Applications Based On The Coupled Mode Theory-Surface Plasmon Polaritons And Bound States In The Continuum

The coupled mode theory is widely used in the field of electromagnetics to analyze specific coupling phenomena and coupling mechanisms.It has been applied in the design and optimization of various microwave devices,including sensors,filters,and other devices related to surface plasmons and bound states in the continuum.However,the existing research on the coupling analysis of surface plasmons is not perfect,and it cannot accurately represent the transmission characteristics after coupling,which is detrimental to the analysis of relevant parameters.Additionally,the existing theoretical studies do not provide detailed coupling analysis of guided modes in the continuum,which poses difficulties in the design of related devices.In this paper,based on the analysis of the coupled mode theory and the calculation of the coupled mode equations,we have achieved the analysis of the coupling coefficients in surface plasmon waveguide structures and the adjustment of bound states in the continuum in metal rectangular waveguides.With the guidance of the coupled mode theory,we have further completed the application design of relevant microwave devices and sensor pairs and conducted relevant experimental verifications.The innovative achievements of this paper are as follows:1.Based on the coupled mode theory,coupling relations applicable to coupled surface plasmons are derived and extended to systems involving multiple objects.To validate the coupling theory,relevant metal spiral structures were designed,and simulations and experiments were conducted.Under the guidance of the coupled mode theory,the amplitude and phase of electromagnetic wave transmission on the surfaces of two and three metal spiral structures were almost perfectly fitted,providing a theoretical foundation for the analysis of multimolecular systems.2.This study introduces the symmetrically protected bound states in the continuum and Friedrich-Wintgen-type bound states in the continuum into an open metal waveguideresonator structure.The existence of bound states in the continuum and their highly resonant high-Q characteristics are demonstrated through coupled mode theory and relevant simulations.Leveraging the high-Q characteristics of the quasi-guided modes on the continuum,a sensor based on the waveguide and resonator is designed.3.The coupling analysis between the waveguide and resonator in the sensor was accomplished using the coupled mode theory.The coupling mode equations accurately express the resonant characteristics on the waveguide transmission curve.By utilizing the coupled transmission expressions,it is demonstrated that the sensor possesses adjustable high precision and sensitivity.Building upon this,the coupling coefficients are replaced with material parameters using the equivalent circuit method,allowing the complete representation of resonances on the transmission curve solely through the dielectric constant and loss tangent.