Resonant waveguide sensing made robust by on-chip peak tracking through image correlation

We demonstrate a solution to make resonant-waveguide-grating sensing both robust and simpler to optically assess, in the spirit of biochips. Instead of varying wavelength or angle to track the resonant condition, the grating itself has a step-wise variation with typically few tens of neighboring "micropads." An image capture with incoherent monochromatic light delivers spatial intensity sequences from these micropads. Sensitivity and robustness are discussed using correlation techniques on a realistic model (Fano shapes with noise and local distortion contributions). We confirm through fluid refractive index sensing experiments an improvement over the step-wise maximum position tracking by more than 2 orders of magnitude, demonstrating sensitivity down to 2 × 10(-5) RIU, giving high potential development for bioarray imaging.