Optical sensing by using Photonic Crystal based Mach-Zehnder interferometer

We demonstrate that Photonic Crystal (PhC) based Mach-Zehnder interferometers (MZIs) can be used to realize optical biosensor by using the Fano resonance of the MZIs. Small analyte presented in the MZIs would, however, excite higher-Q Fano resonance of the system than the big one. The scattering object in the arm would create a resonant path (discrete state) for the MZIs, which interacts with the input broadband continuum spectrum and thus results in the Fano resonance of the system. We can therefore detect the location, size and refractive index of biological analyte (down to approximately 100 nm in size) in the MZIs via the output transmission spectrum. An analytical model, which outlines the sensing mechanism, is presented together with the finite difference time domain computer simulations. Both of them validate the proposed sensing capacity.