【作者】 王子南；

【导师】 任晓敏；

【作者基本信息】 北京邮电大学 ， 电磁场与微波技术， 2009， 博士

【摘要】 本论文的工作是围绕以下项目展开的:以任晓敏教授为首席科学家的国家重点基础研究发展计划（973计划）项目“新一代通信光电子集成器件及光纤的重要工艺创新与基础研究”（项目编号:2003CB314900）;教育部科学技术重大研究项目“基于微结构光纤的新一代光通信器件及系统”（项目编号:104046）,国家高技术研究发展计划（863计划）项目“单结构与多结构集成式光子晶体光纤及器件”（项目编号:2003AA311010）,863计划项目“光子晶体光纤及器件的研制与开发”（项目编号:2007AA032447）,以及国家留学基金委资助项目（学号:2007U48018）。本论文主要对偏振复用光纤通信系统的传输特性以及基于微结构光纤的光通信器件进行了理论和实验研究,主要研究内容和创新点如下:1、对于采用光域偏振解复用技术的偏振复用直接检测系统,研究了偏振模色散和偏振相关损耗对系统性能的影响。研究结果表明:偏振模色散的影响大小很大程度上由两个偏振态上信号的相对时延与信号的频谱带宽决定,而偏振相关损耗的影响大小与相对时延和频谱带宽的相关度很小;通过采用恰当的偏振解复用设置,偏振相关损耗引起的两个偏振态之间的信号串扰可以被完全消除;同时,还研究了偏振模色散和偏振相关损耗的综合效应,发现系统中偏振模色散和偏振相关损耗交替发生作用时,各自引起的串扰并无相互增强的效应。这些结论对偏振复用系统的设计与性能评估具有重要意义。2、针对偏振复用直接检测系统,提出了一种新型的全自动光域偏振解复用技术,该技术使用系统接收端的一个低频电功率探测器输出的幅度信号作为控制信号。该技术基于偏振复用信号的固有特性,因此不需要在信号发送端再附加额外的标识信号。该技术的有效性在2×10 Gb/s的开关键控偏振复用系统上得到了实验验证。3、提出并验证了一种简单而准确的光纤Kerr非线性系数测量方法。该方法基于光信号的非线性偏振旋转,而这种旋转源于两个同时在光纤中传播的光波之间的交叉相位调制效应。利用该测量方法分别测量了标准单模光纤与TrueWave^TMReduced Slope光纤的Kerr非线性系数,与已报道的测量结果吻合得很好。4、与他人合作,研究了非线性偏振散射对偏振复用-波分复用系统的影响。分别实验研究了10-Gbaud的差分四相相位键控、差分二进制相位键控、开关键控的偏振复用-波分复用系统。实验结果表明,通过采用两个偏振方向上的归零信号时域间插的方式,可以显著抑制非线性偏振散射,从而提高偏振复用-波分复用系统对信道间的非线性效应的容限。5、提出了一种用于宽带色散补偿的微结构光纤的设计方案。该光纤具有三角对称的周期性空气孔结构,空气孔直径有三种尺寸:仿真计算结果表明,这种微结构光纤可以在以1550nm为中心的100nm波长范围内,补偿其自身长度98倍的标准单模光纤的色散,色散补偿率偏离度在0.5%之内;同时,以当前的微结构光纤拉制工艺水平为参考,拉制过程中空气孔直径正常的不规则性对这种微结构光纤的宽带色散补偿能力影响很小。6、利用光信号在一段80m长的微结构光纤中的交叉相位调制效应实现了对10GHz时钟信号的全光波长变换,变换带宽超过30nm。该实验所使用的微结构光纤非线性系数约为11W^-1km^-1,其在1530到1570nm波长范围内具有很小的正常色散和平坦的色散曲线。实验结果表明,利用这种微结构光纤可以实现结构紧凑的宽带波长变换器。7、与他人合作,基于四波混频原理,利用一段30m长、在超过100nm的波长范围内具有平坦的低值正色散特性的微结构光纤实现了对10-Gb/s光信号的波长变换。在以1550nm为中心的20nm波长范围内平均转换效率为-19.5dB,转换效率的起伏在±1.4dB之内;波长转换后的信号眼图具有良好的睁眼度。8、与他人合作,以锁模半导体激光器产生的1.6ps脉冲作为泵浦源,以一段80m的色散平坦高非线性微结构光纤作为非线性介质,在1.55μm波长区域产生了谱宽超过100nm的平坦超连续谱。实验中获得的宽带、平坦超连续谱在1503nm到1593nm宽达90nm的波长范围内,具有±2.5dB的平坦度。9、实验实现了一种基于微结构光纤的光纤环激光器。通过微调控制信号的频率,激光器实现了稳定的锁模状态,在C波段获得了重复频率为10GHz、宽度小于8ps的相干光脉冲输出。在该激光器中,采用了掺铒光纤放大器作为腔内增益介质,并使用了一段25m长、具有反常色散、高非线性的微结构光纤作为脉冲压缩介质。通过调整腔内的带通滤波器中心频率可以实现对工作波长的连续调谐,因此该激光器可作为波分复用系统的可调谐光源。10、与他人合作,利用全矢量有限元方法,对椭圆六角对称分布微结构光纤的双折射特性进行了理论分析,得到了双折射大小与结构参量、入射波长间的依赖关系。分析表明:合理设计结构参数可得到10^-3量级大小的双折射;微结构光纤的双折射对光波波长极其敏感,并出现随波长变化快慢轴交换的现象。采用统计的方法对双折射与微结构光纤空气孔直径随机变化的相关性进行了理论分析,计算结果表明由孔径分布不规则所产生的双折射的大小主要取决于孔径的平均值。更多还原

【Abstract】 The research works of this dissertation are supported by the National Basic Research Program of China （973 Project, No. 2003CB314900）, the Foundation for the Key Program of Ministry of Education of China （No. 104046）, the National 863 High Technology Project of China （No. 2003AA311010 and No. 2007AA03Z447）, and the Scholarship Program of China Scholarship Council （No. 2007U48018）.In this dissertation, both theoretically and experimentally, transmission characteristics of polarization-division-multiplexing fiber communication systems, as well as microstructure fiber based devices for optical communication systems, are studied. The main contents and innovations are as follows.1、Polarization mode dispersion （PMD） and polarization dependent loss （PDL） impairments in polarization-division-multiplexing （PDM） signals with optical polarization demultiplexing and direct detection are investigated. We find that the time alignment between the bits in the two polarizations has a significant impact on the PMD impairments, and PMD impairments also depend on the bandwidth of PDM signals, whereas PDL impairments have little dependence on the relative time alignment between the two polarizations and the signal bandwidth. We show that with a proper configuration of the polarization demultiplexing, the PDL-induced crosstalk between the two polarizations can be completely eliminated. The combined effects of PMD and PDL are also studied, and we find that, in the presence of concatenated PMD and PDL, the impairment from one effect does not enhance that from the other. The conclusions are important for the design and the performance evaluation of PDM systems.2、A new automatic optical polarization demultiplexing scheme for polarization-division-multiplexing （PDM） signals, which uses the amplitude signal from a low frequency electrical power detector at the receiver side as a control signal, is proposed. This scheme is based on the intrinsic characteristics of PDM signals and does not need to add a special signal at a PDM transmitter. The effectiveness of this demultiplexing method is experimentally demonstrated in a 2×10 Gb/s on-off-keying （OOK） PDM transmission system.3、A simple and accurate method to measure the Kerr nonlinearity coefficient of optical fibres is proposed and demonstrated. The method is based on the nonlinear polarisation rotations caused by cross phase modulation between two lightwaves of different wavelengths co-propagating in fibres. The Kerr nonlinearity coefficients of standard single mode fibre and TrueWave^TM Reduced Slope fibre measured with this method are in good agreement with the published data.4、In cooperation with other researchers, the impairment of nonlinear polarization scattering on polarization- and wavelength-division-multiplexing （PDM-WDM） systems is investigate. Transmission experiments on 10-Gbaud PDM differential-quadrature-phase-shift-keying （DQPSK）, differential-binary-phase-shift-keying （DBPSK） and on-off-keying （OOK） show that time interleaving return-to-zero signals in two polarizations can significantly reduce nonlinear polarization scattering in PDM-WDM systems and increase system tolerance to inter-channel nonlinearities.5、A microstructure fiber structure is proposed for broadband dispersion compensation. The fiber has a triangular lattice of air-holes along its length, and there are different three air-hole diameters. The dispersion of the standard single-mode fiber, which is 98 times of the length of the microstructure fiber, can be compensated over the entire 100nm wavelength range centered on 1550nm （to within 0.5%）. The influence of the random imperfections of air-hole diameters is also studied for practical applications, and the sensitivity of the broadband compensation capability of the microstructure fiber to the irregularities induced during fabrication process is estimated.6、All optical wavelength conversion of 10-GHz clock signal is demonstrated based on cross-phase modulation of optical pluses in an 80-m long microstructure fiber, and the conversion bandwidth is over 30nm. The experimental microstructure fiber with a nonlinear coefficient of～11W^-1km^-1 has small normal dispersion and it is characterized by flat dispersion curve in the 1530nm to 1570 nm range. The experimental results show that a compact wavelength converter can be realized by utilizing this microstructure fiber. 7、In cooperation with other researchers, all-optical wavelength conversion of 10-Gb/s signal based on four-wave mixing is experimentally demonstrated in 30-m dispersion-flattened microstructure fibers with small positive dispersion. The conversion efficiency was around—19.5dB with the small fluctuation within±1.4dB, covering a conversion bandwidth of 20nm centered at 1550nm. The eye diagram of the converted signal shows good eye opening.8、In cooperation with other researchers, the generation of a flat supercontinuum spectrum of over 100nm in the 1.55μm region by injecting 1.6ps, 10-GHz repetition rate optical pulses into an 80m-long dispersion-flattened highly nonlinear microstructure fiber is demonstrated. The generated flat broadband supercontinuum ranging from 1503nm to 1593nm has the flatness of±2.5dB.9、A fiber ring laser based on microstructure fiber is presented. Through slightly adjusting the frequency of control signal, active mode-locked state is acquired and the laser can produce correlated optical pulses with a high repetition rate of 10GHz and a narrow width of less than 8ps. In this laser, erbium-doped fiber amplifier is used for optical gain, and a 25m long microstructure fiber is used for pulse compression, which has a large anomalous dispersion and a high nonlinear coefficient. The operating wavelength can be altered by changing the central wavelength of the band-pass filter in the fiber ring, thus this laser can be used as the tunable optical source for wavelength-division-multiplexing systems.10、In cooperation with other researchers, the birefringence in microstructure fiber with squeezed hexagonal lattice is numerical analyzed based on full-vector finite element method. The correlation between the birefringence and the structural parameters, incidence wavelength is obtained. The numerical results show that the birefringence is sensitive to wavelength, it can achieved a magnitude of 10^-3 by proper design, and the sign of form birefringence in such microstructure fibers can be changed as the incidence wavelength changes. In the statistical analyses, the correlation between the variation of air hole diameters and the birefringence in the microstructure fiber is obtained; results show that that the birefringence depends on the mean diameter of air holes.更多还原