Browse Prior Art Database

Adjustment and Test of a Magneto-Optic Head

IP.com Disclosure Number: IPCOM000061462D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Bates, KA: AUTHOR [+4]

Abstract

The read signal provided by a magneto-optic (MO) head is the result of differential rotation in the polarization azimuth of the light reflected from the medium being read. This differential rotation is a function of media properties, and is typically quite small, on the order of 1 degree, resulting in a low amplitude read signal. In the ideal case, the reflected light which reaches the MO head detectors remains linearly polarized. If any ellipticity is introduced into the reflected light, from interaction with the media or any of the optical components in the path, for example, the polarization rotation angle is substantially diminished. In order to provide a readable signal of maximum possible amplitude, ellipticity compensation is provided. This is done by using a tilted quarter-wave plate.

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Adjustment and Test of a Magneto-Optic Head

The read signal provided by a magneto-optic (MO) head is the result of differential rotation in the polarization azimuth of the light reflected from the medium being read. This differential rotation is a function of media properties, and is typically quite small, on the order of 1 degree, resulting in a low amplitude read signal. In the ideal case, the reflected light which reaches the MO head detectors remains linearly polarized. If any ellipticity is introduced into the reflected light, from interaction with the media or any of the optical components in the path, for example, the polarization rotation angle is substantially diminished. In order to provide a readable signal of maximum possible amplitude, ellipticity compensation is provided. This is done by using a tilted quarter-wave plate. The degree of tilt determines the amount of phase retardation introduced into the beam. A Faraday rotator 10 is used as an integral part of a test tool. This Faraday rotator provides an AC polarization signal 12, simulating the read signal obtained from written media. The result of this polarization signal, as seen by the data detectors 13 and 14, is the basis for adjustment of the head's quarter-wave plate 11, and/or rejection of the head. An aligned head 15, without a focusing actuator, is used. (The head's focus and tracking components can also be left off the head, until this part of the assembly and test procedure is completed). The Faraday rotator is aligned in light path 12 which normally passes to the media, and a mirror 16 is used to reflect the laser beam light back to detectors 13 and
14. The voltage 26 to the Faraday rotator is calibrated to the double-pass rotation of the light passing through it, by way of a sep...