Absolute Length-Measuring Interferometer Using Heterodyne Signal of Optical-Frequency Comb Laser (6th Report)- Super-heterodyne interferometer using the beat signals of one optical comb and three laser diodes

摘要

A super-heterodyne interference system is developed for absolute distance measurement up to several meters based on multiple-wavelength interferometric method. Three laser diodes and an optical frequency comb are used as the light sources. The repetition frequency of the optical comb is 58.418 MHz with a frequency stability of 10~(-11), and the wavelengths of the laser diodes are 1542 nm, 1542 nm and 1573 nm. There is a frequency difference of 20 GHz between the two laser diodes with the wavelength of 1542 nm. Therefore, two synthetic wavelengths, λ_(s1)=80.5 μm and λ_(s2)=15 mm, are obtained by changing different laser sources using an optical switch, and the interferometer has different measurement ranges. A distance of about 3 m is measured and the stability of the results are 0.32 μm for λ_(s1) and 17 μm for λ_(s2). Since only two of the laser diodes are phased locked to the optical comb, the stability of the carrier envelope offset frequency will influence the measurement stability.