Direct laser writing in glasses using femtosecond lasers has been widely used and extensively studied during the last two decades. This technique provides a robust and efficient way to directly inscribe 3D photonic devices in the volume of bulk glasses. Following direct laser writing, a local refractive index change is induced, that is generally classified under three different types (Type I, II and III). Each type allows the fabrication of its own variety of embedded 3D photonic components. More specifically, type I refractive index change is usually preferred for the formation of photo-inscribed waveguides .
However, in silver containing glasses, direct laser writing induces a novel type of refractive index change, called type A . It is based on the creation of fluorescent silver clusters distributed on the vicinity of the laser-glass interaction voxel  allowing for the inscription of a novel type of waveguides  exhibiting numerous interesting properties. In this paper, a comparative study between Type A and Type I waveguides in silver containing zinc phosphate glasses is presented. The morphology of waveguides, guided mode profile, refractive index profile and propagation losses as well as a thermal stability study are presented. Finally, this study shows the similar functionality of Type A waveguides compared to type I, thus exhibiting some significant advantages leading the way for promising applications based on type A waveguides’.
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