Photonic structures with topological edge states and resonance loops are both important in optical communication systems, but they are usually two separate structures. In order to obtain a photonic system combining properties from both, we design multiple-layer nested photonic topological structures. The nested topological loops not only have topological protection immune to structural disorder and defects, but also possess both the properties of unidirectional propagation and loop resonance. Through mode analysis and simulations, we find that the transport can form diverse circulation loops. Each loop has its own resonance frequencies and can be solely excited in the nested layered structure through choosing its resonance frequencies. As a result, this work shows great application prospects in the area of reconfigurable photonic circuits.

基于麦克斯韦应力张量理论，对多边形金纳米粒子在聚焦场下的光力特性进行了研究。以三角形金纳米粒子为例，从粒子在聚集场中的受力情况出发，分别研究了具有圆对称能量分布的聚焦场和具有三角形能量分布的聚焦场对三角形金纳米粒子的捕获特性。研究结果表明，当使用圆对称聚焦场时，可对边长为50~350 nm的三角形金纳米粒子实现稳定捕获；当使用三角形聚焦场时，在粒子以和聚焦场形状匹配的角度进入聚焦场的情况下，可对边长为100~350 nm的三角形金纳米粒子实现稳定捕获。将圆对称聚焦场和三角形聚焦场对三角形金纳米粒子的捕获特性进行比较，发现三角形聚焦场在x方向的捕获力要强于圆对称聚焦场；而在y方向，三角形聚焦场对粒子的捕获范围要大于圆对称聚焦场。该工作研究了三角形的金属纳米粒子在不同形状聚焦场下的光力捕获特性，为基于非球形金属粒子的光学操纵在拉曼光谱超分辨成像、粒子微加工等领域的应用奠定了理论基础。

具有偏振结构分布的强激光与非线性光学材料相互作用导致了多种新颖的非线性光学效应，反映了材料的非线性光学特性，调制了光场的传播行为。笔者概述了矢量光场激发三阶非线性光学效应的研究进展。首先简要介绍了任意偏振光激发三阶非线性光学效应的理论，如非线性薛定谔方程、光束传播方程、各向同性和各向异性三阶非线性光学系数。也简要介绍了表征三阶非线性光学系数的 Z-扫描技术。在弱聚焦条件下，给出了诸如径向偏振光、杂化偏振光和柠檬型庞加莱光束这三种类型矢量光场的焦场表达式。其次，重点回顾了多种矢量光场激发的各向同性/各向异性三阶非线性光学效应，包括径向偏振光激发的各向异性非线性光学效应、杂化偏振光激发的各向同性和各向异性非线性光学效应、柠檬型庞加莱光束激发的各向同性/各向异性非线性光学效应。最后，简要讨论了矢量光场在非线性偏振旋转、光束整形、可控光场塌缩与成丝和光限幅方面的应用。

We investigate femtosecond laser trapping dynamics of two-photon absorbing hollow-core nanoparticles with different volume fractions and two-photon absorption (TPA) coefficients. Numerical simulations show that the hollow-core particles with low and high-volume fractions can easily be trapped and bounced by the tightly focused Gaussian laser pulses, respectively. Further studies show that the hollow-core particles with and without TPA can be identified, because the TPA effect enhances the radiation force, and subsequently the longitudinal force destabilizes the trap by pushing the particle away from the focal point. The results may find direct applications in particle sorting and characterizing the TPA coefficient of single nanoparticles.

Understanding the nonlinear optical effect of novel materials plays a crucial role in the fields of photonics and optoelectronics. Herein, we theoretically and experimentally investigate the simultaneous presence of third-order locally refractive nonlinearity and thermally induced nonlocal nonlinearity saturation. We present analytical expressions for the closed-aperture Z-scan trace and the number of spatial self-phase modulation (SSPM) rings, which allows one to unambiguously and conveniently separate the contributions of local and nonlocal nonlinear refraction in the case that both effects occur simultaneously. As a test, we study both the local and thermally induced nonlocal nonlinear refraction in fullerene/toluene solution by performing continuous-wave Z-scan and SSPM measurements at two different wavelengths. This work enriches the understanding of the physical mechanism of the optical nonlinear refraction effect in solution dispersions of nanomaterials, which can be exploited for nonlinear photonic devices.

Optical trapping techniques hold great interest for their advantages that enable direct handling of nanoparticles. In this work, we study the optical trapping effects of a diffraction-limited focal field possessing an arbitrary photonic spin and propose a convenient method to manipulate the movement behavior of the trapped nanoparticles. In order to achieve controllable spin axis orientation and ellipticity of the tightly focused beam in three dimensions, an efficient method to analytically calculate and experimentally generate complex optical fields at the pupil plane of a high numerical aperture lens is developed. By numerically calculating the optical forces and torques of Rayleigh particles with spherical/ellipsoidal shape, we demonstrate that the interactions between the tunable photonic spin and nanoparticles lead to not only 3D trapping but also precise control of the nanoparticles’ movements in terms of stable orientation, rotational orientation, and rotation frequency. This versatile trapping method may open up new avenues for optical trapping and their applications in various scientific fields.

The principle of optical trapping is conventionally based on the interaction of optical fields with linear-induced polarizations. However, the optical force originating from the nonlinear polarization becomes significant when nonlinear optical nanoparticles are trapped by femtosecond laser pulses. Herein we develop the time-averaged optical forces on a nonlinear optical nanoparticle using high-repetition-rate femtosecond laser pulses, based on the linear and nonlinear polarization effects. We investigate the dependence of the optical forces on the magnitudes and signs of the refractive nonlinearities. It is found that the self-focusing effect enhances the trapping ability, whereas the self-defocusing effect leads to the splitting of the potential well at the focal plane and destabilizes the optical trap. Our results show good agreement with the reported experimental observations and provide theoretical support for capturing nonlinear optical particles.