Strong optical absorption can be achieved easily based on an array of subwavelength localized resonators. The absorption bandwidth is typically wide since subwavelength metallic resonators are limited by a low quality factor (Q) due to their large material loss and so do dielectric counterparts owing to their weak photon binding. Here, an angle-insensitive narrowband optical absorber is suggested, which consists of subwavelength dielectric cavities buried inside a metal. Within each cavity, a special resonant mode of high Q can be supported, which is absorbed slowly by the metal walls as the electric field is concentrated at the cavity center and leaks slowly into the free space due to the blocking of the top metal film covering the cavities. Such a mode is excited to trap the incident wave in the optical absorption. When low-loss silver is used, one can obtain ultra-narrowband absorption with Q up to 487. At lower optical frequencies, the metal film needs to be punctured so that the incident wave can couple into the cavities effectively. The suggested absorption method may find its promising prospect in thermal radiation, photonic detection, optical sensing, and so on.

PbS colloidal quantum dots (CQDs) can be considered a promising lighting material, but their emission performance is mired by defect sites, strong photo‐induced activity, and interaction with the environment. Here, we utilize periodic silicon metasurface sustaining a symmetry‐protected bound state in the continuum to enhance the near‐infrared emission of PbS CQDs at room temperature. In the experimental investigation, it is observed that the fluorescence of the coated PbS CQDs is enhanced by 10 times by the fabricated metasurface, and the emission peak has a quality factor up to 251 at wavelength 1408 nm. Meanwhile, the potential of this work in sensing is demonstrated by showing that the enhanced emission is disturbed by the introduction of sparse gold nanoparticles. In all, this work confirms that dielectric metasurfaces sustaining bound states in the continuum can be adopted to efficiently improve the emission performance of PbS CQDs which may find various practical applications including on‐chip silicon‐based optical sources and integrated sensors.

We report the observation of a large-angle self-collimation phenomenon occurring in photonic crystals (PCs) composed of nanorods. Electromagnetic waves incident onto such PCs from directions covering a wide range of incident angles become highly localized along a single array of rods, which results in the narrow-beam propagation without divergence. A propagation length of 0.4 mm is experimentally observed over the wavelength ranging from 1540 nm to 1570 nm even in the large incident angle case, which is a very considerable length scale for on-chip optical interconnection.

A high-precision displacement sensing technique based on the detection of asymmetric intensity patterns of Bloch surface waves is proposed, with a sensitivity of 0.122 nm⁻¹ and a resolution better than 10 nm.

In this work, the radiation responses of silicon photonic passive devices built in silicon-on-insulator (SOI) technology are investigated through high energy neutron and ⁶⁰Co γ-ray irradiation. The wavelengths of both micro-ring resonators (MRRs) and Mach-Zehnder interferometers (MZIs) exhibit blue shifts after high-energy neutron irradiation to a fluence of 1×10¹² n/cm²; the blue shift is smaller in MZI devices than in MRRs due to different waveguide widths. Devices with SiO₂ upper cladding layer show strong tolerance to irradiation. Neutron irradiation leads to slight changes in the crystal symmetry in the Si cores of the optical devices and accelerated oxidization for devices without SiO₂ cladding. A 2-µm top cladding of SiO₂ layer significantly improves the radiation tolerance of these passive photonic devices.