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Title: Extrinsic fiber optic displacement sensors and displacement sensing systems

An extrinsic Fizeau fiber optic sensor comprises a single-mode fiber, used as an input/output fiber, and a multimode fiber, used purely as a reflector, to form an air gap within a silica tube that acts as a Fizeau cavity. The Fresnel reflection from the glass/air interface at the front of the air gap (reference reflection) and the reflection from the air/glass interface at the far end of the air gap (sensing reflection) interfere in the input/output fiber. The two fibers are allowed to move in the silica tube, and changes in the air gap length cause changes in the phase difference between the reference reflection and the sensing reflection. This phase difference is observed as changes in intensity of the light monitored at the output arm of a fused biconical tapered coupler. The extrinsic Fizeau fiber optic sensor behaves identically whether it is surface mounted or embedded, which is unique to the extrinsic sensor in contrast to intrinsic Fabry-Perot sensors. The sensor may be modified to provide a quadrature phase shift extrinsic Fizeau fiber optic sensor for the detection of both the amplitude and the relative polarity of dynamically varying strain. The quadrature light signals may be generated by eithermore » mechanical or optical means. A plurality of the extrinsic sensors may connected in cascade and multiplexed to allow monitoring by a single analyzer.« less
Inventors:
 [1];  [2];  [3];  [4]
  1. (Roanoke, VA)
  2. (Blacksburg, VA)
  3. (Scotch Plains, NJ)
  4. (Christiansburg, VA)
Issue Date:
OSTI Identifier:
869229
Assignee:
Center For Innovative Technology (Herndon, VA) NETL
Patent Number(s):
US 5301001
Contract Number:
AC21-89MC25159
Research Org:
Virginia Polytech Inst/St Univ
Country of Publication:
United States
Language:
English
Subject:
extrinsic; fiber; optic; displacement; sensors; sensing; systems; fizeau; sensor; comprises; single-mode; input; output; multimode; purely; reflector; form; air; gap; silica; tube; cavity; fresnel; reflection; glass; interface; front; reference; interfere; fibers; allowed; move; changes; length; phase; difference; observed; intensity; light; monitored; arm; fused; biconical; tapered; coupler; behaves; identically; surface; mounted; embedded; unique; contrast; intrinsic; fabry-perot; modified; provide; quadrature; shift; detection; amplitude; relative; polarity; dynamically; varying; strain; signals; generated; mechanical; optical; means; plurality; connected; cascade; multiplexed; allow; monitoring; single; analyzer; mode fiber; displacement sensor; quadrature phase; surface mounted; phase difference; air gap; phase shift; fiber optic; sensor comprises; light signal; light signals; optic sensor; optical means; single-mode fiber; optic displacement; sic fiber; multimode fiber; air interface; surface mount; conical taper; /356/250/