1 Fibers & Nonlinear Optics, Department of Photonics Engineering, Technical University of Denmark2 Department of Photonics Engineering, Technical University of Denmark3 Rector’s office, Administration, Technical University of Denmark
In this ph.d. work, an experimental and theoretical study on Liquid Crystal (LC) infiltrated Photonic Crystal Fibers (PCFs) has been carried out. PCFs usually, consists of an air/silica microstructure of air holes arranged in a triangular lattice surrounding a core defect defined by a missing air hole. The presence of a LC in the holes of the PCF transforms the fiber from a Total Internal Reflection (TIR) guiding type into a Photonic BandGap (PBG) guiding type, where light is confined to the silica core by coherent scattering from the LC-billed holes. The high dielectric and optical anisotropy of LCs combined with the unique waveguiding features of PBG fibers gives the LC filled PCFs unique tunable properties. PBG guidance has been demonstrated for different mesophases of LCs and various functional compact fibers has been demonstrated, which utilitzes the high thermo-optical and electro-optical effects of LCs. Thermally controlled spectral filters and broadband switching functionalities, electrically controlled switches, polarizers and polarization rotators and an all-optical modulator has been demonstrated. The waveguiding mechanism of anistotropic PBGs fibers has been analyzed and spectral features directly caused by LC anisotropy has been identified. The main sources of loss is discussed and investigated through simulations and experimental verification. The thesis begins with an introduction to LCs and PCFs, with emphasis on the basic properties, which are useful for describing the waveguiding mechanism of LC filled PCFs. The principle of tunable fibers based on LCs is thereafter discussed and an alignment and coating study of LC in capillaries is presented. Next, the Liquid Crystal Photonic BandGap (LCPBG) fiber is presented and the waveguiding mechanism is analyzed through plane-wave simulations and a simple model. Experimental demonstration of thermal, electrical and optical tuning mechanisms for controlling fiber properties is presented.