GeO2 glass ceramic planar waveguides fabricated by RF-sputtering

GeO2 transparent glass ceramic planar waveguides were fabricated by a RF-sputtering technique and then irradiated by a pulsed CO2 laser [1]. Different techniques like m-line, micro-Raman spectroscopy, atomic force microscopy, and positron annihilation spectroscopy were employed to evaluate the effects of CO2 laser processing on the optical and structural properties of the waveguides. The GeO2 planar waveguide after 2h of CO2 laser irradiation exhibits an increase of 0.04 in the refractive index, measured at 1542 nm. Upon irradiation of the surface the roughness decreases from 1.1 to 0.7 nm, as measured by AFM. Besides, structures at nanometric scale on the surface of the samples with dimension from 10 to 50 nm attributed to the presence of GeO2 nanocrystals were evidenced. Attenuation coefficients of 0.7 and 0.5 dB/cm at 1319 and 1542 nm, respectively, were measured after irradiation. Micro-Raman measurements evidence that the system embeds GeO2 nanocrystals and their phase varies with the irradiation time. Moreover, positron annihilation spectroscopy was used to study the depth profiling of the as prepared and laser annealed samples. The obtained results yielded information on the structural changes produced after the irradiation process inside the waveguiding films of approximately 1 µm thickness[1]. As show in figure 1, it could be inferred that the structural changes inside the Germania waveguides films initiate in the film-substrate interface in the direction to the surface. This behaviour was interpreted in terms of the role of the laser heat treatment of the substrate inducing a progressive modification of the films. Additionally, a value for the density of the germania films of 3.15 ± 0.02 g/cm3 was obtained from positron spectroscopy. This research was performed in the framework of the India-Trento Program for Advanced Research ITPAR Phase III research Project and MAE Significant Bilateral Project between Italy and Egypt "Smart optical nanostructures for green photonics" (2013-2015). [1]A. Chiasera, C. Macchi, S. Mariazzi, S. Valligatla, L. Lunelli, C. Pederzolli, D.N. Rao, A. Somoza, R.S. Brusa, M. Ferrari, "CO2 laser irradiation of GeO2 planar waveguide fabricated by rf-sputtering" Optical Materials Express, vol. 3, pp. 1561-1570, 2013.