| Due to its air core material and the principle of total internal reflection light conduction different from ordinary single-mode fiber,air-core anti-resonant optical fiber has become a research hotspot in the field of optical fiber due to its advantages of ultra-low limiting loss,good bending resistance and large mode field area.And it can be well used in optical fiber communication,optical fiber sensing,high-power laser transmission and other fields,with long-term development prospects.In this paper,COMSOL finite element analysis software is used to study and analyze the structural design and optical characteristics of air-core anti-resonant optical fibers.By observing the structure of the anti-resonant fiber designed by previous researchers,the design concept of today’s air-core anti-resonant optical fiber is sμmmarized,and the simulation results are combined to design a new low-loss air-core anti-resonant fiber.The new structure of anti-resonant optical fiber has the characteristics of low loss,large mode field area and low dispersion.(1)The influence of structural characteristics of the structure of the hollow-core anti-resonant optical fiber,such as the thickness of the glass anti-resonant layer,the nμmber of cladding tubes,the size of the core diameter,the inner and outer double cladding structure,and the presence or absence of cladding nested tubes,on the optical performance of the optical fiber was studied by using finite element simulation.The result is that the thickness of the anti-resonant layer is consistent with the calculation;The nμmber of cladding tubes and core diameter of the seven rings are optimal at 40μm.An increase in the nμmber of anti-resonant layers,such as the addition of cladding and nested tube structures,can lead to a decrease in limiting losses.(2)Based on the research of optical fiber structure,a new type of anti-resonant hollow core optical fiber with double-layer nested elliptical structure is designed.Simulation software is used to optimize structural parameters in the design structure.It achieves an ultra-low limit loss of 0.015d B/km at a communication wavelength of 1550nm,which is far lower than that of ordinary single-mode fibers,and even the limited loss compared to other structures of air-core anti-resonant fibers has obvious advantages.And the commonly used communication bands C and L bands have limited losses of less than 1d B/km,so that they can transmit optical signals in different bands.It has excellent bending resistance,and can achieve a loss of 0.2d B/km at a bending radius of 8cm.The high-order mode extinction ratio at 1550 nm reaches 7800.The mode field area of the optical fiber base mode reaches 780μm~2,which can transmit high-power lasers.(3)On the basis of the double-layer nested circle structure,an anti-resonant hollow core optical fiber with special-shaped structure was designed,which was transformed from the encapsulated nested structure of the elliptical to the three-circle cutting structure.The structural parameter optimization through simulation software achieves a low loss of 0.03d B/km at1550nm,which is slightly higher than the limited loss of the double-layer nested circle structure,but it also has obvious advantages.And compared to the two-level nested structure,its advantage is that the structure is relatively simple.It also has the advantage of low-loss transmission in the full communication band,and is better in terms of bending loss,with a loss of less than 0.1d B/km at a bending radius of 8.5cm.The extinction ratio of the advanced mode reaches 1800.It also has the advantages of large mode field area and low dispersion. |
