Design of a phase-shifting optical feedback interferometer using an electrooptic modulator

A laser sensor using optical feedback interferometry has been designed to measure displacements up to several micrometers. For this purpose, a lithium niobate crystal generates a phase shift in order to modulate at a frequency of 580 kHz the optical path difference between the sensor and the target. This setup has been calibrated by means of a commercial optical fiber sensor. The overall accuracy resulting is better than 65 nm for a 1-kHz sinusoidal motion of the target at 10 cm away from the sensor.