US Patent 7738109 Fiber optic sensor using a Bragg fiber

An optical sensor includes a directional coupler comprising at least a first port, a second port, and a third port. The first port is in optical communication with the second port and with the third port such that a first optical signal received by the first port is split into a second optical signal that propagates to the second port and a third optical signal that propagates to the third port. The optical sensor further includes a Bragg fiber in optical communication with the second port and with the third port. The second optical signal and the third optical signal counterpropagate through the Bragg fiber and return to the third port and the second port, respectively.