IMPROVED FIBER OPTIC SENSOR FOR DETECTING VERY SMALL DISPLACEMENTS OF A SURFACE

摘要

A light source (10) coupled to a first fiber optic waveguide (14) which is coupled by a first directional coupler (22) and a second directional coupler (24) to a second waveguide (20). The first waveguide (14) has a phase modulator (60), a delay loop (62) and a polarization controller (68) therein to cause a differential delay time T on counterpropagating coherent light waves phase modulated at a frequency 1M. The first directional coupler (22) has one part connected to a photodector (28) and the second directional coupler (24) as a probe (20D) coupled to the first fiber (14) and the second fiber (20). The probe directs light toward a surface (18) whereupon the counterpropagating waves are shifted in phase by an amount proportional to the amplitude of displacement of the surface (18).