Study on Fano resonance regulating mechanism of Si contained metal–dielectric–metal waveguide coupled rectangular cavity

Abstract

Based on the transmission properties and the photon location characteristics of the Surface plasmon polaritons (SPPs) sub-wavelength structure, a metal–dielectric–metal (MDM) waveguide coupled rectangular cavity structure is proposed. Dielectric material silicon (Si) is introduced in the structure to overcome the high loss of the metal materials. Due to the large refractive index difference between silicon and air, the reflections of SPPs and the incident light at the two ends of the Si–air–Si cavity in the sub-wavelength structure are small meanwhile the transmissions are high, which leads to a wider continuous spectrum. And when the SPPs enter the rectangular cavity in the metal and the phase matching condition is satisfied, the resonance will occur and a narrow transmission spectrum peak will be generated. Through the coupling of the wider continuous state and the narrower isolated state, the Fano resonance will occur. According to the phase-matching condition of resonance, the relationship model between the effective refractive index of the waveguide and the wavelength shift of the resonant peak is established. And with the increase of the length L of the rectangular cavity, the red shift of the resonant peak will occur, which can improve the sensitivity of the sensing structure. The influences of structural parameters L, W and g on Fano resonance are analyzed respectively to optimize the structural parameters by the finite element methods. The Figure of merit (FOM) value can be adjusted and controlled with the change of the structural parameters L, W and g. The FOM value of the optimized structure parameters can attain to 1.19×104. The optimized structure parameters are adopted to discuss the sensing performances of the structure. The results show that the sensitivity of the sensor is about 1612 nm/RIU. The waveguide structure mentioned above can provide effective theoretical references for the miniaturization and high integration of photonic devices and refractive index sensing.