Patent ID: 7359586

Claim:
A fiber optic strain sensor comprising: a length of an optical fiber having an input end and an output end; a first fiber-optical connector optically coupled to said input end and a second fiber-optical connector optically coupled to said output end; a mechanical transducer converting a measured phenomenon into mechanical movement or force that is in proportion with said measured phenomenon, wherein said transducer applies force on a portion of said fiber that induces corresponding strain in said fiber, which provides polarization conversion of a single-mode light passed said optical fiber; wherein the improvement comprises: a second length of optical fiber being proximately located to said first length of optical fiber and having an input end and an output end, wherein said first length of optic fiber and said second length of optic fiber are single-mode ones; and, when strain sensor is mechanically strained, said first length of optical fiber realizes said corresponding compressing or twisting strain, whereas said second length of optical fiber does not realize said corresponding strain; a first fiber-optical polarization analyzer having an input and an output, wherein said input of said analyzer is optically coupled to output end of said length of optical fiber; and said output of said analyzer optically coupled to said second fiber-optical connector; a second fiber-optical polarization analyzer having an input and an output, wherein said input is optically coupled to output end of said second optical fiber; a third fiber-optical connector being optically coupled to said output of said second fiber-optical polarization analyzer; a polarization-maintaining fiber-optical splitter having a single input, a first output and a second output, wherein said single input of said splitter is optically coupled to said first fiber-optical connector, and said first output of said splitter is optically coupled to said input end of said first fiber; a fourth fiber-optical connector optically coupling said input end of said second single-mode optical fiber with said second output of said splitter, wherein said fourth connector comprises an input part and an output part that have ability of axial rotation about each other; therefore, polarization plane of light coming from said second output of said splitter can be turned to align polarization planes of light coming from said first and said second lengths of single-mode optical fibers; said polarization alignment provides initial setup of said sensor—equal amplitude of optical signal on said second and third fiber-optical connectors in the condition when measured parameter is not applied.