Information recording method

Details Information recording method Information recording method

1999-07-06

2002-07-30

Tran, Thang V. (Department: 2653)

Dynamic information storage or retrieval

Binary pulse train information signal

Binary signal processing for controlling recording light...

C369S116000

Reexamination Certificate

active

06426929

ABSTRACT:

BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates generally to an information recording method. More specifically, the invention relates to a method for recording information on a disc which has a recording layer capable of changing to a crystal condition and to an amorphous condition reversibly.
II. Description of the Related Art
With the wide-spread use of multimedia products, read only media such as audio CD and CD-ROM media, as well as the optical information reproducing apparatus used to record and reproduce such discs have been widely used. Due to the desire of users to create their own customized media, write-once discs using a dye technique (commonly known as CD burning), magnetic optical discs (MO) and phase-change discs have also received great attention within the field.
With the advent of reducing the amplitude of the laser diode, minimizing the spot diameter by using a high numerical aperture (NA) objective lens and adopting a thin substrate, high capacity optical discs such as the DVD-ROM, DVD-R, DVD-RAM, DVD-RW have been made possible. Currently, the major focus is erasable DVD media, which will be the next step for recording multi-media with great storage capacity. However, phase-change discs can also provide the functionality of an erasable DVD in a more efficient manner.
In a phase-change disc, information is recorded by changing a recording layer into a crystal condition or an amorphous condition reversibly. It can record and reproduce information only by laser ray from the laser diode. However, it does not require an external magnet, as with MO discs. Furthermore, a phase-change disc is capable of “overwrite recording,” which is the recording and erasing of information at the same time.
For example, a single pulse light waveform of the laser diode using the EFM (Eight Fourteen Modulation) pulse code modulation is used as a general recording waveform for recording information on such phase-change discs. However, in such a single pulse recording method, recording marks are crooked in the form of tears because of the regenerative action and insufficient amorphous phase formation, which falls short of the appropriate cooling speed. Therefore, recording marks with low reflective rates cannot be obtained.
As a conventional recording method for recording information on a phase-change disc, the recording marks are formed by the laser ray of a multi-pulse waveform with some recording power steps reproduced based on a recording rate such as 8-16 pulse code modulation, as shown in FIG.
1
. This known practice solves the above problem.
Marked portions of the multi-pulse waveform comprise a head heating pulse “A” for preheating the recording layer of the phase-change disc until the melting point degree is exceeded, followed by plural serial heating pulses “B,” and serial cooling pulses “C” between pulses “A” and “B.” When the intensity of the head heating pulse A is Pwa, the intensity of the serial heating pulse B is Pwb, and the intensity of the serial cooling pulse C is Pwc. The result is the reproduction of the intensity Pr. Each intensity is set to the following expression.
Pwb≧Pwa>Pwc=Pr
Space portions of the multi-pulse waveform comprise an erase pulse D. When the intensity of the erase pulse D is Ped, the intensity is set to the following expression.
Pwa>Ped>Pwc
Based upon those expressions, the marked portions are formed into an amorphous phase, which is based on the rapid cooling conditions among the heating pulses A, B and the cooling pulse C. The space portions are formed into a crystal phase based on the gradual cooling condition induced solely by heating. Therefore, the reflective rate difference between the amorphous phase and the crystal phase is fully obtained.
A mark position recording method (PPM) and a mark edge recording method (PWM) are used to record information on phase-change discs. Currently, the mark edge recording method is used in response to high density recordings. Since phase-change discs have information at both edges of the recording marks, when recording information on the phase-change discs by the mark edge recording method it is important that sufficient heating and rapid cooling are carried out on the disc and that the edges of the marks are formed clearly. Therefore, high recording power is desired which may be achieved by changing the angle of the disc and increasing the light power of the laser diode. With recent high density recording, it is possible to form minute marks on the disc by using a short wavelength laser and a high NA objective lens. However, in conventional basic recording, when the effective spot diameter of the recording spot and the shortest mark length, which are formed on the disc by the laser ray, are close to each other the shortest mark becomes long. Therefore, it is advantageous to configure a system such that the erase power is high and the edge of the marks are short.
As a point of reference, in the early days of CD-ROM or DVD-ROM technology, the Constant Linear Velocity (CLV) method, which increased recording capacity, was generally used as the speed control method for the spindle motor. However, when the rotating speed of the spindle motor is increased, for the purpose of significantly increasing the information transmission speed, the rotating angle speed has to be constant for the purpose of simplifying the motor control.
Another method, the Constant Angular Velocity (CAV) method, has a constant rotating angular velocity and a constant recording frequency. When using the CAV method, the linear speed on the disc for the laser ray is high and information recording density is low. This method records by moving the laser ray from the inner area to the outer area of the disc. The zone CAV method, commonly referred to as the ZCAV method, divides the disc surface into concentric circles, then records and reproduces using a constant frequency in each zone. The further the zone is to the outer edge, the higher the frequency. This method provides greater recording capacity, while the recording linear density does not change significantly among the zones.
When recording by the CAV and the ZCAV methods, as the laser moves from the inner area to tie outer area of a disc, the linear speed on the disc with reference to the laser ray is high. Therefore, the circuit design can be complicated because measures must be taken into account for the reduced power of the laser or the raise in the channel clock frequency. When recording information on a disc according to the CLV recording method, if the linear speed is too high or too low, the resulting recording may be unsatisfactory because such a linear speed condition causes a deterioration in the overwriting and increases the jitter on the disc.
For the purpose of resolving such a problem, for example, in an information recording method shown in Japanese unexamined patent publish (KOKAI) No 06-12674, when the relative speed between a recording disc and a laser ray is high, a pulse being a little shorter than an input pulse is radiated. However, such a pulse is not a multi-pulse. In an information recording method shown in Japanese unexamined patent publish (KOKAI) No 05-274678, the duty rate of the light pulse when radiating a laser ray in the outer area is greater than when radiating a laser ray in the inner area.
In the above-mentioned information recording method, the light pulse must be changed according to the radial position of the laser ray from the disc's center. This results in a complicated circuit structure for the laser radiating control unit. However, there is a conventional method which makes the multi-pulse width constant in view of time, regardless of the change in linear speed. In such a method, the higher the linear speed and the channel clock frequency, the higher the radiating rate of the multi-pulse is for the channel clock.
However, when recording information on the outer area or the inner area of the optical disc, where the multi-pulse width is constant in view of time, such conditions are n

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