Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal processing for controlling recording light...
Reexamination Certificate
1999-08-12
2004-08-10
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal processing for controlling recording light...
C369S013270, C369S059120, C369S116000
Reexamination Certificate
active
06775218
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical data storage. More specifically, writing high-density multi-level or binary data to an optical disk made of material whose state may be changed upon radiation by a laser beam is disclosed. A region of material is modified using a laser and the controlled formation of the material state and its distribution within the region is described.
BACKGROUND OF THE INVENTION
Information may be stored on an optical disc by creating regions or “marks” having a different reflectivity than the surrounding surface of the disc. In an optical phase change disc, such regions are formed by irradiating the surface of the disc with a writing laser that causes a region to be warmed and melted or partially melted. As the region cools, the region may change to a crystalline or amorphous state or some combination of crystalline and amorphous states. When a reading laser is incident on such a region, the reflected light can be measured and the state of the region can be determined. The state of the region represents stored data. Different levels of reflectivity may represent different data levels.
FIG. 1A
is a cross section of a typical optical phase change disc
100
. Optical phase change disc
100
includes a substrate
102
. A first dielectric layer
104
is deposited on the substrate. A recording layer
106
, which is composed of a phase change material, is deposited on top of dielectric layer
104
. A second dielectric layer
108
is deposited over recording layer
106
. A reflective layer
110
is deposited over dielectric layer
108
. Finally, a protective resin layer
112
is deposited over reflective layer
100
. The layers described above are provided as an example only and that the techniques described herein are applicable to other types of phase change discs as well as other optical discs that utilize different recording mechanisms. U.S. Pat. Nos. 5,136,573 and 5,144,615, (the '573 and '615 patents, respectively) issued to Kobayashi, which are herein incorporated by reference for all purposes, describe techniques for multilevel recording using optical phase change discs. Kobayashi describes lowering the reflectivity of an initially amorphous region by forming crystalline material and that more crystalline material may be formed as the writing laser power is increased. Kobayashi also discloses an overwrite technique that forms a crystalline region using a low level biasing energy and increases the reflectivity by forming a crystalline region at certain spots using energy pulses that create amorphous regions.
FIG. 1B
illustrates the biasing signal disclosed in the Kobayashi patent as well as the different pulse signal levels for creating different amounts of amorphous material. Kobayashi mentions that either power or pulse width may be used to vary the amount of laser energy deposited on a region, but does not disclose a specific scheme for varying pulse width.
FIG. 1C
illustrates the claimed results with reflectivity increasing as the amount of amorphous material formed increases.
Kobayashi discloses different types of written spots. In the '573 patent, a record spot that is smaller than the size of a reading laser beam is disclosed that increases in size as the energy deposited by the writing laser increases.
FIG. 1D
illustrates the varying size of the written region. In the '615 patent, varying length spots that encode information with both their lengths and varying levels of reflectivity that result from different degrees of crystallization are disclosed.
FIG. 1E
illustrates different length marks having different reflectivities.
Kobayashi does not describe a technique for handling spots that are close enough to each other that writing one spot affects the writing of other spots. In order to further increase the density of recorded marks on phase change discs, it would be desirable to develop techniques for placing variable reflectivity marks closer together. Furthermore, it would be useful if more reliable techniques could be developed for varying the reflectivity of a region. A more reliable overwrite process for phase change discs is also needed.
Conventional thinking is that the minimum size of recorded data marks in optical systems (including systems that use a phase change media or other optical recording media) is limited to the size of the reading laser beam and the writing laser beam. While optical techniques have been developed for reducing the laser beam size of both reading and writing lasers, it would be useful if even smaller marks could be made on the disc so that the density of information stored on the disc could be increased.
SUMMARY OF THE INVENTION
A method of writing marks on a phase change material is described. Marks are written in a manner such that their size can be less than the size of the focused spot of a writing laser. By forming marks smaller than the reading laser beam, the reflectivity of a region of material can be varied with great precision. The reflectivity of a region is controlled by varying the relative amount of material in crystalline and amorphous phases. The total amount of crystalline and amorphous material in a region is controlled by creating marks of various sizes or shapes. The mark size and shape is controlled by placing the leading and trailing edges of laser pulses such that the timing of a second laser pulse further modifies the region of material irradiated by a first pulse. Additional modification of the mark size and shape results from controlling the time course of the laser power during the pulse. Existing marks may be directly overwritten by irradiating previously recorded regions with the methods described below.
In one embodiment, a method of recording information on an optical disc is disclosed. The method includes irradiating a region of the optical disc with a first dose of laser energy. A first portion of the region is irradiated with a second dose of laser energy in a manner that causes the first portion of the region irradiated with the second dose of laser energy to be in a different state than a second portion of the region that is not irradiated by the second dose of laser energy.
In another embodiment, a write strategy processor is configured to generate control signals for writing data to an optical disc comprising a processor configured to specify a first laser pulse for irradiating a region of the optical disc with a first dose of laser energy and a second laser pulse for irradiating a first portion of the region with a second dose of laser energy in a manner that causes the first portion of the region irradiated with the second dose of laser energy to be in a different state than a second portion of the region that is not irradiated by the second dose of laser energy.
In another embodiment, a method of recording information on an optical disc includes heating a region of the optical disc with a first dose of laser energy. A first portion of the region is heated with a second dose of laser energy in a manner that causes the first portion of the region irradiated with the second dose of laser energy to be in a different state than a second portion of the region that is not heated by the second dose of laser energy.
In another embodiment, a method of recording data on a phase change optical disc includes melting a region of phase change material and directing energy to a first portion of the region so that the first portion of the region becomes crystalline. The size of the first portion determines the data written to the region.
In another embodiment, a method of recording data on a phase change optical disc includes causing an amorphous mark to be formed within a region of the optical disc wherein the size of the amorphous mark within the region determines the data stored in the region.
In another embodiment, a method of recording data on a phase change optical disc includes irradiating a region of the optical disc with a first pulse of laser energy having a first pulse rising edge and a first pulse falling edge a
Balasubramanian Kunjithapatham
Bashaw Matthew C.
Learmonth Timothy
McDermott Gregory A.
Narayan Raghuram
Christopher P. Maiorana PC
Edun Muhammad
LSI Logic Corporation
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