We review the physics and some applications of photonic structures designed for the realization of strong nonlinear chiroptical response. We pay much attention to the recent strategy of utilizing different types of optical resonances in metallic and dielectric subwavelength structures and metasurfaces, including surface plasmon resonances, Mie resonances, lattice-guided modes, and bound states in the continuum. We summarize earlier results and discuss more recent developments for achieving large circular dichroism combined with the high efficiency of nonlinear harmonic generation.

A dispersion model is developed to provide a generic tool for configuring plasmonic resonance spectral characteristics. The customized design of the resonance curve aiming at specific detection requirements can be achieved. According to the model, a probe-type nano-modified fiber optic configurable plasmonic resonance (NMF-CPR) sensor with tip hot spot enhancement is demonstrated for the measurement of the refractive index in the range of 1.3332–1.3432 corresponding to the low-concentration biomarker solution. The new-type sensing structure avoids excessive broadening and redshift of the resonance dip, which provides more possibilities for the surface modification of other functional nanomaterials. The tip hot spots in nanogaps between the Au layer and Au nanostars (AuNSs), the tip electric field enhancement of AuNSs, and the high carrier mobility of the WSe₂ layer synergistically and significantly enhance the sensitivity of the sensor. Experimental results show that the sensitivity and the figure of merit of the tip hot spot enhanced fiber NMF-CPR sensor can achieve up to 2995.70 nm/RIU and 25.04 RIU⁻¹, respectively, which are 1.68 times and 1.29 times higher than those of the conventional fiber plasmonic resonance sensor. The results achieve good agreements with numerical simulations, demonstrate a better level compared to similar reported studies, and verify the correctness of the dispersion model. The detection resolution of the sensor reaches up to 2.00×10⁻⁵ RIU, which is obviously higher than that of the conventional side-polished fiber plasmonic resonance sensor. This indicates a high detection accuracy of the sensor. The dense Au layer effectively prevents the intermediate nanomaterials from shedding and chemical degradation, which enables the sensor with high stability. Furthermore, the terminal reflective sensing structure can be used as a practical probe and can allow a more convenient operation.

Interaction between photons and phonons in cavity optomechanical systems provides a new toolbox for quantum information technologies. A GaAs/AlAs pillar multi-optical mode microcavity optomechanical structure can obtain phonons with ultra-high frequency (~THz). However, the optical field cannot be effectively restricted when the diameter of the GaAs/AlAs pillar microcavity decreases below the diffraction limit of light. Here, we design a system that combines Ag nanocavity with GaAs/AlAs phononic superlattices, where phonons with the frequency of 4.2 THz can be confined in a pillar with ~4 nm diameter. The Q_c/V reaches 0.22 nm^?3, which is ~80 times that of the photonic crystal (PhC) nanobeam and ~100 times that of the hybrid point-defect PhC bowtie plasmonic nanocavity, where Q_c is optical quality factor and V is mode volume. The optomechanical single-photon coupling strength can reach 12 MHz, which is an order of magnitude larger than that of the PhC nanobeam. In addition, the mechanical zero-point fluctuation amplitude is 85 fm and the efficient mass is 0.27 zg, which is much smaller than the PhC nanobeam. The phononic superlattice-Ag nanocavity optomechanical devices hold great potential for applications in the field of integrated quantum optomechanics, quantum information, and terahertz-light transducer.

In this Letter, we report on the investigations of nonlinear scattering of plasmonic nanoparticles by manipulating ambient environments. We create different local thermal hosts for gold nanospheres that are immersed in oil, encapsulated in silica glass and also coated with silica shells. In terms of regulable effective thermal conductivity, silica coatings are found to contribute significantly to scattering saturation. Benefitting from the enhanced thermal stability and the reduced plasmonic coupling provided by the shell-isolated nanoparticles, we achieve super-resolution imaging with a feature size of 52 nm (λ/10), and we can readily resolve pairs of nanoparticles with a gap-to-gap distance of 5 nm.

为了研究超表面结构的耦合及折射率传感特性，设计了一种由两种长度不同的纳米棒组成的二聚体结构，并研究该结构的透射光谱，共振峰处的电场和电荷分布以及结构参数对透射光谱的影响。本文采用有限元法对光学性能进行仿真分析，采用准静态逼近模型解释了平行双纳米棒结构的耦合机理。在共振波长上模拟电场分布,分析电子振动模式，在透射光谱中出现了不对称线型的双Fano共振。结果表明,双Fano共振是由纳米棒和衬底之间的耦合作用产生的，可以通过结构参数和周围介质的折射率来调控，且基于Fano共振的折射率灵敏度最大可达1.137 μm/RIU。这些研究结果为设计等离激元传感器提供了理论依据。

Plasmonic vortices confining orbital angular momentums to surface have aroused wide research interest in the last decade. Recent advances of near-field microscopes have enabled the study on the spatiotemporal dynamics of plasmonic vortices, providing a better understanding of optical orbital angular momentums in the evanescent wave regime. However, these works only focused on the objective characterization of plasmonic vortex and have not achieved subjectively tailoring of its spatiotemporal dynamics for specific applications. Herein, it is demonstrated that the plasmonic vortices with the same topological charge can be endowed with distinct spatiotemporal dynamics by simply changing the coupler design. Based on a near-field scanning terahertz microscopy, the surface plasmon fields are directly obtained with ultrahigh spatiotemporal resolution, experimentally exhibiting the generation and evolution divergences during the whole lifetime of plasmonic vortices. The proposed strategy is straightforward and universal, which can be readily applied into visible or infrared frequencies, facilitating the development of plasmonic vortex related researches and applications.