Interaction between light and magnetism in magneto‐optical (MO) nanophotonic devices has been actively studied in the past few years. The recent development of MO all‐dielectric resonators and metasurfaces has led to the emergence of various novel MO phenomena that were not observed in their bulk counterparts. For example, a large s‐polarized transverse MO Kerr effect can be observed at magnetic resonance wavelength, which cannot exist in the bare MO films. We review recent developments in nanophotonic devices based on MO materials and focus on different modes and related MO effects in nanophotonic structures with emphasis on recently discovered new MO phenomena in magnetoplasmonics and all‐dielectric nanostructures, such as dark mode, all‐dielectric Mie resonance and waveguide mode. Further, we discuss the potential applications of these nanostructures for biological/chemical sensing, magnetic field sensing, and magnetic field‐controlled active and nonreciprocal metasurfaces.

High-performance infrared thermal imaging devices are widely used in military, biomedical and other fields. Upconversion pixel-less imaging is promising for infrared imaging. In this paper, we propose a hybrid metasurface to achieve high upconversion efficiency of the integrated quantum well infrared photodetector and light-emitting diodes (QWIP-LED). Systematical investigations on the performance of the QWIP-LED, including optical coupling efficiency, light extraction efficiency, and upconversion efficiency, have been carried out via theoretical simulation. We also present the integration time for different devices with different optical coupling structures. Numerical results show that 45° edge-coupled QWIP-LED is not suitable for imaging applications for the low upconversion efficiency. Traditional grating-coupled QWIP-LED can be optimized for real-time thermal imaging. The hybrid-metasurface-based QWIP-LED can achieve a high frame rate above 300 Hz due to the enhanced upconversion efficiency. This work gives a precise description of QWIP-LED performance with different device structures and opens the way for large format upconversion pixel-less imaging.

Broadband upconversion has various applications in solar photovoltaic, infrared and terahertz detection imaging, and biomedicine. The low efficiency of the light-emitting diodes (LEDs) limits the broadband upconversion performance. In this paper, we propose to use surface microstructures to enhance the electroluminescence efficiency (ELE) of LEDs. Systematical investigations on the cryogenic-temperature performances of microstructure-coupled LEDs, including electroluminescence efficiency, luminescence spectrum, and recombination rate, have been carried out by elaborating their enhancement mechanism and light emitting characteristics both experimentally and theoretically. We have revealed that the reason for the nearly 35% ELE enhancement of the optimized structure under cryogenic temperature and weak injection current is the efficient carrier injection efficiency and the high recombination rate in the active region. We also compare studies of the surface luminescence uniformity of the optimized LED with that of the unoptimized device. This work gives a precise description, and explanation of the performance of the optimized microstructure coupled LED at low temperatures, providing important guidance and inspiration for the optimization of broadband upconverter in the cryogenic temperature region.