JPS6244329B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for optically recording or reproducing information by relatively moving a recording medium and a recording or reproducing beam.

Encoded video signals and audio signals can be recorded on a recording medium in a spiral or concentric manner as optical information such as optical transmission characteristics, reflection characteristics, phase characteristics, etc., or the information recorded in this way can be Various optical recording and reproducing methods have been proposed in the past. The feature of this optical recording/reproducing method is that the recording density of information is extremely high. Generally, the recording medium is rotated at high speed, and the laser light emitted from the laser light source is used to record the information. The information is recorded or reproduced by modulating the signal and focusing it on the recording medium.
In such optical recording and reproducing methods, if uneven rotation occurs in the recording medium during recording or if the diameter of the pits on which information is recorded varies,
Errors will occur during playback. For this reason, conventionally, a change point is provided on an information track on a recording medium by redundant bits, and this change point is read as a synchronization or position signal during reproduction. However, in this case, it is necessary to distinguish between the information to be recorded and the redundant bits, so it is necessary to select a code with a small DC component as the information code conversion code, or to select a modulation method that allows self-clocking. This method has the disadvantage that the information modulation method is limited, and the recording density is lowered by that amount because redundant bits are recorded.

An object of the present invention is to provide an optical recording/reproducing method that eliminates the above-mentioned drawbacks, allows high-density recording of information using any modulation method, and accurately detects synchronization or position signals during recording or reproduction. It is not intended to be provided.

In optically recording or reproducing information by irradiating a recording or reproducing beam onto a recording medium, the present invention provides a method for optically recording or reproducing information by irradiating a recording or reproducing beam onto the recording medium. It is characterized in that it uses grooves that cross at right angles and detects a modulated beam from the grooves to use as a synchronization or position signal during recording or reproduction.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an example of a recording medium used in the optical recording/reproducing method of the present invention, and FIG. 2 is a perspective view showing an enlarged part of the recording medium. This recording medium 1 has a disk-shaped base 2 on which grooves 3 are regularly formed radially, and a photosensitive recording material 4 is coated over the entire surface. The grooves 3 can be created by laser beam or by press working from a master disk on which protrusions corresponding to the grooves are formed. To record information on such a recording medium 1, it is rotated at high speed and a laser beam 5 modulated by the information is emitted.
is focused onto the photosensitive recording material 4 via an objective lens 6 movable, for example, in the radial direction of the recording medium 1. In this way, a spiral information track 7 is formed on the recording medium 1 perpendicular to the groove 3, and encoded pits 8 are formed within this track. Here, if the grooves 3 have been formed in the recording medium 1 in advance, and if the output of the laser beam 5 when the pits 8 are not formed is below the photosensitive threshold level of the photosensitive recording material 4, the laser beam 5 will be radial. Each time it crosses the groove 3, the intensity of the reflected light at that part is modulated. Therefore, by detecting this, successive grooves 3 can be detected, and the modulation thereof can be used as a synchronizing signal.

The above-mentioned recording medium 1 can be used as a recording medium for playback as it is, but in general, a master disc for pressing is created based on it, and from this master disc, a large number of recording media for playback, that is, a large number of disks, are created. Creating.

In the present invention, the disk surface is preferably a reflective surface made of a metal coating, a magneto-optical material, etc., except for the pit portion, and the pit portion is transparent. The depth of the radial grooves is set to a value other than an integral multiple of λ/4 with respect to the wavelength λ of the reproduction beam. In this way, as will be explained below with reference to FIGS. 3 and 4, when the beam passes through the groove, the intensity distribution of the reflected light on the pupil plane will be asymmetrical with respect to the optical axis of the reflected beam, and the pit will be It is symmetrical when passing through.

FIG. 3 is a schematic diagram showing how reproduction beams 13 to 13' having a width of 2a are irradiated onto a groove 12 having a width of 2w on the disk surface 11. The direction of the disk surface 11 is taken as the x-axis direction, and the center of the reproduction beam is The direction of , that is, the optical axis is the Z axis. indicates the phase difference given by the groove 12 to the reproduction beam.

FIG. 4 shows that the reproducing beam is in groove 12 with respect to FIG. 3.
δ is the deviation between the center of the groove and the center of the beam spot, and plane X is the observation plane.

Here, for simplicity, we will consider the problem of diffraction due to slits, as shown in FIG. The diffraction pattern due to a slit with a width of 2a is created by Fraunhofer diffraction as follows: A(x) = 2aSin kaX/haX/Z _O where X is the coordinate in the pupil plane direction, k is 2π/λ, and λ is the wavelength of the reproduction beam. , Z _O is the distance between the pupil plane and the groove plane.

The slits, , are each width (a-w+
δ), 2wλ (2-w-δ), so each diffraction is as follows.

However, α=kX/Z _O (pupil plane) The intensity distribution I ₍ – ₎ of the diffraction image on the pupil plane becomes as follows when normalized by the center intensity (α=0).

Note that the diffraction due to a slit with a slit width of 2a at a distance l between the slit centers is as follows: 2asin kaX/Z _O /kaX/Z _O cosKlX/
It can be expressed as _2ZO .

According to equation (1) above, I ₍ 〓 ₎ changes to α due to the change in δ.
There is an asymmetry with respect to

On the other hand, since there is no reflection from the slit on the pit surface, The final term is 1/a ²・2/α ² sin {α/2 (a-w+δ)} sin {α/2 (a-w-δ)} cos α (a+w) = 2/a ² α ² {sin ² α/2(aw) cos ² α/2δ−cos ² α/2(aw) sin ² α/2δ} cos α(a+w).

That is, in this case, I ₍ 〓 ₎ becomes an even function of α regardless of δ, and the intensity distribution on the pupil plane becomes symmetrical.

As an embodiment of the optical reproducing apparatus that utilizes the above-mentioned change in intensity distribution and implements the present invention, the fifth
As shown in the figure, the reflected light from the disk 11 is received by two photodetectors 15A and 15B arranged symmetrically in the moving direction of the groove 12 with the optical axis Z of the reproduction beam in between. Groove 12 depending on the output difference of
A synchronization signal is obtained by detecting the modulated beam from the photodetector, and recorded information is detected by extracting the sum of the outputs of these photodetectors. That is, in FIG. 5, a reproduction beam emitted from a laser light source (not shown) is focused onto an information track on the disk surface 11 via a half mirror 16 and an objective lens 17, and the reflected light from the disk surface 11 is focused on an information track on the disk surface 11. The light is received by photodetectors 15A and 15B through lens 17, half mirror 16, and lens 18. lens 1
8, the image on the surface of the objective lens 17 is detected by a photodetector 15A, 1
This is for forming an image on 5B. In this way, by supplying the outputs of the two photodetectors 15A and 15B to the differential circuit 19 and the summation circuit 20, respectively, the groove 12, that is, the synchronization signal, is transferred from the differential circuit 19 to the summation circuit 20. Information signals can be extracted from. Note that the method of detecting the modulated amount from the groove 12 can be similarly adopted during recording.

FIGS. 6A and 6B show the groove 12 on the disk 11.
2 is a diagram schematically showing the intensity distribution of reflected light on the photodetector surfaces 15A and 15B when the reproducing beam spot 23 scans the pits 22. It is covered. When scanning the groove 12, when the spot 23 touches the edge of the groove 12, the intensity distribution of the reflected light from the disk 11 on the photodetectors 15A and 15B becomes asymmetrical with respect to the optical axis, and the spot 23 When the center of the groove 12 comes to the center of the groove 12, the intensity distribution becomes symmetrical. Therefore, a synchronizing signal as shown in FIG. 7A is obtained from the differential circuit 19 shown in FIG. 5 every time the signal passes through the groove 12.

On the other hand, when scanning the pit 22, the intensity distribution of the reflected light from the disk 11 on the photodetectors 15A and 15B is symmetrical with respect to the optical axis. , Figure 7B
As shown in the figure, an information signal whose level is extremely low in the pit portion is obtained. In addition, in FIG. 7B, the portions indicated by symbols 25A and 25B are groove 1.
This is the modulation amount by 2. As is clear from FIGS. 7A and 7B, the modulation amount due to the pits 22 is not detected in the differential circuit 19, and the modulation amount due to the grooves 12 is only slightly detected in the summation circuit 20, and the information signal is has no effect on the Incidentally, the amount of modulation caused by the groove 12 appearing in the information signal can be made sufficiently smaller than the modulation caused by the pit 22 by increasing the numerical aperture of the objective lens 17 in FIG.

8A, B and C are a partial perspective view of the disk 11 in the case where the pits 22 are also formed in the grooves 12, and diagrams showing the synchronization signal and the information signal, respectively. In this case, if pits 22 are formed in and around the groove, no synchronization signal will be detected, but the synchronization signal in this part will be electrically generated based on the synchronization signal from the groove without pits 22. be able to.

Note that by setting the depth of the groove 12 to be other than an integer multiple of wavelength λ/4 of the reproduction beam, a desired intensity distribution can be obtained, and when the depth is λ/8, the photodetector 15A , 15B becomes maximum. Furthermore, if the grooves 12 are formed densely, clock accuracy can be further improved.

As described above, according to the present invention, since the grooves are formed in advance on the recording medium perpendicular to the main scanning direction, there is no need to form changing points by redundant bits during recording. Therefore, even if an arbitrary method, such as a simple modulation method such as NRZI, is adopted as the information modulation method, errors will not occur during reproduction. Furthermore, information can be recorded at even higher density since there is no need for change points due to redundant bits.

Note that the information obtained from the radial grooves is not limited to the synchronization signal, and information such as the position on the recording medium, sector number, etc. can also be added. Furthermore, although the above example describes a reflective type reproducing device, the present invention can also be effectively applied to a transmissive type if modulation due to grooves and modulation due to pits can be detected separately. .

[Brief explanation of the drawing]

FIG. 1 is a plan view diagrammatically showing the configuration of an example of a recording medium used in the optical recording/reproducing method of the present invention, FIG. 2 is a partially enlarged perspective view of FIG. FIG. 4 is a cross-sectional view schematically showing the state when the recording or reproducing beam is irradiated onto the groove, and FIG. The figure is a diagram showing the configuration of an example of an optical reproducing device embodying the present invention, and FIGS. 6A and B are optical detection of reflected light when passing through grooves and pits in the optical reproducing device shown in FIG. 7A and B are diagrams showing the sync signal and information signal taken out from the differential circuit and summation circuit, respectively. FIG. 6 is a diagram showing a part of the recording medium when pits are also formed in the groove portion, and a synchronization signal and an information signal extracted from this part, respectively. 1...Recording medium, 2...Substrate, 3...Groove, 4...
...Photosensitive recording material, 5...Laser light, 6...Objective lens, 7...Information track, 8...Pit, 1
1...Disc, 12...Groove, 15A, 15B...
...Photodetector, 16...Half mirror, 17...Objective lens, 18...Lens, 19...Differential circuit,
20... Harmonic circuit, 22... Pit, 23... Beam spot for reproduction, 24... Reflection film.

Claims (1)

[Claims] 1. When recording or reproducing information optically by irradiating a recording or reproducing beam onto a recording medium,
As the recording medium, a groove is formed that crosses a plurality of information tracks to be recorded or recorded on the recording medium at almost right angles, and a modulated beam from the groove is detected to perform synchronization during recording or reproduction. or a position signal.