A High-precision Method For Timing Jitter Measurement Based On Self-reference Source

With the wide application of ultra-fast laser technology,it is fairly important to measure the timing jitter characteristics of ultra-short laser pulse with high accuracy.At present,timing jitter has become a core parameter to measure the performance of low-noise systems such as optical combs,low phase noise laser,microwave photon radar and the like.Thus,it has become an important research task with high application values to accurately measure the timing jitter.The traditional direct detection method is limited by the local noise of the microwave oscillator or the noise of the photodetector,resulting in low measurement accuracy,which makes it impossible to achieve high-precision measurement of extremely low timing jitter parameters in practical applications.Optical measuring methods,such as optical heterodyne,optical cross-correlation and so on,are complicate and have relatively high requirements on both the reference source and measured source.In order to realize the measurement of attosecond timing jitter effectively,this paper studies a method of timing jitter measurement with high precision and no reference source,which is mainly based on the long fiber delay line technology and the optical carrier interference technology to achieve the ultra-high precision measurement of timing jitter.Under the premise of high measurement accuracy,it does not need two similar sources to be measured,which greatly reduces the complexity and difficulty of the measurement system.In this paper,theoretical research and simulation are carried out for this method.The following is the main research work completed:1.In this paper,to tackle the problems that the theoretical model of the high-precision reference-free measurement system is not clear,and the core problems are not explained clearly,the noise theory and timing jitter calculation process of the existing measurement system are presented and deduced in detail based on the transmission equations:The power spectral density of voltage noise obtained by the measurement system is transformed into the power spectral density of frequency noise,then to the power spectral density of phase noise and timing jitter.In addition,in the process of analyzing the noise theory,the mechanism of artifact peak,which is one of the core problems of the system,is clarified,making the whole system model and the calculation process of timing jitter clearer and understandable.2.The results of the simulation system show that the noise floor at 10 MHz carrier frequency offset by 10 MHz measured by simulation is7.74×10^-15fs²/Hz（equivalent to-228 d Bc/Hz at 10 GHz carrier frequency）,and the total RMS timing jitter from 10 k Hz to 10 MHz is 244 as,theoretically proves that the measurement system can achieve higher measurement accuracy.3.In order to solve the problem of excessive loss at the fiber interferometer and the delay between the reference signal and the signal to be measured in front of the photodetector,this paper optimizes the system structure significantly.In this paper,the filter subsystem is canceled,and the optical signal output from the acoustooptic modulator is directly used as the reference signal and combined with the original signal to be measured,and then directly enters the signal extraction part.Besides,two polarization maintaining band-pass filters in the interferometer part and the signal extraction part are used to filter the reference light and the light to be measured,which greatly reduces the loss（15 d B）of the measurement system.In addition,a delay adjustment system（fixed optical fiber delay line）is added before the signal measurement part of the new measurement system to ensure that the reference light and the light to be measured achieve the best beat frequency at photodetector.4.In this paper,the second difference frequency combs model is found and put forward in the process of simulation.At a specific repetition frequency,the second difference comb is used as the mixing comb after filtering,which can weaken the influence of the environmental noise and acoustooptic modulation noise on the reference light in the optical fiber interferometer in advance before the signal is amplified,and it can reflect the jitter information more theoretically,which makes the mixing result more reliable.5.In order to better provide theoretical guidance for subsequent engineering applications,this paper compares and simulates some core parameters of the measurement system,and on this basis,summarizes the optimization scheme of the system performance.The simulation explores the relationship between the timing jitter measured by the system and the length of the fiber delay line,the bandwidth of the optical band-pass filter,the type of optical band-pass filter and the electrical band-pass filter,and the best measurement system parameters are selected by comparing the accuracy of each measurement timing jitter,which also provides theoretical guidance for optimizing the measurement system structure and improving the measurement accuracy in subsequent projects.