Based on the evanescent wave resonance, a photonic crystal sensing structure with air slot-porous silicon-air slot Fabry–Perot cavity (F–P cavity) is proposed. Taking the F–P cavity as the sensing unit, when the gas to be detected is filled into the sensing unit, the refractive index of the air slot will be changed and the refractive index of the porous silicon layer will also be varied, both of which will shift the resonant peak and greatly increase the sensitivity of the sensor. By adjusting the structural parameters, the quality factor (Q value) can be optimized. A model for the relationship between the resonant wavelength and the refractive index of the detected organic gas was established, and the refractive index sensing performance was analyzed. The results show that the Q value of the structure can attain to 12312.2 and the sensitivity is about 8661.708 nm/RIU, which can provide effective theoretical reference and technical guidance for organic gas detection with low concentration.

A metal-dielectric-metal (MDM) waveguide coupled disk cavity structure with bimetallic baffle is proposed, which bases on the transmission characteristics of surface plasmon polaritons (SPPs) in subwavelength structure, and the absorption material InGaAsP is filled in the Fabry–Perot (F-P) cavity and disk cavity. The Fano resonance is an asymmetric spectral line formed by the destructive interference between the wide continuous state generated by the F-P resonator and the narrow discrete state interference generated by the disk cavity. Based on the coupled mode theory, the formation mechanism of the Fano resonance of the structure is qualitatively analyzed. The structure was simulated by finite element method to quantitatively analyze the influence of structural parameters and absorption material InGaAsP on the refractive index sensing characteristics. The proposed sensor yields sensitivity higher than 1360 nm/refractive index unit (RIU) and a figure of merit of [Formula: see text] by optimizing the geometry parameters and filling the absorption material InGaAsP. This structure has potential applications for high integration of nanosensors, slow-light devices, and nano-optical switches.