Fiber Raman Amplification Technology For Remote Large-scale Optical Fiber Hydrophone System

Fiber optic hydrophone has the advantages of anti-electromagnetic interference,high sensitivity,small size,light weight,easy to re-use network,good stability,dynamic range and others.With the increasing maturity of fiber optic hydrophone technology and the continuous improvement of application requirements,the scale of optical fiber hydrophone arrays has been expanding and the optical fiber transmission distance has been extended to hundreds of kilometers.Improvement of the signal transmission distance means the transmission loss is increased,the expanding size of the hydrophone array also means more loss,so in order to ensure effective fiber optic hydrophone detection of weak acoustic signals,the optical amplifier must be designed to meet the requirements of optical fiber hydrophone device system gain,bandwidth,noise characteristics etc.Multi-wavelength fiber Raman amplification technology offers wide gain bandwidth,low noise and other advantages,and can be a reasonable choice of technology to design the pump light quantity,wavelength,power to achieve any gain spectrum.So,the fiber Raman amplifier is very suitable for remote large-scale fiber optic hydrophones.In this thesis,the basic characteristics of fiber Raman amplifiers are studied.The numerical simulation of pulsed light and continuous light Raman model is carried out.The influence of nonlinear effects in the fiber Raman amplification system is studied in detail,and the suppression scheme is designed with a focus on the optical fiber Raman amplifier gain flat optimization.The main research results and innovations of this thesis are summarized as follows:?1?.Based on the theoretical model of Raman amplification of pulsed light and continuous light,the fourth-order Adams prediction-correction method is used to numerically calculate the continuous optical amplification,which improves the calculation accuracy and computational efficiency.Combined with the parallel bidirectional algorithm and four order Adams prediction-correction method,the numerical calculation on pulsed light amplification is performed.Since the parallel bidirectional algorithm is more in line with the physical nature of light propagation,the algorithm can combine the Raman amplification process of pulsed light more efficiently and accurately,thus the computational efficiency and calculation accuracy is improved.?2?.The parallel bidirectional fourth-order Adams prediction-correction algorithm is proposed to numerically calculate the theoretical model of stimulated Brillouin scattering in the fiber Raman amplification system.The numerical results show that the forward-pumped Raman pumping light has a great influence on the stimulated Brillouin scattering,and the effect of the backward-pumped Raman pumping light on the stimulated Brillouin scattering is generally negligible.Experiments show that the phase modulation technique that satisfies the parameter matching condition can effectively suppress the stimulated Brillouin scattering in the fiber Raman amplification system without introducing additional phase noise.?3?.A two-step method is proposed to study the theoretical model of modulation instability in the fiber Raman amplification system in which the distribution of the Raman gain of the signal light is calculated first on the condition that the modulation instability is ignored;then the calculated Raman gain distribution is used to replace the fiber loss term in the nonlinear Schr?dinger equation,and the modified Schr?dinger equation is solved to obtain the gain spectrum of modulation instability.The numerical results show that the threshold of modulation instability decreases with the increase of the Raman pump optical power.Under the same Raman pump optical power,the remote fiber optic system of the forward pump has a lower modulation instability threshold compared to that of the backward Raman pump.The experimental system is used to measure the modulation instability gain spectrum and threshold in the fiber Raman amplification system.The test results are in good agreement with the numerical results.?4?.Theoretical and experimental studies are conducted on the optimal design of fiber Raman amplifiers.In the case where the pump wavelength is fixed and not fixed,the genetic algorithm is used to optimize the fiber gain Raman amplifier with a flat gain and flat input of any signal spectrum.Experiments have verified that a fiber Raman amplifier with two fixed wavelength pump sources has flattening output performance for optical signals of any input spectrum.?5?.A 100 km non-relay 16-wavelength and 8-time time-division hybrid multiplexed 128-primary fiber-optic hydrophone system is built.By using four wavelength-fixed Raman pumping sources,the output of any input signal spectrum can be flattened by optimizing the design of the pump power,and the phase noise of the fiber-optic hydrophone can achieve ?-90 dB re rad/Hz^1/2 at 1 kHz.