Design And Characterization Of Controllable Linewidth Guided-mode Resonance Filter

The narrowband filter is served as basic optical elements used widely in the optical field. Guided-mode resonance (GMR) filter, which utilize resonance effect of the waveguide grating structures to realize filter, is different from the traditional optical filter stacked by multiple thin-films. This new type of filter has attracted considerable interest by virtue of their good characteristics, such as simple structures, high efficiency and controllable linewidth. To make GMR filter for practical applications, one need to control the spectral response of the filter effectively, such as symmetry line shape, sideband reflectance, and spectral width. In this paper, physical basis of GMR effects and their unique optical characteristics are investigated by combining planar dielectric waveguide theory and rigorous coupled-wave analysis (RCWA) method. Two different types of GMR filter are presented based on GMR effects and thin film theory, and their main properties are also discussed.Two types of GMR filters are designed in this paper, one type is the strongly modulated dielectric grating GMR filter with shallow grating, and the other is the weakly modulated dielectric grating GMR filter with separation layer. For the first type of GMR filter, the grating layer has the equal refractive index to the waveguide layer, the linewidth of the filter is sensitive to the grating thickness. By adjusting the grating thickness and the grating period, with the total thickness of the grating layer and waveguide layer kept unchanged, one can get different linewidth of spectral response with symmetrical line shape and low-reflection sideband. Since the grating thickness can be controlled effectively by adopted the method, one can simplify the fabrication of the GMR filters in some extent. For the latter type of GMR filter, a separation layer is added between the grating layer and waveguide layer in order to control the coupling strength of the light from an incident plane wave and the leaky waveguide mode that is localized to the waveguide layer. Therefore, the linewidth of the filter can be controlled by adjusting separation layer thickness. It has been discovered that resonance peak of the GMR filter is not sensitive to the grating parameters, such as grating thickness, filling factor and grating profile. Within a reasonable parameter range, resonance peak almost do not change when the grating parameters changes, such as grating thickness, filling factor and grating profile. Therefore, this type of GMR filter is easy to be fabricated, and has good application prospect.At certain extent, these two types of GMR filter are presented in this paper can be used to optimize the fabrication of GMR filters. Therefore, these studies not only have a certain theoretical value, but also have experimental significance.