Carbon ion microbeam fabrication of channel waveguide in tellurite glass (Conference Presentation)

Abstract

Some materials present difficulties for the fabrication of channel waveguides with standard technologies. They may suffer incompatibilities with the physical or chemical processes required in one or more steps involved in the fabrication technology itself or in the standard patterning techniques. An experimental Er3+ doped tungsten-tellurite glass, which gets damaged by standard lithographic techniques is one of such cases. However, this glass is of great interest thanks to its excellent optical and spectroscopic properties, high refractive index (nbulk < 2.0 at 635 nm), low cut-off phonon energy and broad emission bandwidth for the erbium (< 60 nm) within the C band of optical telecommunications. We have therefore successfully demonstrated a novel method of fabrication, namely by focussed C4+ ion beam implantation (FIB). Relatively heavy and swift ions like the ones used in this experiment allow to change the material properties with fluencies even 10 times lower than those required when using light ions. The use of a focussed beam has also allowed us to directly write the channel waveguides on the sample, without the use of any lithographic procedure, which renders the whole process flexible and simpler. The Er3+ doped tellurite glass with 60TeO2–25WO3–15Na2O-0.5Er2O3 (mol. %) composition was prepared by melt-quenching technique. The FIB irradiations were carried out at the 3 MV Tandetron 4130 MC (High Voltage Engineering Europa B.V.) of the Nuclear Physics Institute AV CR, Řež, with 4–6 nA beam current, 1·1014-5·1016 ions/cm2 fluence and the size of the scanning beam was 8 μm × 12 μm. The as-implanted waveguides showed very high propagation losses, about 14-20 dB/cm at 1400 nm, outside the absorption band of Er3+. A stepwise (each step 30 minutes long) thermal annealing allowed to reduce losses. At 150 °C, propagation losses decreased to 1.5 dB/cm. At higher temperatures propagation losses rose again, but at 200 °C coupling losses decreased, so that the best insertion loss, about 5 dB, was measured at this stage. The near-field images showed that the waveguide was monomode up to 1540 nm and that the mode width does not vary significantly with increasing temperature, whereas the estimated depth of the waveguides shows a slight increase. In order to obtain more information about the structural changes caused by the ion beam irradiation, profilometry and Raman characterisation has been carried out on the channel waveguides and also these results will be presented at the conference.