Generating frequency dependant twisted beam shapes using 1DPC nanostructure with graded-index defect layer

We introduce an optical nanostructure device made of one dimensional photonic crystal (1DPC) with a graded-index defect layer, which has the ability of producing frequency dependent twisted beam shapes. The defect layer's refractive index distribution function changes in r and φ directions in cylindrical coordinate. The rays passing through different transverse positions of an introduced structure experience different optical pathways. Thus, the defect mode has transverse dependency and twisted shapes have been generated in transmitted spectrum (phase and amplitude). The incident beam frequency is a factor that can engineer the obtained twisted beam shape. This study demonstrates the ability of the PC structures to produce controllable spiral light beam shapes.