Spatial-dispersion (nonlocal) effects are non-negligible in periodic multilayered metamaterials under certain specific conditions, which cannot be completely understood based on the local effective-medium theory, even though the metamaterials are constructed by deep subwavelength meta-atoms. Here, we present a simple yet robust effective-medium model for such media in which the nonlocal effects are properly considered. Our proposed nonlocal model is established by the analysis of the dispersion relation of the effective medium without any expansion-based approximation, which is applicable for description of the optical behavior of the multilayered metamaterials even under critical conditions, and works well for both TE and TM polarized waves. We believe our model will be a powerful tool for the investigation of electromagnetic nonlocality in the realm of metamaterials and subwavelength optics.

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Herein, a high-performance room-temperature extended-wavelength InAs-based barrier-type photodetector that operates in the 1.5-3.5 μm wavelength range is presented. The experimental results show that the uncooled photodetector exhibits a peak responsivity of 1.47 A W À1 at 3 μm and a peak detectivity as high as 1.6 Â 10 10 cm Hz 1/2 W À1 at zero bias, which is 3-10 times higher than that of available commercial InAs photodetectors. The external quantum efficiency at the peak responsivity is %63%. The nature of the detector's extended spectral response is investigated using numerical computation analyses, which indicate that such improvement is primarily contributed by the InAsSbP window layer.

Broadband long-wavelength infrared (LWIR) optical absorbers have important applications in thermal emission and imaging, infrared camouflaging, and waste heat and biothermal energy utilization. However, the practical application of broadband LWIR optical absorbers requires low-cost and facile fabrication of large-area structures with limited thickness. This paper reports the design and fabrication of an ultrathin, broadband, omnidirectional, and polarization-independent LWIR optical absorber composed of anodized aluminum oxide and highly doped Si using the gradient refractive index strategy. The average absorption of the broadband optical absorber is higher than 95% in the 8–15 μm wavelength range, and it has wide incident angle and polarization tolerances. More than 95% of the optical energy in the wavelength range from 8 to 13 μm was absorbed within a depth of 8 μm, making this absorber the thinnest broadband LWIR dielectric absorber so far. The absorption remained above 90% after annealing at 800 °C in air. The infrared camouflage of the proposed absorber was successfully demonstrated with a human body background. With the advantages of facile fabrication, low-cost materials, restricted absorption thickness, and excellent thermal stability, the developed broadband LWIR optical absorber is very promising for the practical applications mentioned above.

All-inorganic cesium lead halide perovskite quantum dots have recently received much attention as promising optoelectronic materials with great luminescent properties and bright application prospect in lighting, lasing, and photodetection. Although notable progress has been achieved in lighting applications based on such media, the performance could still be improved. Here, we demonstrate that the light emission from the perovskite QDs that possess high intrinsic luminous efficiency can be greatly enhanced by using metallic thin films, a technique that was usually considered only useful for improving the emission of materials with low intrinsic quantum efficiency. Eleven-fold maximal PL enhancement is observed with respect to the emission of perovskite QDs on the bare dielectric substrate. We explore this remarkable enhancement of the light emission originating from the joint effects of enhancing the incident photonic absorption of QDs at the excitation wavelength by means of the zero-order optical asymmetric Fabry–Perot-like thin film interference and increasing the radiative rate and quantum efficiency at the emission wavelength mediated by surface plasmon polaritons. We believe that our approach is also potentially valuable for the enhancement of light emission of other fluorescent media with high intrinsic quantum efficiency.

The importance of tunable subwavelength optical devices in modern electromagnetic and photonic systems is indisputable. Herein, a lithography-free, wide-angle, and reconfigurable subwavelength optical device with high tunability operating in the near-infrared regions is proposed and experimentally demonstrated, based on a reversible nanochemistry approach. The reconfigurable subwavelength optical device basically comprises an ultrathin copper oxide (CuO) thin film on an optical thick gold substrate by utilizing the reversible chemical conversion of CuO to sulfides upon exposure to hydrogen sulfide gas. Proof-of-concept experimental results show that the maximal modulation depth of reflectance can be as high as 90% at the wavelength of 1.79 μm with the initial thickness of CuO taken as 150 nm. Partially reflected wave calculations combined with the transfer matrix method are employed to analytically investigate the optical properties of the structure, which show good agreement with experimental results. We believe that the proposed versatile approaches can be implemented for dynamic control management, allowing applications in tunable photonics, active displays, optical encryption, and gas sensing.

Transparent heat mirrors have been attracting a great deal of interest in the last few decades due to their broad applications, which range from solar thermal convection to energy-saving. Here, we present a flexible Polyethylene terephthalate/Ag-doped Indium tin oxide/Polydimethylsiloxane (PAIP) thin film that exhibits high transmittance in visible range and low emissivity in the thermal infrared region. Experimental results show that the temperature of the sample can be as high as 108 °C, which is ~23 °C higher than that of a blackbody control sample under the same solar radiation. Without solar radiation, the temperature of the PAIP thin film is ~6 °C higher than that of ordinary fabric. The versatility of the large-area, low-radiation-loss, highly-transparent and flexible hydrophobic PAIP thin film suggest great potential for practical applications in thermal energy harvesting and manipulation.

Thermal infrared camouflage as a kind of counter-surveillance technique has attracted much attention owing to the rapid development of infrared surveillance technology. Various artificial optical structures have been developed for infrared camouflage applications under cold ambient environment (low thermal radiation), but the realization of infrared camouflage under a hot environment (high thermal radiation) is also highly desirable and has been rarely reported. Here, a lithography-free, ultra-thin, high performance long-wavelength infrared (LWIR) selective emitter for thermal infrared camouflage in a high radiation environment is proposed and experimentally demonstrated. Experimental results show that our designed selective emitter exhibits average emissivity higher than 90% over the LWIR range from 8 to 14 µm and low emissivity less than 35% outside this window. Numerical simulations were performed to optimize the geometrical structures and reveal that such a selective emission effect is attributed to the combination of multiple hybrid plasmonic resonances. LWIR thermal images show that the selective emitter can perfectly blend into the high radiation backgrounds. Furthermore, it is found that the sample displays angle-independent emission properties, indicating that our emitter offers great potential for application in evading large-angle detection.