We study the peculiarities of light pulse propagation in the quasi-parity-time (quasi-${\cal P}{\cal T}$) symmetric periodic media in the Bragg geometry. Our focus is the investigation of the competition between the Bragg reflection and the ${\cal P}{\cal T}$ symmetry contribution provided different pulse duration. The mechanisms of nonsymmetric interaction between the counterpropagating waves are revealed and the various regimes of the monochromatic and nonmonochromatic wave propagation are determined. It is demonstrated that regardless the gain and loss level, the propagation of so-called long pulses in a quasi-${\cal P}{\cal T}$-symmetric medium is analogous to monochromatic waves propagation in a “pure” ${\cal P}{\cal T}$-symmetric medium. At the same time, the transmittance of the short pulses is accompanied by strong distortions determined by the gain and loss level.

中文翻译：

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准脉冲中光脉冲传播的特殊性$ {\ cal P} {\ cal T} $ 对称周期结构

我们研究了布拉格几何中在准奇偶时间（准$ {\ cal P} {\ cal T} $）对称周期介质中光脉冲传播的特殊性。我们的重点是研究在不同脉冲持续时间下布拉格反射与$ {\ cal P} {\ cal T} $对称贡献之间的竞争。揭示了反向传播波之间非对称相互作用的机理，并确定了单色和非单色波传播的各种形式。结果表明，无论增益和损耗水平如何，所谓的长脉冲在准$ {\ cal P} {\ cal T} $对称介质中的传播都类似于单色波在“纯” $中的传播。{\ cal P} {\ cal T} $对称介质。同时，短脉冲的透射率伴随着由增益和损耗水平决定的强烈失真。