Scalable Nanophotonic Structures Inside Silica Glass Laser‐Machined by Intense Shaped Beams

Abstract

All‐dielectric nanophotonic devices are usually fabricated by engraving arrays of nanoholes at the surface of high‐index materials, to engineer dedicated optical functions. However, their direct 3D integration in the volume of a material is challenging, inaccessible to current planar nanolithography methods. Here is introduced an ultrafast laser‐machining method that opens the possibility to realize scalable arrays of hollow nanochannels directly inside the bulk of silica glass within a single‐step, maskless, and digital approach. Using a custom‐shaped micro‐Bessel beam and by tuning laser pulse durations from femtoseconds to picosecond to boost processing versatility, dense assemblies of nanochannels with adjustable lengths (up to 30 µm), and submicron lattice periodicity (down to 0.7 µm) are achieved. As a proof‐of‐principle demonstration, a gradient‐index metaphotonic structure is realized and its performance is experimentally characterized, demonstrating its relevancy for imprinting phase functions with magnitude up to in the short‐wave infrared spectral range. Results show that the unique flexibility and scalability provided by individual control of each channel opens a new realistic alternative approach for 3D fabrication of monolithic integrated nanophotonic devices inside a wide range of low‐index standard optical materials.