Detecting disturbance using optical gap sensing
First Claim
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1. Apparatus for sensing a physical disturbance, comprising:
- a block of gap material that is optically clear having parallel front and rear sides;
means for positioning and securing said gap material for subjection to a physical disturbance;
a polarizer with axis of polarity preoriented secured to the rear side of said block of gap material;
a source of circularly polarized light projected through the gap material from the front side and through the polarizer to produce a source light beam;
a beam splitter intercepting said source light beam;
a linearly polarized reference light source projecting onto said beam splitter with axis of polarity pre-aligned to coincide with the polarizer axis of polarity when the combined source light beam and reference light source emerge from said beam splitter;
a photoelectric detector generating an output indicative of time averaged power of the combined beam; and
processing circuitry for analyzing the detector output and deriving the change in dimension of the gap material in response to the disturbance.
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Abstract
Apparatus for detecting minute disturbance such as seismic vibrations or the like which utilizes an optically clear gap material as the primary sensing element. The gap material is subjected to the disturbance and any reactive change in width or index is sensed optically by monitoring the light transmission properties of the gap material. A particular type of sensor is disclosed consisting of a length of optic fiber having the tip end covered by the gap material with the distal surface bearing a reflective coating.
25 Citations
14 Claims
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1. Apparatus for sensing a physical disturbance, comprising:
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a block of gap material that is optically clear having parallel front and rear sides; means for positioning and securing said gap material for subjection to a physical disturbance; a polarizer with axis of polarity preoriented secured to the rear side of said block of gap material; a source of circularly polarized light projected through the gap material from the front side and through the polarizer to produce a source light beam; a beam splitter intercepting said source light beam; a linearly polarized reference light source projecting onto said beam splitter with axis of polarity pre-aligned to coincide with the polarizer axis of polarity when the combined source light beam and reference light source emerge from said beam splitter; a photoelectric detector generating an output indicative of time averaged power of the combined beam; and processing circuitry for analyzing the detector output and deriving the change in dimension of the gap material in response to the disturbance. - View Dependent Claims (3, 5, 6, 7)
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2. Apparatus as set forth in claim 2 wherein the source of circularly polarized light comprises:
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a single frequency, coherent source that produces light of selected output wavelength; and an HNCP sheet having a center wavelength equal to said output wavelength of the source, said HNCP sheet intercepting said produced light and converting to circularly polarized light. - View Dependent Claims (4)
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8. Apparatus for sensing a physical disturbance, comprising:
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a selected length of optic fiber of the single mode, polarization preserving type having a source end and a remote tip end placed in sensing disposition at said disturbance; a gap material that is optically clear disposed on the tip end of the optic fiber; a reflective coating placed on said gap with the reflective axis aligned perpendicular to the tip end of the optic fiber; means directing a selected frequency of coherent, polarized source light into the source end of said optic fiber; and means for receiving and analyzing reflected light from said source end of said optic fiber to determine any change in wavelength in response to change in index of said gap material. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification