New strategies to shorten the time response of thermo-optic switches in a glass chip

In recent years we have assisted to an increasing interest towards integrated optical circuits for light modulation or switching [1] . The range of applications is wide, spanning both adaptive circuits for classical/quantum information processing and lab on a chip optofluidic devices for imaging or sensing [2] . In the latter cases, the switching time is less stringent than in telecommunication, but still essential as it affects the final application. In addition, a fundamental requirement is the use of a substrate and of a fabrication technology compatible with microfluidic devices. In this regard, glass is an optimal choice for both optical and fluidic integrated elements, for its transparency, mechanical and chemical properties, and material compatibility. A valuable technique for the fabrication of both fluidic and integrated optics in glass is femtosecond laser micromachining (FLM) [3] , [4] . When a femtosecond laser is focused in a transparent substrate it induces a local modification. Depending on the irradiation parameters, different modifications as refractive index increase, material ablation, or increased etching selectivity can be obtained.