Optical filter with tunable wavelength and bandwidth based on phototunable cholesteric liquid crystals

An optical filter with tunable wavelength and bandwidth is demonstrated using two phototunable cholesteric liquid crystals (CLCs) configured in a reflection mode. In this mode, incident light is first reflected by one Azo-chiral-doped CLC and then by another one. The tuning mechanism, which is based on the pitch modulation of the CLCs that contain an Azo-chiral dopant, can be controlled by two pumping laser beams. The central wavelength can be tuned from 510 to 628 nm, and the bandwidth can be changed from 13 to 79 nm.