Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2000-12-22
2004-05-04
Korzuch, William (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S277000
Reexamination Certificate
active
06731589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate for optical recording media of a so-called land-groove recording type, an optical recording medium, a manufacturing process for optical recording media, and an optical recording/reproducing method. More particularly, this invention is intended to minimize thermal crosstalk between adjoining tracks, that is, between a land and an adjoining groove, minimize a noise, and thus improve a recording density.
2. Description of the Related Art
With the recent trend to digitization of information, there is an increasing demand for media in which a large amount of digital data can be recorded. Media capable of meeting the demand include a so-called phase change optical recording medium, for example, a phase change optical disk, and a magnetooptical disk. The phase change optical recording medium has crystallinity thereof thermally changed to change the optical characteristic thereof, whereby recording is achieved. The magnetooptical disk has a magnetooptical effect thereof changed with application of heat and a magnetic field.
In general, the phase change optical disk or magnetooptical disk has, as seen from a schematic sectional view of
FIG. 9
showing a major portion of the disk, a recording layer
5
formed over a substrate
11
for optical recording media with a transparent dielectric layer
51
between them. The substrate
11
transmits light. The transparent dielectric layer
51
is made of, for example, SiN or ZnS-SiO
2
. The recording layer
5
is a magnetooptical recording layer or a phase change recording layer and so on.
The phase change optical disk is such that changes in reflectance for predetermined light are detected in order to reproduce a recorded information signal. The magnetooptical disk is such that changes in polarization of predetermined light are detected in order to reproduce an information signal.
In these optical disks, guide grooves, that is, groove-like concave parts
2
that are generally referred to as grooves are formed spirally or concentrically on the surface of a substrate of each disk. The concave parts
2
are used to route a laser beam, which is emitted from an optical pickup of a recording/reproducing apparatus, along a train of information areas, or in other words, to produce a tracking servo signal.
For achieving high-density recording, a so-called land-groove recording method is adopted in order to record an information signal both in a groove or in a convex part
3
between the adjoining grooves, or a so-called land.
A technique for recording an information signal in the phase change optical disk or magnetooptical disk is a so-called thermal recording method in which laser light is converged in order to raise the temperature of the recording layer.
In this case, the foregoing land-groove recording method is adopted for attaining a larger recording density. In addition, a cycle of creating a groove, that is, a pitch between a concave part and an adjoining convex part must be minimized.
However, when the cycle of creating a groove is shortened, recording or reproducing becomes more susceptible to thermal interference such as thermal crosstalk, cross-writing, or cross-erasure occurring between adjoining tracks, that is, a groove and an adjoining land. Consequently, a record signal may be undesirably erased or vanished, and a reproduced signal may be deteriorated or faded away. This hinders realization of a high recording density.
For overcoming the above disadvantage, Japanese laid-open patent publication No. 11-25534 has disclosed a magnetooptical disk.
The magnetooptical disk is structured so that a border wall between a groove and a land is an inclined plane and has a width of 160 nm or more. Owing to this structure, a substantial distance between the groove and land is increased in order to minimize the thermal crosstalk.
The modulation degree of a push-pull signal is maximized when the difference D in height between a land and groove is approximately (2m−1)&lgr;/(8n) (where m denotes a natural number that is 1, 2, 3, etc.). Herein, &lgr; denotes the wavelength of laser light used for reproduction, and n denotes the refractive index of a disk substrate. In general, for attaining a sufficiently large modulation degree of a push-pull signal together with a large difference in height D, the condition of (2m−1)&lgr;/(8n)<D<(2m−1)&lgr;/(5.5n) should be satisfied.
The critical frequency of a record signal detectable from an optical disk is proportional to &lgr;/NA where &lgr; denotes the wavelength of laser light and NA denotes the numerical aperture of an objective lens. For attaining a larger recording density, the wavelength of laser light should be reduced and the numerical aperture NA of the objective lens should be increased.
In recent years, the wavelength of laser light emanating from a solid-state laser is converted by using a second harmonic generation element (SHG) and the light source whose wavelength &lgr; falls below 415 nm have been obtained. Furthermore, owing to an advancement of semiconductor laser technologies, the semiconductor laser can produce laser light whose wavelength is about 407 nm.
For example, assume that the wavelength of laser light is 407 nm and the refractive index n of a substrate is 1.55. In this case, for maximizing the modulation degree of a push-pull signal used to extend tracking servo control, the difference in height D between a land (convex part) and an adjoining groove (concave part) should be set to approximately 33 nm, 99 nm, 164 nm, or the like under the aforesaid condition. However, a more intense effect of suppressing thermal crosstalk is required to attain a high recording density. The difference in height D must therefore be set to the largest possible value.
However, when the difference in height D between a land and an adjoining groove is too large, it becomes hard to trace the surface shape of the substrate
11
because of the thicknesses of a transparent dielectric layer
51
and a recording layer
5
formed on the substrate. Assuming that the transparent dielectric layer and recording layer are formed on the substrate through sputtering, a layer is deposited even on a sidewall linking a concave part and an adjoining convex part. This diminishes the width of the concave part. Besides, the deposition of the layer on the sidewall diminishes the number of sputtered particles reaching the concave part. Consequently, a layer formed in the concave part becomes thinner.
The heat capacity of the recording layer differs between a concave part and an adjoining convex part. This leads to a difference in sensitivity between a groove and an adjoining land and causes inhomogeneity of an optical disk.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a substrate for optical recording media, an optical recording medium, a manufacturing process for optical recording media, and an optical recording/reproducing method. Herein, a so-called land-groove recording method in which data is recorded in both a land and an adjoining groove is adopted in an effort to improve a recording density. Thermal crosstalk between the land and adjoining groove can be suppressed effectively. Moreover, inhomogeneity of an optical recording medium between the land and adjoining groove can be suppressed effectively.
According to the present invention, what is referred to as the optical recording/reproducing method includes a method of performing at least one of optical recording and optical reproducing.
Accordingly, the present invention is concerned with land-groove recording.
According to the present invention, a substrate for optical recording media has groove-like concave parts created on at least one surface thereof, and has convex parts each created between adjoining concave parts. A border sidewall linking a concave part and an adjoining convex part has at least a first sidewall plane adjoining the bed of the concave part and a second sidewall plane leading to the apical surface of th
Fujita Goro
Sakamoto Tetsuhiro
Beacham C R
Korzuch William
Sonnenschein Nath & Rosenthal LLP
LandOfFree
Substrate for optical recording media, optical recording... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Substrate for optical recording media, optical recording..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Substrate for optical recording media, optical recording... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3194300