We study the resonances in transmission of a subwavelength dielectric lossless structure, periodic in one direction and infinite in the orthogonal (i.e. the effectively 2D problem). We are interested in the case of an encapsulated grid, deeply embedded into an optically-homogeneous surrounding medium. In the case, even a thin periodic structure, characterized by a positive relative excess of the refractive index, demonstrates full reflectance in a narrow bandwidth due to its waveguide capability. Here we systematically study all existing types of the diffraction spectra of the grids. We show that the diffraction type of the grid is determined by the geometric filling factor and the degree of asymmetry of the grid’s cross section profile. These two parameters are some linear functions of the complex amplitude of the second spatial Fourier harmonic of the material distribution in the grid. The amplitude determines the coupling between two resonant guiding modes. The coupling is relevant for relatively small angles of incidence, for which it substantially modifies the diffraction spectra in the vicinity of the resonances. Also, we revealed a particular type of diffraction grids, which show suppressed resonances at a relatively large angle of incidence but have full reflectance in one resonance if the angle of incidence is sufficiently small.

我们研究了亚波长介电无损结构传输中的共振，在一个方向上是周期性的，在正交方向上是无限的（即有效的二维问题）。我们对封装网格的情况感兴趣，它深深嵌入到光学均匀的周围介质中。在这种情况下，即使是一个薄的周期性结构，其特征是折射率正相对过量，由于其波导能力，在窄带宽内表现出全反射。在这里，我们系统地研究了所有现有类型的网格衍射光谱。我们表明网格的衍射类型是由几何填充因子和网格横截面轮廓的不对称程度决定的。这两个参数是网格中材料分布的二次空间傅立叶谐波的复振幅的一些线性函数。幅度决定了两个谐振引导模式之间的耦合。耦合与相对较小的入射角有关，为此它基本上修改了共振附近的衍射光谱。此外，我们还揭示了一种特殊类型的衍射栅格，它在相对较大的入射角下显示出抑制共振，但如果入射角足够小，则在一个共振中具有完全反射。为此，它实质上修改了共振附近的衍射光谱。此外，我们还揭示了一种特殊类型的衍射栅格，它在相对较大的入射角下显示出抑制共振，但如果入射角足够小，则在一个共振中具有完全反射。为此，它实质上修改了共振附近的衍射光谱。此外，我们还揭示了一种特殊类型的衍射栅格，它在相对较大的入射角下显示出抑制的共振，但如果入射角足够小，则在一个共振中具有完全反射。