The impact of thermal- and photo-annealing of chalcogenide films for optical waveguides

We applied thermal- and band-edge light annealing on an as-deposited As₂S₃ film to mitigate its phase separation and, thus to improve the propagation losses of fabricated optical waveguides. Studies of the film micro structure revealed a difference between atomic bonds and linked phases among the as-deposited, thermally-annealed, and optically-annealed films. We fabricated rib-type waveguides with 4 micron width from 0.85 μm thick films, and measured the insertion losses. Around 0.4 and 0.2 dB/cm propagation losses were obtained in the waveguides produced from as-deposited and annealed films, respectively. The waveguides produced from photo-annealed film showed almost the same propagation losses to those from thermally-annealed material. Our results, however, indicate optical-annealing provides some advantages over thermal annealing for waveguide fabrication, such as the absence of film cracking which observed at high temperature processing.