Li Y.-HKuo C.-YSHENG-LUNG HUANG2021-09-022021-09-02202010044213https://www.scopus.com/inward/record.uri?eid=2-s2.0-85097538329&doi=10.3788%2fgzxb20204911.1149010&partnerID=40&md5=f2b1a5ada8dc88fcf29dcd09bf769d2bhttps://scholars.lib.ntu.edu.tw/handle/123456789/581106Broadly tunable lasers are useful for basic spectroscopy studies, as well as a wide range of applications from optical communications to biomedical imaging. Transition-metal-ions doped solid-state gain media are eminently suitable for generating broadband emissions. Ti3+: sapphire and Cr4+: YAG crystals are 2 successful examples that are now widely used. Glass-clad Ti3+: sapphire and Cr4+: YAG crystal fibers have shown superior performance for broadly tunable lasers in the near infrared wavelength ranges. The tunable Ti3+: sapphire crystal fiber lasers are efficient, and have demostrated the lowest threshold over a 180 nm tuning range. The Cr4+: YAG crystal fiber laser shows a tuning range of 170 nm, limited by the excited state absorption. To celebrate the 60th anniversary since laser invention, a brief historical review and the latest developments of the Ti3+: sapphire and Cr4+: YAG crystal fiber lasers are discussed in the manuscript. The tunable Ti3+: sapphire crystal fiber laser's wavelength sweeping speed is envisioned, and the optical properties are compared with that of the Cr4+: YAG crystal fiber. With well-developed crystalline cores and clads for broadly tunable lasers, it is expected that novel applications, such as ultra-broadband optical fiber communications and cellular-resolution optical coherence tomography, could be evolved to meet the high data rate and high image resolution needs in future. ? 2020, Science Press. All right reserved.Crystal whiskers; Excited states; Fiber lasers; Image resolution; Infrared devices; Laser tuning; Medical imaging; Metal ions; Optical fibers; Optical properties; Optical tomography; Sapphire; Spectroscopy; Transition metals; Yttrium aluminum garnet; Biomedical imaging; Broadband emission; Cellular resolution; Crystalline fiber lasers; Excited state absorption; Latest development; Near-infrared wavelength; Novel applications; Optical fiber communication[SDGs]SDG7review10.3788/gzxb20204911.11490102-s2.0-85097538329