| 题名 | 波分复用通信中光交错复用器的算法和结构研究 |
| 作者 | 张娟 |
| 学位类别 | 博士 |
| 答辩日期 | 2004 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 刘立人 |
| 关键词 | 光交错复用器 波分复用 光通信 双折射 偏振光干涉 |
| 其他题名 | Algorithm and Structure of Optical Interleaver in Wavelength-Division-Multiplexing Technology |
| 中文摘要 | 密集波分复用（DwDM）技术是当前扩大通信容量而普遍采用的技术方案。随着密集波分复用技术的迅速发展，信号频率间隔愈来愈小，这就对DWDM系统的核心光学器件一复用／解复用器提出了越来越高的光谱分辨要求。近年来发展起来的光交错复用器（interleavel）技术，可有效减轻现有的DWDM系统对更小波长间隔要求的负担、使许多成熟的滤波技术得以在新应用中继续发挥作用，同时也大大提高了系统传输容量，并已逐渐成为波分复用系统中的核心技术。在DWDM系统的实际应用中，大的平坦通带和阻带宽度、低的交叉串扰（即高的隔离度），中心频率的可调谐特性等是光交错复用器所必须具有的基本特性，此外，密集波分复用系统的发展趋势也要求光交错复用器能够分离越来越小的频率间隔信道的信号。以上这些特性同时也是国内外研究学者们努力追求的目标。本论文基于同样的研究目标，从偏振光干涉型光交错复用器的角度出发进行研究与设计，主要内容包括：（1）针对干涉型光交错复用器，提出了一种用于光谱平坦化结构设计的傅立叶级数对比的正向搜索算法。其可在较大的平坦通带和阻带范围内得到抖动很小时的所有可能的结构参数的数值解。该算法不受系统各元件必须具有相同位相延迟的限制，因而在设计具有高次阶余弦级数的光谱透射率波形时所需元件数目较少。此外，由于该算法属于正向推导，且计算和搜索过程都可借助于目前计算功能强大的计算机而进行，因而不仅大大简化了计算，可靠性高又可得到多组结构参数，器件性能得以大大提高。该算法应用广泛，不仅适用于基于偏振光干涉原理的各种光交错复用器，还可用于基于双（多）光束干涉原理的各种光交错复用器。（2）系统研究了传统的基于级联双折射晶体结构的偏振光干涉型光交错复用器，并利用傅立叶级数对比的正向搜索算法具体设计了一个三块晶体级联结构的光交错复用器，给出了晶体方位角的多组计算结果。此外，还对每块晶体的厚度和方位角偏离理想情况时，光谱透射率波形所产生的的影响进行了系统分析，研究结果对在实际中制作和应用该光交错复用器具有重要指导意义。（3）提出了一种级联模拟双折射式光交错复用器。其基于偏振光干涉原理，核心元件为级联的多个模拟双折射波片。其中每个模拟双折射波片等效于一个双折射晶体波片，且其等效双折射要比一般的双折射晶体大得多。我们设计了一个简单的实验验证了模拟双折射波片的这一特征。通过调整和控制模拟双折射波片的等效双折射延迟和方位取向，可产生平坦化的光谱透射率，从而实现波分复用信号的奇偶分离。文中给出了该结构光交错复用器的具体设计实例。此外，为了便于实际应用，还分析了该结构光交错复用器的温度特性，提出了两种简单易行、成本低廉的温度补偿方案。该结构的光交错复用器可采用优质和低价的光学材料实现大范围的等效双折射差，最大可高于一般双折射晶体约一个数量级，特别适用于高度密集波分复用信号并可实现其它方法达不到的很小的光谱频率间隔，光学元件加工和装校工艺简单，结构紧凑，作为波分复用的奇偶信号分离器时，具有很低的交叉干扰和大的平坦的通带和阻带宽度。（4）提出了一种级联介质对结构的马赫一泽德尔式光交错复用器。其基于双（多）光束干涉原理，核心元件为由级联的多个介质对构成的滤波器。其中每个介质对由具有不同折射率而结构对称的两介质片构成，且介质对交面镀有部分透射或反射的薄膜。通过调整和控制光在各级介质对中的光程差和介质对交面薄膜的透射率（或反射率）可产生具有平坦通带和阻带特性的光谱透射率，从而实现奇偶信号的分离。文中也给出了该结构光交错复用器的设计实例。该结构的光交错复用器可采用优质和低价的各向同性材料实现大范围的光程差，因而也易于实现频率间隔很小的波分复用信号的分离，并具有结构紧凑、工艺成熟、成本低、可靠性高和性能优良等特点。（5）为了实现DWDM系统中的末端的每个接收机对所需信道的选择，针对级联模拟双折射式光交错复用器，提出了三种可调谐光交错复用器的解决方案，并详细研究了各方案的调谐特性。其中分别利用旋转模拟双折射波片、将模拟双折射波片中的两介质片加工成楔形并使之产生相对滑动和优化切割晶体的横向电光效应，来调节光在各模拟波片中的光程差，从而实现光谱透射率的可调谐特性。这三种调谐方案操作简单、易于实现，其中前两个调谐方案属于机械调谐，第三个调谐方案属于电光调谐。电光调谐方案调谐速度高，通过晶体的优化切割可获得较低的调谐电压（其比以前最常用的利用电光系数乃。的电光结构的调谐电压还要低）。并在实验上通过妮酸铿晶体验证了该结构光交错复用器的电光调谐原理。（6）提出了一种设计格子结构型光交错复用器的简单、有效的新方法。首先从原理上分析和比较了偏振光干涉型和格子结构型光交错复用器，揭示了两者光谱透射率的数学上的等效性，给出了两者结构参数之间的等效关系，继而提出直接利用经简单的傅立叶级数对比的正向搜索算法所得到的晶体的结构参数和该等效关系对格子结构型光交错复用器的结构进行优化设计的新方法。并给出了利用该方法设计两级和三级格子结构型光交错复用器的具体实例。与目前相关文献中所得到的结果相比，利用该方法可以简便地得到具有任意要求的平坦化光谱透射率（信道间隔、通带和阻带宽度、隔离度等）的多组结构参数值。 |
| 英文摘要 | Dense wavelength-division-multiplexing (DWDM) technology is widely used to increase the communication capacity at the present time. With the rapid development of it, the frequency spacing of multiplexing signals becomes smaller and smaller. Higher and higher spectrum resolution is needed for the multiplexer/demultiplexer, the key optical component of DWDM system. Recently developed interleaver technology, which can efficiently alleviate the burden of smaller wavelength spacing required for DWDM system, make many mature filter technique keep up working in new applications and increase the transmission capacity of system greatly at the same time. It gradually becomes the key technology of DWDM system. In the practical applications of DWDM systems, wide flat-passband and stopband, low crosstalk (i.e., high isolation), tunability of center-frequency are the essential properties that interleaver must be possessed of. Besides, the development trend of DWDM technology also requires it can separate signals with smaller and smaller frequency spacing. These properties are the goals that researchers and engineers endeavor to pursue for. This dissertation is based on the same research goals. The main works are listed as the followings: (1) An algorithm based on comparing of Fourier series and positive-direction searching is proposed to produce flattening spectral transmittance for optical interleave! based on interference principle. We can obtain all the numerical solutions of the structural parameters when ripples are relatively small in both the relatively wide passband and stopband. Because the algorithm is not limitted by the same phase delay of each element, it can realize spectral transmittance with high order cosine series by fewer elements. Besides, as it belongs to positive-direction derivation and computers with very strong calculation power can be used to carry out the calculation and searching, the algorithm not only simplifies the calculation process but also produces many choices of structural parameters. Moreover, the performance of device can be improved greatly. The application range of this algorithm is wide. It can be applied to all kinds of interleavers based on the interference of polarized light and two-beam or multiple-beam interference. (2) The interleaver based on interference of polarized light is studied systematically. An interleaver composed of three cascaded crystals is designed by the algorithm mentioned above and many groups of the crystal azimuth angles are given. Besides, the influence of the change of the azimuth angles and thickness of the crystals on the spectral transmittance of the evice is discussed in detail as well. These results are very important for practical manufacture and application of the interleaver. (3) An interleaver based on cascaded analog birefringent structure is proposed. It is based on the principle of the nterference of polarized light. Its key components are analog birefringent wave-plates. Each analog birefringent wave-plate is equivalent to a birefringent crystal wave-plate and its equivalent birefringence is much larger than that of the traditional crystal wave-plate. A simple experiment is carried out to verify this performance of the analog birefringent wave-plate. Throtigh controlling the equivalent birefringent delay and the orientation of the analog birefringent wave- plates, the flattening spectral transmittance can be obtained, and thus the odd and even channel signals can be separated. A design scheme of this configurated interleaver is given as an example. Moreover, for the sake of practical application, the temperature effect of this interleaver is analyzed. Two simple and low-cost methods are proposed to compensate the temperature effect. Large equivalent birefringence can be obtained by utilizing high quality and low cost optical materials (such as optical glass). The biggest equivalent birefringence can be about one order of magnitude larger than that of the tranditional crystal. This interleaver is especially suitable for the separation of dense wavelength division multiplexing signals and can realize very small frequency spacing that can't be obtained by other methods. Besides, the machining and assembling of the optical component are simple. Very low crosstalk and wide flat passband and stopband width can be achieved when separating the odd and even channel signals with this interleaver. (4) A Mach-Zehnder interleaver based on cascaded medium pairs structure is proposed. It is based on the principle of two- or multiple-beam interference. Its key component is a filter composed of several cascaded medium pairs. Each medium pair is composed of two medium plates with same shaped and different refractive index. Partially transmitting (or reflecting) film is deposited on the interface of them. Through controlling the optical path difference in the medium pair and transmissivity (or reflectance) of interfacial film, the flattening spectral transmittance can be obtained, and thus the odd and even channel signals can be separated. A design example of this configurated interleaver is also given. As large range of optical path difference can be obtained using high quality and low cost isotropic optical materials, this interleaver can separate signals with very small frequency spacing. Moreover, it has many advantages, such as compact size, mature technique, low cost, high reliability and good performance. (5) In order to accomplish the channel selection of receiver at the end of DWDM system, three tuning schemes is proposed for the interleaver based on cascaded analog birefringent structure and the tunability performance of each scheme is investigated carefully. The tunability are realized through rotating analog birefringent wave-plates, relative sliding of two wedge-shaped medium plates, and the transversal electro-optic effect of optimum-cut crystals respectively. The three schemes are simple and easy to be carried out. The first two schemes belong to mechanical tuning and the third one belongs to electro-optical tuning. The third scheme has high tuning speed and low tuning voltage (lower than that of the previously considered the most favorable electro-optical configuration using electro-optic coefficient y33). The feasibility of electro-optic tuning for this interleaver is verified by an experiment with LiNbO3 electro-optic crystal. (6) A simple and efficient method for designing lattice-form interleaver is proposed. The principles of the polarization interference type and lattice-form interleavers are analyzed and compared. The equivalent mathematical representation of the spectral transmitance of the two kinds of interleavers is revealed and the equivalent relationship between the structural parameters of the two interleavers is given. Then the new method to optimum design lattice-form interleaver by directly utilizing the structural parameters of crystals obtained by the simple algorithm mentioned above and the equivalent relationship is proposed. The design examples of two-stage and three-stage lattice-form interleaver are given. More choice of structural parameters with any required spectral transmittance (channel spacing, flatness, isolation and ripple) can be conveniently obtained using this method when compared with results presented in references. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15427]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 张娟. 波分复用通信中光交错复用器的算法和结构研究[D]. 中国科学院上海光学精密机械研究所. 2004. |
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