Distributed dynamic strain measurement with a direct detection scheme by using a three-step-phase-shifted double...

Area of Science:

• Optoelectronics
• Fiber optic sensing
• Signal processing

Background:

• Traditional homodyne demodulation techniques face challenges in stability and ease of implementation for distributed sensing.
• Ultra-weak fiber Bragg gratings (UWFBGs) offer potential for distributed sensing but require robust demodulation methods.

Purpose of the Study:

• To develop and demonstrate a stable homodyne phase demodulation method for distributed vibration measurement using UWFBG arrays.
• To improve the signal-to-noise ratio (SNR) and simplify the implementation of fiber optic sensing systems.

Main Methods:

• A novel double-pulse homodyne phase demodulation technique was employed, dividing a probe pulse into three sections with 2π/3 phase differences.
• A simple direct detection scheme was utilized for quantitative vibration measurement along the UWFBG array.
• The method leverages uniform modulation by dynamic strain and result averaging from reflected UWFBG light to enhance SNR.

Main Results:

• The proposed technique demonstrated enhanced stability and ease of accomplishment compared to traditional methods.
• Experimental validation confirmed the effectiveness of the method for monitoring various vibrations.
• An SNR of approximately 44.92 dB was achieved for a 100 Hz, 0.08 rad vibration measurement in a 3 km UWFBG array.

Conclusions:

• The developed double-pulse homodyne phase demodulation method provides a stable and effective solution for distributed vibration sensing with UWFBG arrays.
• The technique offers a higher SNR and simpler implementation, paving the way for advanced fiber optic sensing applications.
• This method enables quantitative and distributed strain monitoring with improved performance characteristics.