Absolute Length-Measuring Interferometer Using Heterodyne Signal of Optical-Frequency Comb Laser (5^th Report)

Reproducibility evaluation and frequency measurement of the beat signal of optical comb and laser diodes

Abstract

We develop a super-heterodyne interference system for absolute length measurements of several meters using two laser diodes and an optical frequency comb as the light sources. The repetition frequency of the optical comb is 58.418 MHz with a stability of 10-11. The wavelengths of the two laser diodes are 1.54 µm and 1.57 µm, and the synthetic wavelength is 80.5 µm. The frequencies of two laser diodes are phase-locked to the different modes of the optical comb. An acetylene stabilized laser is used to evaluate the reproducibility of the beat signal of the laser diodes and the optical comb, which is one important factor of length measurement reproducibility. One Fabry-Perot etalon with high finesse is used to select the frequency of optical comb by a certain frequency interval, and the stability and reproducibility of beat signal can be seen on a spectrograph. The carrier envelop offset frequency of the optical comb can be calibrated by using the acetylene stability laser or by interference method.