Semiconductor nanowires (or other wire-like nanostructures, including nanoribbons and nanobelts) synthesized by bottom-up chemical growth show single-crystalline structures, excellent geometric uniformities, subwavelength transverse dimensions, and relatively high refractive indices, making these one-dimensional structures ideal optical nanowaveguides with tight optical confinement and low scattering loss. When properly pumped by optical or electrical means, lasing oscillation can be readily established inside these high-gain active nanowires with feedback from endface reflection or near-field coupling effects, making it possible to realize nanowire lasers with miniature sizes and high flexibilities. Also, the wide-range material availability bestows the semiconductor nanowire with lasing wavelength selectable within a wide spectral range from ultraviolet (UV) to near infrared (IR). As nanoscale coherent light sources, in recent years, nanowire lasers have been attracting intensive attention for both fundamental research and technological applications ranging from optical sensing, signal processing, and on-chip communications to quantum optics. Here, we present a review of the status and perspectives of semiconductor nanowire lasers, with a particular emphasis on their optical characteristics categorized in two groups: (1) waveguiding related properties in Section 3, which includes waveguide modes, near-field coupling, endface reflection, substrate-induced effects, and nanowire microcavities, and (2) optically pumped semiconductor nanowire lasers in Section 4, starting from principles and basic types of UV, visible, and near-IR nanowire lasers relying on Fabry–Perot cavities, to advanced configurations including wavelength-tunable, single-mode operated, fiber-coupled, and metal-incorporated nanowire lasing structures for more possibilities. In addition, the material aspects of semiconductor nanowires, including nanowire synthesis and electrically driven nanowire lasers, are briefly reviewed in Sections 2 and 5, respectively. Finally, in Section 6 we present a brief summary of semiconductor nanowire lasers regarding their current challenges and future opportunities.
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