Abstract
Optical fiber heterodyne interferometry with the following desirable features has been investigated to measure displacement of an object: it is extremely sensitive, noncontacting and has a linear relation between detector output and displacement. However, other systems have suffered from external disturbance because the reference light arm has a different path from the signal light arm. This paper describes the optical fiber heterodyne interferometer probe free from external disturbance in the optical paths of two fibers used to measure small displacement of an object. The external disturbance is excluded by differentiating the phases of the beat signals from two fibers, which include equal phase fluctuation in the fibers due to the disturbance. To improve the S/N ratio, we coated dielectric reflecting mirrors onto the output ends of the fibers. This probe sensor makes it posible to measure a small displacement of 0.1nm.
