| Under the era of big data, optical amplifiers have been one of the key devices in the optical transmission system with ultra-large capacity and ultra-long distance for the reason of amplifying the signal directly and decrease the cost of devices and the system complexity greatly. Raman fiber amplifier (RFA) has great value in theoretical research and system application, due to its advantages of high gain, wide bandwidth and low noise.There are many questions such as ultra-broad bandwidth, the higher order Raman effect et al., which are worth to study, although RFA is for commercial use before long. Early researches of the higher order RFA broke the limitation of traditional noise, which was not ripe and applicable yet. The higher-order RFA and its mathematical model are focused on. The key performance of gain, noise and bandwidth of higher order-RFA and its application are investigated in this dissertation. The main contents and the achievements are list below:(1) The effect of higher order amplified spontaneous scattering in Raman amplification is investigated. The mathematical model of the higher-order RFA is modified for the variable effective model field area in the specific scale of higher-order pumps, and AVariable-step Ronge-Kutta method based on matrix is put forward, which can decrease its algorithm complexity and calculation time. By solving the modified model, Simulation results indicate that higher order Stokes line can be used as the pump source of higher-order RFA.(2) Some higher-order RFA is designed and their performance of noise are investigated. The noise performance is simulated by comparing higher order RFA with traditional RFA. The effective noise figure of the 2nd-order and the3rd-order RFA are decreased by1.5dB and2.7dB respectively. The theory is pointed out that the lower noise is due to the even distribution of signal power along the fiber, which is also proved by the study of noise performance study of the2nd-order RFA in different pumping schemes. The2nd-order RFA in bidirectional2nd-order pumping scheme can achieve the best noise figure.(3) The structure of broad higher-order RFA is put forward by lower-order pump with small power adjusting bandwidth and higher-order pump with large power providing power, respectively. The method of multi-order pumps with multi-wavelengths is put forward, which extend and optimize the bandwidth of the higher-order broad RFA. The modified genetic algorithm is put forward to find the optimized pumping scheme quickly and exactly. Simulated results from the scheme above indicate:50nm and80nm higher-order Raman spectrum with the gain of24dB and ripple of less than1dB and noise figure less than-3dB over120km span are achieved respectively. The different functions of different order pumps are also analyzed:the1st-order pumps can improve the gain flatness and extend the bandwidth, the2nd-order pumps can increase the gain value, while the3rd-order pump can provide powers for other order pumps and improve the noise figure.(4) The platform of CATV system is experimentally built. The application scheme of the2nd-order RFA is put forward and compared with traditional EDFA. The platform of digital CATV system based on16-QAM modulation is simulated. The roles of3rd-order and1st-order RFA in this system are analyzed by the bit error rate.(5) The gain and bandwidth of the dual-pump fiber optical parametric amplifier combined with Raman effect are investigated. The influence of Raman effect is determined by the real part of Raman response function. The results indicate the parametric gain is changed by Raman effect and susceptible to zero dispersion wavelength fluctuation. But little zero dispersion wavelength fluctuation such as0.2nm is helpful to achieve a flat spectrum with Raman effect. |
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