Highly tunable large-core single-mode liquid-crystal photonic bandgap fiber.

We demonstrate a highly tunable photonic bandgap fiber, which has a large-core diameter of 25 microm and an effective mode area of 440 microm2. The tunability is achieved by infiltrating the air holes of a photonic crystal fiber with an optimized liquid-crystal mixture having a large temperature gradient of the refractive indices at room temperature. A bandgap tuning sensitivity of 27 nm/degrees C is achieved at room temperature. The insertion loss is estimated to be less than 0.5 dB and caused mainly by coupling loss between the index-guided mode and the bandgap-guided mode.