High-Resolution Displacement Measurement using a Femtosecond Frequency Comb

摘要

The work introduces a high-resolution displacement measurement method in a nanometer scale using passive Fabry-Perot cavity. The optical frequency of selected resonant mode of the cavity is monitored during changes of the cavity length. It uses an optical mixing the frequency of a tunable laser with frequency teethes of a femtosecond optical synthesizer (optical frequency comb). The tunable laser diode is locked to a selected mode of the optical resonator to monitor the exact mirror distance of Fabry-Perot cavity. Then a laser diode optical frequency is mixed with the beam from the stabilized femtosecond frequency comb. Due to wide spectrum of the comb and worse signal-to-noise ratio of a beat-note signal a fiber Bragg grating is used for narrow-band selection of desired components of the femtosecond comb. The beat-note signal is processed by a fast photo detector and frequency counter. The displacement of the movable mirror of the Fabry-Perot cavity is calculated on basis of the beat-note signal. The main advantage is in linear course of the scale due to using the Fabry-Perot cavity as measuring device.