Fig. 1. Schematic diagram of DHMC structure

Fig. 2. Calculated results of ERIs of guided even and odd modes in x-polarization and y-polarization. (a) SRI is 1; (b) SRI is 1.333. Insets show modal fields of odd and even modes of two polarizations

Fig. 3. Calculated results of interference spectra with vernier effect for DHMC with different waist lengths L (d=4 μm). (a) SRI is 1; (b) SRI is 1.333

Fig. 4. Simulation results of FSR of DHMC (L=12 mm). (a) Transmission spectra of DHMC with different diameters with SRI of 1.3328; (b) relationship between FSR and diameter of DHMC

Fig. 5. DHMC sensor and its spectrum. (a) Microscopic image before heating; (b) microscopic image after tapering; (c) spectrum in air for DHMC after tapering

Fig. 6. Experimental results of axial strain sensing. (a) Spectrum evolution of DHMC (L=10 mm) with diameter of 6 µm under different axial strains; (b) spectrum evolution of x polarization with axial strain; (c) spectrum evolution of y polarization with axial strain; (d) evolution of vernier spectrum with axial strain; (e) axial strain sensitivity of DHMC with diameter of 6 µm; (f) axial strain sensitivity of DHMC with diameter of 6.5 µm and 7 µm

Fig. 7. Experimental results of temperature sensing. (a) Spectrum evolution with temperature for DHMC with diameter of 6 µm; (b) spectrum evolution of x polarization with temperature; (c) spectrum evolution of y polarization with temperature; (d) evolution of vernier spectrum with temperature; (e) temperature sensitivity of DHMC with diameter of 6 µm; (f) temperature sensitivity of DHMC with diameter of 7 µm

Fig. 8. Experimental setup for refractive index measurement using DHMC

Fig. 9. Experimental results of DHMC (d=5 μm) for RI sensing. (a) Spectrum evolution with SRI; (b) spectrum evolution of x polarization with SRI; (c) spectrum evolution of y polarization with SRI; (d) evolution of vernier spectrum with SRI; (e) RI sensitivity of dip A; (f) RI sensitivity of dip B