Browse Prior Art Database

Automatic Phase Retardation Control for Optical Recording Systems

IP.com Disclosure Number: IPCOM000037908D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-30
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Finkelstein, BI: AUTHOR [+2]

Abstract

This invention dynamically reduces the effects of birefringence and ellipticity in optical recording.

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Automatic Phase Retardation Control for Optical Recording Systems

This invention dynamically reduces the effects of birefringence and ellipticity in optical recording.

Birefringence and other apparitions induce elliptically polarized light, which interferes with data detection. In MO, this induced ellipticity can be of the same magnitude as the Kerr Rotation. A quarterwave plate can be inserted into the readback path to compensate for the induced ellipticity, but the plate must be tuned manually for each type of substrate. Also, since the amount of Birefringence can vary circumferentially as well as radially, the setting of the quarterwave plate is either a compromise for best average performance, or must be continually retuned as track position is changed.

This proposed device uses an LCD as a voltage controlled phase retardation plate to turn elliptically polarized light into linearly Birefringence. The difference signal is low-pass filter whose cutoff frequency is approximately 5 to 20 times the RPs of the disc. This allows the phase retardation to be set dynamically regardless of media type.

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Disclosed anonymously.

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