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Fiber lasers and amplifiers are widely used in intelligent manufacturing, life and health, new generation of information technology, national defense, and military fields. In addition, active optical fibers are key materials for fiber lasers and amplifiers. This study reviews the research progress of key active optical fibers in the infrared band (including near infrared 1 μm, 1.3–1.5 μm, and mid infrared 2–3 μm) and analyzes the research status and development trend of active optical fibers both in China and abroad from the perspectives of gain coefficient, gain bandwidth, and application of special fibers. Moreover, it explores the problems faced by China in this field, including a low localization rate of production equipment and lack of high-end industrialized products, and puts forward the key development strategies, directions, and goals of key active optical fibers in China. Furthermore, we propose several suggestions from the aspects of basic theoretical innovation, sustainable industrial development, policy system construction, high-tech products, circular development of the entire industry chain, and personnel training, thereby promoting the high-quality and rapid development of key active optical fibers in China.

Yttrium aluminum garnet (YAG)-based optical fiber is one of the research hotspots in the field of fiber lasers due to its combined advantages of a wide doping range of rare earth ions and the high mechanical strength of YAG material, as well as the flexibility and small size of the fiber structure. YAG-based optical fibers and related laser devices can be used in communication, sensing, medicine, etc. A comprehensive review of YAG-based optical fibers is provided in this paper. Firstly, the fabrication processes of YAG-based optical fibers are summarized and the structure and properties of fibers are classified and compared. Secondly, according to the optical wavelength regions, rare earth-doped YAG-based optical fibers for the applications of single-frequency and mode-locked fiber lasers are summarized. Lastly, the development challenges in both the fabrication and applications of YAG-based optical fibers are discussed. [ABSTRACT FROM AUTHOR]

Demands are increasing for ultrashort pulse laser in industrial applications, where the gain bandwidth of most optical fiber material is not wide enough, and developing a wide bandwidth gain medium is challenging. Glass–ceramic fibers containing Nd3+/Yb3+ co‐doped YCa4O(BO3)3 nanocrystals were fabricated by the molten core method and successive heat treatment. After a careful heat treatment, Nd3+/Yb3+ co‐doped YCa4O(BO3)3 nanocrystals were precipitated in the fiber core. Enhanced broadband near‐infrared (NIR) emission from 850 to 1150 nm (bandwidth: ∼252 nm) was obtained in the glass–ceramic fiber compared to that of precursor fiber. These results suggest that the Nd3+/Yb3+ glass–ceramic fibers are promising for broadband NIR optical amplifications and lasers. [ABSTRACT FROM AUTHOR]

Due to the excellent infrared transparency, low phonon energy, and high rare‐earth solubility, germanate laser glass has attracted much attention in mid‐infrared fiber lasers for potential coherent laser radar systems, optical detection, remote sensing, and laser surgery. However, radiation‐induce darkening often occurs in fiber lasers that operate in radiation environment. Here, we report a useful strategy to improve the radiation resistance by adding multivalence Bi ions and discuss its radiation resistance mechanism. In order to study the effect of valence states on the radiation resistance of barium gallo‐germanate glass, we adjust the valence states of Bi ions by heat treatment, the potential mechanism of which is discussed in detail based on the absorption, photoluminescence (PL), and Raman spectra. The absorption, electron paramagnetic resonance, and photoluminescence spectra have proved the interconversion of Bi ions between low and high valence, which inhibits the formation of Ge‐related electron center (GEC) and non‐bridging oxygen hole center defects in the irradiation process. In addition, the Bi3+ content increased by heat treatment is beneficial to serve as electron‐trapping centers in γ‐ray irradiation, thus further reducing the formation of GEC. This study provides a simple method to achieve Bi valence regulation, so as to improve the radiation resistance. [ABSTRACT FROM AUTHOR]

High-performance thermoelectric fibers with n-type bismuth telluride (Bi2Te3) core were prepared by thermal drawing. The nanosheet microstructures of the Bi2Te3 core were tailored by the whole annealing and Bridgman annealing processes, respectively. The influence of the annealing processes on the microstructure and thermoelectric performance was investigated. As a result of the enhanced crystalline orientation of Bi2Te3 core caused by the above two kinds of annealing processes, both the electrical conductivity and thermal conductivity could be improved. Hence, the thermoelectric performance was enhanced, that is, the optimized dimensionless figure of merit (ZT) after the Bridgman annealing processes increased from 0.48 to about 1 at room temperature. [ABSTRACT FROM AUTHOR]

The rapid and low‐cost development of multicomponent oxide glasses is a long‐standing issue in condensed matters and materials science. However, traditional experimental approaches based on trial‐and‐error and empirical rules are time consuming and high‐cost. Recently, with the proposal of the materials genome engineering, the "glass genome" has also attracted much attention, which can accelerate the development of multicomponent oxide glasses. Here, we present an alternative and more suitable description of a multicomponent oxide glass as a statistical ensemble of its neighboring glassy compounds (NGCs) in the composition space. Subsequently, the NGCs method was proposed to predict the structural features and physical properties of the multicomponent oxide glass by the statistical averages of structural features and physical properties of the NGCs. What is more, the NGCs method was systematically verified at the atomic‐level view through molecular dynamics simulations. The predicted results through the NGCs method were in good agreement with the simulated results in multicomponent oxide glasses (Na2O‐SiO2 and Na2O‐CaO‐SiO2 systems). This work supports the physical picture of multicomponent oxide glasses and further promotes the development of "glass genome," which will accelerate the research of glass materials. [ABSTRACT FROM AUTHOR]

In the field of multimaterial optical fibers, the demand for high‐performance single‐crystal core glass‐clad multimaterial optical fibers is increasing. However, the applications of single‐crystal fibers are restricted by the complex fabrication processes and the slow growth of single‐crystal materials. Here, a two‐step method is demonstrated to achieve single‐crystal tellurium (Te) core fibers with high crystal quality over the length of the fiber. This method starts with the thermal drawing of a fiber preform into polycrystalline Te core multimaterial fibers (precursor fibers) that are long and mechanically stable. A 532‐nm continuous laser is then employed to recrystallize the Te core in the precursor fiber into a single crystal state along the entire length of the fiber. Experimental studies of these single‐crystal fibers demonstrate that the single‐crystal Te core fibers possess high transmittance (>90% at 2–10 μm) and high thermoelectric performance (ZT values from 0.03 to 0.13 at 300 K temperature). They are superior to previous reports and our previous work. This method works for fabricating various single‐crystal fibers and has important applications in the field of optical fibers, functional fibers, and their integrated devices. [ABSTRACT FROM AUTHOR]