Since the first report of Davis in 1996, ultrafast laser inscription (ULI) has been widely used to fabricate buried optical devices such as active and passive waveguides inside dielectric materials. In this technique, ultra-short and ultra-intense laser pulses are tightly focused inside transparent materials leading to laser-induced nonlinear processes in the focal volume. The energy density deposited into the submicron focal volume can reach several of MJcm −3 and hence, may trigger dramatic

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... anges in a strongly localized region, whereas the surrounding bulk material remains unchanged. This technique can be used from void formation to weak refractive index modification, which is the key feature to create buried optical waveguides. In this chapter, firstly, we review the fundamentals of the ultrafast laser inscription technique to produce optical waveguides inside dielectric materials such as crystals and glasses. Next, as an example, we revise the application of this technique to create buried waveguides inside bioactive glasses and specifically, inside W-TCP eutectic glasses.