A comparative study is given for the sensitivity of several typical Si nanophotonic waveguides, including SOI (silicon-on-insulator) nanowires, nanoslot waveguides, suspended Si nanowires, and nanofibers. The cases for gas sensing (
ncl ~ 1.0) and liquid sensing (
ncl ~ 1.33)
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A comparative study is given for the sensitivity of several typical Si nanophotonic waveguides, including SOI (silicon-on-insulator) nanowires, nanoslot waveguides, suspended Si nanowires, and nanofibers. The cases for gas sensing (
ncl ~ 1.0) and liquid sensing (
ncl ~ 1.33) are considered. When using SOI nanowires (with a SiO
2 buffer layer), the sensitivity for liquid sensing (
S ~ 0.55) is higher than that for gas sensing (
S ~ 0.35) due to lower asymmetry in the vertical direction. By using SOI nanoslot waveguides, suspended Si nanowires, and Si nanofibers, one could achieve a higher sensitivity compared to sensing with a free-space beam (
S = 1.0). The sensitivity for gas sensing is higher than that for liquid sensing due to the higher index-contrast. The waveguide sensitivity of an optimized suspended Si nanowire for gas sensing is as high as 1.5, which is much higher than that of a SOI nanoslot waveguide. Furthermore, the optimal design has very large tolerance to the core width variation due to the fabrication error (∆
w ~ ±50 nm). In contrast, a Si nanofiber could also give a very high sensitivity (e.g., ~1.43) while the fabrication tolerance is very small (
i.e., ∆
w < ±5 nm). The comparative study shows that suspended Si nanowire is a good choice to achieve ultra-high waveguide sensitivity.
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