Effect of CO 2 laser irradiation on the performances of sol-gel-derived Er3+-activated SiO 2 - ZrO 2 and SiO 2 - HfO 2 planar waveguides

Abstract

Erbium activated SiO₂-ZrO₂ and SiO₂-HfO₂ planar waveguides doped with Er³⁺ ranging from 0.5 to 5 mol% were prepared by sol-gel route using dip-coating deposition on silica glass substrates. All the planar waveguides were optimized in order to confine one propagating mode at 1550 nm. The aim of this work is to present an alternative method for planar optical waveguides processing based on CO₂ laser irradiation (wavelength, &lgr;=10.6μm). The effects of pulsed and continuous CO₂ laser irradiation on the optical and spectroscopic properties of the waveguides are evaluated and the thermal conventional annealing effect for this system is reported for comparison. X ray diffraction and optical spectroscopy showed that after an adapted pulsed CO₂ laser annealing, the resulting materials showed a crystalline environment. 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: an attenuation coefficient of 0.8 and 1.2 dB/cm @ 632 nm was measured for silica-hafnia and silica-zirconia waveguides respectively, in respect to the attenuation coefficient higher that 2 dB/cm, measured for thermal annealed waveguides. Upon excitation at 514.5 nm continuous-wave laser light, pulsed CO₂ irradiated silica-zirconia waveguides show the ⁴I_13/2 -> ⁴I_15/2 emission band with a bandwidth of 12 nm. Before and after conventional thermal annealing, the ⁴I_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.