Study Characteristic Of Photonic Crystal Fibers And Their Long Period Gratings

In recent years, as a new kind of optical fiber, photonic crystal fibers (PCF) appeared, its application scope has covered the telecom, sensing technology, optical spectroscopy and pharmacy and so on. It is growing so quickly, is mainly due to its flexible structure has some bizarre unlike traditional fiber properties, including adjustable dispersion characteristics, no deadline single-mode characteristics and adjustable effective mode field area. A long period grating written in a photonic crystal fiber have been found to have high sensitivity in temperature, refractive, index measurement, it also can effectively solve the measurement crossover sensitivities through the reasonable design of structure parameters. Liquid crystal are very sensitive of temperature and electric field, so LCD photonic crystal fibers will combination photonic crystal fibers design flexibility and LCD adjustability organically, and expanded the scope of application of photonic crystal fibers.This paper firstly simulation calculation of three kinds of different structure arrangement PCF based on the finite element COMSOL software, detailed comparative analysis of PCF the differences and similarities between them, and concluded that the applicable condition of various structural fiber, and can provides certain theoretical guidance for design of the different function device based on PCF. Then detailed introduction a nematic liquid crystal E7, and analysis its tunable properties on the temperature and the voltage.Temperature and the voltage continuous regulate LCD photonic crystal fibers are proposed by filling the air hole of PCF core with nematic liquid crystal E7, The effects of temperature and the voltage on PCF transmission properties is studied by the all-vector effective refractive index method and numerical calculation. The results show that dispersion of PCF is reduced due to the existence of LCD, and the dispersion value can adjustable with realize temperature. A high birefringence characteristic of PCF is got using liquid crystal birefringence characteristics through the voltage regulation. These features are valuable for design and application of temperature and voltage modulation PCF optic components.Finally, the properties of long period gratings (LPG) based on PCF is calculated using improved full-vector effective index method, and analysis the relationship between design resonant wavelength and grating period of different structure parameters with PCF. Put forward the long period gratings written into un-doped photonic crystal fiber by co2 laser system, then simulation analysis on the two different structures PCF-LPG's temperature properties by injection LCD in the air hole of PCF. The results showed that big air hole PCF long period grating sensor has high sensitivity. Using electric field characteristics of liquid crystal, plus comb electric field in a core filling liquid of fibers, can formed the long period gratings. The results found that the LPG temperature sensitivity is higher, and can be change of grating period from flexible adjusted electrode distance.