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Optics Express

Lossless nonreciprocity using dual-Raman interference

Lifeng Liu, Yifan Zhan, Shicheng Zhang, Shangqing Gong, Yueping Niu

Published Oct 15, 2025• 2 citations
Publisher

Abstract

Atomic absorption-induced insertion loss poses a fundamental limitation on signal transmission in optical nonreciprocity (ONR) systems. We propose a lossless and magnetic-field-free ONR scheme based on dual-Raman interference in two far-detuned Λ-type three-level systems. In the forward direction, destructive interference cancels the imaginary part of the susceptibility while retaining a large phase shift, enabling absorption-free transmission. In contrast, Doppler shifts arising from atomic thermal motion disrupt the Raman resonances in the backward direction, suppressing both absorption and phase modulation. This direction-dependent optical response yields nonreciprocal phase shifts which, when implemented in a Mach-Zehnder interferometer, enable an optical isolator with 100% forward transmittance and an isolation of up to 37 dB.

DOI
10.1364/oe.573161

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Atomic absorption-induced insertion loss poses a fundamental limitation on signal transmission in optical nonreciprocity (ONR) systems. We propose a lossless and magnetic-field-free ONR scheme based on dual-Raman interference in two far-detuned Λ-type three-level systems. In the forward direction, destructive interference cancels the imaginary part of the susceptibility while retaining a large phase shift, enabling absorption-free transmission. In contrast, Doppler shifts arising from atomic thermal motion disrupt the Raman resonances in the backward direction, suppressing both absorption and phase modulation. This direction-dependent optical response yields nonreciprocal phase shifts which, when implemented in a Mach-Zehnder interferometer, enable an optical isolator with 100% forward transmittance and an isolation of up to 37 dB.
A scheme for optical nonreciprocity is proposed via dual-mode Raman process in thermal atoms. We investigate a far-detuned nonlinear Raman process, with the assistance of the Doppler effect to achieve chiral optical nonlinearity. The resulting Kerr nonlinear absorption is subject to a direction-dependent Doppler shifts seen by the thermal atoms. Moreover, the inter-channel Raman interference could significantly enhance Kerr nonlinear absorption for probe field, leading to the enhancement of the optical nonreciprocity. Simulation results show that the isolation ratio could reach 41 dB and the insertion loss is about 0.16 dB, with bandwidth up to 2π ×48 MHz. Furthermore, the sensitivity of the system is investigated under different strengths of the control and Raman fields.
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 Vortex beams have important applications in a number of physical fields such as optical information processing, optical imaging, etc. Nonreciprocal propagation of light often plays a key role in some occasions in these applications. In this work, we investigate the nonreciprocal propagation of a vortex beam using a far-off resonant Raman process in a Λ -type three-level thermal atomic system. The probe vortex can propagate with high transmission in the backward direction and be well isolated in the forward direction. Via adjusting the strong control field and the atom temperature, the forward transmission of the probe vortex can be further suppressed, and higher isolation can be achieved under the use of a controlled vortex with the same orbital angular momentum. This work may provide reference for experimental studies on the nonreciprocal transmission of vortex beams and find applications in vortex isolators and circulators.
Realization of nonreciprocal transmission with low insertion loss and high contrast simultaneously is in great demand for one-way optical communication and information processing. Here we propose a generic approach to achieving perfect nonreciprocity that allows lossless unidirectional transmission by engineering energy losses. The loss of the intermediate mode induces a phase lag impinging on the indirect channel for energy transmission, which does not depend on the energy transmission direction. When the direct transmission channel coexists with the indirect lossy transmission channel, the dual-channel interference can be tuned to be destructive simultaneously for backward transmission from the rightmost mode to the leftmost mode, and for forward transmission from the leftmost mode to the intermediate mode. The former interference outcome corresponds to 100% nonreciprocity contrast, and the latter guarantees zero insertion loss for forward transmission. Additionally, our scheme also allows a nonreciprocity response over a wide bandwidth by increasing the losses while keeping perfect nonreciprocity at resonance. The robustness against loss indicates that our scheme is advantageous in the implementation of nonreciprocal optical devices with high performance.
Nonreciprocal optical devices, such as isolators and circulators, provide highly desirable functionalities in routing signals. This motivates the active research on high-efficiency nonreciprocal devices, especially for miniaturized and integrable magnetic-free schemes. All the present experimental demonstrations of circulators in optical domains are based on the high-QQQ factor cavity. In this work, we demonstrate a cavity-free optical circulator with low insertion loss by making use of a far-detuned nonlinear Raman process with the assistance of the atomic Doppler effect. Due to the large detuning, the excited state can be adiabatically eliminated, resulting in nearly vanishing absorption. An optical circulator with average transmission of more than $85\mathrm{%}$ and fidelity above 0.980.980.98 is well achieved in an experiment with hot atoms. Our scheme shows the possibility of cavity-free nonreciprocal optical devices with low insertion loss.
We theoretically investigate narrowband nonreciprocal transmission in a Doppler-broadened five-level M-type atomic medium. After Doppler averaging, the M-type system retains a narrow near-resonant electromagnetically induced transparency window that is narrower than that of a standard three-level ΛΛΛ system. This spectral narrowing is associated with the decreasing separation between the two inner dressed states as atomic velocity increases. The transparency window exhibits pronounced direction-dependent transmission, with high forward transmission and strong suppression in the reverse direction. The transparency linewidth and forward-backward probe transmission can be controlled via two independent driving fields, while the central transparency frequency is kept essentially unchanged. The resulting narrowband nonreciprocity supports high forward transmission together with strong suppression in the reverse direction, which is suitable for frequency-selective optical filtering and nonreciprocal optical transmission in thermal atomic media. Our scheme with these specific features is geared towards enabling compact vapor-cell-based nonreciprocal devices for quantum network applications.