Femtosecond laser irradiation applied to Fused Silica (the amorphous form of SiO2) defines a novel technology platform for highly integrated all-optical microsystems and beyond. In contrast with common approaches that rely on combining materials to achieve particular functions, femtosecond-laser fabricated microsystems rely on single material monolith, whose properties are locally and in the three-dimension functionalized by selective exposure. The combination of laser-functionalized zones with different physical properties allows us to direct-write integrated systems without the need for further assembly of packaging steps or without the need for multiple processing steps, like for instance sequences of layers deposition, exposure and etching steps.