Study On Perfect Absorption In Dielectric Metasurfaces Based On Degenerate Critical Coupling Mechanism

Scientists have long been dedicated to exploring the interactions between light and matter,driven by its widespread applications in both military and civil sectors.With the continuous advancement of micro-nano fabrication technology,researchers have gradually extended their vision to the field of artificially engineered metamaterials.By designing the geometry and parameters of metamaterials,scientists can regulate their electromagnetic properties and optimize the performance of optical devices within a controllable range.Superficially engineered metamaterials,or metasurfaces,preserve the outstanding properties of metamaterials while being easier to make and having smaller device sizes.In some metal-based metasurface designs,the existence of Ohmic loss may have adverse effects on applications that have higher temperature requirements.Therefore,for these types of applications,using dielectric metasurfaces is usually a more favorable option.This article mainly proposes a fully dielectric metasurface absorber for such purposes.According to coupling mode theory,a two-port resonator has a 50%absorption limit,which is a barrier that has been difficult to cross in previous research work.Placing a metal back reflector underneath the resonator is one of the existing ways to overcome this limitation,but there is still ohmic loss.In view of the above factors,this paper design a dielectric metasurface perfect absorber based on the degenerate critical coupling theoretical model,and discuss the robustness of the absorption performance of the structure.The main findings of this paper are as follows:（1）To improve the rigorous conditions for realizing degenerate critical coupling,it is proposed that for the same resonator,to achieve degenerate critical coupling,the structure should meet the support of odd and even resonance modes,and realize the critical coupling of the mode at the same resonance frequency.It is pioneered the idea that degenerate critical coupling in a resonator should be achieved when the resonance frequencies of the two modes are equal,i.e.,ω₁=ω₂,γ₁=δ₁=γ₂=δ₂,which has been ignored in some previous degenerate critical coupling mechanisms.（2）A perfect absorption structure of Ga As nanocylindrical metasurface based on degenerate critical coupling mechanism was designed,and the optimal perfect absorption structure parameters were obtained by scanning the height and radius of the cylinder respectively.At the same time,at this wavelength,this paper fit the absorption simulation results with the absorption plot drawn by the absorption formula derived from the degenerate critical coupling,and the data show that the two maintain a high degree of consistency.This work also analyze the dominant resonance mode under this structural parameter,and observe the multipole decompositions of the scattering cross sections and find that electric dipole resonance and magnetic dipole resonance predominate at degenerate critical coupling wavelengths,which is also consistent with our assumption.（3）The robustness of the absorption performance at the captured degenerate critical coupling point was analyzed.By converting the polarization modes TE and TM,it is found that both polarization have high absorption at the degenerate critical coupling wavelength;In addition,this work also scanned the effect of changes in polarization angle on the robustness of its absorption performance,and the results showed that the structure remained high absorption when the polarization angle remained within 25°.