Fig. 1. Poincaré sphere representation method for polarized light^［35］

Fig. 2. （a）Poincaré sphere representation based on spherical cycloids^［39］；（b）Two rotation model of twisted liquid crystal layer^［35］.

Fig. 3. Poincaré sphere model representation of polarization evolution in the classical QHQ structure with wide band circular polarization converter

Fig. 4. Evolution process of polarization trajectory of Poincaré sphere when beam is obliquely incident on A film（a）and QHQ structure（b～d）：（b）wavelength 460 nm，（c）wavelength 530 nm，（c）wavelength 630 nm.

Fig. 5. （a）Anti parallel oriented liquid crystal cell and the graph of phase delay vs. angle^［46］；（b）Achromatic structure and band characteristic diagram^［47］；（c）Polarization conversion efficiency diagram of anti-parallel oriented liquid crystal cells and polar coordinates at different wavelengths^［35］.

Fig. 6. Schematic diagram of QHQ composite structure.（a）Equivalent wideband half wave plate；（b）Equivalent wideband full wave plate；（c）Equivalent broadband wave plate；（d）Oblique incidence coordinate system rotation.

Fig. 7. （A）QHQ achromatic liquid crystal waveplate structure and normalized transmission spectrum^［42］；（B）Structure of QHQ achromatic liquid crystal waveplate and its polarization conversion efficiency in polar coordinates^［35］.

Fig. 8. Extended structure of polarization converter based on TN liquid crystal（A）and simulation of polarization conversion efficiency in polar coordinates（B）：Efficiency plots in voltage-on state for（a）red light，（b）green light，and（c）blue light；Efficiency plots in voltage-off state for（d）red light，（e）green light，and（f）blue light^［51］.

Fig. 9. Schematic diagram of FLC structure ^［35］

Fig. 10. Structure and spectral transmission curve of wide band ferroelectric liquid crystal polarization converter^［63］

Fig. 11. （A）Structure of wide band ferroelectric liquid crystal polarization converter.（B）RGB polarization conversion efficiency chart within a 90° viewing angle range. Switching state：（a）460 nm，（b）530 nm，（c）630 nm；Holding state：（d）460 nm，（e）530 nm，（f）630 nm.（C）Measurement data of polarization conversion efficiency. Switching state：（a）450 nm，（b）532 nm，（c）633 nm；Holding state：（d）450 nm，（e）532 nm，（f）633 nm^［64］.

Fig. 12. Structure of ultra-wide spectrum and ultra large viewing angle ferroelectric liquid crystal polarization converter and its RGB polarization conversion efficiency in the 160° viewing angle range^［65］