Rare-earth-activated glass-ceramic waveguides

This work is focused on sol-gel-derived SiO2-HfO2 and SiO2-SnO2 glass-ceramic waveguides activated by Er3+ and Eu3+ ions. We demonstrate that with optimized fabrication protocols it is possible to succeed in preparation of low-loss GCs waveguides activated by rare-earth ions opening new potentialities for the development of smart and cheap integrated optical circuits. Concerning sol-gel-derived Er3+-activated HfO2-based glass-ceramics the research activity has evidenced that: i) silica-hafnia glass ceramics allow to achieve an attenuation coefficient as low as 0.3 dB/cm at 1542 nm; ii) HfO2 crystalline phase can efficiently enhance the spectroscopic properties of the embedded Er3+ ions; iii) Er3+ ions remain incorporated in tetragonal HfO2 nanocrystals with dimensions of about 3-5 nm depending on the HfO2 content. From a technological point of view patterning of photonic structures on the silica-hafnia film requires photolithography followed by CHF3 reactive ion etching. A more simple approach consists in the exploitation of photorefractive properties. The inclusion of rare-earth elements, by allowing to combine photorefractive and active properties, may provide an effective route to the simple fabrication of integrated optics amplifiers and lasers. In this context we present SiO2-SnO2 glass-ceramic waveguides doped with Eu3+ ions with SnO2 content as high as 25 mol %. Formation and growth of nanocrystals in the parent amorphous waveguides was induced by heat treatment. The formation of tetragonal rutile SnO2 crystals in the films was confirmed by Raman spectra. Photoluminescence measurements indicate that most part of Eu3+ ions are embedded in SnO2 nanocrystals. The excitation spectra clearly evidence the role of interband electronic transition of SnO2 nanocrystals on the luminescence of Eu3+ ions. An attenuation coefficient a low as 0.8 ± 0.2 dB/cm at 632.8 nm was measured in the 75SiO2-25SnO2 glass-ceramic waveguide. Preliminary measurements on the effect of exposure to the UV excimer laser irradiation have shown a modulation of the refractive index of the parent waveguide, suitable to realize optical Bragg gratings in these materials.