Research On Linear Optical Sampling Used In Space Time-Frequency Transfer Transmission

The advancement of science and technology is usually accompanied by the improvement of measurement accuracy.As a physical quantity of great antiquity,time and its precision has been continuously improved with the development of human civilization.At present,the stability of optical clock in the laboratory has reached the order of 10-19.The high-precision clocks play an important role in areas such as basic physics research,precision measurement,positioning and navigation,deep space exploration,and high-speed communication.In order to apply high-precision clocks in these fields,the research on transmission of time(frequency)signals is very important.Among them,the scheme of time-frequency transfer through free-space links has always been the focus of research at home and abroad because of its long transmission distance,wide coverage and convenient networking.The space time-fr equency transfer scheme based on microwave technology is the earliest and most mature,and its daily stability can reach 10-15 orders.The subsequent development of pulsed laser-based time-frequency transfer technology has further improved the accuracy and stability.However,the precision of this scheme cannot meet the requirements of transfering ultra-high precision clocks.With the maturity of femtosecond optical frequency comb,a technology called linear optical sampling has been applied to the space time-frequency transfer experiment,which based on the interference between two optical frequency comb.The stability of experiment used this technology is reached 10-19 orders,and this means that the linear optical sampling presents great potential in the field of space time-frequency transfer.In this paper,the linear optical sampling technique is studied for the application background of long-distance high-precision space time-frequency transfer.The relevant research results are applied in the actual space time-frequency transfer experiment,and good experimental results are obtained.The main contents of this paper include the following four parts:First,in order to meet the requirement of linear optical sampling for high signal-to-noise ratio of output signals,a high performance balanced detector was designed.By analyzing the structural configuration of the balanced detector and theoretically simulating its output noise,a high-performance balanced detector with a bandwidth greater than 100MHz,an equivalent noise power density of 4.88 pW/(?)and a common mode rejection ratio of 52dB is realized.The overall performance is significantly improved compared to commercial balance detectors.Second,the research on linear optical sampling data acquisition and processing system is carried out.In order to meet the real-time requirements in long-distance time synchronization experiments at future,a data acquisition and processing system is designed for the acquisition and quantization of detector signals and real-time processing based on linear optical sampling algorithms.The maximum sampling rate supported by the two analog input channels is 400 MSps,and the highest effective digits achieved are 11.06 and 11.30,respectively,which meets our design requirements.We also implement real-time processing of aquired data in field programmable gate array devices based on the principle of linear optical sampling.In this paper,the most critical logic design:real-time peak finding and real-time slope calculation is shown.The processing time for one frame of data is about 34.5us,which greatly reduced time required compared to offline processing.The processing result is consistent with the offline processing result and the relative error is within 3%.Third,a complete linear optical sampling test system was built to study several important parameters affecting performance,including the power of received signal,the power of local oscillator,dispersion broadening,comb repetition frequency difference,the resolution of acquisition card and the gain of detector.Through the parameter optimization,a system with high precision and high sensitivity is finally realized.The minimum sensitivity is 3.03nW,and the optimal time measurement accuracy is 2.06fs.By studying the influence of these parameters on the accuracy and sensitivity of linear optical sampling,it provides a sufficient basis for the performance optimization of long-distance space time-frequency transfer experiments.Finally,we used two linear optical sampling systems based on self-made balance detectors and two sets of self-made data acquisition and processing systems to build a free-space time-frequency transfer experimental device,which completed the space time-frequency transfer experiment under the 16km round-trip atmospheric link.The transfer experiment achieved a transfer stability of 3.39×10-18 @1640s and a time stability of 1.96 fs@10s.The main innovations of this paper are:1.To meet the requirements of linear optical sampling,a high performancebalanced detector with high gain(160k V/W),high bandwidth(greater than 100MHz)and low noise(4.88 pW/(?))is designed.Its comprehensive performance is superior to the existing commercial balance detectors.2.We designed and implemented a real-time linear optical sampling data acquisition and processing system.The ENOB of its analog input channel has reached 11.3 and the maximum sample rate is 400 MSps.The real-time linear optical sampling data processing was studied.The processing time of single frame data was 34.5us,and the relative error with offline processing result was less than 3%.3.We established a complete linear optical sampling prototype system and studied the influence of various key parameters on system performance by systematically experimentation and analysis.Finally we realized both high precision and high sensitivity in our system through parameter optimization.The minimum sensitivity was 3.03nW and the optimal time measurement accuracy reaches 2.06fs,which provides a solid technical foundation for future space time frequency transfer experiments.4.Based on the research of detector,data acquisition and processing system and linear optical sampling performance,the double optical frequency comb based two-way time and frequency transfer experiment over 16km round-trip atmospheric link was completed.The minimum time deviation is 1.96fs,and the instability is 3.39×10-18 at 1640s.