Optical sensing with disordered photonic crystal waveguides

Optical sensing is of preeminent importance for a variety of applications: it can enable detection of harmful or desired contaminants, it can confirm that expected reactions have taken place and it can be used for quantitative analysis of the processes under study. We report on photonic crystal optical sensors based on disorder-induced light confinement in photonic crystal waveguides in silicon nitride, showing that we can make use of fabrication imperfections as a means to add functionalities to the fabricated devices. We prove their suitability for the detection of liquid contaminants at room temperature and investigate their response to refractive index changes. We also show that temperature can be used to tune and modify the quality factor of the cavity resonances, allowing local temperature sensing. Compared to engineered photonic crystal cavities, making use of disorder as a resource allows the spontaneous formation of tens of high-quality optical cavities in a fabricated device that does not require time-consuming optimizations or exact repeatability of the fabrication process - an important result in view of scalability of photonic crystal sensors.