Low-index-mode photonic crystal nanobeam cavity for refractive index sensing at the 2  μm wavelength band.

We present the design, fabrication, and characterization of a one-dimensional photonic crystal (1D-PhC) low-index-mode nanobeam cavity on the silicon-on-insulator platform for refractive index sensing at the 2 μm wavelength band. A Q-factor of 4.35×105 and an effective mode volume of Veff∼1.95(λ/nSi)3 are theoretically achieved. The measured transmission spectrum of the device immersed in NaCl solutions with different mass concentrations demonstrates a sensitivity of 326.1 nm/RIU and a Q-factor of ∼1144.