反射型导模共振滤波器设计

导模共振滤波器由于其高峰值反射率,低旁带反射,窄带以及带宽可控等优良特性引起了人们极大的关注,采用亚波长光栅的导模共振效应可以实现传统基于高低折射率介质的多层膜滤波器所无法实现的特殊功能,在弱调制模式下,其共振带宽可以被压缩到零点几纳米,但是由于介质表面和空气层的菲涅耳反射,使得偏离或者远离共振区时的反射率偏高,根据等效介质理论,亚波长光栅在远离共振区可以被看为均匀的薄膜,本文通过对导模共振光栅进行单层、双层以及三层抗反射设计,有效的降低了导模共振光栅的旁带反射率,从而在可见光波段获得了性能优良的共振滤波器.

Resonant grating filters based on grating abnormality have attracted much attention in recent years owing to their high peak reflectivity, low sideband reflection and controllable line width of central wavelength. Some special characteristics which are hard to be achieved by multilayer stack alternated with high and low refractive indices can be realized with guide-mode resonance of sub-wavelength gratings whose line width of central wavelength can be compressed to less than one nanometer under the condition of weak modulation of gratings. However,the sideband reflections near or far from the central wavelength are still somewhat high due to Fresnel reflection between air and material. According to the effective medium theory (EMT) sub-wavelength waveguide gratings can be viewed as thin films. In this paper, the sideband reflections of resonant grating filters are effectively reduced through antireflection design based on thin film theory and narrow band resonant filters are attained in the range of visible wavelength with good characteristics.