Research And Implementation On Bias Control Technology Of Electro-Optic Modulator

Featuring the advantages of high transmission frequency and large operating bandwidth,electro-optic modulators have become a widely used device in Radio over fiber system.As a key device of optical signal generation and processing,the stability of its operation directly or indirectly affects the quality of the transmission signal.Therefore,the stable control of the DC bias operating point of the electro-optic modulators has attracted more and more attention.By investigating the research status and development trend of electro-optical modulator bias control in domestic and foreign markets,utilizing the STM32 series development boards,and combining with embedded technology,a software and hardware combined bias control system is designed in this paper.This paper studies and realizes the control technology of the DC bias operating point of the commonly used electro-optic modulator.The specific work is as follows:Firstly,the composition and application scenarios of the analog optical link are analyzed,and the basic composition,working principle and application scenarios of modulators made of several lithium niobate materials are introduced.This paper uses an electro-optical modulator made of lithium niobate as a material.Through discussing and analyzing the influence of the drift of the DC bias point on the system link,the corresponding bias control technology is studied.Aiming at the stable control of the bias control technology,this paper briefly analyzes two basic bias control methods: one is the DC detection method,and the other is the pilot frequency method.Theoretical analysis and mathematical derivation are carried out for both.Aiming at the advantages of large bandwidth and large power distribution range of linear frequency modulated signal(LFM),a bias control method based on LFM is designed and compared and analyzed with the traditional pilot frequency method.Aiming at the application scenario of polarization multiplexing dual parallel Mach-Zehnder modulator(PDM-DPMZM),a bias voltage control scheme based on six pilots is designed,and theoretical derivation,simulation analysis and algorithm analysis are carried out.Theoretical derivation is carried out for the frequency conversion technology with high spurious free dynamic range,and the link simulation verification is built based on the optical simulation platform.A general implementation scheme of bias control technology is proposed based on STM32,which mainly includes two parts: the design of hardware circuit and the design of software logic algorithm:1.For the hardware part of the peripheral circuit,the electronic drawing software Altium Designer is used to drawing the original circuit diagram and PCB design of the hardware circuit such as the photoelectric detection module,I/V amplification module,low-pass filter module,DC voltage generation module,and voltage coupling module..The functions of each module are simulated and verified by electronic design automation software NI Multism.2.For the software design part,based on the C language,it is equipped with the control board of the STM32F103 series.Using ARM’s development software MDK5 to complete the code writing and debugging.These include the pilot signal generation algorithm,the DC sweep voltage generation algorithm,the signal detection algorithm,the Fast Fourier Transformation(FFT)processing algorithm and the algorithm for finding the locked operating point.Finally,through the built test platform,the bias control system in this paper is tested initially,and the control of the minimum operating point of the commonly used electro-optic modulator is realized.After the joint debugging of hardware and software,the expected technical design index is achieved,and the problem of bias point drift of the electro-optic modulator is solved.