Fig. 1. Schematic of refractive index sensor based on trench coupler. (a) Drawing of three-dimensional structure; (b) enlarged view of the trench; (c) optical field distribution of the trench coupler

Fig. 2. Schematic of single mode AlN waveguide. (a) 2D cross section; (b) optical field intensity distribution of fundamental mode TE₀ at 850 nm wavelength

Fig. 3. Intensity distribution |E| of electric field with or without water solution in trench. (a) Without water solution; (b) with water solution

Fig. 4. Change of output efficiency with refractive index of trench filler. Inset shows the partial enlarged drawing in refractive index range of 1.33-1.50

Fig. 5. Schematic of each parameter of the trench

Fig. 6. Relationship between refractive index sensitivity and trench length

Fig. 7. Relationship between refractive index sensitivity and trench width

Fig. 8. Relationship between refractive index sensitivity and angle between incident waveguide and normal of trench sidewall

Fig. 9. Schematic of the sensing measurement system