Multi-mode Coupling Mechanism And Thermal Radiative Property Regulation Of Magnetic Polariton

Thermal radiation is the method of energy transfer as well as the carrier of signal transmission.Thermal radiation is widely used in infrared detection and guidance,energy power and other fields.When the characteristic length of the object is comparable to the wavelength,the interactions between matters and electromagnetic waves produce nano/microscale effects.Magnetic Polariton is a typical nano/microscale effect.Equivalent circuit model establishes the relationship between the electromagnetic field distributions of nano/microstructures and the resonant frequencies of the polaritons by equating the nano/microstructures as circuits,so as to realize the analysis and prediction of the resonant frequency of the Magnetic Polariton.However,when the resonant frequencies of Magnetic Polaritons in the nano/microstructure are close to the resonant frequencies of modes such as Surface Plasmon（Phonon）Polaritons,the accuracy of the existing circuit model is seriously degraded.In addition,the existing circuit model has poor performance in predicting the resonance of Multi-mode and Multi-order Magnetic Polaritons in complex nano/microstructures,and are hard to apply in the case of oblique incidence.Aiming at the problem that the resonant frequency of Magnetic Polariton is difficult to predict under multi-mechanism coupling,this thesis takes the Magnetic Polariton as the research object,and carries out the research on the excitation,suppression,coupling and regulation of the Magnetic Polariton,using the research method combining numerical calculation and experimental verification.The prediction method of Multi-mode and Multi-order Magnetic Polariton in the coupled case and oblique incidence case is proposed.The coupled resonant mechanism of Magnetic Polariton is revealed.A design method for a wavelength-selective optical switch is obtained.The variation law of the temperature effect of Magnetic Polariton is obtained.The main research contents of this thesis include:The coupling mechanism between Magnetic Polariton and Surface Plasmon（Phonon）Polariton is investigated and revealed.The time-varying current circuit formed by Surface Plasmon（Phonon）Polariton will induce a time-varying magnetic field,and the induced time-varying magnetic field acts on Magnetic Polariton current circuit to generate additional current.The above-mentioned coupling behavior of the polaritons is equivalent to the mutual inductance in the circuit model.Equivalent mutual inductor-inductor-capacitor（MLC）circuit model is proposed to describe the resonant frequency of Magnetic Polariton under the influence of Surface Plasmon（phonon）Polariton.The prediction of the resonant frequency of the Magnetic Polariton under oblique incidence is achieved.Establishing the relationship between the geometric parameters of the slit array and grating and the thermal radiative properties from the perspective of structural transformation is proposed.The dispersion relation of the resonant frequency of the Magnetic Polariton in the slit array and the grating is obtained by employing a circuit model,respectively.It is numerically proved that when the grating depth（the height of the slit array）is much larger than the width of the grating groove（slit）,MPn in the grating and the MP（2n-1）in the slit array have approximately equal resonant frequency.Resonant conditions of Multi-mode and Multi-order Magnetic Polaritons are reconstrusted.The current circuits generated when Multi-mode and Multi-order Magnetic Polaritons are excited are independent of each other,and Multi-mode and Multi-order Magnetic Polaritons resonance is described as the superposition of the current ciecuit resonances of each mode.Multi-mode coupled equivalent inductor-capacitor（MCLC）circuit model is further developed as a multi-mode coupled circuit model to realize the prediction of the resonant frequency of Multi-mode and Multi-order Magnetic Polaritons.Magnetic Polariton Coupling mode when the dispersion curves of different Multi-mode and Multi-order Magnetic Polaritons intersect is investigated.The mechanism of suppressed transmission and enhanced absorption of Magnetic Polariton Coupling mode is revealed.The horizontal current circuit and the vertical current loop above excited by Magnetic Polariton Coupling mode form a balance,and the vertical current loop below is suppressed and disappeared,so that the electromagnetic wave is bound in the upper half of the structure,thereby strengthening the absorption and suppressing of transmission.Resonant frequencies of Multi-mode and Multi-order Magnetic Polaritons when filled with dielectric in double-layer slit arrays are investigated.The variation law of Multi-mode and Multi-order Magnetic Polariton dispersion curves under horizontal filling and full filling is analyzed.Combining Magnetic Polariton Coupling and the thermochromic property of VO₂,a wavelength-selective optical switching device is proposed,whose thermochromic property is opposite to VO₂’s.Transmission regulation mechanism of optical switch is revealed.When VO₂ is in the metallic phase,Magnetic Polaritons are excited in the vertical direction to produce high transmission corresponding to the"on"state.When VO₂is in the insulating phase,Magnetic Polaritons are excited in both the horizontal and vertical directions to form Magnetic Polariton Coupling mode,and the electromagnetic wave is bound and dissipated in the upper half of the structure.At this time,the transmittance is extremely low,corresponding to"off"state.Regulating methods of the working wavelength of the optical switch are investigated.The influence of machining deviation on the performance of optical switch is analyzed.Resonance conditions for coupled modes of Magnetic Polaritons in two-dimensional periodic disk arrays and square arrays are established.The structural design method of multi-band wavelength-selective optical switch under circularly polarized light based on circuit model is briefly analyzed.A spectral emissivity experiment system for nano/microscale samples is developed and the spectral emissivity of the Au grating-SiO₂-Au substrate structure is measured at room temperature and high temperature.Resonant wavelengths of Multi-mode and Multi-order Magnetic Polaritons are predicted by MCLC circuit model.The multiple solutions of the circuit model under the combination between structure and material dielectric function are analyzed.The rationality of the proposed MCLC circuit model is verified.The influences of thermal expansion effect,annealing effect and permittivity temperature effect on the Magnetic Polariton during the heating process are evaluated.The resonant wavelength of the Magnetic Polariton is found to be red-shifted with thermal expansion.Thermal expansion effect is the main reason for the change of the absorption peak position of the Magnetic Polariton during the heating process of the annealed micro/nanostructure.The theoretically predicted convert wavelength on the peak change of the Magnetic Polariton during heating process is verified experimentally.