Pure circularly polarized light emission from waveguide microring resonators

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 the maximum intensity, we measure an average polarization impurity of 1.0×10−3 in relative intensity across the resonance FWHM and observe impurities below 10−4 in this range. This constitutes a significant improvement over the ∼10−2 impurity demonstrated in previous works on integrated devices. Photonic structures that allow high circular polarization purity may assist in realizing high-fidelity control and measurement in atomic quantum systems.