High-temperature measurements above 1000 °C are critical in harsh environments such as aerospace, metallurgy, fossil fuel, and power production. Fiber-optic high-temperature sensors are gradually replacing traditional electronic sensors due to their small size, resistance to electromagnetic interference, remote detection, multiplexing, and distributed measurement advantages. This paper reviews the sensing principle, structural design, and temperature measurement performance of fiber-optic high-temperature sensors, as well as recent significant progress in the transition of sensing solutions from glass to crystal fiber. Finally, future prospects and challenges in developing fiber-optic high-temperature sensors are also discussed.

Common methods of ocean remote sensing and seafloor surveying are mainly carried out by airborne and spaceborne hyperspectral imagers. However, the water column hinders the propagation of sunlight to deeper areas, thus limiting the scope of observation. As an emerging technology, underwater hyperspectral imaging (UHI) is an extension of hyperspectral imaging technology in air conditions, and is undergoing rapid development for applications in shallow and deep-sea environments. It is a close-range, high-resolution approach for detecting and mapping the seafloor. In this paper, we focus on the concepts of UHI technology, covering imaging systems and the correction methods of eliminating the water column’s influence. The current applications of UHI, such as deep-sea mineral exploration, benthic habitat mapping, and underwater archaeology, are highlighted to show the potential of this technology. This review can provide an introduction and overview for those working in the field and offer a reference for those searching for literature on UHI technology.

The ocean connects all continents and is an important space for human activities. Ship detection with electro-optical images has shown great potential due to the abundant imaging spectrum and, hence, strongly supports human activities in the ocean. A suitable imaging spectrum can obtain effective images in complex marine environments, which is the premise of ship detection. This paper provides an overview of ship detection methods with electro-optical images in marine environments. Ship detection methods with sea–sky backgrounds include traditional and deep learning methods. Traditional ship detection methods comprise the following steps: preprocessing, sea–sky line (SSL) detection, region of interest (ROI) extraction, and identification. The use of deep learning is promising in ship detection; however, it requires a large amount of labeled data to build a robust model, and its targeted optimization for ship detection in marine environments is not sufficient.

InGaAs/InP-based negative-feedback avalanche diodes (NFADs) for 1550 nm single-photon detection with easy-to-use and low-afterpulsing features have attracted many researchers on lidar and quantum optics. Here we present a fast active-quenching circuit specifically designed to exploit the performance of a multi-mode fiber coupled NFAD for free-running operation by a further suppression on afterpulsing effects. The quenching and recovery processes of the device were characterized using electroluminescent method and a novel dual-pulse method, respectively. Results show that the proposed circuit was capable of reducing the time required for quenching and recovery process of the NFAD by approximately 20 ns, and contributed to a reduction in the number of avalanche carriers by up to 30%. As a result, the total afterpulse probability (TAP) of the NFAD with active quenching was reduced by up to 70% compared with the condition without active quenching, and by approximately 90% compared with a standard InGaAs SPAD at the photon detection efficiency (PDE) of 20%. The TAP of the proposed detector was lower than 11% when the dead time was longer than 200 ns, 600 ns, and 2 μs at the PDE of 10%, 15%, and 25%, respectively, and the usable dead time was down to 80 ns with a TAP of 20.4% at the PDE of 10%, 1550 nm, 223 K, where the DCR was as low as 918 Hz. The low-afterpulsing, low-dead-time, low-DCR features of this compact detector makes it especially suitable for use in lidar applications.

A metal–graphene metamaterial device exhibiting a tunable, electromagnetically induced transparency (EIT) spectral response at terahertz frequencies is investigated. The metamaterial structure is composed of a strip and a ring resonator, which serve as the bright and dark mode to induce the EIT effect. By employing the variable conductivity of graphene to dampen the dark resonator, the response frequency of the device shifts dynamically over 100 GHz, which satisfies the convenient post-fabrication tunability requirement. The slow-light behavior of the proposed device is also analyzed with the maximum group delay of 1.2 ps. The sensing performance is lastly studied and the sensitivity can reach up to 100 GHz/(RIU), with a figure of merit (FOM) value exceeding 4 ${\mathrm{RIU}}^{-1}$. Therefore, the graphene-based metamaterial provides a new miniaturized platform to facilitate the development of terahertz modulators, sensors, and slow-light applications.