Analysis of laser-inscription of waveguides in bulk silicon via ultrashort pulses

Due to their large intensities, ultrashort pulses are capable of inducing permanent modifications well inside transparent materials when tightly focused. One of the main applications of this technique is the realization of 3D waveguides, fabricated by locally controlling the refractive index of the modified material. Whereas such a technique has been largely employed in glasses, waveguide inscription in narrow bandgap semiconductors is much more complicated to accomplish [1] . In this context a great deal of attention has been reserved to Silicon, due to the potential impact of having 3D photonic devices manufactured on electronic and photonic chips. Optical waveguides in bulk Silicon have been now realized, using both longitudinal and transversal writing [2] - [4] . Here, we first discuss the role played by nonlinear optics in the writing process; we then characterize the properties of the waveguides by using a novel technique based upon the transversal shift of the probe beam.