High efficiency broadband liquid crystal polymer vector vortex waveplates

In order to achieve low light loss and a high extinction ratio in a vector vortex waveplate (VVW) based coronagraph, a precise half wave retardation at the operational wavelengths is necessary. The inversely twisted liquid crystal polymer (LCP) layer method was introduced to achieve broadband operation in patterned waveplate applications. The selection of the twist angle and half wave retardation wavelength, and the precise control in fabrication to achieve these values are critical for high efficiency in these type of devices. We numerically simulated the conversion efficiency of inversely twisted LCP to determine the twist angle and half wave retardation wavelength for the designated wavelength range, and experimentally fine-tuned these parameters. The resulted VVW exhibit very high conversion efficiency in the designated wavelength range. Polarimetry measurement revealed that the retardation of the VVW is very close to half wave retardation in a broad wavelength range.