Simultaneous Phase Detection of Multi-Wavelength Interferometry Based on Frequency Division Multiplexing

Simultaneous phases detection in multi-wavelength interferometry (MWLI) is essential for high-accuracy dynamic absolute distance measurement in high-end equipment manufacturing. To address this problem, a simultaneous phase detection scheme based on frequency-division multiplexing (FDM) technique is proposed in this paper. High-frequency sinusoidal phase modulation with non-overlapping frequencies were applied to multiple lasers individually using electro-optic modulators (EOMs), and interference phases of multiple wavelengths were extracted in parallel using phase generated carrier (PGC) demodulation technique from the FDM interference signal. Principles of FDM multi-wavelength interferometry and simultaneous phase detection scheme were illustrated. A FDM dual-wavelength interferometer was constructed to verify the performance of the proposed phase detection scheme by simulation analysis and experiments. Results of simulations show that the resolution, accuracy and nonlinear error of the two demodulated phases are all better than 0.01 degrees. Experiments of nanometer displacement measurement further verified the good performance of the phase detection scheme and its feasibility in dynamic measurement.