【作者】 耿丹；

【导师】 杨冬晓；

【作者基本信息】 浙江大学 ， 电子科学与技术， 2008， 博士

【摘要】 近年来,光子晶体光纤(PCF)技术取得很大的进展。PCF设计灵活,具有无休止单模特性、奇异的色散特性和高非线性的特点,通过合理的设计,PCF的非线性比普通单模光纤的非线性高一到两个数量级。因此,人们对PCF中的非线性进行了大量的研究。受激布里渊散射(SBS)是光纤中重要的非线性效应,它具有阈值低、易发生的特点,使得SBS在光通信系统中既有积极的作用,又有消极的作用。SBS可用做光纤布里渊激光器和放大器,这是其积极的方面。相反,对于光纤中其它的非线性效应,如四波混频(FWM),SBS的发生会减弱FWM的效率,这时需要考虑抑制SBS。本论文从利用SBS和抑制SBS两个角度,分别研究了PCF中的SBS和FWM。论文首先分析了以PCF为增益介质的光纤布拉格光栅F-P(Fabry-Perot)腔中稳态SBS的模型。在考虑PCF损耗的条件下,具体研究了光纤布拉格光栅F-P腔的透射功率、反射功率与输入泵浦波功率的关系;仿真了光纤布拉格光栅F-P腔中的泵浦波和斯托克斯波的功率分布;模拟计算了PCF长度对光纤布拉格光栅F-P腔中SBS阈值的影响。在上述理论研究的基础上,提出了一种新型的以PCF为增益介质的基于光纤布拉格光栅F-P腔的双频布里渊激光器,利用25 m长的高非线性PCF和两个光纤布拉格光栅构成F-P腔,作为布里渊激光器的谐振腔,这种腔结构有益于提高布里渊激光器的转换效率,降低布里渊激光器的阈值。论文研究的布里渊激光器的阈值为35 mW,当输入泵浦波功率为130 mW时,激光器的转换效率为18%。与已报道的PCF布里渊激光器相比,论文利用最短的PCF实现了最低阈值的PCF双频布里渊激光器。在光通信系统中,信号需要通过微波调制到光信号上进行传输,所以微波信号的产生非常重要。论文提出了一种新型的基于PCF双频布里渊激光器的微波发生器,通过选择具有一定反射谱的光纤布拉格光栅,可以使PCF布里渊激光器仅产生一阶斯托克斯波,抑制高阶斯托克斯波的产生,泵浦波和一阶斯托克斯波的频率差落在微波的频率范围内,可以通过泵浦波和一阶斯托克斯波混频得到微波信号。当输入泵浦波功率为57 mW、泵浦波波长在1550 nm附近时,得到了带宽为3 MHz、频率为9.78 GHz的微波信号。与已报道的基于PCF布里渊激光器的微波信号发生器相比,本论文在更低的泵浦波功率下产生了微波信号。在用光纤链路传输微波的系统中,微波信号需要调制到光载波上,然后通过光纤进行传输,这需要解决光载波抑制的问题。论文在理论研究光纤环中SBS模型的基础上,设计了一种新型的基于PCF中SBS的光载波滤波器。滤波器由两个环行器和一段PCF组成的光纤环构成,这种光纤环结构有效地降低了PCF中SBS的阈值,PCF的高非线性可以减小光纤环中的光纤长度。滤波器利用25 m长的高非线性PCF作为布里渊增益介质,当输入光载波功率为70 mW时,微波光子信号获得了3.38 dB的射频增益,有效地减少了滤波后的微波光子信号的光载波功率,实现滤波器中心波长和光载波波长的自动匹配。光通信系统中相位调制信号研究的发展,要求合适的波长转换技术作为支撑,FWM由于对光纤中克尔非线性效应的迅速反应而满足全光系统中波长转换的要求。在色散平坦的PCF中,FWM的相位匹配条件更容易得到满足,有益于提高FWM的波长转换带宽。因此,论文提出了一种基于高非线性色散平坦PCF中FWM的波长转换器。PCF中出现SBS会降低FWM的效率,论文在研究SBS的基础上,通过选取合适的泵浦源抑制了PCF中的SBS,实现了100 nm的波长转换带宽,接近利用PCF中FWM实现波长转换的最大带宽。实验证明,这种波长转换器可以同时完成多路信号的波长转换。更多还原

【Abstract】 In recent years, the photonic crystal fiber (PCF) technology has made great progress. Due to design flexibility of PCF, it has endlessly single-mode characteristic, peculiar dispersion characteristic and high nonlinearity characteristic. Through the rational design of PCF, its nonlinear is typically 1 or 2 orders of magnitude larger than that of a conventional single-mode fiber. Therefore, a lot of research has been carried out about the nonlinear in PCF. Stimulated Brillouin Scattering (SBS) is an important nonlinear effect in fiber, and it has a low threshold, which makes SBS have both positive role and negative role in optical communication system. SBS effect can be used in Brillouin fiber lasers and amplifiers, which is the positive side. On the contrary, for other nonlinear effects in fiber, such as four-wave mixing (FWM), the occurrence of SBS will diminish the efficiency of FWM, therefor SBS needs to be supressed. The SBS and FWM in PCF have been studied in this paper in terms of the use of SBS and suppression of SBS.The steady-state model of SBS in fiber Bragg grating Fabry-Perot (F-P) cavity using PCF for the gain medium is analyzed. Under the condition of considering the PCF loss, the relationship between transmission (reflection) power of fiber Bragg grating F-P cavity and input pump power is studied. Pump power and Stokes power distribution along F-P cavity are simulated. The relationship between the length of the PCF and SBS threshold of fiber Bragg grating F-P cavity is discussed. On the basis of above theory, we provide what we believe to be the first experiment demonstration of dual-frequency Brillouin laser based on fiber Bragg grating F-P cavity using PCF for the gain medium. Resonant cavity of laser consists of 25-m-long highly nonlinear PCF and two fiber Bragg gratings. Such a cavity is beneficial to increasing conversion efficiency and decreasing laser threshold. The laser reaches threshold for input power of 35 mW, and the experimental laser conversion efficiency achieves 18% for input power of 130 mW. Compared to previous PCF Brillouin laser, the PCF dual-frequency Brillouin laser proposed in the paper achieves a minimum threshold using the shortest fiber.In optical communication systems, useful signal is modulated to optical signal with microwave for transmission, therefore, the generation of microwave signal is very important. A novel microwave signal generator based on PCF dual-frequency Brillouin laser is forwarded in the paper. By choosing the fiber Bragg grating with a certain reflection spectrum, PCF Brillouin laser can only produce 1st-order Stokes wave, and suppresses the high-order Stokes waves. Frequency difference between pump and 1st-Stokes wave falls in microwave frequency range, so we may obtain microwave signal through mixing the pump with the lst-order Stokes wave. When pump power is 57 mW and pump wavelength is near 1550 nm, a 9.78 GHz microwave signal whose bandwidth is 3 MHz is obtained. Compared to previous microwave sinal generator based on PCF Brillouin laser, the microwave signal is generated under the condition of lower pump power in the paper.In the microwave transmission systems with fiber link, microwave signals need modulating to optical carrier for transmission, which requires solving the issue of optical carrier suppression. A novel carrier filter based on the SBS in the PCF is provided after a research of SBS model in fiber ring. The fiber ring consists of a section of fiber and two circulators, which serves as carrier filter. SBS threshold in PCF is effectively reduced in this fiber ring structure, and the highly nonlinear PCF can greatly reduce the fiber length in fiber ring. A 25-m-long PCF is used as Brillouin gain medium, when the carrier of 70 mW input the filter, microwave photon signal received 3.38 dB of RF gain. The filter effectively reduces carrier power and realizes automatic match of the center wavelength of the filter and optical carrier.The development of phase modulation signal research in optical communication system calls for a suitable wavelength conversion technology as a support, FWM meets the request of all-optical system due to its instantaneous response of Kerr nonlinearity of fiber. Phase matching condition is met more easily in dispersion flat PCF, which is beneficial to increasing the wavelength conversion range. A wavelength converter based on FWM in a highly nonlinear dispersion flat PCF is provided. SBS will decrease the efficiency of FWM in PCF, so a suitable pump source is selected to suppress SBS on the basis of the research on SBS. We obtain 100-nm wavelength conversion range, which is almost equal to the widest bandwidth of wavelength conversion realized in FWM of PCF. Experiment proved that the wavelength converter can complete the wavelength conversion of multi-channel signal at the same time.更多还原