Temperature Self-Compensated Refractive Index Sensor Based on Fiber Bragg Grating and the Ellipsoid Structure

Area of Science:

• Photonics
• Optical Sensing
• Fiber Optic Sensors

Background:

• Refractive index sensors are crucial for monitoring various physical and chemical processes.
• Existing sensors often suffer from temperature cross-sensitivity, complicating accurate measurements.
• Fiber Bragg gratings (FBGs) offer a robust platform for optical sensing, but require methods for temperature compensation.

Purpose of the Study:

• To demonstrate a temperature self-compensated refractive index sensor.
• To utilize an ellipsoid structure with FBG for enhanced cladding mode excitation and recoupling.
• To achieve reliable refractive index sensing with inherent temperature stability.

Main Methods:

• Fabrication of a sensor combining a Fiber Bragg Grating (FBG) with an ellipsoid structure.
• Excitation and recoupling of cladding modes using the ellipsoid.
• Analysis of reflection spectrum, monitoring Bragg resonant peak for temperature and cladding resonant peaks for refractive index.
• Utilizing the Bragg peak shift as a reference for temperature self-compensation.

Main Results:

• The sensor exhibits two distinct wavelength bands: Bragg resonant peak and cladding resonant peaks.
• The cladding resonant peak shift accurately determines the surrounding refractive index (SRI).
• The Bragg resonant peak shift provides temperature compensation with a sensitivity of 10.76 pm/°C.
• Linear SRI sensitivity of 352.6 pm/RIU and exponential sensitivity up to 4182.2 pm/RIU were observed.
• Sensing performance showed low dependence on the FBG-ellipsoid distance, simplifying fabrication.

Conclusions:

• The proposed FBG-ellipsoid sensor effectively measures refractive index with built-in temperature self-compensation.
• The design simplifies fabrication, making it practical for real-world applications.
• This sensor offers a promising solution for accurate SRI monitoring in environments with temperature fluctuations.