Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1991-02-01
1991-12-03
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
250557, 356401, G01N 2186
Patent
active
050702505
ABSTRACT:
A position detection apparatus has a substrate on which a diffraction grating is formed and an alignment optical system for illuminating the diffraction grating with a pair of coherent light beams having different frequencies from each other from different directions. The intensity of interference fringes formed due to the interference of diffracted beams generated in the diffraction grating is detected photo-electrically. The alignment optical system forms the pair of coherent light by using an optical modulator, and two luminous fluxes from the optical modulator pass through independent optical paths positioned symmetrically with the optical axis of the alignment optical system therebetween and reach the diffraction grating from different directions. The alignment optical system has a stop having an opening having an inclined edge with respect to the direction of the grating components of the diffraction grating, the opening being in conjugation with the substrate.
REFERENCES:
patent: 4616130 (1986-10-01), Omata
patent: 4710026 (1987-12-01), Magome et al.
patent: 4801808 (1989-01-01), Hamasaki
Komatsu Koichiro
Magome Nobutaka
Mizutani Hideo
Ota Kazuya
Nelms David C.
Nikon Corporation
Shami K.
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