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Ultrafast lasers contribute essentially to the development of micro/nanotechnologies, being able to structure materials with utmost precision. Present advances in photonics include the development of optical devices based on laser-induced refractive index engineering. Ultrafast laser photoinscription can confine energy in micro-domains of arbitrary geometries, modifying the material refractive index and laying down the concept of 3D design for efficient optical functions. Here nanoscale precision can deliver high levels of performance. Therefore bypassing the diffraction limit is key for a new range of applications in optics requiring optical access at the nanoscale. We discuss the capability of Gauss and Bessel-Gauss pulses with engineered dispersion to localize light on subwavelength scales. We show how sculpting beams in space and time can bring advantages for controlling the interaction between light and matter and for achieving extreme confinement of energy. We discuss physical mechanisms of photoinscription by following the dynamics of excitation over the entire evolution cycle, serving as guidelines for control. We explore the influence of pulse temporal and spatial design in achieving index structures on 100 nm scales, either in direct focusing or in self-organization schemes in fused silica. Non-diffractive beam excitation takes advantage of this localization and achieve unprecedented high-aspect-ratio structuring. Subsequently we present photonic systems where hybrid micro/nanoscale features can develop advanced optical functionalities. We will show their capability to transport, manipulate and access electrical fields, either for Bragg sensing or for reconstruction spectral information. Finally we indicate a range of applications, from telecom to astrophotonics.
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