Embedded Refractive Index Sensing in Microchannels Using Multiplexed Silicon-on-Insulator Microring Resonators

We describe the use of wavelength-multiplexed microring resonators as refractive index sensors embedded in microfluidic channels for parallel and differential sensing. The sensor geometry consists of two or more identical 45-micron diameter silicon ring resonators fabricated on silicon dioxide coupled to a single input/output bus waveguide. Two modes of sensing are described: parallel sensing with multiple sensors embedded in separate fluidic channels, and increased sensitivity refractive index sensing by the compensation of temperature dependence with a differential temperature referencing measurement. The first set of experiments demonstrates parallel sensing of water and aqueous salt solutions embedded in separate microchannels. The second set of experiments demonstrates the removal of temperature dependence, and thus improved refractive index detection limit, by temperature referencing using a differential measurement between two resonators.