JPS6161236A - Optical disk reproducing device - Google Patents

Abstract

PURPOSE:To make simultaneous reproduction of plural information tracks and tracking error detection at the same time by providing a diffraction grating and a light detector and thereby reproducing information of the first, second and third tracks simultaneously. CONSTITUTION:A beam spot consists of a spot 23b made by 0-order diffracted light and spots 23c, 23a caused by + or - first-order diffracted light, and each of them is irradiated on adjoining information tracks 25, 24, 26. A beam spot 19 irradiated on a light disk 8 is reflected and becomes reflected light 20, and enters a detecting section 22. A tracking error signal 5 is taken out as difference signals of photodiodes 22a, 22c by using a differential amplifier 27. On the other hand, reproduced RF signals are taken out from a photodiode 22b, and by passing outputs of photodiodes 22a, 22c through high-pass filters 28, 29 respectively. The tracking error signal is obtained by raising the intensity of + or - first- order diffracted light out of reflected light, and at the same time, irradiated information track can be read.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an optical disc reproducing device capable of simultaneously reproducing multi-tracks of an optical disc.

(Background of the Invention) In the reproduction of an optical disc, in addition to the first beam for reading information, a second beam is used to detect the tracking error signal of the optical head with respect to the information track by the twin beam method. Third
beam is used.

The twin beam method will be explained below.

Figures 3 and 4 are explanatory diagrams for explaining the operation of the twin beam method, respectively. Figure 3 is a partially enlarged view showing the interface of the optical disk, and Figure 4 is a schematic diagram showing the detection unit. .

In Figures 3 and 4, 1 is a recording pit, 2 a
r 2 b + 2 c are laser spots, 3
Turtle, 3b + 3c are respectively reflected light, 4m, 4b + 4c
are photodiodes, 5 is a tracking error signal, 6 is a differential amplifier, and F is a reproduced RF signal.

In the twin beam method, the laser beam is divided into three parts by a diffraction grating, and the laser beam is divided into three parts with respect to the pit row l on the optical disk so that the laser beams are arranged as shown in Fig. 3 (laser spora) 2a, 2b, 2e.
, and the reflected light 3a+3b+ as shown in FIG.
3c are respectively guided to three photodiodes 4a, 4b, and 4c. The tracking error signal 5 is extracted as a difference signal between the photodiodes 4a and 4c using a differential amplifier 6, and the reproduced RF signal 7 is extracted from the output of the photodiode 4b.

In this conventional method, the information track can only be read one track or bit string at a time.

(Object of the Invention) An object of the present invention is to provide an optical disk reproducing apparatus that uses a multi-beam optical head to simultaneously reproduce a plurality of information tracks and detect tracking errors.

(Summary of the Invention) The feature of the present invention is to irradiate the information surface of an optical disc with a light beam output from a laser light source via a diffraction grating,
The reflected light is guided to a photodetector, and in the optical device (lAe/C) which reproduces the information of The first one of the discs on which the step was selected and irradiated with the 0th order diffracted light.
against Ratsuk.

At least the ±1st-order diffracted light is applied to the second . (3) the diffraction grating is tilted so as to be irradiated biased toward the first track on the rack, and the diffraction grating is spaced apart, and the reflected light of at least the 0th-order diffracted light and the ±1st-order traveling light; and the photodetector (RL, information of at least the first, second, and third tracks), which obtains reproduction information from the The main point is that they can be played simultaneously.

(Embodiment of the invention) The fifth factor is a fruit of the present invention! It is a schematic diagram of the optical head F used in one example.

In FIG. 5, 8 is an optical disk, 10i'! Semiconductor laser, 11 is a laser beam, 12 is a collimating lens, 13
is parallel light, 14)'! Diffraction grating, 16 polarizing beam splitter, 17 quarter wavelength plate, 18 objective lens, 19
2 is a beam spot, 20 is reflected light, 21 is a detection lens, and 22 is a detection section.

As shown in the fifth factor, the laser beam 11 emitted from the semiconductor laser 10 becomes parallel light 13 by the collimating lens 12 and is divided into three by the five-diffraction grating 14 .

Next, these divided light beams are irradiated onto the optical disk 8 as a beam spot 19 via a polarizing beam splitter 16, a quarter wavelength plate 17, and an objective lens 8.

In this embodiment, each of the 0th-order diffracted light and the ±1st-order diffracted light is irradiated onto three adjacent information tracks on the disk as shown in FIG.

Here, number 1171 indicates the beam spot arrangement irradiated onto the disk according to this embodiment. The beam spots include a spot 23b of the 0th-order diffracted light and a spot 23e+23a of the ±1st-order diffracted light, and each of them is irradiated onto adjacent information tracks 25°24 and 26. Note that the inclination of the diffraction grating 14 is determined so that the beam spots 23a and 23e are located on the information tracks 26 and 24, respectively, and are offset from the inner side (beam spot 23b).

Next, each of the beams 19 irradiated onto the optical disk 8 is reflected and becomes reflected light 2o, which is reflected to the objective lens 1.
8. 1/4 wavelength plate 17. Polarizing beam splitter 16. The detection unit 2
2.

FIG. 2 is a detailed block diagram of the detection section 22.

22a, 22b, 22c each indicate a photodiode, 20a, 20b, 20e k'X
Each shows the reflected light focused onto a nuclear 7 otodiode 22a, 22b, 22c. Using a tracking error signal 5-digit differential amplifier 27, photodiodes 22m, 22
It is taken out as the difference number 1 of c. On the other hand, the reproduced RF signal is extracted from the photodiode 22b and by passing the respective outputs of the photodiodes 22a and 22c through high-pass filters 28 and 29, respectively. 30.31 is the reproduction RF signal directly taken out from the photodiode 22b, and 30.31 is the high-pass filter 28.2, respectively.
9 shows the reproduced RF signal taken out through 9.

The 28.29ft high-pass filter is used to remove low frequency components caused by eccentricity of the disc.

In this embodiment, the light intensity of the ±1st order diffracted light of one reflected light is increased so that a tracking error signal can be obtained and at the same time, the irradiated information track can be read.

Next, the diffraction grating at the 5th tjJ ] 4 one-hedral example f:
611th? explain.

In order to obtain a beam spot of the 0th order diffracted light and the ±-r diffracted light at the position described in Section 11, the diffraction grating 14
The design conditions are as follows.

Now, the length λ of the laser beam is 830 nm, and the diffraction grating 14 is
The refractive index n of is 1.5, and the 0th order diffracted light ff1I.

and the scene of the first-order diffracted light ■1 are equal to each other, and their ratio 1. Assuming that /k is 1, the step d of the grid is fJ as follows.
Ru.

In addition, each interval Xft from beam spot 23b to beam spots 23c and 23a in FIG. 1 is 15 μm.
, the deviation δ of beam spot 23& from 23b is 1.8
If the rack pitch is 8 μm (374th position of Y-25 μm), then the inclination angle θ is.

It is calculated as follows.

δ θTomi - 0,12 radians Further, the grating interval l of the diffraction grating 14 is determined by the following equation.

Xθ Here, f is the focal length of the objective lens 18, f,
= 3.6 dragons.

Furthermore, photodiodes 22a and 22 shown in FIG.
If the interval U of c is 600 μm, the detection lens 210
4. Focal length f of a 14-point pheasant f2 objective lens/z18,
=3.6 gates = f, = f, ・-”144+i.

FIG. 7 shows an example of an optical disc 32 played back by the playback device of the present invention. The information track 33 is composed of three tracks, tracks a, b, and C.

PCM music or audio information is directly recorded as a digital signal on track a (for example, it is assumed that it is recorded in IA format that conforms to the audio compact disc standard). Track b contains an image f! which is FM modulated in video format. is recorded. Track C
In , the audio signals for explaining tracks a and bf are time-axis compressed P(, M) and are omitted.

The playback device according to this embodiment allows three tracks a and b to be played.
and C or the information track 33 are played at the same time,
By tracking every 3 tracks, track b
Continuous images in K, music in track aK, or explanatory audio signals in track C can be played back at the same time. At this time, the spots irradiated on tracks a and e are
The arrangement will be as shown in Part 1.

As described above, according to the present invention, the amount of ±1st-order diffracted light is increased by the diffraction grating 14 through which the laser light passes, and by simply changing the inclination of the three spots irradiated onto the tracks of the disk 32, optical Multi-track playback of discs is possible.

Although the above embodiment has been described for the case of three spots, if the diffraction grating 14 increases the intensity of the diffracted light in ±2 or more dimensions, it becomes possible to reproduce even more tracks simultaneously.

(Effects of the Invention) As described above, according to the present invention, there is an effect that simultaneous reproduction of a plurality of information tracks and tracking error detection can be performed simultaneously. Furthermore, if audio for explaining the image is recorded on multiple adjacent tracks other than the track on which one image is recorded, the explanation of the image can be added when playing still images, which has great practical value. .

[Brief explanation of the drawing]

FIG. 1 is a beam spot arrangement diagram according to an embodiment of the present invention, FIG. 2 is a block diagram of a photodetector according to an embodiment of the present invention, FIG. 3 is a diagram of spot arrangement on a conventional disk, and FIG. The figure is an explanatory diagram of the twin beam method, FIG. 5 is a schematic configuration diagram of an optical head, and FIG. 6 is a perspective view of a part of a diffraction grating according to an embodiment of the present invention. FIG. 7 is a conceptual diagram of a disk used in the present invention. 1... Recording bit, 5... Tracking-difference signal. 8...Disc, 10...Laser, 14...
・Diffraction grating, 2Qa, 20b, 20c...-Reflected light,
22a. 22b, 22cm--photodiode, 23a.

Claims (2)

[Claims] (1) In an apparatus for reproducing information on an optical disc by irradiating a light beam output from a laser light source onto the information surface of an optical disc via a diffraction grating and guiding the reflected light to a photodetector, The step is selected so that the light amount of at least the ±1st-order diffracted light is close to the light amount of the 0th-order diffracted light, and at least the ±1st-order diffracted light is The diffraction grating is tilted and the grating spacing is selected so that the irradiation is biased toward the first track on the second and third tracks adjacent to the first track, and at least the 0th-order diffraction light and the photodetector which obtains reproduction information from the reflected light of the ±1st-order diffracted light and obtains a tracking error signal from a differential signal of the reflected light of the ±1st-order diffracted light; An optical disc reproducing device characterized in that information on a third track is simultaneously reproduced. (2) The optical disk reproducing apparatus according to claim 1, wherein the information signal obtained from the reflected light of the ±first-order diffracted light is obtained through a high-pass filter.