Absolute Length-Measuring Interferometer Using Heterodyne Signal of Optical-Frequency Comb Laser (1st Report)

Experimental evaluation of long path heterodyne interferometers with optical frequency comb and continuous-wave laser

Abstract

An optical-frequency comb can be used directly as the light source of long-path interferometers. The interference happens only when a pair of optical comb pulse trains overlaps with each other. So the measurable distance is long, but is discrete in sapce. In this paper, a new heterodyne interference system is presented to evaluate the measurement stabilities of optical-frequency comb and continuous-wave laser diode interferometers. Two optical combs and a laser diode with the same center wavelength are used as light sources for their comparison, and the experiments have been done to measure the distance of 22.5 m and 22.909 m. The result shows that the measurement stability in 50 s of optical comb and laser diode is similar due to the effect of the new heterodyne lock-in technique. The measurement standard deviation decreases to several tens nanometers when the time constant of lock-in amplifier increases to 10 s.