Fiber Loop Mirror Based on Optical Fiber Circulator for Sensing Applications.

Area of Science:

• Photonics and Optical Sensing
• Fiber Optic Sensors
• Interferometry

Background:

• Traditional Fiber Loop Mirrors (FLMs) have limitations in system balancing and sensitivity.
• Discrimination of multiple physical parameters like strain and torsion is crucial for advanced sensing.

Purpose of the Study:

• To present and characterize a new Fiber Loop Mirror (FLM) configuration with two circulators for sensing applications.
• To demonstrate the capability of this new design for strain and torsion discrimination.

Main Methods:

• A novel Fiber Loop Mirror (FLM) configuration utilizing two circulators was designed and implemented.
• Strain and torsion measurements were performed, analyzing interference fringe displacement and Fast Fourier Transformer (FFT) spectral characteristics.
• The system's ability to control Free Spectral Range (FSR) and birefringence was investigated.

Main Results:

• Strain measurement sensitivity achieved was (0.576 ± 0.009) pm‧με^-1.
• FFT-based sensitivities for strain were (-2.1 ± 0.3) × 10^-4 nm^-1 με^-1 (frequency shift) and (4.9 ± 0.3) × 10^-7 με^-1 (amplitude).
• Torsion characterization yielded FFT peak variations of (-2.177 ± 0.002) × 10^-12 nm^-1/° and amplitude variations of (1.02 ± 0.06) × 10^-3/°.

Conclusions:

• The proposed FLM configuration effectively discriminates between strain and torsion.
• This design allows for system balancing, unlike traditional FLMs, and supports high birefringence (>10^-2) for Vernier effect sensors.
• The configuration is versatile, accommodating various fiber lengths and refractive indices for optimized sensing performance.