Silicon-on-sapphire integrated waveguides for the mid-infrared

Abstract
Silicon waveguides are now widely used to guide radiation in the near-infrared, mainly in the wavelength range of 1.1 – 2.2 µm. While low-loss waveguides at longer wavelengths in silicon have been proposed, experimental realization has been elusive. Here we show that single-mode integrated silicon-on-sapphire waveguides can be used at mid-infrared wavelengths. We demonstrate waveguiding at 4.5 µm, or 2222.2 cm−1, with losses of 4.3 ± 0.6 dB/cm. This result represents the first practical integrated waveguide system for the mid-infrared in silicon, and enables a range of new applications.
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