  Here we report the first experimental demonstration of light trapping by a
refractive index front in a silicon waveguide, the optical push broom effect.
The front generated by a fast pump pulse collects and traps the energy of a CW
signal with smaller group velocity and tuned near to the band gap of the Bragg
grating introduced in the waveguide. This situation represents an optical
analogue of light trapping in a tapered plasmonic waveguide where light is
stopped without reflection. The energy of the CW signal is accumulated inside
the front and distributed in frequency. In this experiment a 2 ps free carrier
front was generated via two photon absorption of the pump in silicon waveguide.
It collects approximately a 30 ps long packet of the CW signal. The presented
effect can be utilized to compress signals in time and space.
