Monitoring a substance’s refractive index is a powerful method of optical sensing as many contaminants and processes affect the refractive index. The response of an optical resonator is linked to the refractive index of the materials of which it is composed and a the small change in resonant wavelength is induced when the cladding of the resonator changes. The surface of the ring is functionalised with a range of antigens that are specific to different target compounds.
Monitoring the refractive idnes allows all chemical changes to be tracked regardless of the type, unlike other sensors, each of which are sensitive to only a small subset of possible contaminants. RI sensing can therefore provide event monitoring giving early warning of problems in the network.
The HERCULES project made substantial improvements to the RI detection limit by implementing anhybrid Photonic crystal laser, The laser comprises a III-V gain chip and a silicon nitride based one-dimensional photonic crystal (PhC) which acts as a resonant mirror that sets the operating wavelength. Initial results from the project have been published in Nanophotonics 11, 4183–4196 (2022). A patent application is currently being prepared, and which will be followed by additional publications.
