title: Sensitivity Enhancement in Si Nanophotonic Waveguides Used for Refractive Index Sensing.
abstract: 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 SiO₂ 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.
authors.affiliation: Centre for Optical and Electromagnetic Research, State Key Laboratory for Modern Optical Instrumentation, Zhejiang Provincial Key Laboratory for Sensing Technologies, Zhejiang University, Zijingang Campus, Hangzhou 310058, China. yaocheng@zju.edu.cn.
authors.forename: Yaocheng
authors.initials: Y
authors.lastname: Shi
authors.affiliation: Centre for Optical and Electromagnetic Research, State Key Laboratory for Modern Optical Instrumentation, Zhejiang Provincial Key Laboratory for Sensing Technologies, Zhejiang University, Zijingang Campus, Hangzhou 310058, China. make@coer-zju.org.
authors.forename: Ke
authors.initials: K
authors.lastname: Ma
authors.affiliation: Centre for Optical and Electromagnetic Research, State Key Laboratory for Modern Optical Instrumentation, Zhejiang Provincial Key Laboratory for Sensing Technologies, Zhejiang University, Zijingang Campus, Hangzhou 310058, China. dxdai@zju.edu.cn.
authors.forename: Daoxin
authors.initials: D
authors.lastname: Dai
keywords: nanofiber; nanoslot; nanowire; sensitivity; silicon