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Method for Reading Magneto-Optical Storage Media

IP.com Disclosure Number: IPCOM000061848D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Korth, HE: AUTHOR

Abstract

When their magnetization is reversed, known magneto-optical materials yield only rather small light polarization changes, thus making it difficult to obtain acceptable signal-to-noise ratios in the read signal. Fig. 1 shows an improved reading scheme, according to which a magneto-optical information bearing surface 1 (the magnetization direction being perpendicular to the surface) on an optical disk 2 is illuminated by a light beam 40 from a laser 10 through lens L1, beam splitter 41 and lens L2. Beam splitter 41 is a non-perfect polarizing beam splitter operating such that only a fraction of the beam with the intensity I1, which has been reflected at surface 1, is transmitted.

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Method for Reading Magneto-Optical Storage Media

When their magnetization is reversed, known magneto-optical materials yield only rather small light polarization changes, thus making it difficult to obtain acceptable signal-to-noise ratios in the read signal. Fig. 1 shows an improved reading scheme, according to which a magneto-optical information bearing surface 1 (the magnetization direction being perpendicular to the surface) on an optical disk 2 is illuminated by a light beam 40 from a laser 10 through lens L1, beam splitter 41 and lens L2. Beam splitter 41 is a non-perfect polarizing beam splitter operating such that only a fraction of the beam with the intensity I1, which has been reflected at surface 1, is transmitted. This fraction I2 of about 10 percent passes a plate 42 that rotates the polarization direction by 45OE to impinge on (perfect) polarizing beam splitters 43 and 44. Beam splitters 43 and 44 deflect beam intensities I3 and I4 to lenses L3 and L4, respectively, where they are focussed on photodiodes 45 and 46, respectively. The outputs of these photodetectors are connected to a differential amplifier 47. Non-perfect polarizing beam splitter 41 may be obtained by reducing the number of layers in a conventional multilayer polarizing beam splitter. Fig. 2 shows the polarization diagram with the intensities I1 and the polarization directions of the various partial beams of Fig. 1. Non-perfect polarizing beam splitter 41 increases the polarization a...