Study On Resonance Characteristics And Spectral Symmetry Of The Grating Resonance Coupling

Guided mode resonant filter(GMRF) means that the leaky modes will be inspired in the structure which supported by specific conditions when the waveguide grating structure parameters satisfy certain conditions. The incident energy will reallocate and spectrum will show a sharp narrow-band filtering characteristics when the structure is illuminated by the light with certain wavelength. The highest reflection efficiency of100%, the line width of 0.01 nm and low side band response can be achieved in GMRF.Therefore, the guided mode resonant effect, a physical phenomena of light propagating in sub-wavelength waveguide grating, has been widely used in high-power laser, filters,optical switches and other areas. Typically, the guided-mode resonance filters mainly composed of four parts, which are the cover layer, grating layer, waveguide layer and substrate, respectively. The filter characteristic is very sensitive to the structure parameters such as grating period, cycle duty, the depth of grating and the waveguide layer thickness. Any structure parameters changes may cause the changes of lineshape,which lead to a negative influence on equipment application. Therefore, the research of the physical mechanism of guided mode resonance is very important in controlling the symmetry of spectrum.In this thesis, in order to solve the causes of lineshape symmetry in the guided-mode resonant filter response spectrum, we present a longitudinal dual-channel model to systematiclly demonstrate the behavior that propagating mode travel in both the horizontal and vertical directions when the light couple into waveguide layer. We explain the effect of phase change to the formants in response spectrum after vertical mode coupled out to the diffraction field, and demonstrate the causes of asymmetry lineshapes by using the principle of Fano resonances.In order to verify the correctness of the longitudinal double channel model, we design three different structure parameters GMRF devices and simulate reflected response spectrum through rigorous coupled-wave analysis(RCWA) when TE-polarized light incident. Furthermore, we verify the longitudinal twin channels model by changingthe grating height and observing the variation behavior of lineshape symmetry. At last,the electric field distribution of waveguide layer is simulated and indicate that the guided modes propagating is weakly coupled in the film. By observing the distribution of electric field intensity at the peaks and valleys in reflect spectrum, we find that the symmetry of lineshape changes with the changing of the grating height, which verifies the longitudinal dual-channel model at the same time.The longitudinal double-channel model provides an effective way to avoid the large-scale matrix operations and explains the guided-mode coupling process. This study is significant for controlling line symmetry of GMRF and is helpful to understand the Fano resonance in photonic crystals.