Ultrahigh-speed distributed Brillouin reflectometry

Area of Science:

• Optoelectronics
• Materials Science
• Structural Engineering

Background:

• Optical fibre sensors utilizing Brillouin scattering are crucial for distributed strain and temperature measurements in structural health monitoring.
• Existing real-time distributed strain measurement systems require two-end-access, limiting sensor placement and system feasibility in cases of fiber breakage or high loss.

Purpose of the Study:

• To develop a real-time distributed strain measurement technique for optical fibre sensors using an intrinsically one-end-access reflectometry configuration.
• To overcome the limitations of two-end-access systems in structural health monitoring applications.

Main Methods:

• Employed a correlation-domain technique for high-speed Brillouin gain spectrum acquisition using a voltage-controlled oscillator.
• Converted Brillouin frequency shift to phase delay of a synchronous sinusoidal waveform, then to a directly measurable voltage.
• Utilized a reflectometry configuration enabling one-end access for the optical fibre sensor.

Main Results:

• Achieved a strain sampling rate of up to 100 kHz for single-point measurements, demonstrated by detecting 1 kHz dynamic strain.
• Verified a 100 Hz repetition rate for distributed measurements across 100 points with averaging, by tracking a mechanical wave.
• Identified drawbacks including reduced accuracy, spatial resolution, and limited strain dynamic range in the ultrahigh-speed configuration.

Conclusions:

• Demonstrated the feasibility of real-time distributed strain measurement with a one-end-access optical fibre sensor system.
• The developed correlation-domain technique offers a more flexible and robust solution for structural health monitoring compared to traditional two-end-access systems.
• Further research is needed to address the trade-offs in measurement accuracy, spatial resolution, and dynamic range for practical applications.