In this Ph.D. thesis, an experimental investigation of liquid crystal photonic bandgap (LCPBG) fiber devices and applications is presented. Photonic crystal fibers (PCFs) consist of a cladding microstructure with periodic index
variations and a core defined by a defect of the structure. The presence of liquid crystals (LCs) in the air-holes of the PCF transforms the fiber from a total internal reflection (TIR) guiding type into a photonic bandgap (PBG) guiding type. The light is confined to the silica core by coherent scattering from the LC-filled air-holes and the transmission spectrum presents bandgaps. These bandgaps can be tuned by applying an electric field or by varying the temperature. Therefore, tunable all-in-fiber devices with controllable optical properties
can be realized.
This thesis focuses on the design, fabrication and development of com-pact LCPBG fiber devices. An on-chip design is demonstrated, which not only enables the LCPBG fiber devices more easily applied in fiber based systems, but also can be used as a standard platform to develop LCPBG fiber devices for different applications. Based on this compact design, various LCPBG fiber devices have been achieved. A polarizer with electrically tunable polarization extinction ratio is obtained. An on-chip tunable notch filter based on long-period gratings is presented, exhibiting high polarization sensitivity. A tunable polarization controller using negative dielectric LCs is developed, which can be thermally and electrically controlled to work both as a quarter-wave plate or half-wave plate. An electrically tunable bandpass filter based on two solid-core PCFs filled with different LCs is
fabricated, and the tunability of the bandwidth is achieved by individually or simultaneously controlling the driving voltage of each LCPBG fiber. Finally, the applications for LCPBG fiber devices based on the on-chip platform design have been demonstrated in realizing microwave true-time delay and creating an electrically
tunable fiber laser.