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arXiv:2512.12705 · Optics Express

Unidirectional spectral singularity lasing in a defective atomic lattice

Peng Chen, Xinfu Zheng, D. Chen, Hanxiao Zhang, Dong Yan, Jin-Hui Wu, Hong Wei Yang

Published Apr 23, 2026• 2 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1364/oe.591667

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Optics Letters•Aug 19, 2026•0 citations
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.
Unidirectional lasing is highly desirable for practical high-performance quantum information processing platforms, while most existing schemes still rely on the combination of resonant cavities and nonreciprocal mechanisms. Here, we propose a cavity-free scheme for achieving the onset of narrowband unidirectional reflection lasing (URL) in a single physical system by introducing a coherent gain atomic medium into a one-dimensional defective atomic lattice, where the former amplifies the probe field and the latter provides spatial symmetry breaking and a distributed-feedback mechanism. We show that the threshold condition for URL, characterized by λ + −1 ≃ λ − −1 →0, can be tuned from single-mode to dual-mode by varying the microwave field and the lattice structure. Its underlying mechanism lies in the constructive or destructive interference between the reflections from both sides under distinct Bragg conditions.
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.
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.
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.
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.
Based on spatial symmetry breaking, we propose a tunable unidirectional zero-reflection scheme in a one-dimensional single-defect atomic lattice. Reflection suppression stems from destructive interference between the direct-reflection and multiple-scattering components, whose amplitudes and phases are co-modulated by coherent atomic response, Bragg scattering, and structural asymmetry. The system supports both broadband and narrowband asymmetric-reflection regions, each containing a unidirectional zero-reflection point, with the minimum reflectivity reaching below 10 −6 in one incident direction while remaining above 0.93 in the reverse direction. External coherent fields tune the UZR frequency, and the vacant-region length modulates phase and scattering amplitudes for zero-reflection at discrete incident angles. Boasting robustness against atom number density fluctuations, this work provides an intuitive theoretical framework for directional scattering, promising tunable optical switches, low-back-reflection photonic structures, and asymmetric light-control devices.