Directly written waveguides in chalcogenides
The seminar summarizes the work of our group in photonic devices involving chalcogenide glasses. Photo-induced index and structural changes in these glasses are used in the direct writing of waveguide cores, and in the post-fabrication tuning of silicon-on-insulator devices.
In the first part, I will discuss As2S3 waveguides that are directly written by femto-second laser illumination. Based on a two-photon-induced photo-darkening process, centimeter-length waveguides with a cross-section 2 μm x 1 μm are written in the chalcogenide layer on top of silica-on-silicon substrates. Using this method, we fabricated ring resonators with an unloaded Q value of 180,000 and with an estimated index contrast of 0.05 RIU. Stimulated Brillouin Scattering (SBS) amplification was also observed in these waveguides. The observed Brillouin gain curve was three times wider than expected. Possible explanations will be discussed.
In the second part, I will describe the use of chalcogenide glasses as upper cladding layers in a hybrid chalcogenide-on-SOI platform. The effect of photo-induced mass transfer is employed in the selective photo-removal of As10Se90 upper cladding. Absorption raises the local temperature of illuminated regions above the glass transition value. The temperature gradient initiates a fast lateral flow of the liquid layer, from hot to cold regions. The process is used in the post-fabrication tuning of phase delays and group delays of individual waveguides, and of coupling ratios of directional couplers. Transfer functions of tuned devices remain stable after months.
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