Self-correction of air refractive index in distance measurement using two-color sinusoidal phase modulating interferometry
2021
Abstract A two-color sinusoidal phase modulating (SPM) interferometer based on electro-optic modulator (EOM) is devised for self-correction of air refractive index in distance measurement. Two laser sources with high frequency stability and close wavelengths (633 nm and 782 nm) are used in this scheme. High-accuracy phase demodulation was realized using phase generated carrier (PGC) demodulation techniques with an FPGA-based signal processing board. Experimental results of nanometer displacement measurements show that the resolution and accuracy of PGC demodulation is better than 1°, and the nonlinear error is less than 0.2°. Performance test of two-color SPM interferometer compared with one-color interferometers under dynamic environment were implemented with an arm length difference of 4 m. The results show that, the measured distance of one-color interferometer drifts 4.8 μ m in 600 s, which is caused by the deviation between the measured value of air refractive index and the actual value along the laser propagation path, and this drift reduces to ± 1.5 μ m using two-color interferometer without environmental sensing.
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