Research On Key Technologies Of Few Mode Optical Fiber Communication System Based On Mode Division Multiplexing Technology

With the large-scale application of 5G technology,autonomous driving,cloud computing and other high-tech also flourish,society has put forward higher and higher requirements on the communication network.With the increasing maturity of wavelength division multiplexing(WDM)and polarization division multiplexing(PDM)technologies in single-mode fiber systems,the capacity of traditional single-mode fiber-based communication networks is about to reach the Shannon limit.To break through the theoretical Shannon limit,space division multiplexing(SDM)technology is currently a technology with great development potential to increase optical fiber transmission capacity.Mode division multiplexing(MDM)is a kind of space division multiplexing technology,thanks to the easier design and preparation of few-mode fiber,it has great potential and value for development.For signal damage such as mode crosstalk,mode-dependent loss and differential mode group dispersion introduced in a few-mode fibers,in addition to special few-mode device designs such as strong coupling fibers,mode converters,etc.,a more common solution is to add MIMO at the receiving end Equalization algorithm.Under laboratory conditions,the length of the few-mode fiber is limited,and the cost of the few-mode devices is too high.The use of existing experimental equipment for the longest possible few-mode transmission experiment requires a fiber loop.The main contents are as follows:(1)The few-mode devices,signal impairments,and MIMO equalization algorithms in the Mode Division Multiplexing system are studied.A MIMO Volterra algorithm for intensity modulation and direct detection of Mode Division Multiplexing systems is proposed.The distance is 24km,the signal rate is 10G Baud,and the simultaneous transmission of LP₀₁ and LP_11a modes is realized.When the received optical power is greater than-15d Bm,the bit error rate of the mode LP_11a after using the MIMO Volterra equalization algorithm is improved by an order of magnitude(more than 10 times)compared with the Volterra equalization algorithm alone.(2)A two-mode multiplexing simulation system is built,and the transmission rate is2×20Gb/s and the distance is 48km.An experimental system for direct detection of intensity modulation by mode division multiplexing is built.The signal modulation format is PAM4,the transmission rate is 2×20Gb/s,and the transmission distance is 24km,mode LP₀₁ and mode LP_11a are simultaneously transmitted.And realize the signal modulation format is PAM4,the transmission rate is 2×20Gb/s,the transmission distance is 24km mode LP_11a and mode LP_11b transmit at the same time.(3)Optimized the design of the optical fiber loop to achieve a loop loss of less than 6d B.Completed the timing control system design matched with the loop system.Developed waveguide devices for few-mode fiber loops.Build a few-mode optical loop transmission system.Implements input mode LP01,signal modulation format PAM4,rate of 20Gb/s,the cycle twice fiber loop(48km)transmission.And realized the input mode is LP₀₁ and mode LP_11a,the signal modulation format is PAM4,the rate is 2×20Gb/s,the optical fiber loop cycle(24km)transmission.