JPH04301221A - Optical recording disk and reproducing device - Google Patents

Abstract

PURPOSE:To increase the density of the recording tracks of the disk. CONSTITUTION:A track pitch is widened to the extent at which crosstalks do not arise at every other three tracks. Three pieces of the tracks are subjected to simultaneous reproduction by three beams and the signal processing to cancel the crosstalks with each other is executed, by which the recording density of the optical disk is increased and the reproducing rate is increased as well.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to recording and reproducing of an optical pickup device for reading recorded information on an optical disk using a laser beam.

0002

2. Description of the Related Art Currently, various companies are conducting research on increasing the density of optical discs, and various methods for increasing the density have already been devised. For example, in order to reduce the length and track pitch of recorded pits and obtain a minute beam spot that enables reproduction of the recorded pits, a short wavelength laser in the visible range is used as a light source, and an aperture in the objective lens is used. In some cases, a large number of beams are used, or a super-resolution phenomenon caused by shielding a part of the beam is utilized. In addition, there is a method in which a multiplexed recording film is formed on an optical disk and is read by a plurality of laser beams having different wavelengths. and,
Although it is still far from the practical stage, a method that applies the hole burning effect that can dramatically increase the recording density is also being considered.

[0003] Here, as a conventional technique, ``Double the track density of an optical disk using a crosstalk canceller'', which was announced at the Japan Society of Applied Physics in the spring of 1990, and which is considered to be close to the present invention, will be explained. In this system, both lands and grooves are used as data tracks in order to increase the density of the optical disc, and crosstalk between reproduced signals from adjacent tracks is removed using a three-beam optical head and an adaptive filter. FIG. 5 shows a conceptual diagram of this recording/reproducing method. In the magneto-optical medium 51, the lands and grooves have the same width, and both serve as data tracks. The three-beam optical head 53 simultaneously reads data on three adjacent tracks, and uses the sub-beams 52a, 5
Crosstalk components included in the main beam 52b are removed using the reproduced signal 2c, and an adaptive crosstalk canceller 54 using a digital transversal filter is used to remove the crosstalk components.

0004

[Problems to be Solved by the Invention] When increasing the density of an optical disc, it is desired that the information transfer speed when reproducing the optical disc be high, but in the case of the crosstalk canceller method mentioned in the conventional example, Even if three beams are used, only the information at the center beam spot position can be read as a reproduced signal, and the transfer speed remains the same as before. The present invention uses a light source and optical disc recording technology to provide a recording and reproducing method that makes it possible to further increase the density of an optical disc by effectively utilizing a beam spot used for reproduction and to increase its reproduction speed. It is something.

[0005]

[Means for Solving the Problems] According to the present invention, the recording pit array of an optical disc is recorded so that, when the basic track pitch is 1, the track pitch becomes 2 or more every three tracks. Also, when reproducing this, three beam spots are formed on the recording surface of the optical disc, and each of the three beam spots is located on each of the three tracks lined up with the basic track pitch. An optical pickup is provided. and,
The intensity of each of the three beams that are diffracted by the recording pits on the optical disk and reflected back is detected using a photodiode, etc., and the three signals obtained are processed to detect crosstalk. 3.
The recorded information recorded on three tracks is read simultaneously.

[0006]

[Operation] When the track pitch is narrowed to increase the recording density, assuming the beam spot size is constant, the reproduced signal will be affected by the recorded pits on the adjacent track, resulting in crosstalk signals. will now include. However, if the rate of influence of recording pits on adjacent tracks on crosstalk is known in advance, it is possible to cancel the amount of crosstalk through arithmetic processing.

FIG. 1 shows three beam spots irradiating each of three tracks lined up with a basic track pitch. Amount of crosstalk from the adjacent track Crosstalk from the adjacent track to the signal from the track being traced
When the reproduction signals of tracks a, b, and c are respectively Sa, Sb, and Sc, the reproduction signals of beam spots A, B, and C are SA, SB, and SC.
The track pitch is doubled on the left and right sides of tracks a and c, respectively, and is only affected by crosstalk on one side, so SA = Sa + αSb SB = αSa + Sb + αSc SC =
αSb+ Sc
−(1
).

[0008] SA, SB, SC to Sa, Sb,
To find Sc, Sa={(α2 −1)SA +αSB −α2
SC }/(2α2 −1) Sb=(αSA −S
B +αSC )/(2α2 −1) Sc={α2
SA + αSB + (α2 −1) SC }/(2α
2-1)

- (2). Furthermore, when the method of the present invention is used, it is possible to obtain a reproduced signal by canceling the amount of crosstalk, so that the track pitch can be reduced to about half compared to the case where the present method is not used.

[0009]

[Embodiment] An embodiment according to the present invention will be explained using the drawings. FIG. 2 shows a schematic diagram of the optical system of an optical pickup incorporating this method, and FIG. 1 shows the positional relationship between the beam spot and the track. The laser beam emitted from the laser diode 1 is collimated by the collimating lens 2.
The resulting light passes through the diffraction grating 3 and forms ±1st-order diffraction beams. After passing through a polarizing beam splitter 4 and a 1/4 wavelength plate 5, the beam passes through a reflecting mirror 8 and then passes through an objective lens 6.
The drive coil 9 is placed on the recording pit surface of the optical disk 7 by
The focus is controlled by the +1st order, 0th order, -
The first-order diffraction beam creates three beam spots 21a,
21b and 21c are formed.

As shown in FIG. 1, the recording pit tracks of the optical disc 7 have three tracks as a unit, and the outer track pitch is doubled. Each of the three beam spots undergoes diffraction by the recording pit 22, becomes a reflected beam, passes through the objective lens 6, reflection mirror 8, and quarter-wave plate 5, and becomes a polarized beam. The light is reflected by the splitter 4, enters a return optical system consisting of a plano-convex lens 10, a plano-concave lens 11, and a cylindrical lens 12, and is focused on a six-divided photodiode 13.

FIG. 3 shows the six-divided photodiode 13 and the focused beam spots 34, 35, and 36. By the photodiodes 31, 32, 33,
Detects 1st and 0th order diffracted light. Tracking errors and focus errors are detected by the push-pull method and the astigmatism method, respectively, based on four signals from the central four-part photodiodes 33a, 33b, 33c, and 33d. Then, based on the signals of the photodiodes 31 and 32 and the sum signal of the four-divided photodiodes 33a to 33d,
Through the signal processing of equation (2) described above, a signal with crosstalk canceled is obtained, although the details of the circuit are not shown in the drawings. However, the three beam spots 21a on the optical disc
, 21b, and 21c are not aligned in the radial direction of the optical disc, so a temporal signal shift must be taken into consideration. Therefore, a delay circuit is used. According to this embodiment, when the basic track pitch is reduced to half that of the conventional method, the number of tracks on the optical disc can be increased to 1.5 times that of the conventional method, and the recording density can also be increased to 1.5 times. Can be done.

0012

Effects of the Invention: By using the optical disk recording and reproducing method according to the present invention, the wavelength of the laser used for reproduction, the numerical aperture of the objective lens, and the beam intensity distribution can be changed without changing the beam spot diameter. Since information can be reproduced even if the track pitch of recording pits is narrowed while leaving the data as it is, it is possible to further increase the density of optical discs, and to
Since the data are read simultaneously, the data detection speed during information reproduction can be increased without changing the rotational speed of the optical disc.

[Brief explanation of drawings]

FIG. 1 shows the positional relationship between a beam spot and a track in an embodiment of a disc according to the present invention.

FIG. 2 schematically shows an optical system according to an embodiment of the present invention.

FIG. 3 shows the relationship between a photodiode and a beam spot in an embodiment of the present invention.

FIG. 4 shows the signal detection principle of the present invention.

FIG. 5 shows a conventional crosstalk canceller type optical system.

[Explanation of symbols]

Claims (3)

[Claims] 1. An optical disc on which data is recorded such that when the basic track pitch is 1, the track pitch is 2 or more for every three tracks. [Claim 2] Three beams are used during reproduction, and each of the three beam spots formed by the objective lens is placed on each of the three tracks lined up with the basic track pitch. A recording and reproducing method characterized by the following: 3. Each of the three beams reflected and returned after being diffracted by the recording pit on the optical disk is detected, and the three signals are processed by arithmetic processing means to cancel the amount of crosstalk. A playback device characterized by converting the information into two signals and simultaneously reading recorded information on three tracks.