Fabrication of a void array in dielectric materials by femtosecond laser micro-processing for compact photonic devices

We describe a systematic investigation on void structures fabricated by femtosecond laser irradiation inside dielectric materials for fabrication of a compact optical circuit. Void shapes fabricated in 5 different dielectric materials were compared and the physical constants determining the void shape were discussed. A long void array is obtainable in a material which has a low critical power for self-focusing. It was also indicated that the coefficient of thermal expansion is a dominant governing factor to fabricate a precise void which has a clear boundary. Furthermore, we propose and design a Mach-Zehnder interferometer in fused silica composed of optical waveguides and photonic crystals to verify practical application of a void array. Simulation results of the optical propagation in a Mach-Zehnder interferometer indicated that the photonic crystals using a void array have potential to fabricate compact optical circuits.