amount of movement is ± 0.3 to 0.4 mm).
It is said that the fluctuation of the light shielding amount is large, and that in the finite focusing system, since the light is convergent light instead of parallel light at the light shielding place in the conventional far field, the light beam diameter is small and it is not easy to adjust the light shielding amount. There are drawbacks.

That is, when the peripheral edge of the light flux is shielded in parallel, the distance from the light flux end is 0.6 to 0.8 m for a reflected light flux diameter (diameter) of parallel light of 6 mm.
In the case of convergent light as compared with about m, the beam diameter is about 2 mm, and the beam end distance is about 0.2 to 0.3 mm.

(Purpose of the Invention) To provide an optical system device which has excellent signal detection characteristics, prevents crosstalk, and is suitable for downsizing.

(Outline of the Invention) The optical path between the collimator lens and the objective lens is to be shielded.

(Examples) Examples will be described below with reference to the drawings.

In FIG. 1, the divergent light from the light source (1) is extracted through a diffraction grating (2) into a 0th-order diffracted light beam and a ± 1st-order diffracted light beam, and a collimator for converting the light into parallel light through a half mirror (3). The disk (7) is irradiated through the lens (4), the mirror (5) and the objective lens (6).

The reflected light from the disk (7) is separated from the divergent light through the objective lens (6), the mirror (5), the collimator lens (4) and the half mirror (3), and the concave lens (9) and the cylinder lens (10). It is led to the detector (11) via.

A well-known method such as an astigmatism method or a three-beam method may be used for the focus and tracking detection methods. The reproduction signal is obtained from the 0th order light.

The converged state on the disk (7) is as shown in FIG.

The shielding is performed along both edges of the light beam along the diffraction directions of the 0th and ± 1st order light beams, in other words, along the direction of the spot array on the disc.

FIG. 2 shows the arrangement of the shielding plate (8). Mounted together with the objective lens (6) on the movable part (20), the magnetic circuit (21),
A driving coil (22) is used to drive the coil in the illustrated direction. The pit traveling direction is perpendicular to the paper surface.

The light flux after passing through the cylinder lens (10) for astigmatism is the fourth
Light is received in the state as shown in the figure.

That is, the main light flux L1 and the sub-light fluxes L2, L3 are imaged on the detectors (52), (51), (53) of the detector (11).

At this time, the imaginary line C just indicates the shielding direction and position of the shielding plate (8), and in the substantially circular spot, the portion outside the imaginary line C is not received.

That is, the shielding direction corresponds to shielding the light receiving portion close to the adjacent detector side, and the crosstalk due to the mutual light flux leakage is drastically reduced.

The shielding plate (8) may be configured to completely shield the light with a metal plate or the like, or may be configured to substantially drop the peripheral light to the outside of the detector with a half mirror or the like.

(Effect of the Invention) As described above, according to the present invention, since it is not necessary to place the light shielding plate in the convergent optical path of the finite converging system, it is easy to adjust the light shielding amount and suitable for downsizing.

Moreover, crosstalk on the detector can be prevented when the three-beam method is adopted in the finite focusing system.

It has the above effects.

[Brief description of drawings]

FIG. 1 is a layout diagram of an optical system of an embodiment, FIG. 2 is a configuration diagram of essential parts of the embodiment, FIG. 3 is a diagram for explaining a three-beam method, and FIG. 4 is an explanatory diagram of a shielding direction. Explanation of reference numerals 1 ... Light source, 2 ... Diffraction grating 3 ... Half mirror, 4 ... Collimator lens 5 ... Mirror, 6 ... Objective lens 7 ... Disk, 8 ... Shielding plate 11 ... Detector

Claims (1)

[Scope of utility model registration request] 1. A divergent light beam emitted from a light source is made incident on a diffraction grating to generate a plurality of beams, and then an objective lens is arranged through a half mirror and a collimator lens to arrange the information tracks on a disk substantially linearly. In the optical system device, which irradiates three beam spots, reflects the reflected light through the half mirror and guides it to a photodetector to detect a reproduction signal or the like, in an optical path between the collimator lens and the objective lens. An optical system device characterized in that a shielding plate for shielding the peripheral portion of the light flux is provided in the optical system.