Control of refractive index change using plasma channeling induced by femtosecond laser

To fabricate 3-dimensional photonic device inside transparent materials by fs laser, we have developed a novel method for accurate control of the refractive index change region inside the transparent material by femtosecond laser induced plasma channeling. We use an automatic pulsewidth variable chirped pulse amplification (CPA) fs laser system, which we have developed. We have fabricated single-mode optical waveguides inside fused silica with a 20 μJ incident energy and 0.01 effective numerical aperture (NA) with nonscanning process by focusing the laser beam through plano-convex lens. The measured refractive index change of the fabricated waveguide is on the order of 10^-3. We believe that this technique would be a clever method for 3-dimensional photonic device fabrication.