Study On New Structure Few-mode Optical Fiber With Low Bending Loss

With the rapid development of optical fiber technology and the increasing popularity of optical fiber to the home,in actual use,because optical fibers are often laid in narrow spaces and comers of pipes,the bending radius of optical fibers should be reduced as much as possible to save space.However,the existing bending-resistant optical fibers cannot simultaneously satisfy the characteristics of superior bending-resistant performance,simple structure,and compatibility with ordinary G.652 optical fibers.Therefore,in this paper,in order to realize low bending loss and stable single-mode transmission under the condition of small bending radius,based on the fiber structure of ordinary step-index fiber,through inserting the inner cladding and high refractive index defect layers between the core and the outer cladding,we proposed novel few-mode fibers with loss bending loss and single mode transmissions.Comsol software is utilized for theoretical simulations.The main work completed is as follows:Firstly,a five-layer structure few-mode fiber is designed,and a systematic analysis is carried out for the loss characteristics of LP01 and LP11 modes.The results show that the structural parameters of the optical fiber(the refractive index difference between each layer and the outer cladding,the width of each layer)will affect the bending loss of the two modes.Structural parameters are optimized to guarantee the low bending loss of fundamental mode and filter the higher order modes,meanwhile the fiber is optimized to match with ordinary single mode fibers.In wavelength of 1250nm-1650nm,when the bending radius is 7.5mm,the bending loss of the LP01 mode is always less than 5.6 ×10-3dB/m,when the bending radius is 15mm,the bending loss of the LP11 mode is higher than 1.3dB/m;when the new fiber is spliced with the ordinary G.652 fiber,the connection loss is less than 6.05×10-2 dB.In order to further improve the bending loss performance,a six-layer structure few mode fiber is designed.The influences of structural parameters on the bending loss of LP01 and LP11 modes are also analyzed,and a set of optimal structural parameters is determined;when the bending radius is 7.5mm,the bending loss of the LP01 mode is lower than 2.1×10-3dB/m,when the bending radius is 12mm,the bending loss of the LP11 mode is higher than 2.06dB/m;the connection loss with G.652 fiber is lower than 5.62×10-2 dB.The simulation shows that the bending loss characteristic of the six-layer structure fiber is better than that of the five-layer structure fiber.Finally the five-layer structure optical fiber was selected to be manufactured.The instrument was used to measure the bending loss and connection loss of the optical fiber.In addition,the optical fiber was applied in the EPON network of a substation.The practical test results met the requirements.