Dynamic information storage or retrieval – Storage medium structure – Layered
Patent
1995-12-08
1998-08-18
Edun, Muhammad N.
Dynamic information storage or retrieval
Storage medium structure
Layered
369100, 3692755, G11B 700
Patent
active
057967083
DESCRIPTION:
BRIEF SUMMARY
The present invention is directed in general to optical recording media and systems for recording on such media. More particularly, the present invention is directed to optical media for recording in phase transformation and alloying modes and a system for recording on such media, as well as certain improved optical media constructions.
The alloying mode for recording on optical recording media is one of several different recording modes. In accordance with the alloying mode, the optical recording medium includes lower and upper discrete layers of recording material, one deposited on top of the other on a transparent substrate. As a result, the lower of the two recording layers is presented to a recording or reading laser beam and has a characteristic reflectance. Upon irradiation with a recording laser beam of appropriate power level, the two layers in the region of the irradiation are heated sufficiently to at least partially form an alloy of the materials constituting the lower and upper discrete recording layers. The alloyed portion has a reflectance different from that of the lower layer. The difference in reflectance between the alloyed portions corresponding to recorded information and the unrecorded portions corresponding to the lower recording layer enables reading of the recorded data. Commonly assigned U.S. Pat. No. 4,682,321 discloses an optical recording medium for use in the alloying mode and is incorporated herein by reference.
In designing an optical recording medium, one problem is the selection of recording layer materials which provide a significant difference in reflectance between recorded, i.e., alloyed, and unrecorded portions. The problem of selecting suitable recording materials is further subject to a consideration regarding the desirability to utilize a high recording data rate, which results in a short time duration of exposure to the recording laser beam. Such short duration exposure can limit the extent of alloying and thereby disadvantageously limit the amount by which the reflectance changes due to the alloying. Conversely, the need to provide a relatively long duration exposure to the recording laser beam to ensure proper alloying, undesirably limits the recording data rate.
The phase transformation mode is another of the conventional optical recording modes. In accordance with the phase transformation mode, the optical recording medium includes a single recording layer which may be in a predominantly amorphous or crystalline phase state, depending on the material and the manner of its deposition. Upon irradiation with a recording laser beam of appropriate power level, the irradiated portion transforms its phase state. As a function of the recording material, the reflectances of amorphous and crystalline portions are different, so that the phase transformed portions correspond to recorded information. Commonly assigned U.S. Pat. No. 4,975,355 discloses an optical recording medium for use in the phase transformation mode and is incorporated herein by reference.
It is the present inventors' experience that a constraint on the practice of the phase transformation mode is the need to control the power level of the recording laser beam. They have observed that when higher recording laser power levels are used for the recording layer being in amorphous state, the quality of the recorded signal deteriorates.
Thus, practice of the phase transformation mode includes recording laser power level considerations which are generally different from those of the alloying mode. As a result, it is difficult to utilize the same recording device for recording in both modes, without making some adjustment to the device dependent upon the type of recording mode to be practiced.
Optical recording media in the form of optical discs, whether for practice of the phase transformation mode, alloying mode or other modes, can experience several different structural problems. For example, plastic materials such as acrylic and polycarbonate, are widely used for making disc substrates. Such materials are k
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Koyahara Satoru
Matsubara Motonari
Ohkawa Hideki
Yoshida Nobuhisa
Yoshimaru Tomohisa
Edun Muhammad N.
Kabushiki Kaisha Toshiba
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