Research On Adaptive Control Technology Of MZM Bias Point

With the development of optical fiber communications,Mach-Zehnder modulators(MZM)are used more and more widely.As a key device in the optical fiber communication system,MZM has the advantages of high modulation rate,low transmission loss,low driving voltage and small frequency chirp.However,MZM will have the problem of operating point drift during using,which will affect the modulation system.In order to solve this problem,this article mainly conducts the following research on the bias operating point control of MZM:(1)Introduce the principle of electro-optic effect,from which leads to the concept of half-wave voltage,and elaborate on the working principle of MZM and the position of the best operating point in different modulation formats.Starting from the digital modulation technology,the optical modulation principles of the four modulation modes of OOK,BPSK,DPSK,and QPSK are analyzed respectively,and the simulation of the four modulation modes is realized on the Optisystem platform.It can be seen from the simulation results that BPSK and QPSK have better modulation performance,and the communication performance is relatively stable,but the QPSK modulation and demodulation process is more complicated,so BPSK modulation is more suitable for optical communication systems.(2)Introduce the phenomenon of DC operating point drift,and propose two methods to lock the DC operating point.By comparing the DC power detection method and the pilot signal method,the pilot signal method is finally selected as the method of locking the DC operating point.Through the analysis of the principle of the pilot signal method,the ratio of the first harmonic to the average photocurrent is selected as the MZM bias control scheme.(3)Complete the design of the MZM operating point bias voltage control circuit,and complete the simulation and simulation experiment tests on the Simulink platform to verify the feasibility of the scheme.Build a simulation platform on Simulink,when bias control is adopted,the output phase is significantly improved;build an optical communication system test platform with a communication rate of 10 M,and it can be seen from the eye diagrams before and after the filter control that after the bias operating point is controlled,the communication The effect is greatly improved,and the system works stably.Through multiple measurements,it can be known that the output average optical power fluctuates up to ±5% after the bias point is controlled,which has a good control effect.