Chalcogenide glasses (ChGs) exhibit high refractive indices, broad transparency windows, pronounced nonlinearities, and photo-sensitivity effects. Waveguides are fabricated in ChGs layers using dry etching, nano-imprint lithography, or direct laser-beam writing. Ultra-high stimulated Brillouin scattering amplification was demonstrated in ChG waveguides. Efficient Brillouin scattering requires tight confinement of guided optical and acoustic modes with large overlap.
Here we present waveguides consisted of a ChG core and silica cladding. Devices are fabricated in silica-on-silicon wafers. The silica layer is dry-etched through a Cr hard mask. Etching defines either isolated trenches or isolated pedestals in the silica layer, with widths of 1-3 µm and heights between 0.5-2 µm. A 300 nm-thick layer of As2S3 glass is deposited onto the sample by thermal evaporation. Deposition partially fills the etched silica trenches with a ChG core region, or alternatively forms a core region on top of silica pedestals with air on three sides. A thin upper layer of resist is applied for protection. The waveguide structure provides two potential advantages: tight confinement of both guided optical and acoustic modes in small-area ChG cores, and no processing of the ChG layer following deposition.
The end-to-end losses of a 4 mm-long device with a 600 nm-wide core were 20 dB. Losses are primarily due to coupling to/from fibers at the facets. Four-wave mixing between two continuous-wave pumps of 10 mW power was demonstrated, with efficiency on the order of -60 dB. The linear and nonlinear characterization of longer devices is ongoing.
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