Serrodyne optical frequency shifting for heterodyne self-mixing in a distributed-feedback fiber laser

We describe an all-fiberized coherent detection system at 1.55 microm using heterodyne self-mixing modulation in a distributed-feedback fiber laser. Frequency shifting of the optical feedback is based on serrodyne phase modulation with an integrated electro-optic modulator, which is a significant advance in the simplification of the self-mixing detection scheme for class B lasers. Accurate measurement of the optical phase difference between the laser electric field and the backscattered electric field demonstrates nanometric displacement detection on noncooperative targets.