Disturbance rejection in optical fiber specklegram sensors

Area of Science:

• Photonics and Optical Sensing
• Fiber Optic Sensors
• Signal Processing

Background:

• Optical fiber specklegram sensors offer a low-cost method for measuring physical and chemical quantities.
• Speckle patterns are vulnerable to environmental factors like temperature and mechanical stress, limiting sensor reliability.
• Existing methods for disturbance rejection are often complex or computationally intensive.

Purpose of the Study:

• To develop and validate a robust method for rejecting disturbances in optical fiber specklegram sensors.
• To enhance the reliability and accuracy of specklegram sensing in unconstrained environments.
• To provide a practical solution without resorting to complex phase modulation or machine learning.

Main Methods:

• A reference fiber was used to monitor signal distortions.
• A proportional-integral-derivative (PID) controller-inspired algorithm processed error signals to generate virtual specklegrams.
• Empirical tuning of algorithm parameters was performed to optimize performance.
• A microbending displacement gauge was tested under static and dynamic perturbations.

Main Results:

• The disturbance rejection method achieved a steady-state error of 0.02 and 5.7% undershoot.
• A microbending displacement gauge demonstrated comparable sensitivity (1.26×10^-2µm^-1) and resolution (4.61 µm) to undisturbed cases.
• The system effectively suppressed gradual and abrupt distortions, distinguishing signals from noise.

Conclusions:

• The proposed method successfully rejects disturbances, enhancing the robustness of fiber specklegram sensors.
• This approach offers a practical and effective alternative to complex sensing techniques.
• The findings support the development of reliable fiber specklegram sensors for diverse practical applications.