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State 1 Dark blue bar is a silicon photonic wire waveguide. A packet of light pulses, shown as a train of white balls, is propagating along the silicon waveguide with a speed not much different from a speed of light in vacuum.
State 2 Photonic wire waveguide is butt-coupled to the silicon photonic crystal waveguide defined by a periodic array of holes etched in a silicon membrane.
When the train of light pulses is entering into photonic crystal waveguide the light speed is significantly reduced due to diffraction in a periodic photonic lattice.
In the paper the speed as low as 1/300 of the speed of light in vacuum is measured.
State 3 To control the speed of light electrically two lateral electrical contacts are deposited on top of a silicon membrane. This forms an integrated microheater. The trick is to position the contacts as close as possible to the waveguide core and, at the same time, to avoid excessive parasitic losses due to absorption in metal.
State 4 When the voltage is applied to the contacts the current is passing across the photonic crystal waveguide. This current heats the silicon membrane that in turn results in slight changes in the refractive index of silicon due to thermo-optic effect. Small changes in the material refractive index results in very large changes of the speed of light. Thus light pulses can be accelerated or decelerated on-demand.
