Optical push broom effect by a moving refractive index front in a silicon Bragg waveguide

Area of Science:

• Photonics
• Optoelectronics
• Materials Science

Background:

• Optical signal manipulation is crucial for advanced communication and computing.
• Controlling light propagation in waveguides using dynamic refractive index changes is an active research area.
• Bragg gratings offer wavelength-selective light confinement, but dynamic control remains challenging.

Purpose of the Study:

• To experimentally demonstrate signal trapping via a refractive index front in a silicon waveguide.
• To investigate the 'optical push broom' effect for capturing and compressing continuous-wave (CW) signals.
• To explore the potential applications of this phenomenon in optical signal processing.

Main Methods:

• Generating a 2 picosecond (ps) free carrier refractive index front using two-photon absorption of a pump pulse in a silicon waveguide.
• Introducing a periodic perturbation (Bragg grating) to control the group velocity of a CW signal.
• Propagating a CW signal near the Bragg grating band gap to enable interaction with the refractive index front.

Main Results:

• Successful experimental demonstration of the optical push broom effect, trapping a CW signal within the refractive index front.
• Observed frequency shifting and acceleration of the trapped CW signal to match the front's velocity.
• Accumulation of a approximately 30 ps long CW signal packet within the 2 ps pump-induced front.

Conclusions:

• The refractive index front effectively captures and confines CW optical signals in a silicon waveguide.
• The demonstrated optical push broom effect enables simultaneous temporal and spatial compression of optical signals.
• This technique holds promise for developing novel optical signal processing and data storage devices.