Research On Offset Control Technology Of Electro-optic Modulator For Optical Sampling And Quantization In A/D Convertor System

The development of information technology puts forward higher requirements for ADCs(Analog-to-Digital Converters)with higher bandwidth,faster speed and higher precision.In order to solve the problem that the sampling rate of traditional electronic ADCs is difficult to be further improved,optical ADCs begin to receive attention.Among them,the optical-sampling ADC with electro-quantization has attracted great attention because it can simultaneously utilize the superior performance of optical information processing and the mature technology of electronic quantization.As the core device of optical-sampling ADC,electro-optic modulator plays an important role in the whole ADC system.It has very important application significance and practical value to solve the drift problem of modulator bias point.To solve the problem,this paper studies bias point control technology of the MZ electro-optic modulator and designs a bias point control system of MZ electro-optic modulator based on FPGA and DSP,which lays a theoretical and technical foundation for the development of the optical-sampling ADC,and has important engineering and scientific significance.The paper first introduces the architecture and working principle of optical sampling ADC,analyzes the importance role of the modulator in the system and the necessity of controlling the drift of the operating point of the modulator.Secondly,this paper discusses the composition and working mechanism of optical sampling ADC,analyzes the related theory of the electro-optic modulation.The paper also analyzes the theoretical model of the MZ electro-optic modulator and the drift phenomenon of the working point,then proposes a control scheme for the modulator bias point based on the harmonic ratio of the disturbance signal.Then the hardware control system of modulator based on FPGA + DSP is designed,and the hardware design and Simulation of each module are completed.Then the code of each module is compiled and verified by simulation based on Verilog language,and the processing algorithm of harmonic spectrum data is designed based on DSP.Finally,the test platform of the modulator bias point control system is built,and the performance of the control system is tested and verified.The experimental results of the working point control system of MZ electro-optic modulator show that when the working point of the modulator is set at the orthogonal point,the output optical power of the modulator is stable at-3.2dB,the fluctuation range is not more than 0.15 dB,the first harmonic of the output signal is stable at-50.5dB,and the fluctuation range is not more than 0.6dB.The experimental results show that the system can stabilize the working point of the modulator at the orthogonal point,thus realize the linear modulation of the electrical signal.The research work of this paper has important engineering and scientific significance for the development of modulator control technology.