Sensing mechanism of photonic crystal nanobeam side coupling cascaded aperture chirped nanobeam cavities structure

A photonic crystal nanobeam (PCN) side coupling cascaded aperture chirped photonic crystal nanobeam cavities (PCNCs) structure is proposed to obtain dual-Fano resonances to solve the problem of differential sensitivity. The wider continuous state provided by the photonic crystal nanobeam interferes with the two narrow discrete states generated by the cascaded aperture chirped photonic crystal nanobeam cavities structure to form dual-Fano resonances. Based on the coupled mode theory, the formation mechanism of the dual-Fano resonances is analyzed. The structure is numerically simulated by the finite-difference time-domain method, and the structural parameters are adjusted to optimize the Fano line shape. And the physical mechanism of the differential sensing of the structure and the sensing characteristics are analyzed. The structure can detect the change of the refractive index of the analyte and eliminate the error caused by the interference caused by the change of ambient temperature, which demonstrates the effectiveness of the dual-Fano resonant sensing structure in solving the cross-sensitive problem.