JPS6173246A - Optical reproducing device - Google Patents

Abstract

PURPOSE:To detect a focussing error, by providing an optical means which produces such astigmatic lights that form a linear spot elongated in the direction of an information track and detecting one or both light quantity distributions of two auxiliary reflecting beams becoming astigmatic lights. CONSTITUTION:Parallel lights 4 are divided into a main beam 6 of zero-order diffracted lights, auxiliary beam 24a of (+1)-order diffracted lights, and auxiliary beam 24b of (-1)-order diffracted lights and, at the same time, the auxiliary beam 24a becomes divergent lights and auxiliary beam 24b becomes convergent lights. The divided beams are made incident to an objective lens 9 through a beam splitter 8 and become a convergent beam, but the auxiliary beams 24a and 24b become astigmatic lights and are arranged in one line on an optical disk 10, forming a spot. Each reflecting beam 14, 26a, and 26b proceed in the opposite directions and are made incident to 6-divided photodetectors 27a, 27b, 27c, 27d, 27e, and 27f after they are reflected by the beam splitter 8. A focus error signal is obtained from the difference between the sum of the detector outputs of the photodetectors 27a and 27c and the sum of detecting outputs of the photodetectors 27b and 27d.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical reproducing device that can perform tracking error detection using a three-beam method and focusing error detection using an astigmatism method.

[Background of the invention]

In the above-mentioned optical playback devices, such as optical video disk players and audio disk players, during playback, the light beam from a light source such as a laser is formed into a minute spot by an optical system and always and correctly placed on the information track of the optical disk. It is necessary to focus the light, and therefore a focus and tracking error detection device is provided.

A conventional device using a K, a diffraction grating, and a cylindrical lens is known as described in Japanese Patent Laid-Open No. 57-205833.

FIG. 1 is a configuration diagram showing a focus and tracking error detection device when a phase-type diffraction grating is provided between a collimating lens and a beam splitter as described in the main text of Japanese Patent Application Laid-Open No. 57-205833. be. @1 In the figure, l is a semiconductor laser light source, 2 is a collimating lens, 3 is a diverging beam, 4 is a parallel beam, 5 is a phase type diffraction grating, 6
is the main beam of the O-order diffracted light, 7α, 7h is the sub-beam of the ±1st-order diffracted light, 8 is the beam splitter, 9 is the objective lens, 1
0 is an optical disc, 11 is an information track.

12 is the main spot, 13α, 13h is the sub spot, 14
c Main reflected beam, 15α, 15h are sub reflected beams, 16
is a convex lens, 17 is a concave lens, 18 is a cylindrical lens, 19
α, 19h, 19C, 19d, 20α, 20
A is a 6-segment photodetector.

Next, the operation will be briefly explained. A semiconductor laser beam [1 is used as a light source. The collimating lens 2 is a condensing lens that condenses the divergent light 3 of the light source 1 and converts it into parallel light 4. The parallel light 4 is generated by the phase type diffraction grating 5 into a main beam 6 (solid line) of O-order diffracted light and a sub-beam 7α (dashed line) of +1st-order diffracted light.

- Separated into sub beam 7A (dotted chain line) of the first-order diffracted light,
The separated beams 6.7α and 7b are as follows.

The beam enters the objective lens 9VC through the beam splitter 8 and is made into a focused beam, which is aligned and focused on the optical disk 10 to form a minute spot. In addition, as shown in FIG. 2, the main slots 12. The secondary spots 13oL and 13A are arranged in the arrangement direction y of the information tracks 11, and are aligned with the main spot 120.
Sub spot 137Z on the front and rear.

13A is located. Each of the reflected beams 14 , 15z , 15S from the optical disk IO travels backwards and is reflected by the beam splitter 8 , and then passes through the convex lens 16 . concave lens 17
6-divided photodetector 19α, 1 through 9 cylindrical lens 18
9A, 19-, 1'M, 20α, 20b. As shown in FIG. 3, the main reflected beam 14 is:

Four-division photodetector 19α, 195, 19C, 194
, forming a main spot 21 and a sub-reflected beam 15c.
L.

15b enters photodetectors 20α and 20h, respectively.

Sub-spots 22α and 22h are formed. The concave lens 17 has an interval between the focal positions of the reflected beams 14, 15α, and 15h,
That is, the photodetectors 19α, 19h, 19c, 1
9d.

This is provided to adjust and widen the distance between the photodetector 20α and the photodetector 20b, and can be omitted.

The reproduced signal (video signal, PCM audio signal, etc.) is obtained by the sum of the detection outputs of the photodetectors 19α, 1975, 19C, 19, (1975).

The focus error signal is obtained by the difference between the sum of the detection outputs of the photodetectors 19α and 19C and the sum of the detection outputs of the photodetectors 19h and 1'M due to the astigmatism of the single cylindrical lens 18. Note that the spot 21 is a circle when in a correct focus state, and an ellipse or a line segment when in a defocus state. This focus error signal causes the objective lens 9 to move in the axial direction.

The tracking error signal is obtained from the difference between the detection outputs of the photodetectors 20α and 206. This tracking error signal causes the objective lens 9 to move in the direction X perpendicular to the information track 11 of the optical disk 10. Alternatively, a tracking mirror (not shown) may be provided and rotated.

As described above, conventional focus and tracking error detection devices have the drawback of requiring special and expensive optical components such as a cylindrical lens for focus error detection and a diffraction grating for tracking error detection.

[Object of the Invention] The object of the present invention is to eliminate the above-mentioned drawbacks, eliminate one cylindrical lens, and perform tracking error detection using a 3-beam method and focus error detection using an astigmatism method using only one diffraction grating. Our goal is to provide an optical reproducing device that can.

[Summary of the invention]

In order to achieve the above object, in the present invention, when the main beam is in the correct focus state on the optical disk, one or both of the two sub beams are directed onto the optical disk to track the information. To detect the scene distribution of one or both of the two sub-reflected beams that have become astigmatic light, by providing an optical means that produces astigmatic light that forms a long linear spot in the direction of K. This method is designed to detect focus errors.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a configuration diagram showing the focus and tracking error detection device of the present invention. As shown in FIGS. 5 and 6, the phase type diffraction grating 23 used in the present invention is
The pitch of the grating is changed monotonically with respect to the position of the grating.

Therefore, the parallel light 4 is
At the same time, the sub beam 24cL becomes diverging light, and is separated into the main beam 6 (solid line) of the first-order diffracted light, the sub-beam 24α (broken line) of the +1st-order diffracted light, and the sub-beam 24h (dotted chain line) of the -1st-order diffracted light. 24b becomes focused light. Each of the separated beams 6.24α and 24h enters the objective lens 9 via the beam splitter 8 and becomes a focused beam, but the sub beams 24α and 24b become astigmatism light and can be attached to an optical disc. 10 to form spots in a line. In addition, the main spots 12.corresponding to each beam 6.24.alpha., 24b. As shown in FIG. 7, the sub-spots 25α and 25b are arranged in the arrangement direction 11-h of the information track 11, and the sub-spots 25α and 25h are located before and after the main spot 120. In this state, it becomes a long line in the y direction. optical disc 10
Each of the reflected beams 14, 26α, 26b travels backwards, is reflected by the beam splitter 8, and then passes through the convex lens 16. 6-divided photodetectors 27α, 27h,
27c, 27d.

27g and 27f. The main reflected beam 14 is
The sub-reflected beam 26α enters the photodetector 26g, and the sub-reflected beam 26α enters the photodetectors 27α, 27A, 27c, 27d,
The sub-reflected beam 26h is incident on the photodetector 27f. l@
Figure 8 shows photodetectors 27a, 27h, 27c, 2
The detection surfaces of 7d, 27g, and 27f are shown, and 21,
28α, 28h are the respective reflected beams 14, 2 above each
There are 6α and 26b sponotes.

The reproduced signal is obtained from the detection output of the photodetector 97g.

The focus error signal is obtained by the difference between the sum of the detection outputs of the photodetectors 27α and 27C and the sum of the detection outputs of the photodetectors 27A and 27d. Note that the spot 28α is a circle when in a correct focus state, and an ellipse or a line segment when in a defocus state.

The tracking error signal is sent to the photodetectors 27α and 27A.

The sum of the detection outputs of 27c and 27d and the photodetector 27f
is obtained by the difference in detection output.

In this example, astigmatism was generated using a phase-type diffraction grating in which the pitch of the grating was changed monotonically. It is also possible to generate astigmatism by arranging the lens.

In addition, without using a diffraction grating, the main beam and sub beams are generated by three semiconductor lasers, and one or both of the two semiconductor lasers for the sub beams is a semiconductor laser with astigmatism like a multimode laser. It is also possible to use a laser.

〔Effect of the invention〕

As stated above, according to the present invention, when the main beam is in the correct focus state on the optical disk,
An optical means is provided to make one or both of the two sub-beams into astigmatic light so as to form a long linear spot on the optical disk in the direction of the information track. Since the focus error is detected by detecting the light intensity distribution of one or both of the two sub-reflection beams, omitting the cylindrical lens has the effect of making a hole.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a conventional focus and tracking error detection device, and FIG. 2 is a front view of an optical disc.
FIG. 3 is a front view of a photodetector, FIG. 4 is a configuration diagram showing a focus and tracking error detection device according to an embodiment of the present invention, FIG. 5 is a front view of a diffraction grating, and FIG. 6 is a front view of a diffraction grating. A side view, FIG. 7 is a front view of the optical disk, and FIG. 8 is a front view of the photodetector. 6... Main beam, 10... Optical disk 11... Information track, 12... Main spot 14... Main reflected beam, 23... Phase type diffraction grating 24α, 24b...
Sub-beams 25α, 25h...Sub-spot 7 26α, 26h...Sub-reflected beams 27α-27f...Photodetector. Figure 1 Figure 3 20α 0b

Claims (1)

[Claims] 1. The optical head generates two sub-beams and projects them on both sides of the information track of the optical recording medium onto which the main beam for reproducing information is projected, and modulates the information on the information track. The optical head detects the tracking error of the optical head by detecting two modulated reflected beams obtained by the optical head with two photodetectors, and comparing the detection results of the two photodetectors. In the type reproducing apparatus, when the main beam is in a correct focus state on the optical recording medium, one or both of the two sub beams are directed onto the optical recording medium and onto the information track. The optical device is equipped with an optical means for producing astigmatic light that forms a long linear spot in the direction of , and detects the light intensity distribution of one or both of the two modulated reflected beams that have become astigmatic light. An optical playback device characterized in that a focus error of the optical head is detected.