【作者】 李英；

【导师】 张晓萍；

【作者基本信息】 兰州大学 ， 无线电物理， 2012， 硕士

【摘要】 未来光纤通信系统的发展趋势是更高传输速率、更大信道容量。那么怎么对现有系统朝着这个方向优化升级,并且还要充分考虑到现实推广的成本问题。这就是成为现代光纤通信系统研究领域内的热点课题。本文提出的光学Meyer小波滤波器在优化高速非线性光纤通信链路中具有一定可行性和有效性,为提高系统的输入功率和延长了系统的传输距离,提高全光通信系统的通信质量提供了新的思路。首先本文提出光纤通信系统中基于时域透镜的新型滤波器结构。依据这种新的滤波器结构,利用时域透镜和马赫曾德尔调制器设计并实现光学Meyer小波滤波器。它的优点是可以直接在光域内消除由光放大器噪声、光纤色散和非线性效应共同作用而产生的非线性噪声,避免电域中信号处理方法光电转换中存在的电子瓶颈限制,可满足光纤通信系统更高速率的需求。模拟了几种不同光纤链路以40Gbit/s传输速率强度调制系统传输后接收端信号直接通过本文的光学Meyer小波滤波器。对通过在不同分解层数和不同带宽条件光学Meyer小波滤波器的信号的归一化方差和误码率进行比较。将这些仿真结果与传统光带通滤波器的去噪结果进行对比,验证本文所设计的基于时域透镜的光学Meyer小波滤波器的去噪结果拥有明显优越性,且光学Meyer小波滤波器(一层,带宽为290G)有最低的误码率,所以它是最佳选择。当输入峰值功率为6mW,传输距离为900km时,误码率降低了约11dB；在输入信号峰值功率为10mW时,保持误码率为10-9的条件下,经过本文设计的光学Meyer小波滤波器后传输距离可达到840km大于通过传统光带通滤波器后的715km,明显延长了传输距离。实际应用时充分利用已铺设光纤和设备,只要将光学Meyer小波滤波器放置在系统接收端前就可以升级优化,成本较低便于商业推广。更多还原

【Abstract】 The optical fiber communication system’s evolution is to be with higher bit rate, more channel capacity. How to upgrade the existing commercial fiber links and save the cost in practice is becoming the focus topic in optical fiber communication systems. Optical Meyer wavelet filter based on time lenses proposed in this work can achieve better results than other optical filters so it can improve the channel capability and guarantee the quality of higher bit rate optical fiber communication. And it was feasible and effective for optimize optical communication system. The main work was shown as below:Firstly analyzing basic structure of2-f time lenses sub-system showed its characteristics of Fourier transform for optical signal in all-optical domain and the relation between the dispersion of the dispersive component and the quadratic phase of the phase modulator that is a time lens. According to the relation between input and output optical signal of2-f sub-system, factors that would affect output signal and the methods for avoid these factors were discussed.In this paper we proposed a novel scheme of optical Meyer filter based on time lenses. Then the detailed mathematical derivation was stated and we got important functions about Meyer wavelet decomposition and reconstruction process. According to these functions, an optical Meyer wavelet filter was designed and realized by use of time lenses and Mach-Zehnder modulators (MZMs). It can realize the wavelet decomposition of optical signals in all-optical domain and directly de-noise the distorted optical signal in high bit rate optical communication systems without photo-electric conversion. Numerical simulations were performed in different types of fiber links for intensity modulated (IM) signal when optical Meyer wavelet filter was applied at the end of40Gbit/s multi-span dispersive and nonlinear fiber transmission systems. By comparing Normalized Squared Deviations (NSDs) and Bit Error Rates (BERs) of the signals without de-noising, after optical band-pass filter and optical Meyer wavelet filter, we demonstrated that the nonlinear noise can be removed more effectively by optical Meyer wavelet filter. The BER curves in dispersion compensation links with optical Meyer wavelet filter at1level with290G bandwidth shows the best immunity to nonlinear noise, which can reduce BER about11dB with6mW input power and900km transmission distance, and can extend transmission distance to840km longer than715km that de-noising with optical band-pass filter at BER=10-9when compared with the traditional optical band-pass filter de-noising. And it is convenient to be applied in the existing fiber systems without changing the arrangement of fiber links in use when considering the cost for upgrading fiber communication systems in commercial application.更多还原