Fig. 1. (a) SEM image of a silicon slotted microring resonator like the one used in our experiment. Inset shows the slot waveguide in the ring. Red arrows show direction of light propagation along the bus waveguide (b) cross sectional SEM image of a slot waveguide like the one in (a). (c) calculated mode profile for the major E-field component of the fundamental quasi-TE mode for the waveguide shown in (b). The high concentration of electric field in the gas region makes the resonator more sensitive to changes in refractive index of the gas.

Fig. 2. (a): Photograph of the gas cell affixed to the silicon photonic chip. Dotted line shows the path of the light through the waveguide and the circle denotes the approximate location of the microring. (b) schematic of the experimental setup which was used to measure the resonant wavelength of the microring under different gaseous environments.

Fig. 3. (a) Transmission spectra for the microring resonator in the presence of air (solid) and acetylene gas (dotted) at room temperature and atmospheric pressure pressure. The shift in resonance is due to the difference in refractive index between air and acetylene gas. (b): Change in resonant wavelength as a function of gas pressure for acetylene. Solid and open shapes represent the average of three measurements for increasing and decreasing pressure respectively. Error bars represent the standard deviation of the three measurements for each data point. Dashed line shows the theoretical resonance shift based on the properties of the resonator. The slope of 490nm/RIU determines the sensitivity of the device.