Data detection and optical focus error detection system for rota

Details Data detection and optical focus error detection system for rota Data detection and optical focus error detection system for rota

1987-04-29

1989-01-31

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

250204, 356 45, G01J 120

Patent

active

048017949

ABSTRACT:
A magneto-optic optical disc system which uses the magneto-optic differential data detection channel, with addition only a low pass filter, to also detect focus error. The differential data detection channel includes a pair of photodetectors, the first photodetector being located a predetermined distance within the focal length of the detector lens associated with that photodetector and the second photodetector being located beyond the focal length of the detector lens associated with that photodetector. The output of a differential amplifier receiving the photodetector outputs is the data signal and the output of a low pass filter connected to the output of the differential amplifier is the focus error signal. The dual functionality of the differential data detection channel eliminates a separate optical focus channel, and relative to separate astigmatic focus and data detection channels elmininates a quadrature detector, several optical elements, several electrical elements, and the space they occupy.

REFERENCES:
patent: 4368526 (1983-01-01), Harigae et al.
patent: 4390781 (1983-06-01), Musha
patent: 4460989 (1984-07-01), Russell
patent: 4501493 (1985-02-01), Kubota
patent: 4652737 (1987-03-01), Kowalski et al.

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