All-fiber laser feedback interferometry with 300  m transmission distance

A novel, to the best of our knowledge, interferometry based on the laser feedback technique with long transmission distance is proposed. The system has the advantages of high sensitivity for uncooperative targets and a simple structure. Also, the quasi-common path orthogonally polarized light compensation method is designed to compensate for the drift in long-distance transmission and achieves more than 200 times reduction experimentally. Using a copper block as a target, the displacement resolution of 20 nm is demonstrated experimentally with 300 m transmission distance. The sub-microwatt power consumption of the measurement beam indicates the high sensitivity of the interferometry. The performance, in terms of linearity, is also evaluated. Although a lot needs to be improved, the proposed method is promising for further development toward practical applications, like sensors in remote, nuclear radiative, or other harsh conditions.