Distributed vibration measurement based on a coherent multi-slope-assisted BOTDA with a large dynamic range.

Area of Science:

• Optoelectronics
• Fiber optic sensing
• Signal processing

Background:

• Brillouin optical time domain analysis (BOTDA) is a key technology for distributed strain sensing.
• Enhancing the dynamic range of BOTDA systems is crucial for measuring larger strain variations.
• Current BOTDA techniques face limitations in dynamic range and simultaneous measurement of gain and phase.

Purpose of the Study:

• To propose and experimentally validate a novel technique for enhancing the dynamic range of coherent slope-assisted BOTDA.
• To enable simultaneous demodulation of Brillouin gain and phase shift for improved strain determination.
• To achieve high-resolution and accurate strain measurements over extended fiber lengths.

Main Methods:

• A multi-tone probe and a reference wave are launched into the fiber under test (FUT).
• Simultaneous demodulation of Brillouin gain and Brillouin phase shift for each tone is performed.
• Strain information is extracted using the Brillouin phase-gain ratio of each tone.
• A three-tone probe with a 60 MHz interval was employed in the experimental setup.

Main Results:

• The technique effectively enhances the dynamic range of the coherent slope-assisted BOTDA system.
• An effective measurement frequency span exceeding 180 MHz was verified in a ~2 km single-mode fiber.
• High spatial resolution of 2.5 m and a sampling rate of 1.5 kHz were achieved.
• A vibration signal with 41 Hz frequency and 2546 με amplitude was successfully demodulated.

Conclusions:

• The proposed multi-tone probe technique significantly improves the dynamic range of BOTDA.
• Simultaneous demodulation of gain and phase offers a robust method for strain measurement.
• This advancement holds promise for various applications requiring precise distributed strain sensing.