Femtosecond laser waveguide inscription in linear and nonlinear mid-infrared transparent glasses

In this paper, we report on the fabrication of integrated photonic devices for the mid-infrared spectral range via the femtosecond laser direct-write technique. Utilising this method, the inscription of wavelength-selective fibre-pigtailed directional couplers in synthetic silica glass with ultra-low hydroxide (OH) content is demonstrated. Further, we show that a tailored compositional redesign of zirconium fluoride (ZBLAN) glass enables the fabrication of optical waveguides with record-high numerical aperture and ultra-low propagation losses. Finally, the design and fabrication of nonlinearly coupled waveguide arrays in Gallium Lanthanum Sulphide (GLS) chalcogenide glass is presented and their application as artificial saturable absorbers for mode-locked mid-infrared fibre laser systems is discussed.