Encoder for setting optical path lengths of related beams

Details Encoder for setting optical path lengths of related beams Encoder for setting optical path lengths of related beams

1990-10-30

1992-06-30

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

250237G, 356356, G01B 902, G01D 534

Patent

active

051265621

ABSTRACT:
An encoder includes a first polarizing beam splitter for splitting a beam into first and second beams, and a first .lambda./4 plate arranged in respective first and second optical paths. A first optical device causes the beams to be incident on a diffraction grating so that positive first and negative second mode diffracted beams travel along the first and second optical paths, respectively, and superposes the diffracted beams on each other. A second polarizing beam splitter splits the diffracted beams from each other, and a second .lambda./4 plate is arranged in third and fourth optical paths for the diffracted beams, respectively. A second optical device causes the diffracted beams to be incident on the diffraction grating so that positive and negative first mode rediffracted beams travel along the third and fourth optical paths, respectively, and superposes the rediffracted beams on each other. A converting device causes the rediffracted beams to interfere with each other to form an interfered beam, which is converted into an electrical signal. A difference between optical path lengths of beams incident on the converting device through the first and fourth paths and through the second and fourth paths, and a difference between optical path lengths of beams incident on the converting device through the first and third paths and through the second and third paths are larger than a coherent length of the light source beam.

REFERENCES:
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