Polarized optical filtering from general linearly twisted structures

It is shown that a stack of linearly twisted birefringent plates with arbitrary successive twist angle acts as a spectral filter assuming the total twist equals an odd integer of π/2, and each plate acts as a full wave plate. The classical fan Solc filter is shown to be a very special case of the present concept. Based on this finding, spontaneously twisted structures analogous to the twisted liquid crystals and helical sculptured thin films can basically act as polarization filters if their molecular or nano-rod thickness and the local birefringence satisfy the full waveplate condition. Giving a certain number of full wave plates it is shown that there are many ways to arrange their successive twist and get the same transfer function.