Polarisation rotator consisting of two layers of twisted nematic LC, which shows little dependence on the initial polarisation direction and the wavelength

Performances of typical HWP (half-wave plate) or the one layer of the twisted nematic LC as the polarisation rotator are affected by the wavelength of the incident light and the initial polarisation direction of the incident linear polarisation. A new configuration that two layers of the twisted LC were aligned with the angular difference of 90°, was considered. Theoretical analysis by Jones matrix was used to derive the change of the polarisation state at the proposed configuration and to investigate the dependence on the wavelength and the initial polarisation direction. Commercial LC simulator was used to quantitatively investigate the effectiveness of the proposed configuration. Theoretical analysis and the calculated results show that the performance of the proposed configuration was less dependent on wavelength as compared with the one layer of twisted nematic LC.