Thermal radiation control has attracted increasing attention in a wide range of field, including infrared detection, radiative cooling, thermal management, and thermal camouflage. Previously reported thermal emitters for thermal camouflage presented disadvantages of lacking either tunability or thermal stability. In this paper, we propose a tunable thermal emitter consisting of metal-insulator-metal (MIM) plasmonic metamaterial based on phase-change material Ge₂Sb₂Te₅ (GST) to realize tunable control of thermal radiation in wavelength ranges from 3 μm to 14 μm. Meanwhile, the proposed thermal emitter possesses near unity emissivity at the wavelength of 6.3 μm to increase radiation heat dissipation, maintaining the thermal stability of the system. The underlying mechanism relies on fundamental magnetic resonance and the interaction between the high-order magnetic resonance and anti-reflection resonance. When the environmental background is blackbody, the tunable emitter maintains signal reduction rates greater than 80% in middle-IR and longer-IR regions from 450 K to 800 K and from room temperature to 800 K, respectively. The dependences of thermal camouflage on crystallization fraction of GST, incident angles and polarization angles have been investigated in detail. In addition, the thermal emitter can continuously realize thermal camouflage for various background temperatures and environmental background in atmospheric window in the range of 3–5 μm.

The vortex beam carrying orbital angular momentum (OAM) has attracted great attentions in optical communication field, which can extend the channel capacity of communication system due to the orthogonality between different OAM modes. Generally, atmospheric turbulence can distort the helical phase fronts of OAM beams, which presents a critical challenge to the effective recognition of OAM modes. Recently, convolutional neural network (CNN), as a model of deep learning, has been widely applied to machine vision. In this paper, based on the CNN theory, we make a trade-off between the computational complexity of the system and the efficiency of recognition by establishing a specially designed six-layer CNN structure in CPU station to efficiently achieve the recognition of OAM mode in turbulent environment through the feature extraction of the received LG beam's intensity distributions. Furthermore, we examine the performances of our designed CNN with respect to various turbulence levels, transmission distances, mode spacings, and we have also compared the performances of recognizing single OAM mode with multiplexed OAM modes. The numerical simulation shows that basing on CNN method, the coaxial multiplexed OAM modes can obtain higher recognizing accuracy about 96.25% even under long transmission distance with strong turbulence.

Phase-change materials (PCMs), possessing thermo-optic and thermo-electric properties, have constantly enabled the rewritable optical data storage and the commercialized phase-change memory devices. In particular, Ge₂Sb₂Te₅ (GST) has been considered for configurable photonics applications, such as active dielectric metasurface. In this paper, we report an active absorber with metal-insulator-metal (MIM) scheme with GST in the infrared region. The absorber consists of Al disk and reflective Al film with a GST spacer layer. Extraordinary absorption with peaks of more than 90% can be achieved over a broad bandwidth, attributing to highly confined gap surface plasmon resonance. In addition, the absorption can be tuned via adjusting the proportion of GST crystallization, which is a unique advantage to design active device. Meanwhile, the absorption is polarization-independent owing to its structural symmetry. Furthermore, we introduce the designed absorber to the application of sensing. This nearly perfect absorbing strategy offers great potential in sensing applications due to its flexibility and polarization-independence.

In this paper, we generalize the principle of a generated first-order acoustic vortex (AV) with the acoustic resonances (AR) of a metasurface, from which we have also proposed a method for generating the higher-order AVs by arranging the sequences of the AR metasurface properly. The usable frequency range of the designed AR metasurface has been investigated and is discussed in detail, which is about $4470–4600\text{Hz}$ and covers the range $0.977–1.006f$ ($f=4573.31\mathrm{Hz}$ is the preset working frequency) approximately. Meanwhile, the designed AR metasurface can produce a frequency-adjustable AV field efficiently by adjusting the structure size and parameters of the planar AR layer. By discretizing the continuous phase distribution, the multiplexed AV beam with multiple orbital angular momentum states can also be generated effectively by arranging AR metasurface properly. The generated single and multiplexed AV beams can also be detected with the aid of the acoustic reverse phase plates accordingly.

In this paper, we propose a simple plasmonic structure based on Ge₂Sb₂Te₅ (GST) to realize tunable multiband camouflage and radiation heat dissipation. In the mid-infrared (MIR) (3–5 μm) range, the proposed structure has average emissivity of 0.18 ∼ 0.76 and can be applied in tunable thermal camouflage as the GST’s crystallization fraction increases from 0 to 1. In the 5–8 μm (safe window) range, radiation heat dissipation of the proposed structure may guarantee thermal stability of the system. In the long-infrared (8–14 μm) range, the designed emitter maintains a relatively stable and low average emissivity of 0.13 ∼ 0.19 when the crystallization fraction of GST changes from 0 to 1. In addition, due to surface lattice resonance of plasmonic metamaterial, our designed emitter can also achieve laser radar camouflage at the wavelength of 10.6 μm. We have also analyzed the dependence of the camouflage performance on the GST’s crystallization fractions, polarization angle and incident angle. Moreover, simulated thermal images demonstrate tunable thermal camouflage for various background temperatures and different ambient backgrounds in the MIR ranges.

Since its invention in 2009, Perovskite solar cells (PSCs) has attracted great attention because of its low cost, numerous options of efficiency enhancement, ease of manufacturing and high-performance. Within a short span of time, the PSC has already outperformed thin-film and multicrystalline silicon solar cells. A current certified efficiency of 25.2% demonstrates that it has the potential to replace its forerunner generations. However, to commercialize PSCs, some problems need to be addressed. The toxic nature of lead which is the major component of light absorbing layer, and inherited stability issues of fabricated devices are the major hurdles in the industrialization of this technology. Therefore, new researching areas focus on the lead-free metal halide perovskites with analogous optical and photovoltaic performances. Tin being nontoxic and as one of group IV(A) elements, is considered as the most suitable alternate for lead because of their similarities in chemical properties. Efficiencies exceeding 13% have been recorded using Tin halide perovskite based devices. This review summarizes progress made so far in this field, mainly focusing on the stability and photovoltaic performances. Role of different cations and their composition on device performances and stability have been involved and discussed. With a considerable room for enhancement of both efficiency and device stability, different optimized strategies reported so far have also been presented. Finally, the future developing trends and prospects of the PSCs are analyzed and forecasted.