Spiral-path high-sensitivity silicon photonic wire molecular sensor with temperature-independent response

We demonstrate a new silicon photonic wire waveguide evanescent field (PWEF) sensor that exploits the strong evanescent field of the transverse magnetic mode of this high-index-contrast, submicrometer-dimension waveguide. High sensitivity is achieved by using a $2\mathrm{mm}$ long double-spiral waveguide structure that fits within a compact circular area of $150\mathrm{\mu }\mathrm{m}$ diameter, facilitating compatibility with commercial spotting apparatus and the fabrication of densely spaced sensor arrays. By incorporating the PWEF sensor element into a balanced waveguide Mach–Zehnder interferometer circuit, a minimum detectable mass of $\sim 10\mathrm{fg}$ of streptavidin protein is demonstrated with near temperature-independent response.