JPS63222329A - Optical disk - Google Patents

Abstract

PURPOSE:To obtain a tracking error signal which obviates generation of the offset by track follow-up action and inclination of an optical disk by providing the pits, the reproduction signals of which are smaller or larger than the reproduction signals in the other parts on the optical disk. CONSTITUTION:This optical disk is constituted of a substrate 5, a recording film B, a 2 wavelength separating film C and a recording film A and is provided with the clock pits disposed at every specified time intervals in the concentrical or spiral shape of the depth of an integral multiple of a 1/4 wavelength of a light source for recording and reproducing. A mirror part which consists of the recording film alone and is not recorded with phase pits and signals is formed right behind said part. The optical disk 1 is irradiated with the lambda1 light spot L and lambda2 light spot M disposed in proximity in such a manner that the center spacings equals nearly to the track pitch on the recording films A, B, by which the recording and reproducing are simultaneously executed to the two recording films A, B. The tracking error signal is obtd. from the difference in the reproduction signals of the clock pits.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical disc used in an optical recording and reproducing system, and particularly having a disc format for obtaining servo signals.

2. Description of the Related Art A number of methods have been proposed for recording and reproducing information by concentrating a laser beam into a minute optical spot of 1 μm or less using an aperture lens and irradiating it onto a disk-shaped recording medium. However, in either method, the density within the plane of the medium is determined by the diameter of the light spot irradiated onto the medium, so it is difficult to increase the recording density within the plane without changing the diameter of the light spot.

As a solution to these problems, a method of increasing recording capacity by stacking recording layers in the thickness direction of the medium is proposed, for example, in the Proceedings of the 1988 IEICE General Conference, S.
5-12.

This is number 1. Second. It has a structure that has a layer of color formers of different colors (for example, blue, red, and green color formers) and a color developer above and below the third light absorbing layer, and the first light absorbing layer is irradiated with light. and the second one in blue. When the third light absorption layer is irradiated with light, it exhibits red and green colors, respectively. The light absorption layer can be selected by changing the focal position of the irradiation beam in the depth direction, and recording and reproduction are performed in each absorption layer.

Problems that the invention sought to solve In order to increase the recording density in optical recording, some kind of guide for tracking is required on the disk, but with this type of system, it is necessary to provide the guide for each layer. There is.

Furthermore, conventionally, a groove with a depth of λ/8, for example, is used as the guide track, and the peak value of the light intensity distribution of one reflected light moves on the two-split photodetector depending on the amount of deviation between the optical spot and the groove track. . The tracking error signal was obtained using the so-called push-pull method. However, with this conventional method, as described in Japanese Patent Application Laid-open No. 58-56236, the movement of the aperture lens for track following (hereinafter referred to as track following operation) or the reflected light due to the inclination of the disk, etc. This movement causes an offset in the tracking error signal, causing a problem in that the light spot does not follow the center of the groove track.

Further, even with respect to focus error signals obtained by known means such as the knife method or the astigmatism method, there is a problem in that the reproduced signal when the light spot crosses the groove track causes disturbance and disturbs the focus servo.

In view of the above problems, the present invention provides a focus servo.

The purpose of this invention is to provide an optical disc with easy tracking servo control.

Means for Solving the Problems The present invention is an optical disc having pits (referred to as clock pits) arranged concentrically or spirally at regular time intervals, and the pits are arranged so that the reproduced signal is transmitted onto the disc. It has an optical property that makes the reproduced signal smaller or larger than that of other parts of the optical fiber.

Further, the present invention is an optical disc in which an unrecorded area (referred to as a mirror part) in which no signal is recorded is provided immediately after the clock pit.

Effect: When an optical disc having the above configuration is reproduced using two optical spots placed close to each other in the vertical direction to the track, and the difference between the two reproduction signals from the clock pit is taken, track following operation and offset due to disc inclination are detected. A tracking error signal that does not cause this can be obtained.

Furthermore, if we take the difference between the two reproduced signals from the Mira part,
A focus error signal that is not affected by groove tracks can be obtained.

EXAMPLES The present invention will be described in detail below with reference to the drawings. FIGS. 2a and 2b show a recording medium used in the present invention (hereinafter referred to as optical disk 1).
A cross-sectional view and a top view of one example are shown respectively. The optical disc 1 includes, from the light incident side, a base material, a recording film B, a two-wavelength separation film G,
And it is made up of recorded films. The two-wavelength separation film C has the property of transmitting a light beam with wavelength λ1 and reflecting a light beam with wavelength λ2, for example, and has a λ1 light spot L on the recording film and a λ2 light spot on the recording film B. )M will be irradiated respectively. As shown in the top view, both of the optical grooves are arranged close to each other in a direction perpendicular to the track on the image recording film so that the distance between their centers corresponds to approximately the track pitch. Therefore, λ1. recorded by both optical spots. λ2
The recording pits are formed alternately and without gaps in the direction perpendicular to the tracks, and the recording density is twice that of a single layer. The recording film B, two-wavelength separation film C1, is made by means such as vapor deposition, so the film thickness can be made uniform over a wide range, and since it is within the focal depth of both light spots, the focal position cannot be changed. This makes it possible to simultaneously record and reproduce information on both recording films.

FIG. 1 shows one embodiment of the format used for the optical disc of the present invention. The optical disk is divided into a plurality of sectors in the circumferential direction, and each sector has an address area D and a plurality of cell areas 81 . It consists of The address area consists of address pits having address information for the sector, and each cell is divided into a clock pit, a mirror part MR, and a data area. For example, the address pit and clock pit have a depth of approximately λ/4 (where λ=(λ1+λ
A phase pit consisting of 2)/2) is created when an optical disk is manufactured. A portion of the mirror is an area where only a recording film is recorded and no phase pits or signals are recorded. This clock pit and a portion of the mirror are collectively called a servo area. The data area is an area where data is actually recorded, and as described above, data is recorded along both sides of the dotted line shown in the figure by the two optical slits (L and M).

A method for obtaining a tracking error signal for an optical disc having such a format will be described. FIG. 3 is a diagram showing how a tracking error signal is generated by the clock pit X. FIG. 3a is a diagram of the data area and address area D seen from the top surface of the optical disc.
yy.

The address area shows the trajectory when tracking is turned on. In b, the solid line represents the amount of light reflected from the optical sporatom, and the broken line represents the signal when the amount of reflected light is sampled and held. 0 indicates the amount of light reflected from the light spot B by the solid line, and the signal when the amount of reflected light is sampled and held by the broken line. d shows the sum of the amounts of reflected light from both optical spots, and e shows the difference between signals obtained by sample-holding the amounts of both reflected lights. The clock pits and address pits are composed of, for example, approximately λ/4 phase pits, and when the optical spot reproduces the phase pits, the amount of reflected light decreases. Therefore, by summing the amounts of both reflected lights, a clock signal and an address signal can be obtained as shown in FIG. 3d. If we sample and hold both reflected light amounts at the timing of this clock signal and address signal, the phase shown by the broken line o in Figure 3 will be 18.
A signal inverted by 0 degrees is obtained. By taking the difference between these sampled and held signals, a tracking error signal TR shown in t43, eK is obtained. In the figure, the sample and hold intervals are coarse, but in reality they are finely spaced to more than 1000 during one rotation, so the servo band can be sufficiently covered. Furthermore, since there is no difference in principle between clock pits and address pits, tracking error signals can also be obtained from address pits.

When the tracking control is turned on using the tracking error signal obtained in this way, both spots follow the clock pit and the address pit in between.

As mentioned above, in this method, the tracking error signal is obtained from the difference in the absolute values of the reflected sights of the two party spots, which causes a problem with the conventional method of obtaining it from the phase groove of λ/8 depth. Superimposition of offsets due to disk inclination and movement of reflected light during track following is eliminated. Furthermore, the clock pits and address pits are pits provided along a spiral or concentric circle, and it is not necessary to create wobble pits that are slightly shifted in the radial direction, making it possible to easily format the optical disc.

Next, a method for obtaining a focus error signal will be described.

FIG. 4 shows an example of an optical head, and FIG. 6 shows a path of reflected light in the optical head.

In FIG. 4, a light source with wavelength λ1 (λ1 semiconductor laser 2
) (indicated by a solid line) passes through a two-wavelength separation filter 3 in which a light beam with a wavelength λ1 is transmitted and a light beam with a wavelength λ2 is reflected, and is then sent to a polarizing beam splitter 4. The light passes through the λ/4 plate 6 and is focused on the optical disc by the aperture lens 6)
Narrowed down to.

On the other hand, a light beam (indicated by a broken line) from a light source with a wavelength λ2 (λ2 semiconductor laser 7) is transmitted to a polarizing beam sinter 4,
After passing through the λ/4 plate 8, the light beam of wavelength λ1 is transmitted, λ
The light beam No. 2 is reflected by the reflecting two-wavelength separation filter 9, passes through the λ/4 plate 8 twice, is reflected by the polarizing beam splitter 4, passes through the λ/4 plate 6, and is sent to the optical disc by the aperture lens 6. At the top, the light is narrowed down to M. The relative positions of the light spots L and M are obtained by adjusting the positions of both light sources.

In FIG. 6, the reflected light from the optical disk has a wavelength λ due to the action of a polarizing beam splitter (shown in FIG. 4).
The light beam of wavelength λ2 is guided to the photodetector 10&, and the light beam of wavelength λ2 is guided to the photodetector 10b. The photodetector detects when both light beams are just focused on the recording film surface (b
(shown in the figure) is located approximately midway in the optical axis direction of the position where each reflected light beam forms an image. Furthermore, the photodetector is configured to detect the amount of light at the center of the optical spora) l and ml on the photodetector, and if the difference in the amount of light received by the photodetectors 101L and 10b is taken, the focus error is determined. A signal FIC is obtained.

This will be explained in detail using FIGS. 6a, b, and c. a, b.

In Figure 0, the distance between the aperture lens 6 and the optical disc 1 is short.
Just-focus and far-away cases are shown, respectively. Since the changes in the size of light spora) l and m on the photodetector are reversed around the just focus, the photodetector 1ob receives the light when it is close, and the photodetector 101L receives the light when it is far away. When the amount of light becomes large, and the difference between the two amounts of received light is taken, an S-shaped focus error signal shown in Fig. d is obtained. In figure d, the horizontal axis shows the distance between the aperture lens and the optical disk, and the vertical axis shows the difference in the amount of light received by both photodetectors.

FIG. 6 shows a block diagram of a drive circuit that obtains all signals using this method. The signals received by the photodetectors 10a and 10b are amplified by amplifiers 11 and 12, and then amplified by the differential amplifier 1.
A difference signal is obtained at 3, and a sum signal is obtained at sum amplifier 14. A clock signal and an address signal are obtained from the sum signal by a clock extraction circuit 21, and are guided to a sample hold circuit 16, a delay circuit 22, and a circuit for address demodulation.

The sample and hold circuit 16 samples and holds the difference signal at the timing of the clock signal to obtain a tracking error signal Tic. The Tic signal is sent to the phase compensation circuit 1.
6. Tracking control is realized via the tracking actuator drive circuit 17.

The delay circuit 22 outputs a sample and hold signal slightly delayed from the timing at which the clock signal was obtained, and the sample and hold circuit 18 samples and holds the difference signal. That is, the focus error signal FK is obtained by sampling and holding the difference in the amount of reflected light when the two party spots illuminate a part of the mirror after the clock part. By doing this, the clock pit,
A focus error signal that is not affected by address pits and recording pits can be obtained. Focus control is realized through the FR multiplied signal, the phase compensation circuit 19, and the focus actuator drive circuit 20. Also.

A reproduced signal from the optical disc is obtained from each photodetector.

Effects of the Invention As described above, when using the optical disc configured according to the present invention, a tracking error signal can be obtained from the difference in the absolute value of the amount of reflected light from the clock pit or the address pit. This eliminates the problem of disk inclination and the superimposition of offsets caused by the movement of reflected light during track following operations, which are problems with the phase groove-based method. Furthermore, the clock pits and address pits are pits provided along a spiral or concentric circle, and it is not necessary to create wobble pits that are slightly shifted in the radial direction, making it possible to easily format the optical disc.

In addition, since the focus error signal FIC is obtained from the difference in the amount of reflected light when part of the mirror is irradiated, clock pits and address pits are generated.

A focus error signal that is not affected by recording pits can be obtained.

Furthermore, all signals can be obtained with a single photodetector divided into two parts, and there is no need to change the gain of the control circuit during recording and playback, which greatly reduces the configuration of the optical head and drive circuit. Can be simplified.

Also, since all signals are obtained by time division, TR.

Mutual interference among the FIC, address, and reproduction signals is also eliminated, and a stable total signal can be obtained.

The explanation above uses phase bits with a depth of approximately λ/4 as clock pits, but the same effect can be obtained even if the pits are not phase pits, as long as the reproduced signal is smaller or larger than other parts of the optical disc. The result is obvious.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, FIG. 2 is an explanatory diagram showing an example of a recording film of an optical disc used in the present invention, FIG. 3 is an explanatory diagram of the principle of obtaining a tracking error signal, and FIG. 4
FIG. 6 is a block diagram showing an example of an optical head, FIG. 6 is an explanatory diagram of the principle of obtaining a focus error signal, and FIG. 6 is a block diagram of a drive circuit. 1... Optical disc, L, M... Optical spot, K... Pit (clock pit), MR
...Mirror area, 2.7...Light source. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3

Claims (3)

[Claims] (1) A recording medium that performs recording and reproduction using a minute optical spot, and has pits arranged concentrically or spirally at regular time intervals, and the pits are used to transmit playback signals to other parts of the optical disc. An optical disc characterized by being smaller or larger than the playback signal. (2) The pits arranged concentrically or spirally at regular time intervals have a depth that is an integral multiple of 1/4 of the wavelength of a light source for recording and reproduction. The optical disc described in item 1. (3) Immediately after the pits arranged concentrically or spirally at regular time intervals, there is provided an area where no signal is recorded and where no signal is recorded. The optical disc according to item 1 or 2.