| Abstract: | It is well known that thermally evaporated a-As₂S₃ thin films are prone to oxidation when exposed to an ambient environment. These As₂O₃ crystals are a major source of scattering loss in sub-micron optical integrated circuits. Magnetron sputtering a-As₂S₃ not only produces films that have optical properties closer to their equilibrium state, the as-deposited films also show no signs of photo-decomposed As₂O₃. The TM propagation loss of the as-deposited As₂S₃-on-Ti:LiNbO₃ waveguide is 0.20 ± 0.05 dB/cm, and it is the first low loss hybrid waveguide demonstration. Using the recipe developed for sputtering As₂2S₃, a hybrid Mach-Zehnder interferometer has been fabricated. This allows us to measure the group index of the integrated As₂S₃ waveguide and use it in the study of the group velocity dispersion in the sputtered film, as both material dispersion and waveguide dispersion may be present in the system. The average group index of the integrated As₂S₃ waveguide is 2.36 ± 0.01. On-chip optical amplification was achieved through thermal diffusion of erbium into X-cut LiNbO₃. The net gain measured for a transverse magnetic propagation mode in an 11 [mu]m wide Er:Ti:LiNbO₃ waveguide amplifier is 2.3 dB ± 0.1 dB, and its on-chip gain is 1.2 ± plus/minus 0.1 dB/cm. The internal gain measured for a transverse electric propagation in an 7 [mu]m wide Er:Ti:LiNbO₃ waveguide amplifier is 1.8 dB ± 0.1 dB and is among the highest reported in the literature. These gains were obtained with two 1488 nm lasers at a combined pump power of 182mW. In order to increase further the on-chip gain, we have to improve the mode overlap between the pump and the signal. This can be done by doping erbium into As₂S₃ film using multi-layer magnetron sputtering. The Rutherford backscattering spectroscopy shows that the doping of Er:As₂S₃ film with 16 layers of erbium is homogeneous, and Raman spectroscopy confirms no significant amount of Er-S clusters in the sputtered film. The deposition method was used to fabricate an Er:As₂S₃ waveguide, and the presence of active erbium ions in the waveguide is evident from the green luminescence it emitted when it was pumped by 1488 nm diode laser. |
|---|