Research On The Properties Of Grating Modes In A Single Layer Of Rods

With striking advantages such as small size, highly integrated, high diffraction efficiency and so on, subwavelength gratings have been a hot topic for recent years. Among various rigorous methods to handle the grating diffraction, the modal method, which can also reflect the underly physics, is efficient especially for lamellar gratings because of the fact that only two dominant modes inside the grating are usually involving. In this thesis, we take the narrow-band reflection behavior of a single layer of square dielectric rods as an example to calculate the grating modes in it using the modal method. It is shown that the grating modes can be classified as the noncoupling mode originating from the interaction between optical waves and dielectric and the coupling mode resulting 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 rod arrays and sensitive to their any change. The study for a low-permittivity dielectric rod array shows that the coupling mode is highly excited to provide the transmission component to cannel out that from the noncoupling modes when the extraordinary optical reflection occurs. Our research shows the importance of the coupling mode in anomaly effects and provides a new perspective of analysis for other optical phenomena. A single layer of square dielectric rods can be designed as optical reflection filters, broadband reflectors and omnidirectional reflection by changing the parameters of the structure.