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 ¼m 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.