High dn_o/dT liquid crystals and their applications in a thermally tunable liquid crystal photonic crystal fiber

We have analyzed the physical origins of the temperature gradient of the ordinary refractive index (_odn/dT) of liquid crystals. To achieve a large _odn/dT , high birefringence (Delta n) and low clearing temperature play crucial roles. Based on these guidelines, we formulated two exemplary liquid crystal mixtures, designated as UCF-1 and UCF-2. The dn(o)/dT of UCF-1 is similar to 4x higher than that of 5CB at room temperature. By infiltrating UCF-1 into the air holes of a three-rod core photonic crystal fiber, we demonstrate a thermally tunable photonic bandgap fiber with tuning sensitivity of 27 nm/degrees C at room temperature. The insertion loss is less than 0.5 dB.