Light stopping by reflection from a pump pulse
Light stopping by reflection from a pump pulse lead image
Light stopping is an intricate phenomenon that involves converting a propagating pulse into a standing wave. One way to achieve this is to flatten the dispersion of a medium during light propagation to change the frequency and temporal distribution of light while keeping the wavelength and spatial distribution the same, but the requirement of changing the refractive index locally and in many locations has made this challenging to realize experimentally.
Gaafar et al. proposed an alternative method of light stopping that utilizes a refractive index perturbation moving along a waveguide, leading to a so-called indirect optical transition. In this case, like in a mechanical collision, the light pulse hits a co-propagating mirror and stops.
The mirror is created by propagating a nonlinear pump pulse along the same waveguide, producing a moving refractive index perturbation. Light reflects only from the trailing or leading edges of this perturbation, which are represented as refractive index fronts. An indirect transition is adjusted to stop light without changing the shape of the dispersion relation. The light energy is instead transferred to the zero group velocity mode and later released by a second pump pulse. The authors also showed that indirect transitions close to the band edge can be used to realize a time reversal of optical signals, which sends information back.
The researchers plan to test these effects in nonlinear waveguides with Bragg gratings for optical signal storage applications. The stopped light experiences the same scattering loss per unit time as propagating light. Thus, storage times on the order of several nanoseconds are expected, paving the way for optical signal storage in integrated waveguides and high bit-rate optical telecommunication.
Source: “Pulse time reversal and stopping by a refractive index front,” by Mahmoud A. Gaafar, Jannik Holtorf, Manfred Eich, and Alexander Yu. Petrov, APL Photonics (2020). The article can be accessed at http://doi.org/10.1063/5.0007986 .
