Abstract

Non-Hermitian photonics based on parity-time (PT) symmetry has been considered an effective solution to achieve mode selection for optical or microwave single-mode oscillation. A PT-symmetric system is usually implemented using two mutually coupled elements with identical geometry or a single element based on precise longitudinal refractive index modulation. In this study, we propose a novel scheme to achieve PT symmetry based on polarization mode manipulation in a single optical loop. By controlling the polarization states of two light waves that are propagating along the clockwise (CW) and counter-clockwise (CCW) directions in the single optical loop, two equivalent mutually-coupled loops with identical geometry and a balanced gain and loss are formed. Based on this concept, a wavelength-tunable single-mode fiber laser with a sub-kHz linewidth is realized. The tunability is achieved by thermally tuning the wavelength of an integrated microdisk resonator (MDR) incorporated in the optical loop. Experimental results show that a continuously tunable single-mode laser with a sub-kHz linewidth of 640 Hz and a wavelength tuning range from 1552.953 to 1554.147 nm is realized. The key advantages of using a single optical loop to implement PT symmetry include greatly simplified implementation and highly improved stability. The demonstration opens new avenues to implement high-performance PT-symmetric systems for applications in photonic and microwave photonic systems.

Observation of PT-symmetry in a fiber ring laser

Zhiqiang Fan, Weifeng Zhang, Qi Qiu, and Jianping Yao
Opt. Lett. 45(4) 1027-1030 (2020)

Parity-time symmetric tunable OEO based on dual-wavelength and cascaded PS-FBGs in a single-loop

Pengcheng Liu, Zhanwu Xie, Dongdong Lin, Mengjia Lu, Wei Cheng, Guohua Hu, Binfeng Yun, and Yiping Cui
Opt. Express 29(22) 35377-35386 (2021)

Single-mode narrow-linewidth fiber ring laser with SBS-assisted parity-time symmetry for mode selection

Zhenpeng Deng, Lingzhi Li, Jiejun Zhang, and Jianping Yao
Opt. Express 30(12) 20809-20819 (2022)

Parity–time-symmetric frequency-tunable optoelectronic oscillator with a single dual-polarization optical loop

Peng Li, Zheng Dai, Zhiqiang Fan, Lianshan Yan, and Jianping Yao
Opt. Lett. 45(11) 3139-3142 (2020)

Narrow linewidth parity-time symmetric Brillouin fiber laser based on a dual-polarization cavity with a single micro-ring resonator

Yi Liu, Linyi Wang, Xin Xu, Kai Jiang, Yajun You, Wenjun He, Xuefeng Han, Jiaxin Hou, and Xiujian Chou
Opt. Express 30(25) 44545-44555 (2022)