Fabrication of Quantum Photonic Integrated Circuits by Means of Femtosecond Laser Pulses

Femtosecond laser microfabrication has emerged in the last decade as a powerful technique for direct inscription of low loss optical waveguides in practically any transparent dielectric substrate, showing outstanding versatility. Prototyping of new devices is made rapid, cheap and easy: optical circuits are written directly buried in the substrate, using the laser beam as an optical pen, without any need of costly masks as required by conventional photolithography. Many proof-of-principle demonstrations of integrated optics can be obtained, including splitters, directional couplers, and Mach-Zehnder interferometers. Actually, the road towards applications has just been opened, and the unique capabilities of femtosecond laser micromachining will enable achievements inconceivable with other technologies. In this work, the femtosecond laser fabrication technique is discussed, together with its application to the realization of integrated photonic quantum circuits.