Polarimetric parity-time-symmetric photonic system

The system consists of a single spatial loop, in which two equivalent polarimetric loops are formed by recirculating light waves of orthogonal polarization states in the loop. To achieve PT symmetry, the phase retardance, power ratio, and coupling coefficient between the orthogonally polarized light waves are tuned by controlling PC1 in the birefringent path, and the lasing threshold is tuned by controlling PC2 in the coupled path. PC: polarization controller; Pol.: polarizer; EDFA: erbium-doped fiber amplifier; OC: optical coupler; TOF: tunable optical filter. Credit: Lingzhi Li, Yuan Cao, Yanyan Zhi, Jiejun Zhang1, Yuting Zou, Xinhuan Feng, Bai-Ou Guan and Jianping Yao