Slow-light Faraday effect: an atomic probe with gigahertz bandwidth

TL;DR

This paper demonstrates a broadband, high-transmission slow-light Faraday effect in atomic vapour, enabling fast, wide-range polarisation switching of nanosecond pulses for optical communication applications.

Contribution

It introduces a method to achieve broadband, high-transmission polarisation switching using the Faraday effect in Doppler-broadened media, extending the frequency range beyond narrowband resonant techniques.

Findings

Achieved large polarisation rotations up to 15 pi radians.

Demonstrated distortion-free broadband pulse switching.

Enabled nanosecond pulse manipulation with near-unity transmission.

Abstract

The ability to control the speed and polarisation of light pulses will allow for faster data flow in optical networks of the future. Optical delay and switching have been achieved using slow-light techniques in various media, including atomic vapour. Most of these vapour schemes utilise resonant narrowband techniques for optical switching, but suffer the drawback of having a limited frequency range or high loss. In contrast, the Faraday effect in a Doppler-broadened slow-light medium allows polarisation switching over tens of GHz with high transmission. This large frequency range opens up the possibility of switching telecommunication bandwidth pulses and probing of dynamics on a nanosecond timescale. Here we demonstrate the slow-light Faraday effect for light detuned far from resonance. We show that the polarisation dependent group index can split a linearly polarised nanosecond pulse into left and right circularly polarised components. The group index also enhances the spectral sensitivity of the polarisation rotation, and large rotations of up to 15 pi rad are observed for continuous-wave light. Finally, we demonstrate dynamic broadband pulse switching, by rotating a linearly polarised nanosecond pulse from vertical to horizontal with no distortion and transmission close to unity.