Research On The Confinement Loss And Dispersion In W-type Photonic Crystal Fibers

Photonic crystal is a new type of optical materials; light can be almost perfectly controlled in it. Photonic crystal fiber (PCF) is a new generation of optical fiber which is developed based on photonic crystal technology, and it has a lot of properties, for instance, the endlessly single-mode, high birefringence and other properties. And so it has a very broad application prospects in the fiber laser, fiber sensor, super continuum generation, antennas and photonic crystals optical integrated circuits and other fields.In recent years, an optical fiber with a long wavelength cut-off function——depressed cladding optical fiber is developed. Because its refractive index profile shape is similar to the letter "W", it is also known as W-type fiber. This fiber has a specific filtering function, and so it is one of the most popular research topic of the field of optoelectronics. But the performance of conventional W-type optical fiber is limited by manufacturing process on the existence of limitations and not arbitrarily bending problems. Based on the existing many shortcomings of the W-type erbium-doped fiber, by using of the structure of photonic crystal fiber, this paper present the design and analysis of a novel W-type photonic crystal fiber. The theory studies and the numerical simulation are discussed, mainly including the following:1. The basic principles of finite element method is discussed deeply, and the simulation steps based on the finite element method is analyzed. Then we research on the perfectly matched layer (PML) and optimize the choice of the PML.2. Based on the study and analysis of the W-type fiber and the common photonic crystal fiber, this paper presents a new type of W-type photonic crystal fiber. And it is simulated by using the finite element method. The results show that the diameters of the holes of the first layer and the ratio of hole diameter to pitch have a great influence on the fiber loss. By selecting reasonable optical parameters, the W-type photonic crystal fiber has a greater difference with the common PCF in the confinement loss and dispersion for 600nm to 1800nm band.3. A W-type photonic crystal fiber is created by using the post-processing techniques of the PCF, including controlled hole collapse and taper.4. We measure the confinement loss of the W-type photonic crystal fiber: A setup based on supercontinuum light source is used for measuring the confinement loss of the W-type PCF. The measured confinement loss is in agreement with the simulation results, which proves the filtering properties of the fibers.