Temperature dependence of refractive index in blue phase liquid crystals

The refractive indices of a class of Blue-Phase liquid crystals (BPLCs) and their temperature dependence have been measured and analyzed. In general, the thermal index gradients in blue phases, BPI and BPII, are both larger than in isotropic liquid state; the index gradient of BPII phase is steeper than that of BPI, and is attributed to the difference between the expansion coefficients of simple and body-centered cubic lattices. Besidestheir obvious importance in photonics and nonlinear optical processes and applications, the investigation of the phase dependence of the index gradient also provides a useful wayfor phase identification of BPLCs, namely the second-order and weakly first order phasetransitions corresponding to the ISO/BPII transition and the BPII/BPI transition. copy; 2013 Optical Society of America.