Pure circularly polarized light emission from waveguide microring resonators

TL;DR

This paper demonstrates a passive integrated waveguide microring resonator that emits highly pure circularly polarized light with impurity levels below 10^-4, advancing integrated photonics for atomic quantum control.

Contribution

It introduces a novel design of perturbed waveguide microring resonators that achieve near-perfect circular polarization purity, surpassing previous integrated device capabilities.

Findings

Achieved polarization impurity below 10^-4 at emission axis.

Utilized symmetries and mode components to enhance polarization purity.

Demonstrated significant improvement over prior integrated polarization devices.

Abstract

Circularly polarized light plays a key role in many applications including spectroscopy, microscopy, and control of atomic systems. Particularly in the latter, high polarization purity is often required. Integrated technologies for atomic control are progressing rapidly, but while integrated photonics can generate fields with pure linear polarization, integrated generation of highly pure circular polarization states has not been addressed. Here, we show that waveguide microring resonators, perturbed with azimuthal gratings and thereby emitting beams carrying optical orbital angular momentum, can generate radiated fields of high circular polarization purity. We achieve this in a passive device by taking advantage of symmetries of the structure and radiated modes, and directly utilizing both transverse and longitudinal field components of the guided modes. On the axis of emission and at maximum intensity, we measure an average polarization impurity of $1.0 \times 10^{-3}$ in relative intensity across the resonance FWHM, and observe impurities below $10^{-4}$ in this range. This constitutes a significant improvement over the ${\sim}10^{-2}$ impurity demonstrated in previous work on integrated devices. Photonic structures allowing high circular polarization purity may assist in realizing high-fidelity control and measurement in atomic quantum systems.