Research On Digital Signal Jitter Measurement Technology Based On High Speed Optoelectronic Analog-to-Digital Conversion

Optical fiber communication technology has been widely used in various fields and is one of the most critical communication technologies in modern information transmission.In an optical fiber transmission system,the digital signal jitter is an important parameter to judge the transmission quality of the system.Especially for an encrypted optical fiber transmission system,the jitter parameter will seriously affect the performance of the encrypted transmission.At present,the test of jitter performance mainly relies on imported instruments.In this dissertation,according to the requirement of 2.5-Gb/s digital optical signal jitter measurement,the core technology of optical sampling and electrical quantization is proposed,the algorithm and software of eye diagram recovery and jitter measurement are designed,the prototype of eye diagram measuring instrument is developed,and the digital optical signal jitter measurement of2.5-Gb/s and 10-Gb/s SDH,and 1.25-Gb/s Gigabit Ethernet is completed.The main research content completed is as follows:1.Based on the photoelectric analog-to-digital conversion principle of optical sampling and electrical quantization,a digital optical signal jitter measurement system is proposed,which realizes the direct sampling of intensity-modulated digital optical signals in the optical domain,considering the advantages of broadband and high speed of optical sampling and the characteristics of high quantization bits of electrical quantization.According to the periodicity and repeatability of the high-speed digital optical signal,the principle of equivalent random sampling is adopted to design optical sampling.The optical sampling rate is reduced to the level of the signal rate,which not only satisfies the eye diagram recovery and jitter measurement of the high-speed digital optical signal but also satisfies the matching of the rate and bandwidth of the subsequent electrical quantization chip.2.The analog-digital conversion of optical sampling and electrical quantization is composed of optical sampling,clock and electrical pulse generation,optical pulse broadening,photoelectric conversion,and electrical quantization.Under the control of the bias circuit,the Li Nb O₃ MZM modulator works with the amplitude of the sampling electrical pulse to complete the sampling of digital optical signal in the state of high extinction ratio and obtains the sampled optical pulse sequence.Then the optical pulse broadening is realized through the superposition of multi-channel optical fiber delay and photoelectric conversion,which matches the bandwidth and rate of the subsequent electrical quantization chip.The cost performance of optical sampling and electrical quantization is improved.Optical sampling and electrical quantization are synchronized by optical fiber transmission delay matching.Aiming at 2.5-Gb/s NRZ digital signal of SDH,the relationship between sampling accuracy and sampling pulse width is analyzed theoretically.The optimized design parameters are 80-ps sampling optical pulse width,1.5-GHz repetition frequency,and matching photoelectric conversion and electrical-quantization circuits.3.The digital signal period is reconstructed with the known digital optical signal rate and the precise sampling cycle time based on the random equivalent sampling principle.The clock recovery algorithm is proposed based on the eye diagram’s open area.The algorithm has the characteristics of fast convergence,high efficiency,and high precision,and the high-precision clock and eye diagram are obtained through multiple iterations.The software of clock and eye diagram recovery is developed,and the software of jitter analysis and Q parameter test is designed,including the histogram and Q parameter of digital optical signal jitter,which can obtain the peak-peak value,mean square value,average value of jitter and bit error rate.4.The digital optical signal jitter test principle prototype is designed.The development of various functional modules,software,and principle prototype are completed,including a set of 19-inch 3U chassis hosts and a set of eye diagram recovery and jitter measurement software.The technical problems such as Li Nb O₃ MZM modulator’s bias control and drive circuit,sampling pulse generation circuit,optical pulse broadening,and optical delay matching are solved.The experimental test system has been established for the eye diagram and jitter recovery of 1.55-μm band 2.5-Gb/s SDH digital optical signals.The measurement results of the principle prototype is compared with that of the real-time digital oscilloscope.The experimental results show that the prototype has a pretty good test performance and can effectively monitor the digital signal jitter,Q parameter,and bit error rate and meet the test requirements of the optical fiber transmission system.5.The engineering application research is carried out based on completing the principle prototype.Eye diagram and jitter measurement for 1.31-μm and 1.55-μm band digital optical fiber transmission systems including 2.5-Gb/s and 10-Gb/s SDH,and 1.25Gb/s gigabit Ethernet,and an optical fiber transmission device that can be used in secure optical fiber communications are performed by using the principle prototype.The digital optical signals with different communication bands,rates,and signal formats are tested.The test results show that the prototype can accurately measure the eye diagram and jitter characteristics of digital optical signals of transmission equipment,provide accurate criteria for the performance of optical modules of core devices,and meet the needs of an encrypted optical fiber communication system for direct measurement of digital optical signals.