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Read/write Optical Head Compensation for Birefringence of Plastic Cover of Optical Disk

IP.com Disclosure Number: IPCOM000059842D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Karst, DL: AUTHOR [+4]

Abstract

Most optical disks use a clear plastic cover plate over the data layer of the optical disk to protect the data area from damage due to contamination and handling. The read and write beams pass through this cover and undergo an undesirable retardation due to the plastic cover. In a typical optical storage system this additional retardation adds to the desired retardation of the system's quarter-wave plate. To compensate for that additional retardation, the system's quarter-wave plate is modified to provide a retardation of l/4 wave minus the average retardation caused by the disk cover plate.

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Read/write Optical Head Compensation for Birefringence of Plastic Cover of Optical Disk

Most optical disks use a clear plastic cover plate over the data layer of the optical disk to protect the data area from damage due to contamination and handling. The read and write beams pass through this cover and undergo an undesirable retardation due to the plastic cover. In a typical optical storage system this additional retardation adds to the desired retardation of the system's quarter-wave plate. To compensate for that additional retardation, the system's quarter-wave plate is modified to provide a retardation of l/4 wave minus the average retardation caused by the disk cover plate.

In the above figure, source light beam l0 is linearly polarized in a plane such that the light is passed by beam- splitter l2 to quarter-wave plate l4. The light is focused by objective lens l6, through cover l8 onto media 20. The reflected light passes back through cover l8, lens l6 and plate l4. The reflected light out of plate l4 is linearly polarized in a plane such that it is reflected by beam splitter l2 along optical path 22.

Plate l4 in the above apparatus is not a quarter-wave plate because it does not provide a full quarter-wave of phase retardation to one component of the light. Instead, the componen retarded an amount equal to a quarter wavelength of the source light less the amount "R" of retardation that occurs in media cover l8.

Because the phase retardation provided by plat...