【作者】 桂林；

【导师】 林金桐；

【作者基本信息】 北京邮电大学 ， 电磁场与微波技术， 2011， 博士

【摘要】 光波群速度的调控是近年来光电子学的研究热点,具有重要的理论意义,并在光通信、光传感和微波光子学等方面具有重要的应用价值。目前快慢光的调控主要包括基于原子体系中的大色散机理、波导结构设计和光波非线性放大等方法。光纤参量放大器(FOPA)中的快慢光调控主要基于光波非线性放大实现,由于能提供几十吉赫兹的带宽和几十皮秒的可调谐延时,在高速光通信系统中具有潜在应用价值。论文针对宽带与窄带光纤参量放大器中的快慢光机理进行了深入研究,论文主要工作如下：1)研究了宽带光纤参量放大器中信号光延时的综合特性,解析得到了最大延时的波长与抽运光功率、抽运光波长以及光纤色散参数之间的定量关系。仿真分析了单个高斯脉、确定比特序列和伪随机序列三种宽带输入信号的延时特性,仿真结果表明信号带宽等于50GHz时,在原有的大延时波长上,延时量减小为原来的一半,但眼开度代价仅为0.46dB。最后还讨论了抽运光功率与光纤长度的选取方法,研究结果表明在相同增益的条件下,长光纤更有利于慢光的产生。2)分析了FOPA增益谱边带的延时特性,提出了一种近零增益条件下信号光延时的可调谐方案,给出了信号光波长与抽运光功率、波长和光纤色散参数之间的定量关系。仿真实现了信号光增益1.29至3dB时,10GHz信号光延时(超前)时间0到22.4ps范围内的调谐。该机理为全光缓存与同步等应用中与增益无关的延时实现提供了新思路。3)研究了包含SRS效应的窄带光纤参量放大器中的快慢光增强特性。提出了同时考虑受激拉曼散射极化率实部与虚部的理论分析模型,得到了SRS与光参量过程同时作用时的完整相位变化解析式。研究结果表明在不同的拉曼作用强度下,均有SRS增强快慢光现象,但是增强的频率区域不同。以外快慢光增强的频率区域还会随抽运光功率或者光纤长度的不同而发生变化。论文给出了拉曼频移约为14THz(SRS效应最强的区域)时,不同非线性作用强度下最大快慢光产生的条件和计算信号光波长的定量公式。仿真结果表明带宽为1.5GHz和1GHz时,可分别实现大于200ps和300ps的延时。在该信号光波长上,群折射率的变化达到10-4量级,比常规SRS作用下FOPA中的群折射率高了近一个数量级。4)研究了FOPA中偏振态变化以及放大过程中信号光饱和两种非理想情况下的延时变化特性。通过分析抽运光、信号光和闲散光波取不同偏振态情况下的延时特性,得出了FOPA中光波偏振态对快慢光影响的解析表达式。此外,还分析了信号光饱和对延时的影响,仿真分析结果表明当信号光位于增益谱边带的延时增强频率区域时,延时量仅为小信号条件下的一半。5)提出了一种利用光纤参量放大器增益谱的波长相关性进行微波频率测量的新方法。该方法可以通过抽运光功率的变化调谐微波频率的测量范围。通过光纤参数和初始信号光功率的优化选择,用500mW的抽运光功率和3公里光纤仿真实现了频率范围为25-45 GHz的微波频率测量。更多还原

【Abstract】 Recently, controlling the group velocity of light becomes a key issue in photonics. Its importance not only lies on the theory, but also attributes to its potential values in the area of optical communication, optical sensor technology and microwave photonics. Up to now, the method generating the slow and fast light mainly contains: the large dispersion in atom system, the design of waveguide structure and the nonlinear amplification of signal wave. The slow and fast light in FPOA is realized by the nonlinear amplification of signal wave. We theoretically investigate the phenomenon of slow and fast light in both the wideband FOPA and the narrowband FOPA because this new mechanism contains following advantages:relatively large delay bandwidth, the delay time fitted for high speed telecommunication and the tunable ability for delay time. The major contributions of this paper can be summarized as follows:1) The comprehensive characters of delay time in fiber optical parametric amplifier are investigated theoretically. The analytical relation between the maximum delay time and the dispersion parameters, pump power, pump wavelength in this type of FOPA is deduced. Then the delay character of single pulse, data stream with certain bit pattern and pseudo random data stream are analyzed comprehensively. The results show that the delay time will reduce to the half of the value under narrow band condition when the signal with the bandwidth 50GHz is located at the wavelength with maximum delay time. Finally, the selection of pump power and fiber length is present, and long fiber benefits to the large delay time when the signal gain is fixed.2) The delay time in the band-edge of gain spectrum of wide band FOPA is deduced for the first time, and a novel method is proposed theoretically to generate the slow and fast light with large bandwidth and low gains. In our scheme, the formula of the signal wavelength is demonstrated, and then signal waves will be delayed or advanced with low signal gains because of the peculiar feature of signal gain and phase shift in certain signal wavelength region. At last, the simulation results of delayed signal waves are shown. The tunable range of delay(advanced) time is from Ops to 22.4ps for the signal bandwidth of lOGHz, and their signal gains are from 1.29dB to 3dB. This proposal can provide the new mechanism to make tunable delay time independent of the signal gain in both optical buffer and synchronization.3) By considering both the real and imaginary part of the Raman susceptibility, a delay time formula in the stimulated Raman scattering assisted fiber optical parametric amplifier is presented to calculate the delay time spectrum. The wavelengths with maximum delay and advanced time are calculated numerically. Then we find some frequency regions with the enhanced slow and fast light in both stokes and anti-stokes regions, which is the result of the interaction between the stimulated Raman scattering and four-wave-fixing effect at the strong absorption region. Simulation shows that the delay time by using signal waves with 1.5GHz and 1 GHz can reach over 200ps and 300ps, respectively. The group index can reach the order of 10-4, which is ten times larger than the former delay time in conventional frequency regions.4) The changes of delay time are investigated in two nonideal cases:the changing of polarization states and signal saturation. By analyzing the delay time with different polarization states of pump wave, signal wave and idler wave, we propose a formula containing the changing of polarization states in FOPA. Then the influence of the signal saturation on the delay time is analyzed. The results show that the delay time calculated numerically is only one half of the result from the analytical formula when the signal wave is located in the band-edge of the gain spectrum in FOPA.5) We propose an approach to measure the microwave frequency in optical domain with adjustable measurement range and resolution by using four wave mixing process in the single mode fiber. Results show that the measurement range of this scheme can be adjusted easily by changing the pump power. After the elaborate selection of the fiber parameters and initial signal power, the measurement range 20-45 GHz is obtained by choosing 500 mW pump power and 3km fiber.更多还原