Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1988-11-30
1990-08-28
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
3692751, 369 4411, G01J 120, G11B 700
Patent
active
049527878
ABSTRACT:
A light beam which is to be focused onto a recording medium is provided with astigmatism. By focusing the light beam having tghe astigmatism with a focusing lens, two orthogonal focal lines having a circle of least confusion at almost a center position therebetween are formed at remote positions. On the recording medium surface are previously formed two kinds of pits which provide identical modulation to the light beam when the recording medium surface is located at the circle of least confusion position and provide different modulations to the light beam when the recording medium surface is deviated from the circle of least confusion position. The light reflected by the recording medium surface and passed through the focusing lens is detected by at least one photo-detector which is disposed in the reflected light beam flux so as to detect the light amount. The signal modulated by at least one of the two kinds of pits is extracted from the output of the photo-detector to extract from the phase or level of the extracted signal a focus error detection signal which is set to a zero or in-focus point when the recording medium surface is located at the circle of least confusion position between the two focal lines.
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Maeda Takeshi
Nakamura Shigeru
Hitachi , Ltd.
Messinger Michael
Nelms David C.
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