It is because that the coupling term due to polarization and the ignored term due to the weakly guiding approximation are as small as the second order, and they are just the same.

最后认为这是由于偏振耦合项是二阶小量，而弱导近似忽略了与之相等的二阶小量耦合项。

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Under the first-order approximation of Taylor expansion, the analytic expression for the defect mode frequency is derived, from which the coupling factor is deduced.

利用泰勒展式的一级近似，得到了缺陷模频率的解析表达式，进而得到紧束缚理论中的耦合因子。

youdao

Under rotating wave approximation, the total coherent Hamiltonian of photon-phonon coupling system driven by incident field is introduced.

在旋转波近似下，得到在入射光驱动下光子-声子耦合体系的总的相干性哈密顿算符。

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