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Apparatus for measuring relative movement using a diffraction grating having an orthogonally polarized input beam

  • US 5,436,724 A
  • Filed: 10/02/1992
  • Issued: 07/25/1995
  • Est. Priority Date: 10/03/1991
  • Status: Expired due to Fees
First Claim
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1. An apparatus for effecting a measurement of relative movement by the use of a diffraction grating, comprising:

  • a light beam generating portion generating a light beam including light wave components having planes of polarization orthogonal to each other;

    an interference optical system for directing the light beam from said light beam generating portion to the diffraction grating, the light beam directed by said interference optical system being diffracted by the diffraction grating to thereby at least create two diffracted light beams of different orders, said interference optical system causing the polarization condition of at least one of the two diffracted light beams to vary and causing said two diffracted light beams to to enter said diffraction grating again, so that two rediffracted light beams diffracted by the diffraction grating are directed in the same direction and are superposed; and

    a detecting system for causing said two rediffracted light beams to interfere with each other and detecting the interfering light beam, the relative movement of said diffraction grating and said interference optical system being measured by the detection by said detecting system;

    said interference optical system having in at least a portion of the optical path from the diffraction grating to said detecting system a polarization maintaining optical fiber for propagating the two rediffracted light beams therethrough.

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