Broadband optical vortex generation from patterned cholesteric liquid crystals

Singular optics is an emerging field, in which an optical wave with a helical wavefront is handled for optical manipulation and nanofabrication. We present a method to generate optical vortices via reflection from cholesteric liquid crystals with planar alignment. Numerical and experimental results show that the device is operable at multiple wavelengths with theoretically high conversion efficiency (lossless) without requiring fine-control of retardation. Although the operational wavelength range is limited by the birefringence and helix pitch of the material, broadband operation is possible by expanding the reflection band width by either introducing a pitch distribution or stacking multiple devices.