CO2 laser annealing on erbium-activated glass-ceramic waveguides for photonics

Silica-based sol-gel waveguides activated by Er3+ ions are one of the most important materials for integrated optics devices. In this paper, we present an alternative method combining sol-gel route and CO2 laser annealing for planar optical waveguides processing. The effects of pulsed and continuous CO2 laser irradiation on the optical and spectroscopic properties of SiO2-ZrO2 and SiO2-HfO2 planar waveguides are evaluated and the thermal conventional annealing effects for these systems are reported for comparison. All the planar waveguides, doped with 0.5 and 5 mol% Er3+, were prepared by sol-gel route using dip-coating deposition on v-SiO2 substrates. An increase of the refractive index of approximately 0.04 at 1.5 μm has been observed on 70SiO2-30HfO2 planar waveguide after continuous CO2 laser annealing. A similar refractive-index variation was detected in all SiO2-ZrO2 planar waveguides after CO2 laser irradiation. We have observed, moreover, that continuous CO2 laser annealing can lead to waveguides with a lower attenuation coefficient with respect to the attenuation coefficient measured for thermal annealed waveguides. Upon excitation at 514.5 nm continuous-wave laser light, on the irradiated sample, the shape is found to be almost independent on the time and irradiation power with CW laser annealing but a decrease of the FWHM of approximately 46-12 nm has been observed on planar waveguides after pulsed laser annealing. Before and after conventional thermal annealing, the 4I13/2 level decay curves present a single-exponential profile with a lifetime of 4.0 and 5.7 ms, respectively, but the lifetime increases up to 7.0 ms, after pulsed laser annealing treatment. X-ray diffraction and optical spectroscopy showed that after an adapted pulsed CO2 laser annealing, the resulting materials showed a crystalline environment.