System and method for beam farfield shift focus compensation

Details System and method for beam farfield shift focus compensation System and method for beam farfield shift focus compensation

1989-08-29

1990-06-26

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 4411, G01J 120

Patent

active

049374400

ABSTRACT:
A system and method for maintaining focus of a laser beam on the surface of an erasable magneto-optic disk during erase operations is disclosed. The laser beam exhibits beam farfield shift during erase operations, complicating the maintenance of optimal focus. An optical detector is exposed to laser light reflected to the disk to generate signals governing operation of a focusing lens' servo system. A digital signal processor is included in the servo system and is programmed to compensate for beam farfield shift by generation of an offset correction signal during periods of erase power operation. The offset correction signal is generated by the digital signal processor by comparison of optical detector output signals generated during operation of the laser source where no beam farfield shift occurs and the output signals generated where beam farfield shift is occurring, but the system is known to be in focus.

REFERENCES:
patent: 4663750 (1987-05-01), Hamanaka et al.
patent: 4695158 (1987-09-01), Kotaka et al.
patent: 4866688 (1989-09-01), Ohtake et al.

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