Bragg reflection from periodic helicoidal media with laterally graded refractive index

Light interaction with a columnar structure of InxAl1-xN where each column is a layered periodic helical medium with laterally graded refractive index is considered. It is demonstrated that such a columnar structure can be presented as a stack of layers with a gradient of the refractive index. To calculate reflectance in the proposed model, the 2 × 2 characteristic matrix method adopted for a gradient index medium was applied. The influence of the refractive indices (including absorption), parameters of the twisting, and thickness of the periodic structure on reflectance is studied. Cases of normal and oblique incident light are considered. The presented medium is a one-dimensional photonic crystal that can be utilized in many devices for light manipulation.