The index of refraction of waveguide structures can be varied by altering carrier
concentration. The waveguides preferably comprise semiconductors like silicon that
are substantially optically transmissive at certain wavelengths. Variation of the
carrier density in these semiconductors may be effectuated by inducing an electric
field within the semiconductor for example by apply a voltage to electrodes associated
with the semiconductor. Variable control of the index of refraction may be used
to implement a variety of functionalites including, but not limited to, tunable
waveguide gratings and resonant cavities, switchable couplers, modulators, and
optical switches.
