Sony Corporation

Yutaka Kasami

Atsushi Fukumoto

Koichi Yasuda

Katsuhiro Seo

Yuji Kuroda

Shigeki Takagawa

Kazumine Ito

Osamu Kawakubo

An optical recording medium is disclosed which incorporates a recording layer made of a phase-change material. The optical recording medium has a structure such that the ratio Ac/Aa of absorptance Ac realized when the recording layer is in a crystal state and absorptance Aa realized when the recording layer is in an amorphous state is 0.9 or higher. Moreover, a crystallization enhancing layer for enhancing crystallization of the phase-change material is formed which is made to contact with at least either surface of the recording layer. Since control of the absorptance and enhancement of crystallization are simultaneously performed, the difference between the physical properties of crystal and those of amorphous can be reliably compensated for. Thus, a satisfactory direct overwriting can be performed even under high speed and dense conditions.

Optical recording medium

An optical disc on or from which information signals are recorded/reproduced by irradiation of a laser light beam is disclosed. The optical disc has a plurality of top surfaces, a plurality of bottom surfaces, and a plurality of portions formed on a major surface of a disc substrate of the optical disc. The portions separate the top and bottom surfaces from each other. A recording track is constituted by each top surface and each bottom surface. Each bottom surface and each top surface have a first width, while each portion has a second width. The recording track has a track pitch P defined by the sum of the first width and said second pitch. The pitch is related with the second width and the spot diameter of the playback light &phgr; by a formula and P<&phgr;/2 and 0.1 &mgr;m<second width &lE;&phgr;/2.5.

Optical disc having narrow recording track relative to light spot diameter

A method of initializing a phase-change optical disk which is capable of preventing enlargement of an amount of jitter which takes place when the number of overwriting operations does not exceed several times. The surface of the phase-change optical disk, on which information signals will be recorded, is crystallized. Then, signals are recorded with marks and spaces in grooves along tracks of the phase-change optical disk so that initialization is performed. The initialization is performed in such a manner that the length of each of spaces is shorter than a shortest length of spaces of information signals.

Method of initializing phase-change optical disk to prevent jitter increase due to low level overwriting

A phase change optical recording medium which enables optimum direct overwrite even under high speed high density conditions without degrading repetition durability or storage stability of recorded signals. To this end, the phase change optical recording medium has a recording layer formed at least of a phase change material and is recorded and/or reproduced with a laser light beam having a wavelength ranging between 380 nm and 420 nm. A ratio Ac/Aa, where Ac is the absorption rate of said recording layer in a crystalline state and Aa is the absorption rate of said recording layer in an amorphous state, is not less than 0.9, and a crystallization promoting layer promoting the crystallization of the phase change material is contacted with at least one surface of the recording layer. By exploiting the absorption rate control and the crystallization promotion in combination, it is possible to positively compensate the difference between the physical properties of the crystal phase and those of the amorphous phase to realize optimum direct overwrite.

A multiple-recording-layer optical recording medium has a plurality of recording layers to be initialized by exposure to light, with a transparent layer interposed between the recording layers. Light is applied simultaneously to the to the recording layers to initialize the recording layers simultaneously.

Growing community of inventors

Kanagawa, Japan

Yutaka Kasami