Optical sensing devices

Claim 1

An optical fiber sensing system, for very accurate measurement of the effects of a physical phenomena, comprising: a light source means for producing a light beam; a first multimode optical fiber, connected to said light source means, for receiving and transmitting said light beam; beam splitting means, connected to said first fiber, for receiving said light beam and dividing said light beam into a signal light beam and a reference light beam, each of said signal and reference beams being of equal phase and amplitude; sensing means for receiving said signal beam and said reference beam from said beam splitting means, said sensing means being divided into a signal chamber and a reference chamber such that said signal beam and said reference beam experience all environmental effects equally, said signal chamber being further arranged so as to further expose only said signal beam to said physical effect to be measured thereby modulating said signal beam in proportion thereto; path length adjusting means, for receiving said reference beam from the reference chamber of said sensing means and changing the pathlength of said reference light beam to equal the path length of said signal light beam, thus assuring temporal coherence therebetween; beam recombining means for receiving said signal beam from the signal chamber of said sensing means and said reference beam from said path length adjusting means, said recombining means combining said signal beam and said reference beam in such a way as to form a fringe pattern having at least a center fringe and a fringe in quadrature relationship with the center fringe; non-transparent plate means, fixedly attached to said recombining means for receiving center fringe and the fringe in quadrature relationship therewith and separating all the light energy of said center fringe from all the light energy of the fringe in quadrature relationship with said center fringe in such a way that 90° phase quadrature is maintained between said signal and reference light beams; a zero order, multimode optical fiber, attached to said plate means, for receiving and transmitting therethrough said center fringe light energy from said plate means; a first order, multimode optical fiber, attached to said plate means, for receiving and transmitting therethrough the fringe in quadrature relationship with said center fringe light energy from said plate means; a first photodetector means, connected to said zero order fiber, for receiving said center fringe light energy and converting said light energy to a proportional zero order electrical signal; a second photodetector means, connected to said first order fiber, for receiving the fringe in quadrature relationship with said center fringe light energy and converting said light energy to a proportional first order electrical signal; and data processor means, connected to said first and said second photodetectors for receiving said zero order and said first order electrical signals, and processing said signals in such a way as to extract said physical effect measurement therefrom.