JP2636563B2 - optical disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk, and particularly to a read-only optical disk on which high-density recording is performed, or an optical disk for high-density recording having a read-only recorded portion.

[0002]

2. Description of the Related Art A read-only optical disk or an optical disk having a read-only recorded portion is used for a music information recording disk, a video information recording disk, a computer memory, a document file disk, a data base, and the like. It can be, for example, a compact and widely used read-only optical disc that records music information.
On a disc (CD), digital audio data for about 75 minutes is recorded on one side of a plastic substrate optical disc having a diameter of 120 mm by a change in irregularities (pits).
Also, for example, a laser disk (LD), which is widely used as a read-only optical disk on which video information is recorded, has an analog video signal of about 30 minutes due to a change (pit) of unevenness on each side of a plastic substrate optical disk having a diameter of 300 mm. Is recorded. And, for example, the CD
Is defined so that reproduction is performed using a reproduction light having a wavelength of about 780 nm. However, the depth of the pits is set so that tracking information can be obtained even by reproduction using a single reproduction light beam by a so-called push-pull method. Is manufactured to about 110 nm. The shortest pit length is less than 0.9 microns to reduce the waveform interference between pits, the track pitch is 1.6 microns to reduce crosstalk between adjacent tracks, and the lens used for reproduction is reproduced. A numerical aperture (NA) of about 0.5 is used in consideration of the stability of the liquid crystal display.

[0003] In recent years, in view of ease of handling, low cost, and other points, there has been a demand for smaller playback devices and optical disks, as well as devices and optical disks with even higher performance. From the viewpoint as described above, there is a problem that the above-mentioned optical disk having a diameter of 300 mm is too large, and the amount of recorded information is too small with an optical disk having a diameter of 120 mm. For example, in the above-mentioned optical disk having a diameter of 120 mm, when an information signal to be recorded is compressed and recorded, a high-quality moving image of about one hour is obtained only by compressing the information signal by the current compression technology. Images cannot be recorded and reproduced, and in order to be able to record and reproduce high-quality moving images of about one hour on an optical disk with a diameter of 120 mm, the recording density must be several times higher than the recording density of current CDs. Is required.

[Problems to be solved by the invention]

By the way, in order to perform high-density recording / reproduction on an optical disk, the reproduction light used for reproduction from the optical disk has a short wavelength. An SHG element is used as a reproduction light source when reproducing from an optical disk. A lens having a large numerical aperture is used as a lens used in an optical system for reproducing data from an optical disk. Although various means such as a semiconductor laser used as a light source of reproduction light in an optical disk reproducing device, which can oscillate light of a short wavelength, are finally reaching a practical stage. Even this semiconductor laser can oscillate light having a wavelength of around 670 nm. Therefore, when this semiconductor laser is used, the recording density is calculated to be 1.36 times higher than that of a conventional device using light having a wavelength of 780 nm. It only enables the reproduction of an optical disk (a large laser such as an argon ion laser or a helium cadmium laser can be used to obtain light on the order of 400 nm. It is not practical to use it as the light source of the reproduction light in the reproduction apparatus of (1). S
At present, the HG element is unsatisfactory in terms of performance, price, size, etc., as being used as a light source of reproduction light in a general optical disk reproduction apparatus. The numerical aperture of the lens is 1 or less in principle, and the practical limit is about 0.6. Therefore, when the lens having a numerical aperture of 0.45 used in the conventional apparatus is changed to a lens having a numerical aperture of 0.6, the reproduction of an optical disk having a recording density 1.78 times higher than that of the conventional apparatus is calculated. Becomes possible. As described above, even if a laser beam having a wavelength of 670 nm is used as the reproduction light and a lens having a numerical aperture of 0.6 is used, 1.36 × 1.78 = 2 as compared with the conventional apparatus. .4
It only enables reproduction of an optical disk having a higher recording density than a conventional CD.

When the track density is increased by decreasing the track pitch in an optical disc, the problem of an increase in crosstalk between adjacent tracks becomes a problem.
The information recorded on the two tracks is simultaneously detected using three light beams, and the intensity and time of the information detected from the two outer tracks are adjusted to correct the information detected from the center track. The problem can be solved by applying a known crosstalk canceling means. However, there is a problem that as the track density is increased, the tracking error signal becomes smaller and tracking control cannot be performed. For example, the wavelength of the reproduction light is 780n
m, when the numerical aperture of the lens is 0.45, the limit of the number of tracks from which individual tracks can be separated and read, that is, the cut-off frequency f is 1150 lines /
mm. f = 2 · NA / λ = 1150 (lines / mm) Since the track pitch is 0.87 μm, when the wavelength of the reproduction light is 780 nm and the numerical aperture of the lens is 0.45 as described above, However, when the track pitch of the optical disc to be reproduced becomes 0.87 μm or less, it becomes impossible to perform the tracking operation because the track cannot be distinguished despite the fact that diffracted light from the pits is generated. Become. Therefore, if the track pitch is slightly widened from the above-mentioned 0.87 micron, the track can be separated, but the tracking control operation becomes unstable because the obtained tracking error signal is small. This point is the same whether the reproduction light is performed by one light beam or by three light beams. However, the above problem is that the tracking error signal is obtained from the diffracted light of the information pit. Instead, the problem can be solved by providing a guide groove for generating a tracking error signal. By the way, in an optical disc provided with spiral or concentric guide grooves, the recording density is doubled by using both the guide grooves and the non-guide grooves arranged alternately in the radial direction as recording areas. However, as described above, the wavelength of the reproduction light is 670 n
By using a laser beam of m and a lens having a numerical aperture of 0.6, 1.36 × 1.78 = 2.4 on calculation.
For an optical disc capable of reproducing data at a recording density higher than that of a CD (by a factor of 2), both the guide groove portions and the non-guide groove portions which are arranged alternately in the radial direction as described above are used as recording areas. When used, the recording density of the optical disk is 4.8 times that of a CD. However, in the case of an optical disk in which the recording of information signals in the recording area is recorded in a manner of changing unevenness as described above, The problem is that the recorded content of the information signal and the tracking error signal interfere with each other and a good reproduction operation is not performed, and a solution to the problem has been demanded.

[0006]

SUMMARY OF THE INVENTION According to the present invention, both a guide groove portion and a non-guide groove portion which are formed by providing spiral or concentric guide grooves and which are alternately arranged in the radial direction are formed. An optical disc used as a recording area, in which information signals targeted for recording / reproduction are recorded by a change in unevenness corresponding to the information signals targeted for recording / reproduction in the recording area. Setting the height between the surface of the guide groove portion and the surface of the non-guide groove portion to 1/15 to 1/20 of the wavelength of the reproduction light used for reproducing the information signal from the optical disk. A numerical value obtained by multiplying the above-described unevenness change amount for recording an information signal by the above-described unevenness change amount value by the refractive index of the constituent material of the portion is used for reproducing recorded information from the optical disk. Ira To provide an optical disc comprising set to be substantially equal to a quarter of the wavelength of the reproduction light that.

[0007]

According to the present invention, both the guide grooves and the non-guide grooves, which are formed by providing spiral or concentric guide grooves and are alternately arranged in the radial direction, are recorded and reproduced as recording areas. Height between the surface of the guide groove and the surface of the non-guide groove on the optical disc on which the recording of the information signal targeted for recording / reproduction is performed by the change in the unevenness corresponding to the information signal Is one of the wavelengths of the reproduction light used for reproducing the information signal from the optical disc.
/ 15 to 1/20, and the amount of change in the unevenness for recording an information signal is obtained by multiplying the numerical value of the amount of change in the unevenness by the refractive index of the constituent material of the portion. Since the numerical value is set to be substantially equal to 1/4 of the wavelength of the reproduction light used for reproducing the recorded information from the optical disk, the difference between the recorded content of the information signal and the tracking error signal can be obtained. Reproduction of both signals is performed favorably.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The specific contents of the optical disk of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a perspective view of a part of the optical disk of the present invention, and FIG. 2 is a diagram showing the relationship between the depth of a guide groove, the amount of reflected light and a tracking error signal.
FIG. 1 is a perspective view of a part of an optical disk showing a schematic structure of the optical disk of the present invention. In FIG. 1, illustration of a reflective film, a protective film and the like is omitted. In FIG. 1, 1
Is a substrate of an optical disk. The substrate 1 is provided with a spiral or concentric guide groove G. The substrate 1 is made of a plastic material transparent to the reproduction light. The reproduction light incident from the surface 1a side of the substrate 1 passes through the substrate 1 and then faces the signal surface facing the surface 1a. The light is reflected by a reflection film (not shown) provided on the side 1b, returns inside the substrate 1, and exits from the surface 1a. On the signal surface 1b, non-guide grooves (land portions) L, L.
, And guide grooves (grooves) G, G... Are sequentially and alternately formed. And the above-mentioned non-guide groove portion (land portion) L,
The information signal to be recorded / reproduced is recorded as a change in unevenness in both L... And the guide groove portions (groove portions) G, G. In the figure, portions indicated as P, P... Are concave portions (pits) P provided corresponding to information signals, and portions between the pits P are convex portions provided corresponding to information signals. It is.

As described above, in the optical disk of the present invention, non-guide grooves (land portions) L, L... And guide grooves (groove portions) G, G formed alternately on the signal surface 1b side of the substrate 1 sequentially.
Are used as recording areas, and the radial width of each of the non-guide grooves (land portions) L, L ... and the radial width of each of the guide grooves (groove portions) G, G ... The width is substantially equal. In FIG. 1, Hg is the height between the surface of the guide groove portion G and the surface of the non-guide groove portion L, that is, the depth (or the depth) of the guide grooves G, G in each guide groove portion (groove portion) G, G. And Hp in the figure is a non-guide groove (land) L, L... Used as a recording area.
And the depth (or height) of the pits P recorded in each of the guide groove portions (groove portions) G. Then, the depth (or height) Hg of the aforementioned guide grooves G, G.
Is based on a characteristic indicating the relationship between the depth of the guide groove shown in FIG. 2 and the amount of reflected light and the tracking error signal.
1/15 to 1/2 of the wavelength of the reproduction light so that both the amount of reflected light and the tracking error signal can be obtained with sufficient magnitude.
The depth (or height) is set to about 0.

Each non-guide groove portion (land portion) L, L... Used as a recording area on the optical disc, and each guide groove portion
(Groove portion) Depth of pit P recorded on G
(Or height) Hp is a numerical value obtained by multiplying the above-described depth Hp of the pit P by the refractive index n of the constituent material of the substrate 1.
The value is set to be substantially equal to 1/4 of the wavelength of the reproduction light used for reproducing the recorded information from the optical disk.

In the optical disk of the present invention, as shown in FIG. 1, the pits P, P corresponding to the information signal are also provided at the bottom of the guide grooves G for generating the tracking error signal.
Since P is provided at a depth of 1/4 of the wavelength of the reproduction light, the tracking information generated in the guide groove G has a small amount of reflected light at the pit P portion. The period of the change in the amount of light due to the change is extremely shorter than the period of the tracking information, such as 10 minus the third power, and the influence appears to be averaged. In a reproducing apparatus that reproduces information, information processing in the guide groove G does not cause a substantial adverse effect on tracking information due to a change in unevenness due to an information signal. When tracking information is obtained by using three light beams in the optical disk of the present invention having the above-described configuration, unevenness recording by an information signal provided in a guide groove is performed. In order to minimize the influence of the above, the racking light beam is preferably located near the boundary between the guide groove G and the non-guide groove L.

When tracking the guide grooves G, G... On the optical disk and when tracking the non-guide portions L, L. When information is reproduced from the pit string recorded in the non-guide portions L, L.
When information is reproduced from the pit train recorded in the above, it is necessary to invert the polarity of the tracking signal. Therefore, when recording a continuous information signal, it is preferable to record continuously in the guide grooves G, G... Or to record continuously in the non-guide grooves L, L. Is good.

The manufacturing steps of the optical disk of the present invention are exemplified as follows. (1) Wash the glass disk after mirror polishing. (2) A photoresist is applied to a glass disk. (3) Expose and develop the pattern of the guide groove on the photoresist film. (4) The glass disk is etched using the photoresist film as a mask to form guide grooves in the glass disk. (5) The glass disk is washed after removing the photoresist film. (6) Apply a photoresist film. (7) Exposure and development of the photoresist film with information to be recorded using recording light near 450 nm by an argon laser, a krypton laser, a helium cadmium laser, or the like. (8) As in the case of CD and LD, a mother, a master, and a stamper are sequentially formed from the above-mentioned glass disk, and an optical disk is obtained using the manufactured stamper. Needless to say, the optical disc of the present invention can be applied to a write-once optical disc in which information is recorded by drilling.

[0014]

As will be apparent from the above description, the optical disk of the present invention has guide grooves formed in the form of spiral or concentric guide grooves and arranged alternately in the radial direction. An optical disc on which an information signal to be recorded / reproduced is recorded by a change in unevenness corresponding to an information signal to be recorded / reproduced with both the portion and the non-guide groove as recording areas The height between the surface of the guide groove portion and the surface of the non-guide groove portion is set to 1/15 to 1/20 of the wavelength of the reproduction light used for reproducing the information signal from the optical disc; The amount of change in the unevenness for recording an information signal is obtained by multiplying the numerical value of the change in the unevenness by the refractive index of the constituent material of the portion is used for reproducing the recorded information from the optical disc. By being set to be substantially equal to one quarter of the wavelength of the reproducing light,
The information signal targeted for recording / reproducing is recorded by the change of the concavo-convex corresponding to the information signal targeted for recording / reproducing with both the guide groove part and the non-guide groove part as the recording area. Thus, it is possible to favorably reproduce both the recorded content of the information signal and the tracking error signal on the optical disk whose recording density is doubled, and the conventional problem described above by the present invention. Is well resolved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a part of an optical disc of the present invention.

FIG. 2 is a diagram showing the relationship between the depth of a guide groove, the amount of reflected light, and a tracking error signal.

[Explanation of symbols]

Reference numeral 1 denotes a substrate of an optical disk, G denotes a spiral or concentric guide {groove guide groove (groove)}, L denotes a non-guide groove (land), P denotes a concave portion (pit) provided corresponding to an information signal. ,

Claims (1)

(57) [Claims] The present invention uses a guide groove portion and a non-guide groove portion which are formed by providing spiral or concentric guide grooves and which are arranged alternately in the radial direction sequentially as a recording area. An optical disc in which recording of an information signal to be recorded / reproduced is performed by a change in concavity and convexity corresponding to the information signal to be recorded / reproduced in a recording area, wherein the guide described above is provided. The height between the surface of the groove and the surface of the non-guide groove is set to 1/15 of the wavelength of the reproduction light used for reproducing the information signal from the optical disk.
The numerical value obtained by multiplying the numerical value of the change amount of the unevenness for recording the information signal by the refractive index of the constituent material of the portion and setting the value to 1/20, An optical disc set to have a value substantially equal to 1/4 of the wavelength of the reproduction light used for reproducing the recorded information from the optical disc.