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Photonics Research

Broad-intensity-range optical nonreciprocity based on feedback-induced Kerr nonlinearity

Lei Tang, Jiang-Shan Tang, Haodong Wu, Jing Zhang, Min Xiao, Keyu Xia

Published Apr 19, 2021• 25 citations
Publisher

Abstract

Nonreciprocal light propagation plays an important role in modern optical systems, from photonic networks to integrated photonics. We propose a nonreciprocal system based on a resonance-frequency-tunable cavity and intensity-adaptive feedback control. Because the feedback-induced Kerr nonlinearity in the cavity is dependent on the incident direction of light, the system exhibits nonreciprocal transmission with a transmission contrast of 0.99 and an insertion loss of 1.5 dB. By utilizing intensity-adaptive feedback control, the operating intensity range of the nonreciprocal system is broadened to 20 dB, which relaxes the limitation of the operating intensity range for nonlinear nonreciprocal systems. Our protocol paves the way to realize high-performance nonreciprocal propagation in optical systems and can also be extended to microwave systems.

DOI
10.1364/prj.413286

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Nonreciprocal light propagation plays an important role in modern optical systems, from photonic networks to integrated photonics. We propose a nonreciprocal system based on a resonance-frequency-tunable cavity and intensity-adaptive feedback control. Because the feedback-induced Kerr nonlinearity in the cavity is dependent on the incident direction of light, the system exhibits nonreciprocal transmission with a transmission contrast of 0.99 and an insertion loss of 1.5 dB. By utilizing intensity-adaptive feedback control, the operating intensity range of the nonreciprocal system is broadened to 20 dB, which relaxes the limitation of the operating intensity range for nonlinear nonreciprocal systems. Our protocol paves the way to realize high-performance nonreciprocal propagation in optical systems and can also be extended to microwave systems.
Optical nonreciprocity is an essential property for a wide range of applications, such as building nonreciprocal optical devices that include isolators and circulators. The realization of optical nonreciprocity relies on breaking the symmetry associated with Lorentz reciprocity, which typically requires stringent conditions such as introducing a strong magnetic field or a high-finesse cavity with nonreciprocal coupling geometry. Here we discover that the collision effect of thermal atoms, which is undesirable for most studies, can induce broadband optical nonreciprocity. By exploiting the thermal atomic collision, we experimentally observe magnet-free and cavity-free optical nonreciprocity, which possesses a high isolation ratio, ultrabroad bandwidth, and low insertion loss simultaneously. The maximum isolation ratio is close to 40 dB, while the insertion loss is less than 1 dB. The bandwidth for an isolation ratio exceeding 20 dB is over 1.2 GHz, which is 2 orders of magnitude broader than typical resonance-enhanced optical isolators. Our work paves the way for the realization of high-performance optical nonreciprocal devices and provides opportunities for applications in integrated optics and quantum networks.
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Nonreciprocal optical devices are important in wide areas, ranging from optical telecommunications to signal processing. Here, we experimentally realize the magnet-free and cavity-free optical nonreciprocity based on phase-matched four-wave mixing (FWM) in hot atoms. Specifically, the isolation of more than 20 dB and insertion loss less than 1 dB without using any optical cavity can be achieved simultaneously. Our results provide general insights into a broad class of parametrically modulated nonreciprocal behavior, paving the way toward optimal nonreciprocal devices based on the nonlinear FWM process.
Nonreciprocal optical devices play a pivotal role in modern optical systems and advanced quantum technologies. Nonreciprocal devices based on optical nonlinearity have garnered significant attention due to their compatibility with on-chip photonics fabrication techniques. However, when the opposite-propagating continuous waves are incident to such nonlinear nonreciprocal devices simultaneously, achieving dynamic nonreciprocity has remained a formidable challenge. In addition, the devices relying on nonlinear resonators suffer from limited bandwidths. In this paper, we theoretically propose a method for achieving an on-chip isolator and quasicirculator by employing a nonlinear Mach-Zehnder interferometer. Harnessing the chirality between self- and cross-Kerr nonlinearities in the nonlinear arm of the interferometer, our device achieves remarkable dynamic nonreciprocity. We obtain an isolation contrast of $\ensuremath{\geqslant}0.9$ for the optical isolator and fidelity of $\ensuremath{\geqslant}0.97$ for the optical quasicirculator, and a broad bandwidth of 20nm20\phantom{\rule{3.33333pt}{0ex}}\text{nm}20nm for both. Our protocol paves a way to realize a broadband on-chip nonlinear nonreciprocal device.
Hot atoms have been demonstrated to be a promising platform for the manipulation of optical fields. However, the thermal motion of atoms results in the broadening of spectral lines, which is accompanied by a reduction in the light-atom interaction. In this study we propose a nonreciprocal optical system that significantly enhances the strength of the light-atom interaction by unidirectionally compensating for the broadening associated with two-photon processes, employing inhomogeneous light shifts in a $\mathrm{\ensuremath{\Lambda}}$ system. Utilizing the density matrix formalism, we provide a detailed description of the dynamics and examine the nonreciprocity in two distinct detuned regions. In the far-detuned region, a room-temperature nonreciprocity with an isolation of 37.3dB37.3\phantom{\rule{0.28em}{0ex}}\mathrm{dB}37.3dB and a transmission of 0.99 can be achieved. Furthermore, in the near-resonance region, the ultrabroad bandwidth of the nonreciprocal window can reach gigahertz. Our findings pave the way for the realization of high-performance optical nonreciprocity and present opportunities for applications in integrated optics and quantum networks.