Demodulation Method of F-P Sensor Based on Wavelet Transform and Polarization Low Coherence Interferometry

Area of Science:

• Optical Metrology
• Sensor Technology
• Signal Processing

Background:

• Polarized low-coherence interferometry (PLCI) is a key technique for demodulating Fabry-Perot (F-P) sensors.
• Conventional methods are susceptible to noise and dispersion, affecting interference fringe analysis.
• Accurate demodulation is crucial for precise F-P sensor measurements.

Purpose of the Study:

• To develop an advanced data processing method for PLCI to improve Fabry-Perot sensor demodulation.
• To mitigate the impact of noise and dispersion on interference fringe data.
• To achieve higher accuracy and resolution in F-P cavity length measurements.

Main Methods:

• Application of wavelet tools for extracting information from fringe extremum locations and envelope centers.
• Wavelet threshold denoising (WTD) algorithm to eliminate electrical noise.
• Complex Morlet wavelet for fringe envelope extraction, followed by precise extremum location tracking for demodulation.

Main Results:

• The proposed method successfully extracts fringe envelopes and predicts extremum locations.
• Accurate demodulation of an air Fabry-Perot cavity (length 17–20 μm) was achieved.
• Experimental results demonstrated a repeatability accuracy better than 6.04 nm and a resolution below 4.0 nm.

Conclusions:

• The wavelet-based data processing method offers a robust approach for PLCI demodulation of F-P sensors.
• The technique effectively overcomes noise and dispersion challenges, enhancing measurement precision.
• This method significantly improves the accuracy and resolution of F-P sensor characterization.