Ultra-Sensitive Fiber Refractive Index Sensor with Intensity Modulation and Self-Temperature Compensation

Area of Science:

• Optoelectronics
• Fiber Optic Sensing
• Nanophotonics

Background:

• Refractive index (RI) sensing is crucial for biochemical and biomedical applications.
• Existing sensors often face challenges with sensitivity, temperature crosstalk, and cost-effectiveness.

Purpose of the Study:

• To propose and fabricate a novel in-line modal interferometer for highly sensitive RI sensing.
• To demonstrate effective discrimination and compensation of temperature crosstalk.
• To evaluate the sensor's stability, repeatability, and potential for practical applications.

Main Methods:

• Cascading a single-taper and a multimode-double-cladding-multimode (MDM) fiber structure.
• Utilizing the evanescent field in the taper for RI interaction.
• Employing the RI-free nature of MDM for temperature compensation.

Main Results:

• Achieved RI sensitivities of 516.02 dB/RIU (single-pass) and 965.46 dB/RIU (double-pass).
• Demonstrated effective temperature crosstalk compensation with a cross-sensitivity of 8.49 × 10^-5 RIU/°C.
• Exhibited high measurement stability (~0.99) and low repeatability error (<4.8‱).

Conclusions:

• The proposed compact fiber optic sensor offers ultra-sensitive and stable RI detection.
• The integrated MDM structure effectively mitigates temperature cross-sensitivity.
• The sensor's cost-efficiency and performance make it highly promising for biochemical and biomedical sensing.