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Title: Interferometric fiber optic displacement sensor

A method is presented to produce a change in the optical path length in the gap between two single mode optical fibers proportional to the lateral displacement of either fiber end normal to its axis. This is done with the use of refraction or diffraction at the interface between a guiding and non-guiding media to change the direction of propagation of the light in the gap. A method is also presented for laying a waveguide on a cantilever so that the displacement of the tip of the cantilever produces a proportional path length change in the gap by distancing the waveguide from the neutral axis of the cantilever. The fiber is supported as a cantilever or a waveguide is deposited on a micromachined cantilever and incorporated in an interferometer which is made totally on a silicon substrate with the use of integrated-optic technology. A resonant element in the form of a micro-bridge is incorporated in the ridge waveguide and produces a frequency output which is readily digitizeable and immune to laser frequency noise. Finally, monolithic mechanical means for phase modulation are provided on the same sensor substrate. This is done by vibrating the cantilever or micro-bridge either electrically or optically.
Inventors:
 [1]
  1. (M.I.T. Branch P.O. Box 301, Cambridge, MA 02139)
Issue Date:
OSTI Identifier:
869913
Assignee:
Farah, John (M.I.T. Branch P.O. Box 301, Cambridge, MA 02139) CHO
Patent Number(s):
US 5420688
Contract Number:
FG02-90ER81033
Research Org:
Optisensors, Inc., Cambridge, MA (United States)
Country of Publication:
United States
Language:
English
Subject:
interferometric; fiber; optic; displacement; sensor; method; produce; change; optical; path; length; gap; single; mode; fibers; proportional; lateral; normal; axis; refraction; diffraction; interface; guiding; non-guiding; media; direction; propagation; light; laying; waveguide; cantilever; tip; produces; distancing; neutral; supported; deposited; micromachined; incorporated; interferometer; totally; silicon; substrate; integrated-optic; technology; resonant; element; form; micro-bridge; ridge; frequency; output; readily; digitizeable; immune; laser; noise; finally; monolithic; mechanical; means; phase; modulation; provided; vibrating; electrically; optically; frequency output; laser frequency; resonant element; displacement sensor; path length; optical fibers; fiber optic; optical fiber; silicon substrate; optical path; single mode; mode optical; mechanical means; phase modulation; optic displacement; micromachined cantilever; frequency noise; lateral displacement; sensor substrate; fibers proportional; interferometric fiber; /356/250/