CO 2 laser annealing on erbium-activated glass–ceramic waveguides for photonics

Abstract

Silica-based sol–gel waveguides activated by Er 3+ 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 CO 2 laser annealing for planar optical waveguides processing. The effects of pulsed and continuous CO 2 laser irradiation on the optical and spectroscopic properties of SiO 2–ZrO 2 and SiO 2–HfO 2 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% Er 3+, were prepared by sol–gel route using dip-coating deposition on v-SiO 2 substrates. An increase of the refractive index of approximately 0.04 at 1.5 μm has been observed on 70SiO 2–30HfO 2 planar waveguide after continuous CO 2 laser annealing. A similar refractive-index variation was detected in all SiO 2–ZrO 2 planar waveguides after CO 2 laser irradiation. We have observed, moreover, that continuous CO 2 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 4 I 13 / 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 CO 2 laser annealing, the resulting materials showed a crystalline environment.