JPH02137130A - Optical pickup device - Google Patents

Abstract

PURPOSE:To eliminate the generation of a false focusing signal by arranging an optical system so that the direction of two lattices, which generate a moire stripe, can be almost orthogonal with the direction of a pit string in an optical disk. CONSTITUTION:For two lattices 7 and 8 to make the moire stripe, a light transparent part and a light opaque part are respectively formed in a parallel stripe shape with a fixed interval. One lattice is arranged in front and back of an optical path with an interval in a condition to be rotated only by a fine angle. These two lattices 7 and 8 are arranged so as to be almost orthogonal with the pit string of an optical disk 6. Further, a second beam splitter 10 is arranged between the two lattices 7 and 8 and a beam is incident through a condenser lens 11 to a two-divided photo-detecting element (or a four-divided photo- detecting element) 14 to detect a tracking signal. This two-divided photo- detecting element (or four-divided photo-detecting element) 14 is used as the detecting means of a data (RF) signal as well. Thus, the false focusing signal is prevented from being generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device that performs automatic focusing and tracking in a pickup device or the like used for recording and reproducing optical discs.

[Prior Art] Japanese Patent Application No. 62-60007 filed by the same applicant as an automatic focusing device in a pickup device of an optical disk device
No. 63-3273 filed by N.B.Philips Fluiranbenfabriken Co., Ltd.
A method using moiré fringes, as shown in Japanese Patent No. 0, has been developed.

[Problems to be Solved by the Invention] These conventional techniques are promising in terms of focusing using moiré fringes, but the pit rows on the optical disk act as a diffraction grating, that is, the pits cannot be accurately positioned on the pits. When the light does not converge, that is, when it is not fully focused, the light hits multiple pit rows, and the light reflected by these pit rows acts just like light from a diffraction grating. There is a risk of interference between the pit row and the grating that generates moire fringes, that is, moire fringes that generate false focusing signals.

The object of the present invention is to provide an optical system arrangement that does not generate such false focusing signals, and also to provide an optical pickup device in which push-pull tracking is also incorporated into the same optical system.

[Means for Solving the Problems] The present invention solves two problems that cause moiré fringes in an apparatus that performs focusing and tracking by forming dot-like images of semiconductor laser light on the pit surface of an optical disk using an imaging lens. In addition to adopting an optical arrangement in which the direction of the lattice fringes and the direction of the pit rows of the optical disk are substantially orthogonal to each other, the system also uses a push-pull method to perform tracking using the same optical system. .

In this invention, in order to perform focusing and tracking using the same optical system, a beam splitter is provided between or in front of the two gratings that generate moiré fringes, and one of the light beams split by this beam splitter is used to generate moiré fringes. The other beam is used for the push-pull method, that is, for tracking. Furthermore, as is well known, a four-split light receiving element is arranged behind the beam splitter for focusing, and a four-split or two-split light receiving element is arranged behind the beam splitter for tracking.

Furthermore, preferably, in the arrangement of the two gratings, the other grating is placed at the position of the Talbot image of the grating closer to the objective lens side.

[Function] By arranging the two lattice stripes that generate moiré fringes so that the direction of the stripes is orthogonal to the direction of the pit rows of the optical disk, the light beam is accurately focused on the pit rows of the optical disk. If not, the pit rows will be hit by light over a wide area, so in this case, the multiple pit rows will act as a diffraction grating, and moiré will occur between this and the two gratings that generate moiré fringes for focusing. Stripes no longer occur, and therefore false focusing signals no longer occur.

Further, by providing a beam splitter between or in front of the two gratings that generate moire fringes for focusing, it becomes possible to detect the focusing signal and the tracking signal using the same optical system.

Furthermore, by placing two gratings that generate moiré fringes, one grating at the position of the Talbot image of the other, it is possible to generate the clearest moiré fringes, creating an optical pickup device with high precision. can do.

[Example] Hereinafter, the present invention will be described in detail based on the drawings. 1st
The reason is that in the optical path diagram showing the configuration of the optical pickup of the present invention, the emitted light 2 from the semiconductor laser 1 passes through the collimator lens 3.
The light beam becomes a parallel light beam 2a, travels straight through the beam splitter 4, is converged by the objective lens 5, becomes a convergent light beam 2b, and forms an image on the pit surface 6a of the optical disk 6. The light beam reflected by the pit surface 6a travels in the opposite direction along the optical path, is converged by the objective lens 5, turns right at a right angle by the beam splitter 4,
First grating 7° beam splitter that creates two moire fringes 10. The light passes through the second grating 8 and enters the four-part light-receiving element 9 . A focusing signal is obtained by this four-division light receiving element 9.

As described in Japanese Patent Application No. 62-60007, the two gratings 7 and 8 are gratings in which light transmitting portions and non-transmitting portions are formed in parallel stripes at a certain interval, and one The gratings are rotated by a small angle α and placed at intervals at the front and rear of the optical path, and these two gratings 7 and 8 and the pit row of the optical disk 6 are arranged to be approximately perpendicular to each other.

Furthermore, in this embodiment, a second beam splitter 10 is arranged between two gratings 7.8, and a two-split light receiving element (or a four-split light receiving element) for detecting a tracking signal via a condensing lens 11. (divided light receiving element) 12. This two-split photodetector (or four-split photodetector) 12 is also used as a data (RF) signal detection means.

The relationship between the light receiving elements 9, 12 and the signals is shown in Fig. 2 (A) and (B).
), the focusing signal S
2 is a four-part light receiving element (p,, pg, P3, p4
; The direction connecting pt, pz and pg, P should be approximately parallel to the direction of the stripes of the lattice). Let the output signals be 5inSs, Sol, and S4, respectively.

SF” (S□+S4)−(s*+s,I).

Additionally, the tracking signal S7. In the case of , if s, , s,' is the output signal of the two-split photodetector (Q, , Q,; the direction connecting Q, , Q is parallel to the pit row), then S□”SS
-5t”.

Note that the data (RF) signal S1 is <S, =S! '＋
82'.

This example is the first example. Since the beam splitter 10 is inserted between the two gratings of the second grating 7.8 to perform tracking detection, the optical system can be configured more compactly.

Next, the first grating 7 and the second grating 8 that generate moiré fringes will be explained. The second grating 8 is disposed across the beam splitter lO from the first grating 7, and is spaced apart by the Talbot distance. The Talbot distance here means the radius of curvature R of a wavefront on a grid with a grid spacing d.
It is the distance at which a clear Fourier image of the first grating 7 can be obtained when light with nine wavelengths λ is incident, and is expressed as follows. At this time, since the beam splitter 10 is inserted, the optical path length of the Talbot distance pattern is extended by the refraction line of the glass material of the beam splitter 10. For example, the thickness pattern 1. If a beam splitter with a refractive index n is placed between gratings 7 and 8, the distance between the gratings at this time may be set as follows.

Next, a second embodiment will be explained based on FIG. 3. This example differs from the example shown in FIG. 1 above in that a beam splitter for splitting tracking signals and focusing signals is disposed in front of the two gratings.

That is, the beam splitter 10' is placed immediately after the beam splitter 4, and splits the light for tracking detection, converges it with a condenser lens 11'', and makes it incident on the two-split or four-split light receiving element 12.This example In this case, a grating that causes moiré fringes is not inserted into the tracking detection light beam, so the tracking signal can be made more accurate.

[Effects of the Invention] A focusing signal due to moire fringes can be detected without generating a false focusing signal due to the effect of a diffraction grating formed by a pit row of an optical disk.

Furthermore, tracking using the push-pull method and focusing using moiré fringes can be performed using the same optical system.

[Brief explanation of the drawing]

FIG. 1 is an optical path diagram showing the configuration of an optical pickup device according to an embodiment of the present invention. FIGS. A block diagram for explaining signal extraction. FIG. 3 is an optical path diagram showing the configuration of an optical pickup device according to another embodiment of the present invention. l @ 1111 5... 6 a building, 8φ fist, l O... l 1... semiconductor laser, 3... beam splitter objective lens
, 6... Optical disc pit surface, 7... First grating, second grating, 9... Quadrant light receiving element beam splitter converging lens, 12... Two split light receiving element Fig. r

Claims (1)

[Claims] 1. Moiré fringes are generated in an optical pickup device in which light from a semiconductor laser is imaged into dots on a pit surface of an optical disk by an objective lens, and focusing and tracking are performed using light reflected from the pit surface. The optical system is arranged so that the direction of the two gratings and the direction of the pit row of the optical disk are approximately perpendicular, and a beam splitter is provided in front of or between the gratings, and a focusing signal is provided behind one optical path. An optical pickup device in which a four-division light-receiving element for detection is provided, and a two-division (or four-division) light-receiving element for tracking signal detection by a push-pull method is arranged behind the other optical path via a converging lens. 2. The optical pickup device according to claim 1, wherein the second grating is arranged at the Talbot image position of the first grating, the grating generating two moiré fringes.