Guiding light through optical bound states in the continuum for ultrahigh‐Q microresonators

Light is usually confined in photonic structures with a band gap or relatively high refractive index for broad scientific and technical applications. Here, a light confinement mechanism is proposed based on the photonic bound state in the continuum (BIC). In a low‐refractive‐index waveguide on a high‐refractive‐index thin membrane, optical dissipation is forbidden because of the destructive interference of various leakage channels. The BIC‐based low‐mode‐area waveguide and high‐Q microresonator can be used to enhance light–matter interaction for laser, nonlinear optical and quantum optical applications. For example, a polymer structure on a diamond membrane shows excellent optical performance that can be achieved with large fabrication tolerance. It can induce strong coupling between photons and the nitrogen–vacancy center in diamond for scalable quantum information processors and networks.

     

Photoionization Cross Section for H@Cn${\text{H@C}}_{n}$ Implanted in Nonideal Classical Plasmas

In this study, photoionization cross sections of guest hydrogen atom in endohedral fullerene (${\text{H@C}}_n$) modeled by the Woods–Saxon confinement potential implanted in the nonideal classical plasma (NICP) under spherical confinement are reported for the first time in the related literature. The relevant wave equation is solved numerically via the tridiagonal matrix method and then the energy levels, bound and continuum wave functions are interpreted. Plasma effect is examined by considering plasma temperature and density and is evaluated in the photoionization process. Since the plasma modifies the discrete and continuum spectra by changing the potential energy of hydrogen atom, it closely affects the overlapping of the wave functions of ground state and continuum state. This effect has a distinct response on photoionization resonances. Using different values of endohedral confinement parameters, which means regarding different types of fullerenes, detailed analysis of energy levels, bound and continuum wave functions, and photoionization cross sections are provided by evaluating confinement width, depth, smoothing effect and distance from the spherical encompassement center. The photoionization process of ${\text{H@C}}_n$ implanted in the NICP (nonideal classical plasma) is highly sensitive to both plasma and endohedral confinement. At this sensitivity, Cooper resonance character is like an encoder for fullerene structure.     

Perfect Narrow-Band Absorber of Monolayer Borophene in All-Dielectric Grating Based on Quasi-Bound State in the Continuum

Borophene has the unique optical properties of two-dimensional materials and its own anisotropic characteristics. This work proposes a perfect narrow-band absorption structure to enhance the interaction of light with the monolayer borophene inserted into two different dielectric gratings. The structure efficiently improves absorption efficiency based on the quasi-bound states in the continuum (Q-BIC). The absorption characteristics are numerically simulated and theoretically analyzed by using the rigorous coupled-wave analysis (RCWA) method and the finite element method (FEM). The absorption efficiency of the monolayer borophene is high, up to 99.18% with a full-width at half maximum (FWHW) of 0.62 nm, achieving nearly perfect narrow-band absorption. Moreover, the mechanism of enhanced absorption of monolayer borophene is verified by the coupled mode theory (CMT), which indicates that the nearly perfect absorption is also derived from the critical coupling. At the same time, the influence of the thickness and width of the two layer dielectric structure on the absorption efficiency is theoretically analyzed. Furthermore, due to the anisotropic optical properties of the structure for TE and TM polarized light, a narrow-band polarization plate or sensor can be realized. The structure designed provides a new possibility to enhance the interaction between monolayer borophene and light.     

基于多体作用的原子/连续耦合方法的先验误差估计

本文研究理想晶体发生位错时如何发生形变,应用本地化拟连续方法(QCL)、基于能量的拟连续方法(QCE)、非本地化拟连续方法(QNL),分析了多体作用下Frenkel-Kontorova模型在一维情形中先验误差分析,推导了该误差估计与原子模型解的光滑性的关系,并且由于考虑的是一维原子链,该误差还具备超收敛性.本文将一致性误差分析分解为模型误差和粗粒化误差,并推导出基于负范数的误差估计,稳定性分析将均匀应变扩充为非线性应变.最后利用数值实验说明了本文的分析结果.