Enhanced Distributed Fiber Optic Vibration Sensing and Simultaneous Temperature Gradient Sensing Using Traditional...

Area of Science:

• Optics
• Materials Science
• Sensor Technology

Background:

• Distributed fiber optic sensing (DVS) is crucial for infrastructure monitoring.
• Traditional methods using single mode fiber (SMF) with coherent optical time domain reflectometry (C-OTDR) face limitations like nonlinear responses and sensitivity fading.
• Enhancing DVS performance without complex interrogators is an ongoing challenge.

Purpose of the Study:

• To investigate the impact of femtosecond laser-inscribed scattering dots on SMF for DVS applications.
• To improve the functionality and performance of C-OTDR-based sensing systems.
• To enable quantitative temperature gradient measurements and linearize the sensing response.

Main Methods:

• Modification of standard SMF by inscribing equally-spaced scattering dots using a femtosecond laser.
• Utilizing single-wavelength amplitude-based C-OTDR for sensing.
• Analyzing the formation of quasi-distributed interferometric sensing zones between scattering dots.
• Characterizing the fiber's response to temperature variations and signal demodulation.

Main Results:

• Increased local sensitivity in sensing zones, transforming the transfer function to that of a two-beam interferometer.
• Linearized phase response to temperature variations, mitigating sensitivity fading.
• Enabled demodulation of low-frequency signals and quantitative determination of local temperature gradients from C-OTDR intensity traces.
• Demonstrated tunability of dot reflectivity and attenuation via inscription parameters.

Conclusions:

• Femtosecond laser-inscribed scattering dots offer a simple, robust, and cost-effective method to enhance DVS performance.
• This modification improves C-OTDR functionality, providing a linear temperature response and enabling quantitative measurements.
• The approach avoids the need for advanced interrogator technology or complex fiber structures like FBG arrays.