Optical encoder diffraction gratings for eliminating diffracted

Details Optical encoder diffraction gratings for eliminating diffracted Optical encoder diffraction gratings for eliminating diffracted

1997-03-17

1998-09-01

Le, Que

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

25023114, 356373, H01J 314

Patent

active

058013784

ABSTRACT:
The amount of the light beam passing through two diffraction gratings is output as an electrical signal by a photo detector. The amount of relative displacement of the diffraction gratings is detected according to the electric signal (output signal) that changes in proportion to the relative displacement. Groove portions and ridge portions are alternately arranged on the first diffraction grating, through which the light beam passes and undergoes wavefront modulation by mutual interference of the zeroth-order diffracted light. This eliminates interference of the zeroth-order diffracted light with a diffracted light of another order, and eliminates changes in the fundamental wave component of the output signal caused by changes in the gap between the two diffraction gratings. The output signal can be made not to include a high-order component by a predetermined modification to at least one of either the array pitch or width of a transparent portion in the second diffraction grating.

REFERENCES:
patent: 5661295 (1997-08-01), Fukui et al.

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