A semiconductor waveguide includes a section containing free charge,
either electrons or holes, which can be steered into or removed from the
path of the beam under the control of electrical signals. The mobile
charges come from a potential well which may be either filled or depleted
under electrical control. When the well is filled, the charges speed the
beam propagation, introducing a phase change. When the well is emptied
the beam propagates with extra delay. The phase shifter allows very high
speed modulation of the beam using low voltage and low power electronics.
The device can be created using standard silicon processing techniques,
and integrated with other optical components such as splitters and
combiners to create amplitude modulators, attenuators and other optical
devices.