Patent ID: 6211962
Filing Date: 2001-04-03
Classification: G01D,G01J,G01K,G01M,G02B

Abstract:
Optical sensing apparatus for sensing a plurality of phenomena, the apparatus including a plurality of stages connected in series order from a first stage to a last stage, each said stage comprising:(a) a polarization-maintaining sensing fiber having different propagation constants for light in first and second polarization modes, said sensing fiber having input and output ends;(b) launching means for launching light in both of said polarization modes into said sensing fiber at said input end, whereby light will propagate in both of said polarization modes to the output end;(c) combining means for combining light propagated to the output end of the sensing fiber in both of said polarization modes into one or more common polarization modes, whereby the amplitude of the combined light will vary with the phase relationship between the light propagated in the first mode and the light propagated in the second mode at the output end of the fiber; and(d) exposure means for mounting the sensing fiber so that the sensing fiber is exposed to a phenomenon to be sensed and so that such phenomenon will alter the length of the sensing fiber, the difference between said propagation constants, or both, whereby said phase relationship and said amplitude will vary with the phenomenon to be sensed,the combining means of each stage other than the last stage being connected to the launching means of the next stage in said series so that combined light from each said stage other than the last stage in the series will be launched into the sensing fiber of the next stage in the series.