Properties of grating modes and their effect on reflection behavior of a periodic array of parallel rods by modal method

We analyze the property of the grating modes given by the modal method in a periodic array of parallel square rods. It is shown that the grating modes can be classified as the non-coupling mode originating from the interaction between optical waves and dielectric and the coupling mode from the inter-rod interaction. The non-coupling mode, therefore, can be excited in any case, in comparison with the coupling mode denoting a geometrical resonance of a rod array and sensitive to any change of structure. The coupling and non-coupling modes determine the optical properties of the array together. The study for a low-permittivity dielectric rod array shows that when the high reflectance is achieved, the coupling mode is excited to provide the transmission component to cancel out that from the non-coupling modes. Our results could provide the basis for understanding and optimizing optical devices based on rod arrays.