JPS6260731B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical disc reading device.

Optical discs are attracting attention, in which unevenness is recorded on the disc surface in accordance with a recording signal, and the information is read out using light in a non-contact manner during reproduction. This method allows recording and reading of large amounts of information, enables mass duplication, and is resistant to the effects of dust and scratches. Uses are being considered. This video disc is described in the magazine ``PHILIPS TECHNICAL'', for example.
REVIEW), 1973, pages 178-193;
VLP'SYSTEM). According to this paper, a video disc input signal is frequency modulated to become a synthesized FM signal, which is converted into a rectangular pulse signal. This pulse signal is input to a laser modulator, and the laser beam is turned on and off to expose the photoresist coated on the disk or evaporate the deposited metal thin film. The areas irradiated with the laser light become pits (holes), and depending on the signal, a pattern is recorded in which the pits have the same width but vary in length. The information recorded in this manner is irradiated with coherent laser light and changes in the reflected light are read out. When coherent light is irradiated onto pits on the disk surface, the optical path length of the light reflected from the pits changes depending on whether the pits are present or not. Therefore, the light interferes with each other, and if this interference light is detected with a photodetector such as a photodiode,
The intensity of the light associated with the bits, that is, the information is read out. The recorded pit size is 0.8μm
Since the track pitch has a size of 1.66 μm, the readout device must focus the readout light beam to about 1 μm, and must have an automatic focus adjustment mechanism and an automatic tracking mechanism for disk surface runout and rotational axis runout. The size of the pit is about the same as the wavelength of the recording light and the wavelength of the readout light, and the track pitch is set so as not to be affected by crosstalk with adjacent tracks, so the recording density and capacity based on the above parameters are This was considered the limit of optical recording. An object of the present invention is to provide an optical readout method that reduces the amount of crosstalk in appearance and enables high-density, large-capacity readout.

The optical readout method of the present invention involves simultaneously irradiating light onto each of three adjacent information tracks of a disk-shaped recording medium in which information is stored in an optically readable form in the form of a track. By performing an arithmetic process of multiplying each signal of the information light from the information tracks on both sides of the information track by the respective crosstalk amount and subtracting it from the signal of the information light from the information track in the middle, It is configured to read out signals from the information track.

Hereinafter, this invention will be explained in detail with reference to the drawings. FIG. 1 is a diagram for explaining the conventional method, showing a track arrangement of pits 2 recorded on a recording material and a light beam 1 for reading information. When the light beam 1 illuminates the pit 2, a change in the intensity of the reflected light occurs, so the presence of the pit 2 is detected and read out as information. Even when the light beam 1 is irradiating the center of a pit, since the light beam 1 has a Gaussian intensity distribution and its base is widening, the light also enters pits in adjacent tracks. The amount of crosstalk that occurs due to this can be obtained by calculating a cumulative distribution function by integrating a Gaussian distribution (probability density function) in one-dimensional approximation. Second
The figure shows a pit width of 0.8μm and a light beam diameter of 2W of 1.0μm.
This figure shows the change in the amount of crosstalk depending on the track interval, where m is the track interval. track pitch
The amount of crosstalk when 3.2W = 1.6 μm is less than 10 ^-5 , which is not a problem as a signal level. However, the track pitch is 2.5W=1.25μm.
If it is narrowed to , the amount of crosstalk will be 10 ^-3 or more, which will cause a considerable problem in signal S/N.
The track pitch cannot be narrowed below 1.6 μm.

FIG. 3 is a diagram for explaining the reading method according to the present invention. 3 as a readout light beam
Light beams 1, 1', 1'' are used, which are separated from the central beam 1 by a track spacing in the direction orthogonal to the tracks. Therefore,
In Figure 3, light beam 1' is on track -1, light beam 1 is on track 0, and light beam 1'' is on track +1.
The center of the beam will be irradiated. Letting the amount of crosstalk of each optical beam to the adjacent track be k, the amount of signal light obtained from each optical beam 1, 1', 1'' is S,
S′, S″ can be written as follows.

S=kS _-1 +S ₀ +kS ₊₁ (1) S′=kS _-2 +S _-1 +kS ₀ (2) S″=kS ₀ +S ₊₁ +kS ₊₂ (3) Here S _-2 , S _-1 , S ₀ , S ₊₁ , and S ₊₂ represent the amount of signal light obtained when a light beam is incident on the center of each track.The contribution from the second adjacent track is considered small and will be ignored here.

From these equations (1), (2), and (3), S−kS′−kS″ = (1−2k ² )S ₀ −k ² S ₋₂ −k ² S ₊₂ (4) is obtained, and k The value of ₂ is uniquely determined by the track pitch and the size of the light beam, and this value is sufficiently small to obtain the signal _S0.Equation (4) means that the amount of light from each light beam is expressed as ( By calculating as shown in equation 4), an information signal S ₀ can be obtained, and the amount of crosstalk is 2k.
can be reduced from 2k ² (1-2k ² ) to 2k ² .
Therefore, the track pitch of recorded pits can be narrowed, and higher density can be achieved. Second
From the figure, since the crosstalk is 2k to 10 ^-5 for a track pitch of 3.2 W, a track pitch of 2.5 W is allowed to reach 2k ² to 10 ^-5 . This makes it possible to record and read information at a density 1.28 times higher than conventional technology (3.2W/2.5W). Since the recording capacity of optical disks is extremely large at ¹⁰⁹ bits, even an increase in capacity of just under 30% can bring out a significant effect.
FIG. 4 is a diagram showing an example of an apparatus used to realize the high-density optical reading method according to the present invention. Laser beams of different wavelengths emitted from each semiconductor laser 10, 11, 12 are transmitted to a half mirror 1.
3 and 14 into one light beam, and the lens 1
After being made into parallel light at step 5, it is reflected at half mirror 16 and guided to lens 17. Laser light is lens 1
A spot of 1 μmφ is focused on the disk 3 rotated by the motor 4, but the positions of the semiconductor lasers 10, 11, and 12 are separated by a minute distance (for example, 1.25 μm) from each other with respect to the optical axis. Therefore, the light beams of each laser are lined up at intervals of 1.25 μm. Each light beam is reflected by the pit of each adjacent track, and the laser beam is reflected by the lens 17, the half mirror 16, the lens 15, the half mirror 13, 1
4, the process returns to each semiconductor laser 10, 11, and 12. In semiconductor lasers, a self-coupling effect has been discovered that causes the emitted light to return to the active region of the semiconductor laser, causing changes in the amount of laser light and driving current.This self-coupling effect can be used to detect information from the returned light. can do. In Figure 4, the return light from different semiconductor lasers also enters each semiconductor laser, but the wavelength of each semiconductor laser is at least
If the difference is 100 Å, these light-induced self-coupling effects will not occur. Therefore, the information recorded on the three adjacent tracks mentioned above is read simultaneously. The read signal is multiplied by the amount of crosstalk by an arithmetic circuit to perform processing corresponding to equation (4). As shown in FIG.
The signals from the semiconductor laser 11 are attenuated by the attenuator 33 to a value multiplied by the crosstalk amount k, and a readout signal is obtained by subtracting these signals from the signal from the semiconductor laser 11. light beam and disk 3
Tracking and focusing signals for maintaining the relative positions of are well known and are described below. The reflected light from the disk 18 passes through a lens 17, a half mirror 16, a lens 19, a half mirror 20, and is guided to a two-sided split light receiver 21. Since the light amount distribution is unevenly distributed on the light receiver 21 depending on the relative positions of the track and the light beam, tracking deviation can be detected. Further, the light reflected by the half mirror 20 is guided to a four-sided split light receiver 23 via a wedge 22. When the disk 18 deviates from the focal position of the lens 17, the two-dimensional beam shape on the light receiver 23 changes to an asymmetrical elliptical shape, so that focusing deviation can be detected. Laser beams from each of the semiconductor lasers 10, 11, and 12 are incident on these detectors, and the displacements from each track are added, so tracking and focusing are easier than in the case of one laser beam. The signal becomes more reliable.

Although a device based on a signal readout method using a self-coupling effect has been described as an embodiment, the effects of the present invention can also be obtained even when a light receiving element corresponding to a light source is provided and signals are detected separately. it is obvious.

As described above in detail, according to the present invention, reading of high-density, large-capacity recording becomes possible by apparently reducing the amount of crosstalk.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the conventional information reading method, Figure 2 is a diagram showing the amount of crosstalk, and Figure 3 is a diagram for explaining the conventional information reading method.
FIG. 4 is a diagram for explaining the information reading method according to the present invention, FIG. 4 is a diagram showing an example of a device used to realize the present invention, and FIG. 5 is a diagram showing a signal processing circuit. In the figure, 1, 1', 1'' are light beams, 2 is a pit, 3 is a disk, 10, 11, 12 are semiconductor lasers, 13, 14, 16, 20 are half mirrors, 15, 17, 19 are lenses, Reference numerals 21 and 23 are area-divided light receivers, and 22 is a wedge.

Claims (1)

[Claims] 1 Light is simultaneously irradiated onto each of three adjacent information tracks of a disk-shaped recording medium in which information is stored in an optically readable form in the form of tracks, and information on both sides of the middle information track among the three information tracks is collected. Reading out the signal of the middle information track by performing an arithmetic process of subtracting the signal obtained by multiplying each signal of the information light from the track by the amount of crosstalk from the signal of the information light from the middle information track. A high-density optical readout method featuring: