Study Of Diffraction Characteristics Of Triangular Surface-relief Subwavelength Grating

Optical diffraction is a physical phenomenon that have great applied value, the grating of subwavelength microstructures hold several specific properties beyond the ordinaries. Because characteristic size of grating of subwavelength microstructures is close to wavelength, we must use rigorous vector diffraction theory to research their properties. It is shown that guided-mode resonances with narrowband occur on certain conditions in research process.In this dissertation, the characteristics of triangular surface-relief subwavelength grating are analyzed by using Effective-medium theory and vector diffraction theory, and we compare the results. We find that the calculating result of Effective-medium theory and vector diffraction theory is similar, when ratio of grating depth to grating period is large, so we can use Effective-medium theory in this situation. But the guided-mode resonances with narrowband will occur when ratio of grating depth to grating period is small. Effective-medium theory can not be used, we must use vector diffraction theory. We analyze the principle of guided-mode resonances thoroughly, and we find the reason of occurance of guided-mode resonances. When guided-mode resonances occur, for TE wave and TM wave, their resonant peaks locate the same position for certain parameter condition. In this case, the grating possesses nonpolarized sensitivity, spectral and angular sensitivities and high reflection with narrowband. When we study triangular surface-relief subwavelength grating coated by film, we discover that the diffraction efficiency is higher than that of common subwavelength grating. Triangular surface-relief subwavelength grating coated by film can keep the high-quality within a certain variational range of parameters. Thus it is convenience for fabrication of this kind of coated subwavelength grating. Subwavelength grating coated by film presents nonpolarized sensitivity and characteristics of narrowband, spectral and angular sensitivities. These characteristics of subwavelength coated by film grating is better than that of common subwavelength grating. We use its characteristics to develop such those well-performed as high-reflectors, high-transmission, narrowband filters, high-efficiency and low-consume switch components. Its characteristics have great significance for research and fabrication of new type of optical components.