Sol-gel-derived photonic structures

The sol-gel technique is a very flexible, relatively simple, and low-cost method to fabricate many different innovative photonic structures characterized by specific functionalities. During synthesis, starting from the molecular level, compounds or composites with well controlled composition can be obtained as thin films, powders or monoliths. These materials can be used to prepare such structures as waveguides, photonic crystals, coatings, and bulk glasses including spheres, rings and other geometries exploited in optical resonators fabrication. The present lecture is focused on some recent results obtained in the sol-gel-derived photonic structures. To emphasise the scientific and technological interest in this kind of systems and the versatility of the sol-gel route, the glass-based nano and micrometer scale range systems, such as planar waveguides and photonic crystals, as well as nanocrystalline particles and glass-ceramic layers are discussed. Particularly, the syntheses, structures, and luminescent properties of the following systems are described: silica-hafnia glass and glass- ceramic waveguides, nanosized tetraphosphates, and inverse silica opals. The attention is focused on the spectroscopic properties of rare earth activated materials that due to the light emission can be used in the integrated optics area covering application in sensing, biomedical diagnostic, telecommunication, lighting, and photon management