Study On Optical Resonance And Mode Coupling Characteristics In HBN/Grating Hybrid Regime

Hexagonal boron nitride(h BN)is a special material with unique natural hyperbolic dispersion.It can excite hyperbolic phonon polaritons(HPP)in the mid-infrared band,which makes it promising in sub-diffraction focusing,imaging etc.However,due to the large wavevector of HPP,it cannot be excited by the propagating wave in free-space,leading to the low absorption rate(20%)of the plain h BN.Coupled optical mode can effectively increase the absorption of resonators and hence enhance light-matter interaction.Recently,HPP in h BN and its coupling characteristics has raised an increasing interest for its potential in optoelectronic device applications including photoelectric detection,super-resolution imaging,optical switches,optical sensing.Based on the rigorous full-wave simulation and theoretical analysis,this thesis is mainly focused on the optical resonance and mode coupling in the coupled composite grating structure.The main contents are listed as follows:(1)Strong coupling between hyperbolic phonon-polaritons(HP)and magnetic polaritons(MP)is theoretically studied in a hexagonal boron nitride(h BN)covered deep silver grating structure.It is found that MP in grating trenches strongly interacts with HP in an anisotropic h BN thin film,leading to a large Rabi splitting with near-perfect dual band light absorption.Numerical results indicate that MP-HP coupling can be tuned by geometric parameters of the structure.More intriguingly,the resonantly enhanced fields for two branches of the hybrid mode demonstrate unusually different field patterns.One exhibits a volume-confined Zigzag propagation pattern in the h BN film,while the other shows a field-localization near the grating corners.Furthermore,resonance frequencies of these strongly coupled modes are very robust over a wide-angle range.The angleinsensitive strong interaction of hyperbolic-magnetic polaritons with dual band intense light absorption in this hybrid system offers a new paradigm for the development of various optical detecting,sensing and thermal emitting devices.(2)We designed a coupled structure of h BN-multilayer dielectric-metal.Mode coupling between h BN HPPs and Tamm plasmon polaritons(TPPs)is theoretically studied in this coupled resonator.Our simulation results show that HPPs in h BN film can simultaneously stong interplay with TPPs in h BN/DBR and DBR/Ag interfaces,leading to a strong multiple mode coupling featuring a larger Rabi split and a dual-band perfect light absorption at mid-IR frequencies.Additionally,we find that the mode coupling system is sensitive to the incident angle.Our findings pave a new way for the design of many optoelectronic devices such as optical detectors,switches and light emitting devices.(3)The resonance modes and its absorption response have been studied in a peridodic dielectric tetramer grating/gold resonator in the near-infrared region numerically and theoretically.Numerical calculations and theoretical analysis show that the magnetic dipole resonance can be excited in this proposed resonance metasurface structure,enabling a perfect absorption with extremely narrow linewidth.By breaking the symmetry of the arrays,we found that the absorption response and field localization of the device is greatly relied on the in-plane polarization direction of incident light,rendering a dynamically tunable selective light-matter interaction enhancement in the proposed metasurfaces.This thesis concerntrates on the investigation of optical modes and its coupling attributes in the coupled grating resonators.The relevant research results in this paper lays the groundwork for controlling the mode coupling in nanoscale,holding the potential in designing a large variety of near-and mid-infrared photoelectric devices.