摘要
随着P2P技术和交互式视频等业务的蓬勃发展,1M、2M带宽的DSL网络已经逐渐无法满足人们的需求。为此,不少人提出了“光进铜退”的发展策略,用光信号来代替电信号进行传输。由此,信号传输速率可达Gbit/s的FTTx网络的发展受到了人们广泛的重视。
但是,全光网络的高成本却让运营商们却步。中国联通的最新报告披露:每户FTTx用户的建设成本高达2000-4000元人民币,这意味着FTTx技术还很难与DSL技术进行竞争。因此,如何在不断提高光网络信号质量的同时降低光网络的成本迫在眉睫。而将昂贵的光器件集成无疑是一个很好的解决方案。
上世纪五十年代,基于硅材料的集成电路的出现使得电子器件的成本大大降低,并由此给世界带来了革命性的变化。今天,硅材料再一次受到了人们的瞩目――硅基材料被认为是构建集成光子器件的理想平台。这意味着价格高昂的光通信系统器件将有可能像电子元器件那样被集成在一块芯片上,成本、体积、功耗都将显著降低。这无疑将成为光通信领域的一次革命。
本文围绕硅波导的信号处理技术开展了如下工作:
基于硅波导的全光信号处理
随着光通信技术的发展,不同类型的光网络不断涌现,而不同的网络有不同的最佳传输码型。所以,当信号要跨网络传输时,就需要在网络之间的交换节点对信号进行码型转换。鉴于信号在传输后的质量已经较差,在进行码型转换的同时还希望对信号进行整形。
本论文在介绍了使用硅基波导进行光信号处理的基本原理的基础上阐述了使用硅基器件实现将信号质量较差的不归零幅度(NRZ-ASK)调制码转换到高质量的归零幅度(RZ-ASK)调制码的方法;以及将信号质量较差的NRZ-ASK码转换到高质量的归零相位(RZ-PSK)调制码的方法。这项技术在未来的全光网络中会有重要应用价值。
基于硅波导的电光调制器
现在最为常用的电光调制器是马赫曾的调制器,该调制器使用方便,调制产生的信号质量较高,但是,这种调制器体积较大,不利于集成。为此,人们研制了硅基电光调制器。但现有的硅基电光调制器尚不能调制某些复杂码型,如抗非线能力强的RZ信号以及频谱利用率很高的四相位键控码(QPSK)和十六位正交振幅调制(16QAM)等信号。本文在介绍和比较传统电光调制器的基础上提出了若干种新的基于硅波导的电光调制器。通过仿真验证了使用硅基电光调制器调制QPSK和16QAM。此外,本文提出了一种通过对硅基微环进行混合调制产生RZ信号的方式。
With the rapid development of P2P technology and the interactive video services, traditional DSL access networks can no longer satisfy people's dailyrequirements. Thus, the "Optical Fiber Substituting Copper Wire" strategy has been proposed and the FTTX network that can support Gbit/s transmission has received much attention.
However, the develeopment of the all optical network has been impeded due to the high cost: it is revealed in the report from China Unicom that it will cost 2000-4000RMB for the construction of each FTTx user, which seriously reduced the competitiveness of FTTx. Therefore, it becomes an important topic to reduce the cost of the optical network while upgrading the transmission quality. Undoubtedly, integrating the expensive optical components in a chip is a good solution.
In 1950s, the invention of silicon based integrated circuit has significantly cut the cost of the electronic and electrical devices and even brought about a revolutional change to the whole world. Today, silicon device attracts the worldwide attention again as it is widely recognized as an ideal material for the farication of integrated optical circuit. This means that the expensive optical devices can be integrated in a small chip like electronic components. Both cost and power consumption will be reduced in a large amount. This will undoubtedly lead to a revolution in the optical field.
To accelerate the development of silicon based optical devices, my thesis focuses on the researches of the key technologies of all optical signal processing based on silicon waveguides and novel electro-optic modulators as follows:
All-optical regenerative format conversion:
With the development of the optical communication, optical networks of different types are emerging. As various networks needs its corresponding format signal for transmission, it is evitable to do format conversion when signal is transmitting across different type networks. Furthermore, as the quality of the signal is degraded after transmission, it is required that noe only format conversion but also regeneration can be accomplished in the optical network exchange unit.In my theies, basic principle of signal processing employing silicon waveguide is introduced. Also, the method to realize the format conversion from low quality NRZ-ASK signal to high quality RZ-ASK signal and the format conversion from low quality NRZ-ASK signal to high quality RZ-PSK is proposed and demonstrated. This technique will play important role in the next generation all optical networks.
M-QAM and RZ signal Eletro-Optic Modulators based on silicon waveguides:
In my theies, traditional modulators are introduced. After that, several new proposed silicon based modulators have been demonstrated. QPSK and 16QAM signals are generated by simulation. Besides, a RZ signal generator is proposed by both changing the refractive index and the coupling coefficient between silicon ring and waveguide.
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