Planar ring resonator waveguides are fabricated in thin films of As2S3 chalcogenide glass, deposited on silica-on-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 photo-induced 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.

In this Letter, we study the characteristics of a selectively buried glass waveguide that is fabricated by the backside masking method. The results show that the surface region appears when the width of the backside mask is larger than 7 mm. Here, the glass substrate is 1.5 mm thick. It is also found that the buried depth evolution of the transition region remains almost unchanged and is independent of the width of the backside mask. The loss of the transition region is only 0.28 dB at the wavelength of 1.55 μm if the surface condition is good enough.