Study On All-solid Photonic Bandgap Fiber And Long Period Grating

Due to easier analysis, splicing and doping, all-solid photonic bandgap fiber bears potential application in the area of sensing, communication and so on, leading to the importance of research on the fiber. The structure of the paper is as follows:firstly, we show the basic background about photonic crystal fiber, especially photonic bandgap fiber, such as development, characteristics and applications, and the relevant background about long period fiber grating is also provided. Then the modal characteristics are analyzed through some theoretical analysis methods. Next we focus our sight on the fundamental characteristics about supermodes and photonic bandgap in all-solid photonic bandgap fiber, on long period fiber grating and on cascaded long period fiber gratings inscribed in the all-solid photonic bandgap fiber with low bend loss. The main contents are shown as follows:1. We design the band structure in all-solid photonic bandgap fiber. Based on tight-binding model, we analyze the influence of doping on band structure. Then new types of fiber structures are designed, whose claddings consist of low-index rings and new high-index rods and who have unique band structures. The broadband only higher order mode propagation is finally achieved through modulating the refractive index of the fiber core. The validity of our design is confirmed by comparing the confinement loss and bend resistance of different fiber structures.2. The long period fiber gratings are fabricated in the all-solid photonic bandgap fiber with low bend loss by means of point by point inscription using carbon dioxide laser. We identify the higher order resonances by phase-matching condition. Based on the coupled mode theory the theoretical model is set up to understand the coupling mechanism of the fiber gratings. The simulated evolution of light intensity and grating spectrum agree with the experimental results well. In addition, the temperature responses of the fiber gratings are studied in both theory and experiments. 3. Mach-Zehnder interferometers are realized by cascaded long period fiber gratings written in the all-solid photonic bandgap fiber with low bend loss through point by point inscription using carbon dioxide laser. The influence of beam length on interference fringe spacing and contrast are analyzed in both theory and experiments. In the end, we give a brief illustration of the temperature responses of the interferometers.