Overcoming EDFA slow transient effects in a combined Golay coding and coherent detection BOTDA sensor

Area of Science:

• Optoelectronics
• Fiber optic sensing
• Signal processing

Background:

• Brillouin optical time domain analysis (BOTDA) sensors are crucial for distributed strain and temperature sensing.
• Erbium-doped fiber amplifiers (EDFAs) are often used in BOTDA systems but can introduce distortions.
• The Brillouin gain spectrum (BGS) is susceptible to distortions from EDFAs, impacting measurement accuracy.

Purpose of the Study:

• To investigate the impact of EDFAs on Brillouin spectrum measurements in BOTDA sensors.
• To evaluate the suitability of Brillouin phase spectrum (BPS) as an alternative to BGS for accurate measurements.
• To demonstrate the successful implementation of Golay coding and coherent detection with phase fluctuation elimination.

Main Methods:

• Experimental analysis of BGS and BPS in the presence of an EDFA pre-amplifier.
• Comparison of measurement accuracy using BGS versus BPS.
• Implementation of phase fluctuation compensation techniques.
• Integration of Golay coding with coherent detection for enhanced BOTDA performance.

Main Results:

• EDFAs were found to have a negligible impact on the shape of the Brillouin phase spectrum (BPS).
• Using BPS instead of BGS successfully avoided a ∼5.4 MHz Brillouin frequency shift error caused by the EDFA.
• Phase fluctuations in the optical fiber were successfully eliminated.
• The combination of Golay coding and coherent detection was realized after phase compensation.

Conclusions:

• Brillouin phase spectrum (BPS) is a more robust parameter than Brillouin gain spectrum (BGS) for BOTDA sensing when EDFAs are used.
• Utilizing BPS with EDFA pre-amplifiers significantly improves measurement accuracy by eliminating frequency shift errors.
• The successful implementation of Golay coding and coherent detection, coupled with phase compensation, enhances the overall performance and reliability of BOTDA systems.