Self-similarity of optical rotation trajectories around the Poincare sphere with application to an ultra-narrow atomic bandpass filter

TL;DR

This paper explores the self-similarity of optical rotation trajectories on the Poincare sphere in magneto-optic effects, leading to the design of an ultra-narrow atomic bandpass filter with superior performance.

Contribution

It introduces a novel visualization method for magneto-optic effects and demonstrates an improved ultra-narrow optical filter using cascaded Faraday and Voigt cells.

Findings

Achieved a 0.56 GHz noise bandwidth in the optical filter.

Demonstrated a figure-of-merit of 1.22 GHz$^{-1}$, surpassing previous filters.

Provided physical insight into magneto-optic rotation via Poincare sphere trajectories.

Abstract

We present an investigation of magneto-optic rotation in both the Faraday and Voigt geometries. We show that more physical insight can be gained in a comparison of the Faraday and Voigt effects by visualising optical rotation trajectories on the Poincare sphere. This insight is applied to design and experimentally demonstrate an improved ultra-narrow optical bandpass filter based on combining optical rotation from two cascaded cells - one in the Faraday geometry and one in the Voigt geometry. Our optical filter has an equivalent noise bandwidth of 0.56 GHz, and a figure-of-merit value of 1.22(2) GHz$^{-1}$ which is higher than any previously demonstrated filter on the Rb D2 line.