Optical bound states in the continuum (BICs) have recently stimulated a research boom, accompanied by demonstrations of abundant exotic phenomena and applications. With ultrahigh quality (Q) factors, optical BICs have powerful abilities to trap light in optical structures from the continuum of propagation waves in free space. Besides the high Q factors enabled by the confined properties, many hidden topological characteristics were discovered in optical BICs. Especially in periodic structures with well-defined wave vectors, optical BICs were discovered to carry topological charges in momentum space, underlying many unique physical properties. Both high Q factors and topological vortex configurations in momentum space enabled by BICs bring new degrees of freedom to modulate light. BICs have enabled many novel discoveries in light–matter interactions and spin–orbit interactions of light, and BIC applications in lasing and sensing have also been well explored with many advantages. In this paper, we review recent developments of optical BICs in periodic structures, including the physical mechanisms of BICs, explored effects enabled by BICs, and applications of BICs. In the outlook part, we provide a perspective on future developments for BICs.

Optical nanoparticles are nowadays one of the key elements of photonics. They do not only allow optical imaging of a plethora of systems (from cells to microelectronics), but, in many cases, they also behave as highly sensitive remote sensors. In recent years, it has been demonstrated the success of optical tweezers in isolating and manipulating individual optical nanoparticles. This has opened the door to high resolution single particle scanning and sensing. In this quickly growing field, it is now necessary to sum up what has been achieved so far to identify the appropriate system and experimental set-up required for each application. In this review article we summarize the most relevant results in the field of optical trapping of individual optical nanoparticles. After systematic bibliographic research, we identify the main families of optical nanoparticles in which optical trapping has been demonstrated. For each case, the main advances and applications have been described. Finally, we also include our critical opinion about the future of the field, identifying the challenges that we are facing.

Mechanical forces play an important role in the behaviour of cells, from differentiation to migration and the development of diseases. Optical tweezers provide a quantitative tool to study these forces and must be combined with other tools, such as phase contrast and fluorescence microscopy. Detecting the retro-reflected trap beam is a convenient way to monitor the force applied by optical tweezers, while freeing top access to the sample. Accurate in situ calibration is required especially for single cells close to a surface where viscosity varies rapidly with height. Here, we take advantage of the well contrasted interference rings in the back focal plane of the objective to find the height of a trapped bead above a cover slip. We thus map the viscous drag dependence close to the surface and find agreement between four different measurement techniques for the trap stiffness down to 2 μm above the surface. Combining this detection scheme with phase contrast microscopy, we show that the phase ring in the back focal plane of the objective must be deported in a conjugate plane on the imaging path. This simplifies implementation of optical tweezers in combination with other techniques for biomechanical studies.

中波红外成像在**侦察、遥感测绘、航天航空等领域发挥了重要作用。现有中波红外焦平面主要采用碲镉汞、二类超晶格、锑化铟等块体半导体材料，其性能优异、稳定性高。然而，其复杂的材料制备及倒装键合工艺限制了块体半导体焦平面阵列的批量化制备及低成本应用。胶体量子点作为一种新兴液态半导体材料，具有光谱调控范围“宽”、合成规模“大”、制备成本“低”、以及加工工艺“易”等优势，为新型红外焦平面阵列研发提供了全新的思路。碲化汞量子点采用“热注法”合成，并通过旋涂方法实现与硅基读出电路的直接电学耦合，阵列规模及像元间距为640×512及15 µm。在80 K工作温度下对焦平面阵列进行了性能测试，碲化汞焦平面阵列响应截止波长达到4.6 μm、比探测率为2×10¹⁰ Jones、噪声等效温差51.26 mK（F#=2）、响应非均匀性3.42%且有效像元率高达99.99%，展现了较好的成像性能，为非倒装键合体制中波红外成像焦平面的制备提供了新的方案。

The photosensitivity of silicon is inherently very low in the visible electromagnetic spectrum, and it drops rapidly beyond 800 nm in near-infrared wavelengths. We have experimentally demonstrated a technique utilizing photon-trapping surface structures to show a prodigious improvement of photoabsorption in 1-μm-thin silicon, surpassing the inherent absorption efficiency of gallium arsenide for a broad spectrum. The photon-trapping structures allow the bending of normally incident light by almost 90 deg to transform into laterally propagating modes along the silicon plane. Consequently, the propagation length of light increases, contributing to more than one order of magnitude improvement in absorption efficiency in photodetectors. This high-absorption phenomenon is explained by finite-difference time-domain analysis, where we show an enhanced photon density of states while substantially reducing the optical group velocity of light compared to silicon without photon-trapping structures, leading to significantly enhanced light–matter interactions. Our simulations also predict an enhanced absorption efficiency of photodetectors designed using 30- and 100-nm silicon thin films that are compatible with CMOS electronics. Despite a very thin absorption layer, such photon-trapping structures can enable high-efficiency and high-speed photodetectors needed in ultrafast computer networks, data communication, and imaging systems, with the potential to revolutionize on-chip logic and optoelectronic integration.

A kind of optical data storage medium based on electron-trapping materials, Y3Al5O12:Ce3+ fluorescent ceramic, was developed by vacuum sintering technology. The medium shows sufficiently deep traps (1.67 and 0.77 eV). The properties of trap levels were researched by thermoluminescence curves, and the optical storage mechanism based on Ce3+ ion doping was proposed. More importantly, the data can be written-in by 254 nm UV light, and readout by heating (300°C). This work expands the application fields of fluorescent ceramics, and it is expected to promote the development of electron-trapping materials.