Absolute Length-Measuring Interferometer Using Heterodyne Signal of Optical-Frequency Comb Laser (4th Report)

Super-heterodyne interference system using laser diodes and optical frequency comb

Abstract

We develop a super-heterodyne interference system for absolute length measurements of several meters. The light sources are multiple laser diodes and an optical frequency comb. The repetition frequency of the optical comb is stabilized to GPS, which is 58.418 MHz with a stability of 10^-11. The wavelengths of the two laser diodes are 1.54 μm and 1.60 μm, and the frequencies are phase-locked to the different modes of the optical comb with different offset frequencies Δ₁ and Δ₂. The super-heterodyne signal of laser diodes and the optical comb will be (Δ₂ -Δ₁). The two-beam interference system for length measurement is based on a Michelson interferometer and the multiple-wavelength method is used. The synthetic wavelength can be changed by locking the frequencies of the laser diodes to different modes of the optical comb, and then the step-by-step measurement can be realized. The final stability of the system will be determined by the acetylene stabilized laser.