Fig. 1. Schematic diagram of sensor structure. (a) IE-HOW; (b) UOW

Fig. 2. Simulation analysis results of light field distributions under different d for UOW and IE-HOW. UOW: (a) d=8 μm, (b) d=6 μm, and (c) d=4 μm; IE-HOW: (d) d=8 μm, (e) d=6 μm, and (f) d=4 μm

Fig. 3. Fabrication of devices. (a) Preparation progress of IE-HOW; (b) microscope image of MBC (Insert is physical image of IE-HOW)

Fig. 4. Experimental setup for RI sensing based on IE-HOW

Fig. 5. Experimental results of RI sensing based on UOW. Transmission spectra at different RI: diameters are (a) d₁; (c) d₂; (e) d₃; fitting relationship curve between wavelength and RI: diameters are (b) d₁; (d) d₂; (f) d₃

Fig. 6. Experimental results of RI sensing based on IE-HOW. Transmission spectra at different RI: diameters are (a) d₁; (c) d₂; (e) d₃; fitting relationship curve between wavelength and RI: diameters are (b) d₁; (d) d₂; (f) d₃

Fig. 7. Comparison of maximum RI sensitivity of UOW and IE-HOW under different d

Fig. 8. Temperature response and stability test based on IE-HOW. (a) Spectral wavelengths at different temperatures; (b) wavelength stability within 1 h (Insert is transmission spectrum of structure)