The Implementation Research Of Optical Phase-locked Loop And Optical Modulation System

In recent years,the Internet coming into the era of rapid development,social networks,cloud computing and storage,multimedia and other business need massive data transmission and high concurrency requirements of the implementation which test the capacity of the communication system.Therefore,the optical network,as the core of the general communication network,faces with great pressure and challenge.Now,the large-scale commercialization of 100G technology has started,the technologies beyond-100G being also under urgent research and development.The coherent optical communication,which has a high receiving sensitivity,can realize coherent optical reception in the condition of close to the quantum limit in practice.Based on the reason above,the coherent optical communication becomes the focus of domestic and foreign research institutions,scholars,and communication experts after dozens of years of silence.In the model of coherent optical communication system,transmitting end and receiving end are two important components for the whole system.In the transmitter,the implementation of high order modulation format,the linear amplification of source signals,the stabilization of the bias point and modulation technology are all key points for modulator.At the receiving end,the optical phase locked loop technology is an important guarantee to realise analog coherent optical receiver.Based on coherent optical communication,the main research contents of this thesis and the results obtained are listed in the following:(1)The basic principle of intensity modulation transmitter is studied,the implementation scheme of a prototype designed,performance parameters such as eye diagrams,spectra,bit error rate tested in the experiment.The experimental results show that the eye pattern quality of the modulation signal quality is good,BER=0,EVM=9%at a transmission rate of 10 Gbps.(2)The theory of DP-QPSK modulation is studied.The design scheme of DP-QPSK modulation transmitter is presented.The performance of the prototype is evaluated and analyzed by relevant indicators including the spectrum diagram,eye diagram,constellation,and bit error rate.Compared to the low order modulation format,implementation and test of the DP-QPSK optical modulation system is more complex.From the experimental results,we know that the prototype can realize the modulation rate close to 100G,by means of optical modulation analyzer,eye eyelid clarity and constellation symmetrical are well,BER = 10-12,EVM = 11%,the performance of modulation transmitter is good.(3)The subcarrier balanced optical phase-locked loop structure is studied.The verification design for performance of the referred OPLL above is proposed,the construction of the verification experiment platform and performance testing work completed.The feasibility,reliability and stability of design are verified by the result of comparing manual adjustment frequency locking experiment with automatic adjustment frequency locking experiment.The experimental results show that in a 8GHz wide deviation frequency range,automatic search frequency can be successfully achieved.When the gap frequency range is within 2.4GHz between signal laser and local laser,the frequency control board can quickly reduce it to less than 10 MHz in a few seconds.Once the value falls less than 3MHz,the entire OPLL system will step into the stable state and maintain the state in a long time.(4)The strategy of FPGA+DSP is adopted to realize frequency locking algorithm in the OPLL.The algorithm using traversing search combined with varying step adjustment is proposed,the stable frequency tracking for the OPLL is realized.The experimental results demonstrate that the OPLL system will return the initialization state,automatically,after the failure of frequency tracking happens.Such an action improves the fault tolerance performance of the system.Furthermore,the algorithm shortens the response time of frequency locking,improves the stability of optical phase-locked loop,which has great significance to improve the overall performance of homodyne coherent system.