Magneto-optic read-out method and apparatus with polarization co

Details Magneto-optic read-out method and apparatus with polarization co Magneto-optic read-out method and apparatus with polarization co

1987-02-17

1988-09-27

Cardillo, Raymond F.

Dynamic magnetic information storage or retrieval

Head

Read only detector using light for reading magnetically...

369 13, 369110, 365122, G11B 1100

Patent

active

047746157

ABSTRACT:
Disclosed herein are an improved method and apparatus for optically reading pre-recorded magnetic information on a magneto-optic recording element. The invention addresses the technical problem of minimizing the adverse effect of unpredictable variations in the state of polarization of the beam of radiation used for read-out. Such variations may be produced, for example, by birefringence variations in a transparent layer or substrate through which the recorded information is recovered. According to the invention, the undesired polarization variations are sensed from the system's output signal, and an error signal representative of such variations is produced. Such error signal is used to adjust the state of polarization of the read-out beam prior to detection by the system's detector elements. Preferably, the read beam is directed through the combination of a quarterwave plate and a Faraday rotator, and the error signal is used to control the magnetic field of the Faraday rotator. In effect, the combination of the quarterwave plate and Faraday rotator behaves like a variable phase retardation plate as far as the resultant output signal is measured by differential detection is concerned.

REFERENCES:
patent: 4243850 (1981-01-01), Edwards
patent: 4410277 (1983-10-01), Yamamoto et al.
patent: 4503324 (1985-03-01), Yokata
patent: 4652737 (1987-03-01), Kowalski et al.
patent: 4729122 (1988-03-01), Itoh

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