Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1987-12-21
1989-05-30
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
369 45, G01J 120
Patent
active
048353787
ABSTRACT:
Apparatus for scanning a radiation-reflective information plane (2). A scanning beam of radiation (b) from a diode laser (4) is focused by an objective lens (6) on the information plane and the beam reflected therefrom is deflected by a composite diffraction grating (9) so as to form two asymmetrical radiation spots (V.sub.1, V.sub.2) respectively focused on respective pairs of photodiodes (18, 19; 20, 21). The relative outputs of the photodiodes in each pair control focusing of the scanning beam on the information plane. The photodiodes in each pair are separated by a strip (22',23') positioned so that it is at an acute angle to the line (22, 23) along which the asymmetrical reflected radiation spot formed on the relevant diode pair becomes displaced as a result of variations in the wavelength of the scanning beam. Such angle is set so the separating strip is on the line along which the center of the intensity distribution of such radiation spot becomes displaced as a result of such variations. Consequently, such variations do not affect the relative outputs of the photodiode pairs and so are prevented from affecting focusing of the scanning beam on the information plane.
REFERENCES:
patent: 4665310 (1987-05-01), Heemskerk
patent: 4672187 (1987-06-01), Fujita et al.
patent: 4712205 (1987-12-01), Smid et al.
patent: 4733065 (1988-03-01), Hoshi et al.
Eason Leroy
Shami Khaled
Tamoshunas Algy
U.S. Philips Corporation
Westin Edward P.
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