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US 5,569,517 AGranted
Optical information medium
AssigneeTDK Corporation
InventorsJunji Tominaga, Susumu Haratani, Ryo Inaba, Tsuneo Kuwahara
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AssigneeTDK Corporation
InventorsJunji Tominaga, Susumu Haratani, Ryo Inaba, Tsuneo Kuwahara
Estimating the term…
An optical information medium has on a substrate (2) with information-carrying pits (21), a light transmittance control layer (3) including a lower dielectric layer (31), a mask layer (32) and an upper dielectric layer (33). The mask layer has an original state before irradiation of reading light. Upon irradiation of a reading light beam to define a beam spot, the mask layer undergoes a crystal-to-crystal transition in a region (H) of the beam spot depending on the intensity distribution of the beam spot. Multiple reflection condition changes in the transition portion so that the beam spot contributing to read-out is limited to the transition or transition-free region (H or L). The transition temperature is in the range of 200.degree. to 450.degree. C. The mask layer returns to the original state after passage of the beam spot. The invention is also applicable to an optical recording medium having a recording layer above or below the transmittance control layer.
An optical information medium comprising a substrate having pits formed on one surface for carrying information and a light transmittance control layer on the substrate surface including a lower dielectric layer, a mask layer and an upper dielectric layer, and further comprising:
An optical information medium comprising a substrate, a light transmittance control layer on a surface of the substrate and including a lower dielectric layer, a mask layer and an upper dielectric layer, and a recording layer formed at least one of above and below said light transmittance control layer, and further comprising:
Dependencies are inferred from the claim text.