Study On The Sensing And Coupling Characteristics Of Dual-Core Photonic Crystal Fibers

It is known that dual-core photonic crystal fiber(PCF) is the fundamental structureof many important optical devices. PCFs are divided into two different kinds of fibers.The first one, index-guiding PCF, guides light by total internal reflection. The secondone uses the photonic band-gap effect to guide light. In this thesis, we will study them,especially, we will focus on the coupling and temperature sensing characteristics.We propose a new type of dual-core PCF with varying air holes based on totalinternal reflection. The effective index, coupling length, group velocity dispersion(GVD) and inter-modal dispersion (IMD) are evaluated by using a vector finite elementmethod. Then, we change the diameter d of the small air hole between the two cores toanalyze the effects on the coupling length, GVD and IMD. We find that the couplinglength changes with d,and an ultra flattened zero GVD in the wavelength range of0.9to2.0μm can be realized. We also investigate its application on fiber couplers.The decoupled characteristics and the mechanism of surface modes in hollow dual-core photonic band-gap PCF are studied. We introduce a silica ring at the core-claddinginterface to analyze its effect on the effective index and the core-confined energy. Wefind that we can control the surface modes by adjusting the normalized thickness of thesilica ring, so that we can change the decoupled wavelength. The influence of the coreradius on the surface modes and the decoupled wavelength are studied too. The optimalrange of core radius that is free of surface modes is from0.9Λ to1.05Λ when thenormalized thickness of the silica ring is set to1.A hollow dual-core PCF filled with liquid sensitive to temperature is analyzed, andthe coupling properties as well as the IMD are investigated. We find that with theincrease of the wavelength, the coupling coefficient will decrease first and then increasefor a certain temperature. Especially, the zero IMD can be achieved at the minimumcoupling coefficient. Moreover, by adjusting the temperature and/or the structureparameter d/, we can realize zero IMD in an extremely wide wavelength rangeincluding both1.31μm and1.55μm.