Highly Tm ³⁺ doped germanate glass and its single mode fiber for 2.0 μm laser

Abstract

Highly Tm ³⁺ doped optical fibers are urgently desirable for 2.0 μm compact single-frequency fiber laser and high-repetition-rate mode-locked fiber laser. Here, we systematically investigated the optical parameters, energy transfer processes and thermal properties of Tm ³⁺ doped barium gallo-germanate (BGG) glasses. Highly Tm ³⁺ doped BGG glass single mode (SM) fibers were fabricated by the rod-in-tube technique. The Tm ³⁺ doping concentration reaches 7.6 × 10 ²⁰ ions/cm ³, being the reported highest level in Tm ³⁺ doped BGG SM fibers. Using ultra short (1.6 cm) as-drawn highly Tm ³⁺ doped BGG SM fiber, a single-frequency fiber laser at 1.95 μm has been demonstrated with a maximum output power of 35 mW when in-band pumped by a home-made 1568 nm fiber laser. Additionally, a multilongitudinal-mode fiber laser at 1.95 μm has also been achieved in a 10 cm long as-drawn active fiber, yielding a maximum laser output power of 165 mW and a slope efficiency of 17%. The results confirm that the as-drawn highly Tm ³⁺ doped BGG SM fibers are promising in applications that require high gain and high power from a short piece of active optical fiber.