Wavelength-switched phase interrogator for extrinsic Fabry-Perot interferometric sensors

Area of Science:

• Optical sensing technologies
• Fiber optic sensor interrogation
• Interferometric sensing

Background:

• Extrinsic Fabry-Perot Interferometric (EFPI) sensors are widely used for precise measurements.
• Accurate phase interrogation is crucial for EFPI sensor performance.
• Existing methods face challenges in speed and stability.

Purpose of the Study:

• To develop a high-speed, stable phase interrogation system for EFPI sensors.
• To investigate the use of a polarization-maintaining fiber Bragg grating (PMFBG) for wavelength switching.
• To propose and validate a new algorithm for EFPI sensor data processing.

Main Methods:

• Utilizing a wavelength-switched unit with a PMFBG for dual-wavelength measurements in a single optical path.
• Employing an electro-optic modulator for high-speed (10 kHz) polarization switching.
• Implementing an ellipse fitting differential cross multiplication (EF-DCM) algorithm for phase demodulation.

Main Results:

• Achieved a minimum phase recovery of 0.42 μrad/√Hz at 100 Hz with stable intensity fluctuations (±0.8 dB).
• Successfully demonstrated stable demodulation of three EFPI sensors with different cavity lengths at 200 Hz.
• Validated the EF-DCM algorithm's effectiveness in interrogating EFPI sensor gap length variations.

Conclusions:

• The developed system offers a stable and efficient method for EFPI sensor phase interrogation.
• The PMFBG-based wavelength switching and EF-DCM algorithm provide robust performance.
• This technique is suitable for interrogating EFPI sensors with diverse cavity lengths.