Design And Experiment On The Circuit Of Fiber Raman Amplifier By TDM Pumping Based On FPGA

As an important part of modern communication network,optical fiber amplifier has always been the focus of research.Fiber Raman Amplifier(FRA)has been widely used in dense wavelength division multiplexing(DWDM)communication systems because of its characteristics such as arbitrary operating wavelength,flexible gain band and distributed amplification.However,the fiber Raman amplifier has its own disadvantages,such as uneven gain and interference noise.In order to solve the problem of uneven gain,the main method is spatial wave division multiplexing(WDM).It can obtain relatively flat gain by pumping multiple wavelengths,but the nonlinear effect between multiple light waves is easy to cause low signal-to-noise ratio,leading to the decline of system performance.In this thesis,the basic principles of FRA and time division multiplexing(TDM)are introduced at first.Then,TDM technology is combined with FRA to achieve flat gain and avoid nonlinear effect between different light waves to improve system performance.According to the theoretical analysis,the experimental structure model of TDM pumping FRA is constructed,and the functions of each part are summarized.Then the drive circuit system of TDM pumping FRA system is designed and experimented in detail.The driving circuit is designed based on the characteristics of the semiconductor laser.The main work and innovation points are as follows:(1)The delay circuit with 300 ms delay is designed to avoid the impact damage caused by the inrush current to the laser.On this basis,the common mode filter network is added to filter out the burr and make the input voltage more stable.At the same time,the protection circuit is designed to protect the laser from overcurrent.(2)A high stability constant current source is designed and realized by means of digital and analog mixing.Compared with the constant current source of pure analog circuit,after adding the digital proportional,integral and derivative(PID)algorithm control part of field programmable gate array(FPGA),the digital circuit has strong anti-interference ability,which can overcome the shortcoming of the random noise caused by external factors in the analog circuit and the current fluctuation.The digital circuit control of pure FPGA will lead to the control algorithm being too complicated,which will easily lead to excessive overshoot.When combined with the analog circuit,the analog circuit will feed back the processed signal to the FPGA,which can reduce the complexity of the control algorithm and achieve higher stability.(3)For metal oxide semiconductor field effect transistor(MOSFET)design,a half bridge drive circuit is added to solve the problem that it can not conduct normally in the circuit based on the bootstrap principle.A power supply module is designed to convert the 220 V AC of the mains into the 5V DC with small ripple and stable voltage,so as to provide a stable 5V power supply and a reference voltage of 3.3V for the circuit in this thesis.(4)Based on the MAX1978 chip design,a high precision laser temperature control circuit(TEC)is realized.The temperature is collected by the thermistor of the laser.Based on the principle that the TEC integrated inside the laser can be cooled and heated,the temperature compensation is realized by using the external analog PID compensation network of MAX1978 to achieve a high precision temperature control.In view of the above circuit design,this thesis builds the actual circuit for experimental test,and carries on the error analysis on the experimental results.The constant current source achieves a high stable output of 0.3%,and the precision of temperature control circuit reaches0.01?.Function tests are carried out on each module of the circuit,including delay circuit,protection circuit,half bridge drive circuit and power module,all of which can meet the design requirements.It lays a foundation for the experimental follow-up work of TDM pumping FRA system.