  It has recently been shown that silicon nanophotonic waveguides can be used
to construct all of the components of a photonic data transmission system on a
single chip. These components can be integrated together with CMOS electronics
to create complex electronic-photonic integrated circuits. It has also emerged
that the high field confinement of silicon nanoscale guides enables exciting
new applications, from chipscale nonlinear optics to biosensors and light-force
activated devices. To date, most of the experiments in silicon waveguides have
been at wavelengths in the near-infrared, ranging from 1.1-2 microns. Here we
show that single-mode silicon nano-waveguides can be used at mid-infrared
wavelengths, in particular at 4.5 microns, or 2222.2 1/cm. This idea has
appeared in theoretical literature, but experimental realization has been
elusive. This result represents the first practical integrated waveguide system
for the mid-infrared in silicon, and enables a range of new applications.
