Femtosecond-Laser-Written Waveguide Lasers at ∼2 μm

In this work, we review our recent results on fabrication, optical characterization and continuous-wave and passively Q-switched 2μm laser operation of active waveguides (WGs) produced by femtosecond direct laser writing (fs-DLW) in thulium and holmium doped low-symmetry (monoclinic) crystals. Fs-DLW was performed by 120-fs / 1-kHz pulses at 795 nm [1]. Various depressed-index photonic micro-structures were fabricated, Fig. 1, such as buried channel WGs with circular and hexagonal (lattice-like) cladding, surface WGs with a half-ring cladding, and straight WGs and Y-branch splitters with a rectangular cross-section. The WG core size was in the range 40–100 μm, comprising both fundamental- and multi-mode WGs.