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Resumen:
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Photonics was born with the advent of lasers. Lasers provided the kind of light required for the development of active and passive photonics devices. Ultrafast pulsed lasers provided, in addition, enough optical power to study the interaction of light with matter beyond the linear regime. Non-linear optical phenomena are the base for the development of non-linear laser processing of transparent materials (dielectrics), a laser processing approach that has unique characteristics in terms of resolution, versatility and 3D-processing capabilities for the production of photonic devices. Fs-laser writing has been indeed successfully applied to the production of a large variety of high performance passive and active devices in 2D and 3D configuration. In spite of this success, sub-surface fs-laser writing has several limitations that hamper its widespread application for the production of photonics devices. The first one is the limited refractive index contrast (?n) that can be achieved using conventional modification mechanisms (i.e. local glass matrix densification, or polarizability changes, generation of point defects or changes in the glass network configuration). With a few exceptions, the maximum index contrast achievable is normally below 10-2, which limits the performance of the produced devices. Also, the presence of optical nonlinearities is inherent to the propagation of fs-laser pulses inside dielectrics. When the material shows a high non-linear refractive index, as it happens in crystalline materials or glasses with a high linear refractive index, the distortion of the desired energy deposition profile severely affects the control over the morphology of the structure. Finally, fs-laser processing can be similarly used for micro-structuring applications at the surface of dielectrics in order to produce active and passive surface waveguides. However, scattering losses at the channel walls produced by fs-laser ablation usually lead to high losses that strongly limit the performance of fs-laser structured surface waveguide-based devices...
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