JPH08138266A - Device for reading optically recorded information - Google Patents

Abstract

PURPOSE: To prevent a reproduced signal from deteriorating in quality due to the nearest neighboring track or the next nearest neighboring track even when track pitches are made short by illuminating a plurality of optical spots and arranging these so as to include the maximum level of information of i-th track to be read in any optical spot. CONSTITUTION: An optical beam generated from a light source 1 is divided into 5 by a diffraction grating 2, reflected on a beam split 3 and projected to an optical disk 5 via an objective lens 4. The optical beam reflected by the optical disk 5 is returned to the beam splitter 3 via the objective lens 4 and after passing this, it reaches light detectors 6 to 10 for detecting the reflection strengths of the 5 optical spots on the disk. When information of i-th track on a recording medium is to be read, the optical spots are arranged so as to read the information of the i-th track to its maximum, a detected signal obtained therefrom is calculated by an adder 20 and a reproduced signal with crosstalk completely eliminated is outputted.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for reading a recording signal of an optical recording medium such as an optical disk, and more particularly to a cross generated between adjacent tracks from an optical disk recorded at high density using a plurality of light spots. The present invention relates to an optical recording information reader that reproduces information by removing talk.

[0003]

[0002]

[0004]

2. Description of the Related Art In recent years, high-definition television systems have been put into practical use, and recording of high-definition television signals on discs has come into practical use. To do this, a lot of information has to be recorded on the disc, with the current technology 30 cm in diameter to record one hour of video and audio.
Disc is required, and further miniaturization of the disc is required from the viewpoint of handling.

[0005]

In the conventional recording / reproducing method for an optical disc, one method for reducing the size of the disc is as follows.
A method has been adopted in which the track interval, that is, the track pitch, is made shorter than that at present. However, when the track pitch is shortened with respect to the diameter of a predetermined light spot, the leak amount of adjacent track information, so-called crosstalk, increases and the quality of the reproduced signal deteriorates.

[0006]

In order to remove the crosstalk, for example, a method as disclosed in JP-A-3-41622 has been proposed.
FIG. 4 is a diagram showing the arrangement of light spots in this method.
In the figure, 41 to 45 are tracks on which information is recorded, 401 to 403 are light spots, and 411 to 413 are the centers of the respective light spots. Center of light spot 4
12 is on track 43, 411 and 413 are track 4
Irradiation is performed so as to be at a position away from 3 by 1/2 the track pitch. From these light spots, the reproduction signals in which the information of the three tracks 42, 43, and 44 are mixed are read out. There is a predetermined relationship between the reproduction signal and the information recorded on the track,
By calculating each reproduction signal based on this relationship, the information of the three tracks can be independently extracted.

[0007]

FIG. 3 shows a case where the track pitch is further shortened in the above method. 31 to 31 in the figure
Reference numeral 37 is a track on which information is recorded.
305 is a light spot, and 311 to 315 are the centers of the respective light spots. In this method, when the track pitch is further shortened as shown in FIG.
2 and 314 also read the information of the tracks 32 and 36 (re-adjacent tracks) further outside the adjacent tracks 33 and 35, so that the track pitch is limited to the range in which the re-adjacent track signal component does not affect the reproduction signal. There was a problem that it could not be shortened.

[0008]

In short, when one main beam and two sub-beams are used, the information of the adjacent track (re-adjacent track) of the track irradiated with the two sub-beams is detected, so that three beams are used. Information on five tracks is detected. Here, the condition that the information from the two adjacent tracks, which are re-adjacent tracks among the five tracks, can be ignored is necessary for good and accurate reproduction of information. That is, a track pitch is required in which the sub-beam does not reach the re-adjacent track, and if the track pitch is shortened beyond this, the reproduction signal will be significantly deteriorated.

[0009]

Further, even when a total of five beams of one main beam and four sub-beams are used to obtain the information of the re-adjacent track, as in the case of using three beams,
Since it detects 7 tracks with 5 beams,
The condition that the information from the two tracks at both ends of the seven tracks (re-adjacent tracks again) can be ignored is necessary for accurate reproduction of the information.

[0010]

Even if the number of light spots is increased in this way, if the track pitch width is shortened beyond the condition that the information of the two tracks at the two ends of the plurality of tracks irradiated by the light spots can be ignored. There is a problem that the reproduction signal is significantly deteriorated.

[0011]

[0009]

[0012]

Although it has been considered to shorten the track pitch in order to further increase the recording density of the optical disc, the above method involves reduction of the spot diameter of the light beam. Unless the track pitch is shortened, more crosstalk components are mixed in, and the above method has a problem that it is difficult to obtain an accurate reproduced signal from which crosstalk is sufficiently removed.

[0013]

Therefore, the present invention has been made in view of the above points, and an object of the present invention is to reproduce a reproduced signal due to crosstalk from re-adjacent tracks or re-adjacent tracks even when the track pitch is shortened. An object of the present invention is to provide an optical recording information reader that does not cause deterioration.

[0014]

[0011]

[0015]

In order to solve the above-mentioned problems, the present invention is an optical recording information reading device for reading information recorded on a recording medium having a track structure,
A light source that emits a light beam for reading information on the recording medium, a photodetector for photoelectrically converting a read signal by a plurality of light spots formed by the light beam, and a signal output of the photodetector or the A reading means for calculating the signal output of the photodetector by delaying the signal output and outputting the reproduction signal, when reading the information of the i-th track of the recording medium, reading in all of the plurality of light spots The signal is characterized in that the information of the i-th track is contained in the maximum, and the ratio of the information of each track in the read signal of each light spot is different from each other.

[0016]

[0012]

[0017]

According to the present invention, when reading the information of the i-th track on the recording medium, a plurality of light spots are irradiated, and the information of the i-th track is included in the maximum in the read signal of any light spot. The detection signal from the light spots thus arranged is calculated, and the reproduction signal from which crosstalk is completely removed is output.

[0018]

[0013]

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the configuration of a recording signal reading apparatus for an optical disc using five light spots according to the present invention. In the figure, a light beam generated from a light source 1 is divided into five by a diffraction grating 2, reflected by a beam splitter 3, and irradiated onto an optical disk 5 via an objective lens 4. The light beam reflected by the optical disk 5 returns to the beam splitter 3 via the objective lens 4, is transmitted there, and photodetectors 6, 7, 8, 9 for detecting the reflection intensity of each of the five light spots on the disk. It reaches 10. The signal delay elements 11 to 14 correct the time delays of the respective detection signals so that they have a temporal relationship adjacent to each other in the radial direction, and the signals are multiplied by a predetermined coefficient in the coefficient amplifiers 15 to 19, and the adder / subtractor 20 makes five signals. The reproduction signal is output by taking the sum and difference of the outputs of the coefficient amplifier.

[0021]

In the configuration of FIG. 1, the light spots on the disc are arranged as shown in FIG. In FIG. 2, track 24 is a predetermined track from which information is currently read, tracks 23 and 25 are adjacent tracks adjacent to the predetermined track, tracks 22 and 26 are re-adjacent tracks adjacent to the adjacent track, and track 21. , 27 are re-adjacent tracks next to the re-adjacent track. 20
1, 202, 203, 204, 205 are 5 on the disc
Represents two light spots.

[0022]

Now, assuming that the track pitch is p, the center 213 of the light spot 203 is on the track 24, and the centers 211 and 215 of the light spots 201 and 205 are ½p away from the track 24. , 20
Centers 212 and 214 of 4 are 1/4 as seen from the track 24
In this example, the centers of the respective light spots are arranged at positions separated by p. In this embodiment, five tracks are simultaneously illuminated by five light spots.

[0023]

Specifically, in FIG. 2, the light spot 2
01 illuminates four tracks of tracks 22, 23, 24, 25, light spots 202, 203, 204 illuminate five tracks of tracks 22, 23, 24, 25, 26, and light spot 205 tracks. 23, 24, 2
Irradiates four tracks of 5 and 26. The five light spots 211 to 215 are configured to irradiate five tracks 22 to 26 at the same time.

[0024]

Further, the track pitch p is selected so that the irradiation range of each light spot is 2.45p in radius of the light spot. That is, one light spot is configured to be able to read information of 4.9p, and each light spot is set as described above so that the five light spots read only the information of the tracks 22 to 26. It is arranged. The irradiation range is a range in which the adjacent track information is read in an amount such that the influence of crosstalk is a problem.

[0025]

The information read by the light spot is arranged so that the information of the track 24 to be read is contained in the maximum in any light spot. The conditions therefor are not limited to 1/2 p and 1/4 p from the track 24 to the center of the light spot, and any light spot may be arranged as long as the distance does not exceed 1/2 p. 1 /
2p and 1 / 4p are convenient because the 0th order, ± 1st order, and ± 3rd order of the diffraction grating can be used.

[0026]

Further, the light intensities and shapes of the light spots 211 to 215 are all the same for simplification of description, but they may be different. For example, if the spot shapes are made different by giving different aberrations or defocuses to each spot, the ratio of information can be changed even if the spot intervals are the same. Therefore, the degree of freedom in design is improved, and it can be designed to be adapted to a plurality of disks having different track pitches.

[0027]

In this embodiment, the distance between the light spots in the track tangential direction is constant, but it need not be constant.
Generally, the diffraction grating is designed so that a large number of odd-order diffracted lights are emitted. Therefore, when 0-order, ± 1st-order, and ± 3rd-order diffracted lights are used, the intervals of the five light spots in the track tangential direction are 2: 1 :.
A ratio of 1: 2 is convenient. Also, when reading a disc that has sample pits that are displaced from the track center, such as the sample servo method, it is easy to read by selecting the interval of the optical spot in the track tangential direction with respect to the sample pit interval. become.

[0028]

Next, a method of reproducing the information recorded on the track from the read signal by the light spot will be described.

At a certain point of time, the information recorded on the track 22 is P22, and similarly, the information on the tracks 23 to 26 is P23, P24, P25, and P26, respectively.
The signal outputs read by the light spots 201 to 205 while the information P24 on the track 24 is being read will be represented as Q201 to Q205, respectively.

[0030]

The crosstalk rates of the light spots arranged as shown in FIG.
The relationship between the recorded information and the reproduced signal when the wavelength is 4 μm and the wavelength of the light source is 780 nm is calculated. The relationship between the recorded information and the reproduced signal varies depending on the track pitch, the wavelength of the reading light, the disc structure, the aberration, etc., but as an example, the signal ratio when the disc having the ideal pit shape in the case of no aberration is reproduced is simulated. The result is as follows.

[0031]

[0022]

[0032]

[Equation 1]

This 5 × 5 matrix is a matrix showing the relationship between the signal outputs Q201 to Q205 and the information P22 to P26 recorded on the tracks when the light spots are arranged as shown in FIG. In order to obtain the relation of P from Q, it is necessary to calculate the inverse matrix of the 5 × 5 matrix of the equation (1) and solve it for P.

[0033]

[0024]

[0034]

[Equation 2]

Therefore, when the crosstalk removal calculation is performed using the equation (2), the value of the recording information P24 of the track 24 to be read is Q201 to Q205, and the crosstalk is completely removed. Desired.

[0035]

Further, the effect is confirmed by concrete numerical values. For example, when information is recorded on the disc such that 0 and 1 are repeated for each track, that is, 0, 1, 0, 1, on the same radius of the disc of tracks 22 to 26.
When the signal obtained when the information of 0 is recorded is calculated according to the 5 × 5 matrix of the equation (1),

[0036]

[0027]

[0037]

(Equation 3)

When this is restored by the crosstalk removal calculation of the equation (2),

[0038]

[0029]

[0039]

[Equation 4]

Basically, it is possible to completely restore the information recorded on the disc as required by the equation (3). Also, not only the information on the track 24 but also the tracks 22, 2 illuminated by five light spots
It can be seen that the information of 3, 25, and 26 are also reproduced in perfect form at the same time.

[0040]

In addition, the signal of the track 24 to read the irradiation position of each light spot is the track 2.
By arranging at a position that becomes larger than the signals of 2, 23, 25, and 26, the accuracy of the reproduced signal can be focused and enhanced, so that when the light amount is small, jumping in, and dark noise of the photodetector. It is possible to suppress the adverse effects due to such factors.

[0041]

For comparison, a comparison will be made with the case of the conventional method of irradiating a light spot at a position ½ of the track pitch away. Under the same conditions as in this embodiment except for the arrangement of the light spots, one light spot detects information of 5 tracks as shown in FIG. 3, and therefore the light spots at both ends read information of adjacent tracks and re-adjacent tracks. I will end up. That is, considering that the information of 7 tracks is read by 5 light spots, the relationship between the signal output of the light spots arranged as shown in FIG. 3 and the recorded information is expressed by a 5 × 7 matrix.

[0042]

[0033]

[0043]

(Equation 5)

Of these, the central 5 × 5 matrix (5 × 7
A reproduction signal is obtained by obtaining an inverse matrix (in the dotted line frame of the matrix) and performing a crosstalk removal calculation on the result.

[0044]

[0035]

[0045]

(Equation 6)

From the above, it can be seen that a large error is included in the reproduced signal when comparing the prior art with this embodiment. This error deteriorates the quality of the reproduced signal. Moreover, the information of 5 tracks is not reproduced in a perfect form as in the embodiment.

[0046]

In the above-mentioned embodiment, the reproduction of the information of one track (track 24) has been described, but the information of five tracks (tracks 22 to 26) illuminated by five light spots is calculated from the equation (2). Also reproduced as a perfect form with crosstalk removed. Therefore, information of 5 tracks can be obtained at the same time. Not only the information of 5 tracks can be obtained from the 5 light spots, but the information of 3 tracks can be obtained from the 3 light spots by a similar method.

[0047]

Although the focus control and tracking control methods have not been described, it goes without saying that various methods are possible and a plurality of light spots can be used for tracking control. For example, a conventionally known three-beam method or an actuated push-pull method can be used. Since the light spot for reading the track information is also used for tracking detection, conventionally, the power of the reading light was distributed only to the eyes for tracking detection, whereas in the configuration of the present application, all the reading light is detected as a signal. Therefore, the amount of light used for signal detection is increased and a high quality reproduced signal can be obtained.

[0048]

[0039]

[0049]

As described in detail above, according to the present invention,
When reading the information of the i-th track on the recording medium, a plurality of light spots are irradiated, and the light spots are arranged so that the information of the i-th track is contained in the maximum in the read signal of any light spot. It is possible to calculate a detection signal from the optical spot of, and output a highly accurate reproduction signal with crosstalk completely removed. Further, since information on all tracks illuminated by a plurality of light spots can be simultaneously obtained in a perfect form without crosstalk, it is effective for reproduction of a high recording density type optical disc having a short track pitch.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical recording information reader according to the present invention.

FIG. 2 is a diagram showing a positional relationship between a track and an optical spot on an optical disc when five optical spots are used in the present invention.

FIG. 3 is a diagram showing a positional relationship between a track and an optical spot on an optical disc when a track pitch is reduced by a conventional method and five optical spots are used.

FIG. 4 is a diagram showing a positional relationship between tracks and a light spot on a conventional optical disc.

[Description of Reference Signs] 1 light source 2 diffraction grating 3 beam splitter 4 objective lens 5 optical disk 6-10 photodetector 11-14 signal delay element 15-19 coefficient amplifier 20 adder / subtractor 21-27 track 201-205 optical spot 211-215 Center of light spot

Claims (6)

[Claims] 1. An optical recording information reading device for reading information recorded on a recording medium having a track structure, the light source irradiating a light beam for reading information on the recording medium, and the light beam. And a photodetector for photoelectrically converting a read signal by a plurality of light spots, and a calculation for calculating a signal output of the photodetector or a signal output obtained by delaying the signal output of the photodetector and outputting a reproduction signal. When reading the information of the i-th track of the recording medium, the read signal in all of the plurality of light spots includes the information of the i-th track at the maximum, and the read signal of each light spot is read. An optical recording information reading device characterized in that the ratio of information of each track in a signal is different from each other. 2. The optical recording information reader according to claim 1, wherein the number of the plurality of light spots is three or more. 3. The information of the i-th track is read by the plurality of light spots.
A device for reading the optical recording information described. 4. The optical recording information reading device according to claim 2, wherein the information on the tracks illuminated by the plurality of light spots or the information on some of the tracks is read at the same time. 5. i-1 to i + using three light spots
5. The optical recording information reader according to claim 3, wherein the first three tracks are illuminated. 6. i-2 to i + using five light spots
5. The optical recording information reading device according to claim 3, wherein the second five tracks are irradiated.