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News & Views
Parity-Time symmetry helps breaking a new limit
http://orcid.org/0000-0002-9743-3480
Wan Wenjie wenjie.wan@sjtu.edu.cn

1
http://orcid.org/0000-0002-9604-9743
Jiang Xiaoshun jxs@nju.edu.cn

2
1 https://ror.org/0220qvk04 grid.16821.3c 0000 0004 0368 8293 University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai, 200240 China
2 grid.41156.37 0000 0001 2314 964X National Laboratory of Solid State Microstructures and College of Engineering and Applied Science, Nanjing University, Nanjing, 210093 China
19 9 2024
19 9 2024
2024
13 257© The Author(s) 2024
2024
https://creativecommons.org/licenses/by/4.0/ Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Parity-Time (PT) symmetry is an emerging concept in quantum mechanics where non-Hermitian Hamiltonians can exhibit real eigenvalues. Now, PT symmetric optical microresonators have been demonstrated to break the bandwidth-efficiency limit for nonlinear optical signal processing.

Parity-Time symmetric micro-resonators utilizing nonlinear four-wave mixing, now surpass the bandwidth-efficiency limit for optical signal processing, achieving a remarkable 100-fold efficiency boost.

Subject terms

Microresonators
Nonlinear optics
issue-copyright-statement© Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP), CAS 2024
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pmcParity-Time (PT) symmetry has emerged as a key concept in quantum mechanics, allowing non-Hermitian Hamiltonians to exhibit entirely real eigenvalues under specific conditions1. This symmetry plays a crucial role in systems where balanced absorption and amplification coexist, leading to a phase transition called PT-symmetry breaking and the emergence of complex eigenvalues beyond a critical threshold. PT symmetry has significant implications in optics and photonics, particularly in areas such as waveguides2, microresonators3,4 and lasers5. Practical applications of PT symmetry include loss-induced transparency2, unidirectional invisibility6, and enhanced sensing capabilities7,8. The controllable manipulation of gain and loss in PT-symmetric systems has opened up new possibilities for advanced signal processing, communication technologies, and optical devices, paving the way for innovative solutions across various disiplines.

Recently, in a newly published paper in eLight9, Jing Xu from Huazhong University of Science and Technology, China and Minhao Pu from Technical University of Denmark, have jointly demonstrated a PT-symmetric microresonator system. This innovative system not only enhances light intensity but also enables high-speed operation, overcoming the limitations of conventional setups based on single resonators. By combining PT symmetry with near-exceptional point operation10, a new nonlinear optical signal processing (NOSP) system utilizing four-wave mixing (Fig. 1) achieves a remarkable two-orders-of-magnitude improvement in efficiency. Using a highly nonlinear AlGaAs-on-Insulator platform, NOSP at nearly 40 gigabits per second is demonstrated with a remarkably low pump power of one milliwatt.Fig. 1 Schematic the PT-symmetric coupled microresonators for ultrafast nonlinear optical signal processing.

The intracavity field distribution of signal, pump, and idler wave indicated by blue, green, and red colored shades, respectively. The signal and idler wave pulses in the cavities depict high-speed data-encoded signal and idler waves

The breakthrough addressed a critical challenge in implementing nonlinear optical signal processing, which demands high-intensity light fields. While NOSP shows promise for enhancing optical communication networks with ultrafast processing speeds and improved efficiency, generating and maintaining the necessary high-intensity light fields has posed a significant challenge. This obstacle has hindered the practical realization of NOSP systems for high-speed, high-capacity optical communications. These results pave the way for fully chip-scale NOSP devices with integrated pump laser, promising applications in optical communication networks and classical or quantum computation. Furthermore, the synergy between PT symmetry and NOSP presents new opportunities in amplification, detection, and sensing, addressing the need for both speed and efficiency.
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References

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