2.1 μm waveguide laser fabricated by femtosecond laser direct-writing in Ho³⁺, Tm³⁺: ZBLAN glass

We report the first Ho³⁺ doped waveguide laser, which was realized by femtosecond direct-writing of a depressed cladding structure into ZBLAN glass. Tm³⁺ sensitizing allows the 9 mm long Ho³⁺ gain medium to be conveniently pumped at 790 nm, achieving an optical-to-optical slope efficiency of 20% and a threshold of 20 mW. The potentially widely tunable laser produces up to 76mWat 2052 nm and also operates at shorter wavelengths near 1880 nm and 1978 nm for certain cavity configurations.