Characteristics Analysis Of Special Optical Fiber And Grating Based On Magnetic Fluid At 2?m Wavelength Band

Microstructured optical fibers,namely photonic crystal fibers or porous optical fibers,have the advantages of flexible structure design and unique photoconductive properties that are not found in general optical fibers and are widely used in the fields of optical fiber communication,optical fiber sensing and fiber laser.As a new type of functional material,magnetic fluid nano-functional material has many excellent optical properties,such as refractive index modulation,which can change its own refractive index under the influence of external magnetic field.Due to the prominent optical properties of microstructured optical fibers and magnetic fluids,the combination of microstructured optical fibers and functional materials is a new trend.This article mainly does the following work after referring to a large number of documents:(1)Three kinds of microstructured optical fibers are designed,it is ten-hole micro-structure optical fiber,four-hole micro-structure optical fiber and improved four-hole micro-structure optical fiber.The ten-hole microstructured optical fiber structure is as follows:four perpendicularly arranged circular air holes symmetrical about the center of the circle are respectively arranged on two sides of the core,two large oval air holes filled with magnetic fluid are arranged in the Y direction,the ten holes surround the fiber core.The four-hole microstructured optical fiber structure is as follows:there are two pairs of oval air holes perpendicular to each other in the optical fiber cladding,two larger oval air holes in the vertical direction and two smaller oval holes filled with the magnetic fluid in the horizontal direction,a rectangular fiber core is formed surrounded by the four holes.(2)The finite element simulation software COMSOL was used to simulate the birefringence of the fiber in the 2?m band,confinement loss characteristics and the effective refractive index difference in the X and Y directions.Through the analysis of the first two kinds of optical fiber structures,the four-hole micro-structured optical fiber with better performance is finally obtained.The simulation results show that the mode birefringence of the optical fiber structure can reach the order of 10-3 and the confinement loss is less than 10-11 order,achieving the design goals of high birefringence and low confinement loss at the same time.(3)According to the effective core refractive index of the improved four-hole microstructured fiber,two kinds of microstructured fiber gratings are designed,it is polarization Bragg grating and phase shift fiber gratings.The effect of the grating length,refractive index modulation depth,modal birefringence on the grating properties is analyzed in detail.Finally,the relationship between the external magnetic field and the center wavelength of the grating is obtained by the relationship between the external magnetic field and the refractive index of the magnetic fluid,the relationship between the refractive index of the magnetic fluid and the effective refractive index of the core,and the relationship between the effective refractive index of the core and the central wavelength of the optical fiber.