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 underwater hyperspectral imager enables the detection and identification of targets on the seafloor by collecting high-resolution spectral images. The distance between the hyperspectral imager and the targets cannot be consistent in real operation by factors such as motion and fluctuating terrain, resulting in unfocused images and negative effects on the identification. In this paper, we developed a novel integrated underwater hyperspectral imaging system for deep sea surveys and proposed an autofocus strategy based on liquid lens focusing transfer. The calibration tests provided a clear focus result for hyperspectral transects and a global spectral resolution of less than 7 nm in spectral range from 400 to 800 nm. The prototype was used to obtain spectrum and image information of manganese nodules and four other rocks in a laboratory environment. The classification of the five kinds of minerals was successfully realized by using a support vector machine. We tested the UHI prototype in the deep sea and observed a Psychropotidae specimen on the sediment from the in situ hyperspectral images. The results show that the prototype developed here can accurately and stably obtain hyperspectral data and has potential applications for in situ deep-sea exploration.

A watt-level, high-efficiency single-frequency distributed Bragg reflector (DBR) fiber laser emitting at 1941 nm was demonstrated using a Tm³⁺-doped yttrium aluminum garnet (Tm:YAG) crystal-derived silica fiber (TYCDSF). The TYCDSF, featuring a core doping concentration of Tm₂O₃ as high as ∼12.17 wt.% and a gain coefficient of 5.10 dB/cm at 1941 nm, was fabricated through the molten core method (MCM). By employing a 16-mm-long TYCDSF and in-band core pumping with a 1610 nm fiber laser, a stable single-frequency laser with a maximum output power of 1030 mW and a slope efficiency of 50.83% for absorbed pump power was achieved. The laser exhibited an optical signal-to-noise ratio exceeding 66.5 dB and a laser linewidth of approximately 40.75 kHz. To the best of our knowledge, this is the first demonstration of a watt-level single-frequency laser based on YAG crystal-derived silica fiber (YCDSF). Moreover, the slope efficiency achieved in this work is the highest reported for single-frequency lasers in the 2-μm band.