Ultrafast 2.1-μm Mode-Locked Tm:Ho:ZBLAN Fiber Laser

Ultrafast lasers at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2\mu \mathrm{m}$</tex> have attracted attention due to their potential applications in ultrabroadband mid-IR coherent light generation and soft x-ray high harmonic generation. From the above background, in recent years, the development of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2\mu \mathrm{m}$</tex> femtosecond oscillators using Ho-doped or Tm-Ho-doped silica fiber has been conducted. Although these silica-based active fibers have been widely studied, we focused on Tm-Ho-doped ZBLAN (Tm:Ho:ZBLAN) fiber as gain medium because <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.9\mu \mathrm{m}$</tex> mode-locked lasers using ZBLAN as a host material have demonstrated shorter pulse durations [1], [2]. However, mode-locked operation in 2 μmusing Tm:Ho:ZBLAN fiber had not been achieved. In this work, we demonstrated a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.1\mu \mathrm{m}$</tex> Tm:Ho:ZBLAN mode-locked laser.