Thin twisted-nematic device achieves achromatic polarization rotation

Researchers at Pennsylvania State University (University Park, PA) have theoretically and experimentally demonstrated a simple device for achromatic polarization rotation based on the eigenmode of a twisted-nematic (TN) structure. The experimental device consisted of a thin (1.9-µm) TN liquid-crystal (LC) cell placed between two homogeneous LC waveplates. The TN cell had a specific twisted angle and was oriented parallel to a specific linear polarization angle of incident radiation. The homogeneous LC cells were oriented such that the entrant and emergent polarizers were parallel to the entrant and emergent directors of the TN cell. The purpose of the homogeneous LC cells was to transform the polarization state of all wavelengths between the linear polarization state and their corresponding eigenmodes. The theoretical explanation of the device was based on a Poincaré-sphere model representing the state of polarization as a curve on the PS. By combining the homogenous LC cell with the TN cells, the researchers achieved an emergent polarization rotation of 90° compared to incident polarization with almost 100% transmission over a wavelength range of 450 to 700 nm. Contact Zhizhong Zhuang at [email protected].