Research On Key Technologies Of Multi-core Optical Fibers And Their Devices

In order to break through the capacity limit of the existing single-mode optical fiber transmission system and meet the needs of large-capacity high-speed optical communication,space division multiplexing technology based on multi-core optical fiber has made great progress in recent years.In the aspect of sensing application,the appearance of multi-core optical fiber has injected new blood into the optical fiber sensing technology.As a new sensing medium,multi-core optical fiber greatly enriches the functions and types of optical fiber sensors.However,many key technical problems still need to be solved in the practical application of multi-core fiber.The first problem is the design and manufacture of multi-core fiber.For weakly coupled multi-core fiber,cross-talk between cores is a difficult problem in the design and preparation.The second problem is the design and manufacture of the key integrated devices of multi-core fiber.The multi-core fiber cannot be used in the field of large-capacity high-speed optical communication or sensing without the support of various functional key devices.In this paper,multi-core fibers and their key integrated devices were studied,and two types of multi-core fiber were designed and fabricated.Based on the existing multi-core fiber in the laboratory,several key integrated devices including multi-core fiber fan-in/out device,fiber end reflector and connector were developed,which solved the problem of limited application of multi-core fiber to a certain extent.This research focused on multi-core fiber and key integrated devices,and carried out research in the following aspects:Firstly,based on the design and manufacture of multi-core fiber,the structural parameters of multi-core fiber,such as core distance and core refractive index profile,were optimized based on the key performance parameters of multi-core fiber such as cross-talk between cores,mode field area and cut-off wavelength.This paper introduced two kinds of techniques for manufacturing multi-core fiber by hole-drilling method and stack method,and used stack method to produce four-core single-mode fiber and 19-core single-mode fiber with high fiber core density.Secondly,several kinds of key integrated devices including multi-core fiber fan-in/out device,connector,modular fan-in/out device and fiber end reflector were studied.In order to solve the problem of independent-separation connection of each core of multi-core fiber,multi-core fiber fan-in/out devices were designed and fabricated based on the construction principle of"vanishing core".The materials required in this method,including transition multi-clad fiber and porous quartz tube,are optimized.Multi-core fiber fan-in/out device including four core fiber and 19 core fiber has been successfully prepared.The average insertion loss of a 19-core fan-in/out device is less than 1.6 d B,and the average crosstalk between cores is less than-54.8d B.Aiming at the problem of connection of multi-core optical fiber,connectors with low insertion loss and high return loss performance were developed and combined with fan-in/out device to form a modular integrated device,and a convenient mirroring test method for this device was proposed.To solve the problem of optical path coupling of different cores,the reflectors prepared at the end of multi-core fiber were proposed.These reflectors have flexible structure design and simple preparation method,which can realize the low loss series coupling of any two core channels of multi-core fiber,and have important applications in the field of fiber sensing.Finally,two kinds of multi-core fiber sensors were constructed by using the above key integrated devices.Firstly,fiber Bragg gratings were fabricated on seven core fiber and diagonal core reflector was fabricated on the fiber end.The diagonal core reflector connects two grating paths on the diagonal core of seven-core fiber in series,and finally realizes the bending sensing with double sensitivity.The maximum curvature sensitivity is 225.9 pm/m^-1 within the curvature range from 0 to 6.9 m^-1.Secondly,the fiber Bragg gratings and F-P cavity were integrated in the seven-core fiber,and the wedge reflector was prepared at the fiber end.Finally,the three-parameter sensor of bending,axial strain and temperature was realized at the same time,so as to realize the multi-parameter high-precision sensing in the complex environment.These two kinds of sensors are just examples of applications of multi-core fibers and their key components.In fact,with the continuous development of multi-core fibers and their key integrated components,their combined applications can open a door to a new world with rich and diverse possibilities.