Polarimetric parity-time symmetry in a photonic system

Lingzhi Li,Jiejun Zhang,Jianping Yao,Bai-Ou Guan,Yanyan Zhi,Xinhuan Feng,Yuting Zou,Yuan Cao

doi:10.1038/s41377-020-00407-3

Abstract

Parity-time (PT) symmetry has attracted intensive research interest in recent years. PT symmetry is conventionally implemented between two spatially distributed subspaces with identical localized eigenfrequencies and complementary gain and loss coefficients. The implementation is complicated. In this paper, we propose and demonstrate that PT symmetry can be implemented between two subspaces in a single spatial unit based on optical polarimetric diversity. By controlling the polarization states of light in the single spatial unit, the localized eigenfrequencies, gain, loss, and coupling coefficients of two polarimetric loops can be tuned, leading to PT symmetry breaking. As a demonstration, a fiber ring laser based on this concept supporting stable and single-mode lasing without using an ultranarrow bandpass filter is implemented.

Highlights

A parity-time (PT) symmetric system is a special non-Hermitian system of which its Hamiltonian possesses real eigenvalues
We propose and demonstrate that a PTsymmetric system can be implemented in a single spatial unit based on polarimetric diversity, which supports singlewavelength operation
As the gain and loss coefficients are increased to values greater than the coupling coefficient, PT symmetry breaking occurs

Summary

Introduction

A parity-time (PT) symmetric system is a special non-Hermitian system of which its Hamiltonian possesses real eigenvalues. For a long-cavity laser, for which it is preferable to have low phase noise, a narrow linewidth, and high optical power, single-mode lasing is challenging due to the small mode spacing[5,6,16,17,18,19,20,21,22,23,24]. For a long-cavity laser such as a fiber laser with a cavity length on the order of tens of meters, a high-Q optical filter is needed, making the system costly and endowing it with poor stability[25,26]

Methods

Results

Conclusion