Numerical Simulation On Photonic Crystal Fiber Gratings And Couplers

Nowadays, with the tremendous progress on the techniques and crafts of the Photonic Crystal Fiber (PCF), a number of researches have been focused on how to further design the in-PCF devices in order to meet the need of today's communication and sensing. Taking the advantages of the unique optical properties of PCF such as abnormal dispersion, controllable modes and polarization, this work focuses on the analysis and design of the in-PCF devices such as fiber gratings and fiber couplers.Firstly, the analytical method of PCF is derived. The guiding mode property can be obtained by employing the plain-wave expansion method on solving the main equation of waveguide, which reveals the physical essence that the monochromatic wave guiding within the photonic crystals can be divided into more than 1000 freely-translational plain waves. This approach simplifies the process of simulation. In addition, the method to obtain the interaction of different modes is the mode-coupling theory. Because there are many in-fiber devices using the mode coupling properties, such as the fundamental mode coupling with the leaking mode, forward and backward coupling, the mode-coupling theory can be applied to simulate and design these devices.Secondly, the simple method for calculating the resonance spectra of the PCF gratings is proposed. By using the effective index method, an effective step-index fiber substitutes for the PCF in the calculation of the fundamental mode and higher order modes coupling. The method is valid since the mode coupling resonances calculated this way match closely to experimental results for both the fiber Bragg grating and the long period grating.Finally a novel PCF coupler is designed as the air-silica PCF with one hole injected with refractive index matching liquids, where coupling occurs between the fundamental mode of PCF and the modes of liquid hole. The coupling length is achieved as short as 1mm. It is versatile for application as the optical properties can be controlled by liquid index, temperature and inject position. The higher order mode couplings are also achieved.