【作者】 刘瑞；

【导师】 陈向飞；

【作者基本信息】 南京大学 ， 材料物理与化学， 2014， 硕士

【摘要】 光子通信技术作为当今信息社会重要的通信技术,发展极其迅速。如今光子通信对光网络传输容量的需求是过去的数万倍,曾经分立式的光子器件已经无法满足增长如此迅速的容量需求,波分复用技术的出现,引领光通信领域进入了光子集成的时代。在当今超大规模并行光子集成领域,许多光子器件中都会用到波导光栅滤波器,如分布反馈式(Distributed Feedback,DFB)激光器、光栅耦合器等。本论文对波导光栅滤波器的结构和性质作了研究,归纳出其反射谱中存在的一种特殊性质——积分不变性,即如果波导光栅的相位沿着腔长径向变化,而折射率调制强度不发生改变的时候,无论光栅本身的结构如何变化,最终所得到的反射谱中积分面积会基本保持不变。论文结合波导光栅的制作工艺,将这一特殊性质应用在波导布拉格光栅的精度研究中。第一章绪论中,简要介绍了光子通信的发展趋势,讲述了从最初的分立器件到如今光子集成的现代通信的历史进程。在众多光子器件中,详细介绍了波导光栅滤波器,给出了波导光栅的基本结构以及几种常见波导光栅的折射率调制特性。通过介绍两个实际光栅结构的制作工艺,提出波导光栅制作中误差的存在,本论文研究波导光栅的原理及特性,很大程度上是为了能够更加正确的认识和理解波导光栅制作工艺中存在的误差,从而更加有效的控制布拉格波长的精确度。第二章从理论的角度出发,对波导光栅的基本原理做了推导。首先建立光栅的基本传输模型,通过相位匹配原理确定光栅周期和反射波长之间满足的基本条件：布拉格条件。然后采用弱折射率光栅中常用的理论手段——耦合模理论,来分析波导光栅中前向波和后向波之间存在的数值方程,之后用传输矩阵模型来求解耦合模方程的解析解,通过最后求得的传输矩阵,我们可以得到光栅的一些基本传输特性,如反射、透射、时延等结果。最后,将理论方法应用在几种常见光栅的仿真中,给出其各自的特征谱线。这一章中提到取样结构中的等效思想,这对于利用重构等效啁啾技术(REC)来制作DFB激光器有着指导意义。第三章中,我们将耦合模理论的解析求解过程具体应用到弱折射率波导光栅的反射谱中,并且利用其耦合系数的傅里叶变换和实际空间光栅反射系数之间的关系,首次提出弱折射率光栅的反射谱中一个特殊的性质——积分不变性。在这一特性的证明过程中,我们设计了五种不同的结构,分别计算其积分性质,最终得以验证积分不变性的正确性。为了能够实际应用这一性质,我们通过改变光栅的耦合系数,寻找积分不变性的适用范围,得出只有在弱折射率的情况下,光栅反射谱中的积分不变性才有实际意义。最后,我们将这一性质应用到两个实际光谱分析的案例中,对波导光栅中禁带宽度的问题和光栅制作误差对光谱的影响问题作了合理的解释,并首次提出了利用估算禁带宽度来重构啁啾光栅的耦合系数。第四章中,我们将误差分析的方法应用到DFB激光器的取样光栅制作中,由于激光器波导光栅工艺中确实存在难以避免的制作误差,在对器件的测试过程中,激射峰位置的判断会受到误差概念的影响,本章中,我们首先通过理论推导,得出误差高斯分布函数可以通过控制期望和标准差来控制误差光栅的取样周期范围。然后通过人为的设计取样误差的均值,来计算不同误差范围情况下,取样波导光栅的+1级激射峰位置,最终的仿真结果告诉我们,取样光栅存在误差的情况下,激射波长的位置基本不发生飘移,腔长的增加可以提高波长的精确度,但是随着误差范围逐渐远离理想光栅的周期,激射峰的反射率衰减的很快。更多还原

【Abstract】 As an important communication technology in today’s information society, photonic communication technology develops rapidly. The requirements for optical network transmission capacity now are tens thousands times than past, as a result of which, discrete photonic devices can’t meet the capacity requirements.The photonic integrated circuit has opened a new window in the field of optical communication with the emergence of Wavelength Divison Multiplexing(WDM) technology. Among so many photonic devices, the waveguide Bragg grating plays an important role. It can be used in the Distributed Feedback (DFB) lasers, grating couplers and so on. This thesis focuses on the structures and properties of waveguide grating filter, and proposes a special property for the first time, namely integral invariance of reflective spectrum for weak-coupled waveguide Bragg grating, that is if only the grating phase is changed along the cavity and index modulation strength is uniform, the integral of the reflective spectrum of arbitrary grating profile nearly maintains a constant.In the first chapter, we give a brief introduction of the trend of the photonic communications development by telling a story from the original discrete device to the photonic integrated circuit of modern communication. We introduce the waveguide grating in details, and show the basic structures and properties of refractive index modulation of several common waveguide gratings. Then combined with the actual fabrication process of two grating structures, we proposed the existence of waveguide gratings’manufactural errors. In fact, this thesis is written in order to have a deeper understanding of the fabrication errors in the waveguide gratings.In chapter two, we derive the basic principle of waveguide grating. First we make a basic model of the transmission in the grating, and use the phase matching principle to confirm a relationship between the reflective wavelength and grating period, which is called "Bragg condition". Then we use the coupled-mode theory to analyze the relationships between the forward wave and backward wave. And to solve the equation of Coupled Mode Theory(CMT), we choose a way called transfer matrix method. By this method, we can get some basic transmission characteristics of the waveguide grating, such as the reflection spectrum, transmission spectrum and time delay. Finally, we carry out a simulation of several examples of common gratings. The sampling structure mentioned in this chapter is very important for the reconstruction equivalent chirp technology, especially in the design of DFB lasers.In chapter three, we utilize the CMT to analyze the reflection spectrum of the weak-coupled waveguide gratings. Also we raise a special property which has never been proposed before, which is the integral invariance of reflective spectrum for weak-coupled waveguide Bragg grating. To demonstrate this characteristic, we design five different structures with the same coupling coefficient and calculate their areas of reflection spectrum. Then we change the coupling coefficient to verify the scope of application and find that if only the refractive index is weak and grating phase is changed along the cavity, the integral invariance works well. At last, we apply this feature to analyze two cases, and give a reasonable explanation to the problems of the forbidden band width and the manufactural errors in the waveguide grating. And we put forward a method to reconstruct the coupling coefficient of the chirp grating though the estimation of the band width. In the last chapter, the error analysis method is applied to the sampling waveguide grating fabrication in the DFB lasers. Due to the existed errors in the process of waveguide grating manufacture of lasers, the judgment of the peak position of laser is always affected by the inevitable errors. In this part, we build a mode of error confirmed to gaussian distribution, and then by controlling the expectations and standard error of this gaussian distribution function, we can calculate the transmission spectrum of different error range. The final simulation results tell us that even if the sampling grating has errors, the lasing wavelength can keep constant. But as the error range drifts from the ideal grating period, the reflectivity of the peak decays quickly.更多还原