Study On Optical Amplification Technology For Fiber-Optic Time And Frequency Transfer Based On Bidirectional WDM Transmission

Time and frequency plays a supporting and guaranteeing role in many fields,such as basic scientific research(time and frequency measurement and basic physical quantity measurement,etc.),national defense construction(maritime aerospace and satellite navigation,etc.)and social development(financial systems,Internet of things and high-rate communication,etc.)as a basic physical quantity.In recent years,with the continuous improvement of the performance of atomic clocks,the traditional ways of time and frequency transfer using coaxial cable or free-space link cannot meet the demand of high-precision and high-stability time and frequency transfer in the future.Due to the advantages of low loss,wide bandwidth,high stability and anti-electromagnetic interference,optical fiber can be applied to high-precision and high-stability time and frequency transfer.However,for long-distance time and frequency transfer,bidirectional optical amplifier is essential for relay amplification because of fiber transmission loss.On one hand,the bidirectional optical amplifier needs to meet the characteristics of high symmetry and effective suppression to the backscattering noises.On the other hand,it is hoped that the bidirectional optical amplifier can be compatible with unidirectional optical amplifiers in existing communication networks.Based on the development demand of long-distance and high-precision fiber-optic time and frequency transfer technology,this thesis designs and implements a wavelength division multiplexed bidirectional transmission unidirectional optical amplification(WDM-BTUOA)scheme for bidirectional time and frequency transfer system.This scheme can effectively block the cumulative amplification of backscattering noises and can be compatible with unidirectional optical amplifiers in existing communication networks.The main work of this thesis includes:1)The characterization method of fiber-optic time and frequency transfer performance and the theoretical basis of erbium-doped fiber amplifier are elaborated.Combined with the basic model of the fiber time and frequency transfer system,the different requirements of the bidirectional optical amplifier for time and frequency transfer are analyzed.The signal-to-noise ratio model(SNR)of fiber time and frequency transfer system is given.The noises introduced by each part of the system and its influence on time and frequency stability are analyzed.The main sources that affect the system asymmetry and its characteristics are also analyzed.2)A bidirectional optical amplification scheme WDM-BTUOA is designed and applied to the two-way time and frequency transfer system based on bidirectional WDM transmission.The structure and working principle of WDM-BTUOA are elaborated.At the same time,the number and gains of K equidistantly placed WDM-BTUOAs in the long-distance fiber link are simulated and optimized,so that the fiber link can work at the best received SNR.3)A long-distance two-way time transfer based on WDM transmission testbed is built in laboratory,and the performance of long-distance fiber-optic time transfer system employing the WDM-BTUOA and single path bidirectional amplifier(SPBA)for relay amplification respectively are tested and compared.Under the condition of same rubidium clock,the time deviations(TDEVs)of less than 130 ps/s and 12 ps/10~4s,can be achieved over 2100 km fiber links adopting 21 equivalent WDM-BTUOAs.The measured bidirectional transmission delay asymmetry fluctuation of single WDM-BTUOA is 0.7 ps.The combined uncertainty introduced by 21 WDM-BTUOAs are evaluated to be better than 1.7 ps after calibration.The feasibility of WDM-BTUOA scheme is also verified in a passive phase noise compensation system for fiber-optic radio frequency transfer with a nonsynchronized source over 100 km fiber link.