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

Silicon waveguides are now widely used to guide radiation in the near-infrared, mainly in the wavelength range of 1.1 - 2.2 microm. 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 microm, 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.