Ultrasensitive optofluidic resonator refractive index sensor

We report an optofluidic resonator refractive index sensor based on an integrated structure constructed by a free-space coupling architecture. It uses a symmetrical metal-cladding hollow-core waveguide and a prism to generate surface plasmon polarization. The sensor achieves very high sensitivity by coupling the core mode to ultrahigh-order modes in the waveguide layer that can obtain a refractive index of a detailed low-order value of 1×10−6. We demonstrate the device through infiltration of different fluids into the hollow core along an optofluidic resonator. A detection limit of 1.0×10−6 refractive index units has been derived from measurements. The presented method can be applied to the detection of molecular structures and biochemistry.