High-Q ring resonators directly written in As₂S₃ chalcogenide glass films

Planar ring resonator waveguides are fabricated in thin films of As₂S₃ chalcogenide glass, deposited on silicaon-silicon substrates. Waveguide cores are directly written by scanning the focused illumination of a femtosecond Ti:sapphire laser at a central wavelength of 810 nm, through a two-photon photo-darkening process. A large photoinduced index change of 0.3–0.4 refractive index units is obtained. The radius of the ring resonator is 1.9 mm, corresponding to a transmission free spectral range of 9.1 GHz. A high loaded (intrinsic) Q value of 110,000 (180,000) is achieved. The thermal dependence of the resonator transfer function is characterized. The results provide the first report, to the best of our knowledge, of directly written high-Q ring resonators in chalcogenide glass films, and demonstrate the potential of this simple technique towards the fabrication of planar lightguide circuits in these materials.