Optical fiber surface waveguide with Fabry-Perot cavity for sensing.

Area of Science:

• Photonics and Optical Sensing
• Fiber Optic Sensors
• Interferometry

Background:

• Optical fiber sensors are crucial for various measurement applications.
• Fabry-Perot interferometers (FPIs) offer high sensitivity but can be affected by environmental factors.
• Existing sensors often face challenges with temperature cross-sensitivity and robustness.

Purpose of the Study:

• To propose and demonstrate a parallel structured optical fiber FPI sensor.
• To achieve simultaneous refractive index (RI) and strain sensing.
• To minimize temperature cross-sensitivity while enhancing measurement sensitivity.

Main Methods:

• Fabrication of two FPI cavities using a femtosecond laser: one on the fiber surface waveguide for sensing and one in the fiber core for referencing.
• Utilizing an X-coupler to direct light to the surface waveguide, enabling interaction with the surrounding medium via evanescent field.
• Leveraging the Vernier effect from the parallel FPI structure to amplify measurement sensitivity.

Main Results:

• Achieved high sensitivities of ~843.3 nm/RIU for refractive index and ~101.8 pm/µε for strain.
• Demonstrated low temperature cross-sensitivities of ~9.6×10⁻⁶ RIU/°C and ~7.956×10⁻² µε/°C.
• The sensor exhibited high robustness, compact size, and enhanced measurement sensitivity.

Conclusions:

• The proposed parallel structured FPI sensor effectively measures refractive index and strain with low temperature cross-sensitivity.
• The Vernier effect significantly enhances the sensor's measurement sensitivity.
• This robust and compact sensor design holds promise for advanced optical sensing applications.