Tdk Corporation

Osamu Murakami

Hideki Hirata

Toshifumi Tanaka

Hideo Kobayashi

Giichi Shibuya

Optical recording media include substrates of a larger diameter formed by injection molding a copolymer of ethylene with a cyclic olefin. The media are adapted for high speed rotation with the benefits of a high output, high C/N, and low noise level. When a protective substrate of glass is attached to the polyolefin substrate such that the recording layer is inside, there is obtained a light-weight rigid disk which experiences minimal axial runouts and hence, minimal focusing errors during high rotational speed operation.

Optical recording medium

An optical recording disk is constructed using an injection molded substrate of a cyclic polyolefin having a recurring structural unit of the formula: ##STR1## wherein R.sub.1 and R.sub.2 are independently selected from hydrocarbon groups. The disk has a diameter of at least 200 mm, and is rotated at 1,800 rpm or higher during recording/reproducing operation. Despite a larger diameter, the disk experiences minimized occurrence of double refraction during high speed rotation, ensuring high outputs with a high C/N and a low noise level.

Optical recording disk

An optical disk in a cartridge can be identified when loaded in a disk drive system, by changing the openness of a hole in the cartridge to impart at least four types of identifying information, and detecting the openness of the hole by a sensor in the drive system. To establish four different states, two small and large apertures are formed in major walls of the cartridge to define a through window and a shield member is fixedly or slidably mounted between the walls so as to clear or shield a portion or the entirety of the through window.

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Nagano, Japan

Osamu Murakami