【作者】 董建绩；

【导师】 黄德修； 张新亮；

【作者基本信息】 华中科技大学 ， 光学工程， 2008， 博士

【摘要】 随着光传输技术的发展,光通信网络中单个信道的比特率越来越高,而信道数目也在不断增加,这就要求光交换技术从光-电-光交换向全光交换转变。全光信号处理技术,如波长转换、逻辑门和3R再生等将是实现全光交换技术(包括光突发交换和光分组交换等)的基本功能单元。半导体光放大器(SOA)在全光信号处理技术中具有非常大的吸引力,表现为非线性系数高、功耗低、输出效率高、体积小、成本低、易于和其他光电子器件集成等。根据实验室现有的40Gbit/s高速光通信平台和各种不同性能的SOA器件进行高速全光信号处理技术的实验研究,全光信号处理技术覆盖了全光波长转换、全光码型转换、全光逻辑门及其组合逻辑、超宽带(UWB)射频信号的光学产生等。概括全文的研究成果和贡献,有如下几个方面:(1)研究了SOA实现全光信号处理的基本原理,推导了SOA中最基本的光场传输方程和载流子速率方程,分析各种非线性效应的原理及其应用。总结了迄今为止几种常用的SOA理论模型及其各自的适用范围,并根据本文的全光信号处理要求提出了一种超快SOA模型,提供了数值计算方法求解。(2)首次从系统响应函数出发,推导了基于瞬态交叉相位调制(T-XPM)效应的波长转换解析公式,该公式直观的解释了基于T-XPM效应实现同相和反相转换的原理,并将文献中的实验报道和公式计算结果对比,发现结果十分吻合。从实验上分别实现了从10Gbit/s到40Gbit/s的同相和反相波长转换,当滤波器失谐量较小时,得到反相的波长转换结果,此时交叉增益调制(XGM)占主导作用,而滤波器的失谐起到加速增益恢复的作用;当滤波器失谐量较大时,可以得到同现波长转换,此时交叉相位调制(XPM)占主导作用,而滤波器起到提取啁啾信息的作用。(3)将SOA和失谐滤波器相结合,研究各种全光码型转换的实现方法。首先从理论上提出了基于T-XPM效应的非归零(NRZ)到归零(RZ)的码型转换,同时对码型转换的性能参数做了深入的分析。其次,将SOA和滤波器相结合,可以实现NRZ到伪归零(PRZ)的转换,可以得到反相的波长转换,输出结果取决于滤波器的失谐量。最后,利用SOA的自相位调制(SPM)效应实现了NRZ到PRZ的转换和NRZ信号的2R再生功能,当滤波器选择蓝移时,就可以抑制NRZ信号的畸变,从而实现信号的2R再生,反之当滤波器选择红移时,就能提取这种过冲脉冲,而抑制信号的直流分量,最终实现NRZ到PRZ的转换。(4)全面研究了基于SOA的各种逻辑门及其高级逻辑组合器件。首先提出并实验报道了基于T-XPM效应的全光逻辑NOR和OR门,工作速率为40Gbit/s,从理论上也研究了线宽增强因子和输入信号脉宽对输出信号质量的影响。其次考虑四波混频(FWM)效应,首次实现了可重构的多功能逻辑门,包括NOR门、OR门、NOT门、AND门和XNOR门,工作速率同样为40Gbit/s。最后从理论上提出了基于单个SOA和若干个并联的滤波器组合的全光半加器和全加器。滤波器相对于探测光中心波长进行不同的漂移就可以提取不同的逻辑输出,得到“进位”位和“求和”位。(5)系统研究了基于SOA的全光超宽带(UWB)射频信号产生方法。首先利用T-XPM效应实现了超宽带monocycle脉冲,滤波器选择蓝移和红移分别得到一对极性相反的monocycle脉冲。其次利用SOA的增益饱和效应,直接从dark RZ信号中提取monocycle波形,实验研究了注入电流、输入信号脉宽和波长对超宽带频谱的影响。接着提出了一种基于XGM效应的无滤波方案产生monocycle脉冲,实验表明当信号波长在C波段变化或者输入功率从-10dBm到6dBm之间变化时,输出结果稳定。最后利用单模光纤的色散特性对NRZ-DPSK信号进行微波滤波,从而获得超宽带doublet脉冲和triplet脉冲。(6)研究了基于SOA的FWM效应的全光信号处理技术。首先给出了SOA的FWM理论模型,然后根据该模型从理论上提出并模拟了一种全光比特误码检测器,该器件是利用两级级联的SOA的逻辑NOT门和AND门来完成的,结果表明该方案对于40Gbit/s的RZ信号和10Gbit/s的NRZ信号均能胜任。其次从实验上报道了FWM效应实现各种调制速率、各种调制格式的波长转换功能。特别地,对40Gbit/s的NRZ信号实现了单信道到三信道多波长转换。最后利用FWM效应实现了单信道到双信道的NRZ到RZ码型转换,输出的双信道分别对应FWM效应产生的两个边带频率,转换光信号的Q值均大于6。更多还原

【Abstract】 As the bit rate of one wavelength channel and the number of channels continue increasing in the telecommunication networks thanks to the advancement of optical transmission technologies, switching is experiencing the transition from the electrical domain to the optical domain. All-optical signal processing, including wavelength conversion, optical logic gates and signal 3R regeneration, etc, is one of the most important enabling technologies to realize optical switching, including optical circuit switching, optical burst switching and optical packet switching.Semiconductor optical amplifiers (SOAs) are very promising in all-optical signal processing because of their high nonlinearities, low power consumption, high power efficiency, small footprint, low cost, and ease to be integrated with other semiconductor optoelectronic devices. In this dissertation, some all-optical signal processing techniques based on SOAs which are related with the 40Gbit/s optical communication system, such as all-optical wavelength conversion, all-optical format conversion, all-optical logic gates, and all-optical ultrawideband (UWB) pulse generation, have been demonstrated. Several research achievements and contributions are summarized as the followings:Firstly, the basic principle for SOA-based all-optical signal processing is investigated. The propagation equation for the optical field and the rate equation for the carrier density in SOA are derived. And the principle and applications for nonlinearities of SOA are discussed. Different SOA models and their applications are summarized. A novel ultrafast SOA model is presented and the numerical arithmetic is provided.Secondly, an analytical formula for wavelength conversion of transient cross phase modulation (T-XPM) is deduced from the viewpoint of impulse response function. The analytical formula can interpret accordingly the polarity evolution of wavelength conversion. The calculated detuning of the filter by the formula is found to agree well with the published experiment results. We experimentally demonstrate both inverted wavelength conversion and non-inverted wavelength conversion at 10Gbit/s and 40Gbit/s. In the inverted wavelength conversion, the filter detuning is small and it is useful to accelerate the amplitude recovery, where the XGM dominates this process. However, in the non-inverted wavelength conversion, the filter detuning is relatively large, and it acts as frequency- amplitude conversion. And the XPM is dominant. Thirdly, a variety of format conversion schemes are presented using single SOA and a detuning filter. NRZ-to-RZ format conversion by T-XPM effect is theoretically demonstrated. Some important parameters are analyzed. NRZ-to-PRZ and inverted wavelength conversion of NRZ signal have been demonstrated with the same structure. At last, simultaneous SOA-based NRZ-to-PRZ conversion and 2R regeneration of amplified NRZ signal using self phase modulation (SPM) are investigated. The blue shifted filter can suppress the distortion of NRZ signals, and obtain 2R regeneration. Conversely, the red shifted filter can extract the frequency chirp and suppress the direction current components. Hence the NRZ-to-PRZ format conversion is obtained.Fourthly, a variety of SOA-based logic gates and the advanced logic circuits are investigated. Both logic NOR and OR gates at 40Gitb/s based on T-XPM effect are presented for the first time to our knowledge. The impact of linewidth enhancement factor and input pulsewidth on output performances is analyzed. Then multifunctional logic gates at 40Gbit/s, including NOR, OR, NOT, AND, and XNOR, are demonstrated based on single SOA and optical filtering by considering the four-wave mixing (FWM) effect. At last, optical half /full adders based on single SOA and several optical bandpass filter are theoretically proposed. Different logic functions are realized by different filter detuning. Fifthly, the optical UWB pulse generation based on SOAs is systematically studied. We propose a scheme for optical UWB monocycle generation based on T-XPM effect. A pair of polarity-reversed UWB monocycle pulses is achieved by locating the probe carrier at the positive and negative linear slope of the filter, respectively. Then we demonstrate a simple and compact scheme to generate UWB monocycle pulses utilizing gain saturation of the dark RZ signal in an SOA. The UWB frequency spectra at different injected currents, different input pulsewidth, and different input wavelengths are analyzed. Later, a filter-free scheme for UWB generation by XGM of single SOA is proposed and demonstrated. The system shows good stability when the input probe power varies from -10dBm to 6dBm and the probe wavelength varies in the whole C-band. At last, a simple method to generate UWB doublet and triplet pulses from NRZ-DPSK signals is experimentally demonstrated by the dispersion of single mode fiber.Sixthly, all-optical signal processing based on FWM effect of SOAs is investigated. A typical SOA FWM model is presented. And we propose all-optical bit error monitoring system (BEMS) based on the FWM model. The BEMS is realized by cascaded SOAs, which implement logic NOT and logic AND, respectively. The results show this scheme is competent for 40Gbit/s RZ format and 10Gbit/s NRZ format. Then wavelength conversion based on FWM in an SOA for various bit rate and various data formats is experimentally investigated. Especially, for 40Gbit/s NRZ signals, multi-wavelength conversion from single channel to triple channels is obtained. At last, all-optical single-to-dual channel format conversion from NRZ to RZ using FWM in single SOA is demonstrated. Based on FWM, two sideband components are generated and both channels are RZ formats. And all the converted RZ signals have a Q factor larger than 6.更多还原