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Optics Express

Reconfigurable nonreciprocity with low insertion loss using a simple two-level system

Yiqi Hu, Shicheng Zhang, Xinyi Kuang, Yihong Qi, Gongwei Lin, Shangqing Gong, Yueping Niu

Published Nov 23, 2020• 11 citations
Publisher

Abstract

Nonreciprocal light propagation is essential to control the direction of the light flow. Here, we report the realization of magnetic-free optical nonreciprocity using a simple two-level system driven by a pump field in warm atoms. In our experiment, we not only demonstrate less than 0.5 dB of insertion loss and up to 20 dB of isolation but also provide flexible and reconfigurable operations of the isolation bandwidth, frequency, and direction. Nonreciprocal scheme with these characteristics may find important applications in photonic devices.

DOI
10.1364/oe.409850

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Nonreciprocal light propagation is essential to control the direction of the light flow. Here, we report the realization of magnetic-free optical nonreciprocity using a simple two-level system driven by a pump field in warm atoms. In our experiment, we not only demonstrate less than 0.5 dB of insertion loss and up to 20 dB of isolation but also provide flexible and reconfigurable operations of the isolation bandwidth, frequency, and direction. Nonreciprocal scheme with these characteristics may find important applications in photonic devices.
A scheme for magnetic-free optical nonreciprocity in an ensemble of four-level cold atoms is proposed by exploiting the directional four-wave mixing effect. Using experimentally achievable parameters, the nonreciprocal optical responses of the system can be observed and the conversion on nonreciprocal transmission and nonreciprocal phase shift can be implemented. These nonreciprocal phenomena originate from the directional phase matching, which breaks the time-reversal symmetry and dynamic reciprocity of the cold atomic system. Moreover, by embedding the cold atoms into a Mach-Zehnder interferometer and choosing proper parameters, a two-port optical isolator with an isolation ratio of 79.70 dB and an insertion loss of 0.35 dB and a four-port optical circulator with a fidelity of 0.9985 and a photon survival probability of 0.9278 can be realized, which shows the high performance of isolation and circulation. The proposal may enable a new class of optically controllable cavity-free nonreciprocal devices in optical signal processing at the low light level.
Abstract Nonreciprocal devices, such as isolators, are of great importance for optical communication and optical information processing. To bypass the limitation of a strong magnetic field imposed by the traditional Faraday magneto-optic effect, many alternative mechanisms have been proposed to demonstrate magnetic-free nonreciprocity. However, limited by the drive-induced noise, the noiseless isolator capable of working in the quantum regime has yet to be realized in the experiment. Here, we show a noiseless all-optical isolator with genuine single photons in hot atoms. We experimentally study this mechanism using an open V-type level scheme and demonstrate a low insertion loss of 0.6 dB and high isolation of 30.3 dB with bandwidth up to hundreds of megahertz. Furthermore, the nonreciprocal direction can be truly reversed only by tuning the frequency of the pump laser with the same setup. Our scheme relies on widely used optical technology and is thus universal and robust.
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.
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 devices operating at the single-photon level are fundamental elements for quantum technologies. Because magneto-optical nonreciprocal devices are incompatible for magnetic-sensitive or on-chip quantum information processing, all-optical nonreciprocal isolation is highly desired, but its realization at the quantum level is yet to be accomplished at room temperature. Here, we propose and experimentally demonstrate two regimes, using electromagnetically induced transparency (EIT) or a Raman transition, for all-optical isolation with warm atoms. We achieve an isolation of 22.52 ± 0.10 dB and an insertion loss of about 1.95 dB for a genuine single photon, with bandwidth up to hundreds of megahertz. The Raman regime realized in the same experimental setup enables us to achieve high isolation and low insertion loss for coherent optical fields with reversed isolation direction. These realizations of single-photon isolation and coherent light isolation at room temperature are promising for simpler reconfiguration of high-speed classical and quantum information processing.
Achieving multiwavelength nonreciprocal optical devices, which can realize nonreciprocal (perfect one-way) transmission for two or more wavelengths at the same time, without magnetic materials is challenging, but is highly desirable for densely integrated multiwavelength photonic components. The authors experimentally realize multiwavelength magnetic-free optical nonreciprocity using optical pumping of warm 85{}^{85}85Rb atoms, with the assistance of Doppler effect. This scheme may have advantages in decreasing the number of optical isolators, and thus can reduce the complexity of an integrated multiwavelength system.