Fourier optics and light stopping with nonlinear fronts
In this proposal we draft the route towards experimental realisation of different index front-induced optical transitions close to the band edge of a periodical waveguides. Namely, light stopping, time lens, and ultrafast arbitrary waveform generation are considered. For that we propose to utilise silicon waveguides with Bragg gratings and operate them close to the band edge. The moving refractive index front will be generated in the same waveguide via instantaneous Kerr effect from the copropagating switching/pump pulse. To avoid the losses via free carrier generation we plan to use mid-infrared (MIR) radiation for the pump pulse.The proposed effects are utilising the theoretical concepts developed by our group in recent year which we now plan to demonstrate experimentally. In case of light stopping, like in a mechanical collision, the light pulse hits a propagating front and stops. Here, the light energy can be transferred to the zero group velocity mode and later released by a second front with an opposite slope. In case of a so-called optical push broom, the signal pulse is trapped by the index front with a simultaneous frequency change and compression. As we have recently shown theoretically the trapping in the front is equivalent to Fourier optics observed at the focal plane of conventional lenses. This effect allows not only pulse compression but also the transfer of information from real to reciprocal space and vice versa. Thus, a defined spectral composition of the signal can be converted in a designed short temporal pulse, allowing for customizable wave form generation.The proposed system will provide signal temporal compression, light stopping, and pulse structuring in integrated optics technology. The extension to the MIR pump pulse allows utilisation of established silicon waveguide technology with large nonlinearity and strong field confinement.