Control of beam propagation in optically written waveguides beyond the paraxial approximation

TL;DR

This paper investigates beam propagation beyond the paraxial approximation in optically written waveguides, demonstrating diffractionless propagation and beam steering using complex atomic vapor structures and coherent control fields.

Contribution

It introduces a method to control and steer light in waveguides beyond the paraxial approximation using atomic vapor and tailored control fields, including branched waveguide structures.

Findings

Paraxial approximation is insufficient for accurate beam propagation description.

Tilted Gaussian beams enable selective steering of probe light.

Adjusting control beam width and pump intensity improves transmission.

Abstract

Beam propagation beyond the paraxial approximation is studied in an optically written waveguide structure. The waveguide structure that leads to diffractionless light propagation, is imprinted on a medium consisting of a five-level atomic vapor driven by an incoherent pump and two coherent spatially dependent control and plane-wave fields. We first study propagation in a single optically written waveguide, and find that the paraxial approximation does not provide an accurate description of the probe propagation. We then employ coherent control fields such that two parallel and one tilted Gaussian beams produce a branched waveguide structure. The tilted beam allows selective steering of the probe beam into different branches of the waveguide structure. The transmission of the probe beam for a particular branch can be improved by changing the width of the titled Gaussian control beam as well as the intensity of the spatially dependent incoherent pump field.