Optical Vernier sensor based on a cascaded tapered thin-core microfiber for highly sensitive refractive index sensing

Area of Science:

• Optical sensing
• Fiber optics
• Nanotechnology

Background:

• Refractive index (RI) sensing is crucial for various applications, including biochemical analysis.
• Existing RI sensors often face limitations in sensitivity and complexity.
• Tapered fiber structures offer potential for enhanced optical sensing performance.

Purpose of the Study:

• To propose and investigate a novel RI sensor based on a cascaded tapered thin-core microfiber (TTCMF).
• To utilize the Vernier effect for enhanced RI sensitivity.
• To compare the performance of series and parallel TTCMF sensor configurations.

Main Methods:

• Fabrication of TTCMF structures through arc discharging and flame heating.
• Cascading two identical SMF-TTCMF-SMF structures with slightly different free spectral ranges (FSRs) to induce the Vernier effect.
• Experimental measurement and analysis of RI sensitivity and temperature cross-sensitivity for single, series, and parallel sensor configurations.

Main Results:

• Achieved high RI sensitivities of -15,053.411 nm/RIU (series) and -16,723.243 nm/RIU (parallel).
• RI sensitivities were amplified by 4.65x (series) and 5.16x (parallel) compared to a single TTCMF sensor.
• Low temperature cross-sensitivities of 1.302×10⁻⁵ RIU/°C (series) and 2.92×10⁻⁶ RIU/°C (parallel) were observed.

Conclusions:

• The cascaded TTCMF sensor effectively utilizes the Vernier effect for significantly enhanced RI sensitivity.
• The parallel configuration demonstrated superior RI sensitivity and lower temperature cross-sensitivity.
• The proposed sensor offers a simple structure, convenient fabrication, and high performance, making it suitable for biosensing applications.