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Recording and Readout System

IP.com Disclosure Number: IPCOM000090312D
Original Publication Date: 1969-Mar-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Voegeli, O: AUTHOR

Abstract

Information is recorded on a magneto-optical material S by light beam L. The recording material is followed by a dichroic polarizer Pd, which has its major axis of transmission oriented along the x-axis. Pd therefore, absorbs the y-component of the incident radiation A3y more strongly than it does the x-component A3x. When Pd is chosen such that it has a transmittance ratio transmittance x/transmittance y = absolute A3y absolute/2//absolute A3x absolute/2/, then after Pd the light has components of equal magnitude in the x and y direction, i.e., absolute A4x absolute = absolute A4y absolute.

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Recording and Readout System

Information is recorded on a magneto-optical material S by light beam L. The recording material is followed by a dichroic polarizer Pd, which has its major axis of transmission oriented along the x-axis. Pd therefore, absorbs the y- component of the incident radiation A3y more strongly than it does the x- component A3x. When Pd is chosen such that it has a transmittance ratio transmittance x/transmittance y = absolute A3y absolute/2//absolute A3x absolute/2/, then after Pd the light has components of equal magnitude in the x and y direction, i.e., absolute A4x absolute = absolute A4y absolute.

When the material exhibits circular dichroism, the two components of A4 are not in phase. In general, A4 is elliptically polarized.

The ellipticity of A4 is eliminated by retarder R. After R the light is then linearly polarized at an angle +/-45 degrees, depending on the direction of magnetization. The two orthogonal directions of polarization are subsequently discriminated by polarizer P2. A Faraday rotation as well as circular dichroism contribute to the read signal.

For writing the information, the storage location is heated by the light absorbed in it. Therefore, the reading efficiency improves with increasing transmittance of the storage film and the writing efficiency decreases. Hence, the operating conditions represent a compromise between the opposing requirements for reading and writing the information.

In employing material S and the d...