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Optics Continuum

Amplified nonreciprocal and unidirectional reflection in a defective atomic lattice via spontaneously generated coherence

Qiong-Yi Xu, Chen Peng, Duanfu Chen, Han-Xiao Zhang, Dong Yan, Hong Chun Yang

Published Mar 24, 2026• 0 citations
Publisher

Abstract

Simultaneously realizing nonreciprocity and signal amplification in the same physical system cannot only greatly enhance the efficiency of nonreciprocal photonic devices but also facilitate their integration. We propose a scheme to achieve gain-assisted nonreciprocal or even unidirectional reflection amplification by exploring spontaneously generated coherence (SGC) activated by a weak incoherent pump in a defective atomic lattice. The numerical results show that the monochromatic to two-color nonreciprocal reflection amplification (the maximum of reflectivities R l ≃ 10 4 and R r ≃ 10 2 ), and even unidirectional reflection amplification ( R l ≃ 10 2 and R r ≃ 10 −4 ) can be modulated freely by adjusting the relative phase ϕ , the dipole moment angle θ and the parameters of defective atomic lattice, e.g., the number and period of vacant lattice cells, the period of filled lattice cells, and so on. This indicates that nonreciprocal reflection amplification can be enhanced and modulated via the SGC effect and multiple reflections within the atomic lattice. Such efficient nonreciprocal amplification can be effectively applied to integrated chips, thereby advancing the development of quantum information technology.

DOI
10.1364/optcon.592284

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Simultaneously realizing nonreciprocity and signal amplification in the same physical system cannot only greatly enhance the efficiency of nonreciprocal photonic devices but also facilitate their integration. We propose a scheme to achieve gain-assisted nonreciprocal or even unidirectional reflection amplification by exploring spontaneously generated coherence (SGC) activated by a weak incoherent pump in a defective atomic lattice. The numerical results show that the monochromatic to two-color nonreciprocal reflection amplification (the maximum of reflectivities R l ≃ 10 4 and R r ≃ 10 2 ), and even unidirectional reflection amplification ( R l ≃ 10 2 and R r ≃ 10 −4 ) can be modulated freely by adjusting the relative phase ϕ , the dipole moment angle θ and the parameters of defective atomic lattice, e.g., the number and period of vacant lattice cells, the period of filled lattice cells, and so on. This indicates that nonreciprocal reflection amplification can be enhanced and modulated via the SGC effect and multiple reflections within the atomic lattice. Such efficient nonreciprocal amplification can be effectively applied to integrated chips, thereby advancing the development of quantum information technology.
Improving the performance of non-reciprocal photonic devices is one of the key factors for promoting the development of quantum networks. To achieve this goal, we propose a scheme to realize multicolored unidirectional reflection amplification in the defective atomic lattice, with all atoms trapped in each filled lattice cell being driven into a four-level diamond-type coherent gain atomic system by two coupling fields and two probe fields. Therefore, this scheme simultaneously achieves light amplification (resulting from the joint effect of the coherent gain atomic system and the distributed feedback mechanism of the atomic lattice) and non-reciprocity (arising from the symmetry-breaking effect of the defective atomic lattice) in a single physical system. Furthermore, we propose a reasonable scheme for obtaining equivalent results by reducing the energy level structure, and through numerical simulations and calculations, it is concluded that perfect unidirectional reflection amplification requires that the two-photon resonance is not only located in the gain region, but also satisfies the Bragg condition. This scheme can be used to design non-reciprocal photonic devices that are easily integrable, high-efficiency, and capable of flexible multi-channel manipulation.
The novel and ingenious scheme we propose for achieving unidirectional reflection lasing (URL) involves integrating a one-dimensional (1D) defective atomic lattice with a coherent gain atomic system. Its physical essence lies in the fact that the right-side reflectivity is drastically reduced due to the destructive interference between primary and secondary reflections, whereas on the left-side primary reflection is effectively suppressed and the secondary reflection is efficiently enhanced, ultimately reaching the lasing threshold. Through numerical results and further analyses, we have elucidated how to precisely tailor the lattice parameters and coupling fields to control destructive interference point (DIP), thereby realizing URL and enabling its active modulation. Our scheme is experimentally feasible and not only effectively circumvents the stringent conditions faced in directly realizing URL, providing a new pathway, but also beneficial for integrating active photonic devices into compact quantum networks and may improve the efficiency of optical information transmission.
Assisted by the probe gain, we propose a scheme to realize the amplified unidirectional broadband reflection in a one-dimensional defective atomic lattice. In this system, some lattice cells are intentionally designed to prevent atom trapping and exhibit a periodic distribution, in order to break the spatial symmetry of light propagation and form a well reflection band. While the filled lattice cells of 87Rb^{87}\mathrm{Rb}87Rb atoms are driven into the closed three-level $\mathrm{\ensuremath{\Delta}}$-type configuaration, which can realize the amplification of the probe field. By optimizing parameters and reasonable settings, it is obvious that our scheme not only yields a flexible and adjustable broadband unidirectional reflection amplification, but also has reduced the requirement for probe gain and greatly shortened the length of defective atomic lattices.
We propose an efficient scheme for achieving mode-tunable unidirectional reflection lasing (URL) by establishing a coherent gain atomic system to amplify the probe field and ingeniously designing a one-dimensional (1D) defective atomic lattice. This lattice not only replaces the resonant cavity to provide a distributed feedback mechanism but also breaks the spatial symmetry of the probe susceptibility. Correspondingly, the URL can be characterized by a non-Hermitian degenerate spectral singularity (NHDSS), where the two eigenvalues of the inverse scattering matrix are engineered to satisfy λ S −1 + ≃ λ S −1 − →0. This intriguing NHDSS depends on the probe susceptibility and the Bragg condition, both of which can be modulated by adjusting the external driving fields and lattice structure, rendering the scheme experimentally feasible. Our approach achieves both nonreciprocity and lasing oscillation in a single system, significantly enhancing the efficiency of optical information transmission and facilitating the integration of active photonic devices into compact quantum networks.
High-performance non-reciprocal photonic devices can improve the efficiency of optical quantum manipulation, information processing, and quantum simulation effectively. The enhanced optical signal can simultaneously amplify the weak signal output by the quantum system and isolate the sensitive quantum system from the back-scattered external noise, which is the core technology of high-performance photonic devices. In our previous work ( 2023 Opt. Express 31 38228 ), we have achieved dynamic control of unidirectional reflection amplification based on four-wave mixing gain and the use of coupling field intensity varying linearly with position. In this work, we design a simple three-level closed loop coherent gain atomic system, setting the intensity of coupling field to be varying with position step shape to break the spatial symmetry of probe susceptibility, and achieving perfect non-reciprocal reflection light amplification. In contrast, the stepped variation of coupling field intensity is easier to adjust in experiment, greatly reducing the difficulty in the experiment. Specifically, the system introduces phase modulation. By changing the phase, the frequency region of probe gain and absorption can be switched, which makes the modulation of reflection amplification more flexible.
It is important to elaborate on versatile strategies for achieving the perfect nonreciprocal reflection amplification, which is the key technology of high-quality nonreciprocal photonic devices. In this work, we ingeniously design a coherent four-level N-type atomic system to harness the nonreciprocal light amplification, in which the uniform distribution of atoms is driven by two strong coupling fields and a weak probe field. In our regime, the strength of the two control fields is designed with linear variation along the x direction to destroy the spatial symmetry of the probe susceptibility, leading to the nonreciprocity of the reflection. In particular, the closed-loop transitions to amplify the probe field are due to the combined effect of the control fields and spontaneous emissions. The numerical simulation indicates that the perfect nonreciprocal reflection amplification can be realized and modulated by the appropriate settings of the control fields and the detuning, Δc. Our results will open a new route toward harnessing nonreciprocity, which can provide more convenience and possibilities in experimental realization.