Optical polarization states of a liquid-crystal blue phase II

The advantages and uniqueness of blue-phase-based electro-optical devices are predicted. In this paper, we present relevant electro-optics behaviors of the transmitted and reflected lights of BPII and try to explain those phenomena through studying the polarization states of the lights. There are two stages of electro-optical behaviors seen in an in-plan-switching BPII cell. Because of the Kerr effect, the birefringence of the linear polarized light is induced and saturated 0.021 at 150 V, and the Kerr constant is $\approx 3 \times 10^{-10}\; {\textrm{mV}}^{-2}$≈3×10−10mV−2. As the applied voltage is stronger (>200 V), the influence of the deformation of the lattice structure dominates the transmitted/reflected intensity at different wavelengths, which causes a discontinuous change in the transmitted light intensity and a huge variation in the azimuth angle ($80^{\circ }$80∘) of the polarization state of the transmitted light. As a result the deformation of the lattice structure of the BPII not only induces a linear birefringence but also induces a change in optical rotatory power and then affects the polarization state of the light. These experimental results show that the electro-optical nature of the BPII cell is more complicated than the well-known BPI phase. They also show that BPII can be used not only in transflective devices, but also in field-tunable optical devices.