Abstract
Mid-infrared (MIR) lasers operating in the 2–6 μm region are important for spectroscopy, sensing, communications, medicine, lidar, and electro-optical applications. Chalcogenide glasses and glass-ceramics are attractive MIR gain-media candidates because of their broad infrared transparency and low-phonon-energy hosts. This review focuses on recent progress in chalcogenide glasses and glass-ceramics toward practical MIR laser operation. Rare-earth-doped glasses and fibers are discussed from early MIR emission studies to recent Tb
3+
-, Ce
3+
-, and Pr
3+
-based laser demonstrations, with particular attention to low-loss fibers. For rare-earth-doped glass-ceramics, dopant partitioning among nanocrystals, and glass-crystal interfaces is examined as a key factor governing spectroscopic performance. Transition-metal-doped systems, including Cr
2+
-, Co
2+
-, Fe
2+
-, and Ni
2+
-activated materials, are reviewed with emphasis on crystal-field engineering and crystallization-induced optical loss. Bulk, fiber, waveguide, and microcavity platforms are further compared in terms of gain-loss balance and their suitability for practical MIR laser operation.