Abstract

Photonic saturable absorbers (PSAs) based on arrays of coupled, nonlinear waveguides [1,2] are robust components for integration in mode-locked fiber lasers and do not suffer from photobleaching like conventional dye molecules. PSAs exploit the formation of a discrete spatial soliton [3] in the waveguide array to modulate the throughput of the device with the input pulse power. Challenges of the photonic approach to saturable absorption are i) ensuring low insertion losses of the device, and ii) low peak power saturation threshold (kW or below). The last point is facilitated by embedding the array in a highly nonlinear medium. In this respect, chalcogenide materials are promising materials for the realization of PSA, building up on three specific advantages; mid-infrared transparency; strong nonlinearities; and the possibility of writing 3D photonic structures via direct laser writing. Here we demonstrate the function of a laser-fabricated, kW-range saturable absorber with large modulation depth in Gallium Lanthanum Sulfide (GLS) chalcogenide glass [4] and model its nonlinear behavior by means of a discrete-continuous spatiotemporal Unidirectional Maxwell Equations solver.

© 2015 IEEE