The concept of parity-time ( ##IMG## [http://ej.iop.org/images/2040-8986/22/6/065605/joptab8b24ieqn3.gif] {$\mathcal{P}\mathcal{T}$} ) symmetry in optics could potentially provide emerging solutions to exploit the benefits of optical gain in optical processing. With this regard, ##IMG## [http://ej.iop.org/images/2040-8986/22/6/065605/joptab8b24ieqn4.gif] {$\mathcal{P}\mathcal{T}$} and quasi- ##IMG## [http://ej.iop.org/images/2040-8986/22/6/065605/joptab8b24ieqn5.gif] {$\mathcal{P}\mathcal{T}$} symmetry were studied in thick optical diffraction gratings by derivation of explicit analytical expressions using the coupled-wave theory and verified by numerical calculations. The conditions to observe ##IMG## [http://ej.iop.org/images/2040-8986/22/6/065605/joptab8b24ieqn6.gif] {$\mathcal{P}\mathcal{T}$} and quasi- ##IMG## [http://ej.iop.org/images/2040-8986...] {$\mathcal{P}\mathcal{T}$}

中文翻译：

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## IMG ## [http://ej.iop.org/images/2040-8986/22/6/065605/toc_joptab8b24ieqn1.gif]和准## IMG ## [http：// ej。 iop.org/images/2040-8986/22/6/065605/toc_joptab8b24ieqn2.gif]在厚衍射光栅中使用耦合...

奇偶时间的概念（## IMG ## [http://ej.iop.org/images/2040-8986/22/6/065605/joptab8b24ieqn3.gif] {$ \ mathcal {P} \ mathcal {T } $}）光学中的对称性可能会提供新兴的解决方案，以利用光学处理中光学增益的优势。因此，## IMG ## [http://ej.iop.org/images/2040-8986/22/6/065605/joptab8b24ieqn4.gif] {$ \ mathcal {P} \ mathcal {T} $}和准-## IMG ## [http://ej.iop.org/images/2040-8986/22/6/065605/joptab8b24ieqn5.gif] {$ \ mathcal {P} \ mathcal {T} $}对称通过使用耦合波理论推导明确的解析表达式，对厚光学衍射光栅进行了研究，并通过数值计算进行了验证。观察条件## IMG ## [http://ej.iop.org/images/2040-8986/22/6/065605/joptab8b24ieqn6.gif] {$ \ mathcal {P} \ mathcal {T} $}和准-## IMG ## [http：//ej.iop。