The Design Of A Tunable Sagnac Filter Of Magnetic Control Based On Photonic Crystal Fiber Grating

FBG Fiber Bragg grating sensor is developing rapidly in recent years. It’s a new kind of optical fiber sensor. FBG Fiber Bragg Grating sensor has many remarkable characteristics, such as:it is not easy to be influenced by electromagnetic, it is easy to be combined with waiting external test parameters, and so on. Because of its sensing properties and structure of the system, FBG Fiber Bragg Grating sensor is being used and studied very extensive.Fiber Bragg Grating Sagnac filter is a common fiber-optic sensor. In previous, Sagnac filter couldn’t change its value if the fiber couplers and fiber grating type and length have been selected. It can not be modulated transmission of light transmission characteristics. If we want to change the scope of filter, we have to re-build the system. That is somewhat cumbersome and not always to the introduction of the insertion loss, filter characteristics affect the accuracy. If we use a tunable filter, Sagnac filter can make changes in a certain range, ultimately achieving the aspects of the center wavelength can be tuned to achieve, and is the filter characteristics of the Sagnac filter is more flexible.In this paper, we will study FBG Fiber Bragg Grating Sensor, Photonic Crystal Fiber Grating and Magnetic Fluid. And based on their theories, we will at last study them as the whole. Magnetic field can change the refractive index of Magnetic Fluid, so we based this theory put forward a kind of tunable Sagnac Filter of Magnetic Control.This paper studied the various characteristics of fiber grating analysis, and proposed a design idea about magnetic fluid combined with the photonic crystal fiber grating. The essence of this design idea is filling magnetic fluid into the photonic crystal fiber grating cladding. When the applied magnetic field changes the refractive index of magnetic fluid, photonic crystal fiber grating cladding of the equivalent refractive index will change too. So that, the fundamental mode photonic crystal fiber crystal fiber grating and cladding mode coupling resonance change summit, at the same time, it will change the photonic crystal fiber grating reflection spectrum. And we combine with this kind of photonic crystal and Sagnac filter. Because Sagnac filter’s output spectrum is based on photonic crystal fiber Bragg grating’s reflection spectrum, so when the spectrum of photonic crystal fiber grating’s changing, the Sagnac filter’s output spectrum will change too, that is what we say, it achieves the purpose of magnetic tuned Sagnac filter.The main research contents of this paper include:(1) Study of the characteristics of photonic crystal fiber grating; Study of the relationship between its own structure and properties.(2) According to the model of fiber grating Sagnac filter and characterization of photonic crystal fiber grating Sagnac filter transmission characteristics and to find a suitable for the photonic crystal fiber grating paper.(3) Combining with the photonic crystal fiber grating filled with magnetic fluid and Sagnac filter to be a new tunable Sagnac filter which could be tuned with magnetic. Using an external magnetic field to tune the wild of Sagnac filter’s output spectrum, and study of its filtering range and related properties.