中科院半导体材料科学重点实验室知识库

在光纤通信器件集成化、小型化的趋势下，高可靠性、低成本的光子集成芯片将成为未来光纤通信的主角。作为光发射芯片核心部件，激光器的性能是直接决定整个光子集成芯片性能的关键。由于在光子集成器件中仍然难以集成光隔离器，芯片内和芯片外的光反射将对整个光子集成器件的性能有较大的影响。在光接入网中为了降低光发射模块的成本也希望能够省去光模块中成本占比较高的隔离器。激光器抗反射研究在激光器应用于通信系统的早期曾有过广泛研究，但是在分立光隔离器引入光模块后，相关研究也随之减少。随着接入网、数据中心对光模块成本和数量需求的提升，激光器抗反射研究又引起人们关注。提高激光器的抗反射能力是实现高可靠性、高性能、低成本光子集成芯片的重要环节，并具有很高的研究价值和应用前景。另一方面，在光子集成芯片中，无源波导损耗也是影响集成器件性能的关键因素。波导损耗的精确快速表征对光子集成芯片的设计和优化具有重要参考意义。目前波导损耗测量主要采用双端耦合的方式，测试系统复杂，耦合难度大。寻找一种测量精确且简单易行的波导损耗表征方法是光子集成中的重要问题。

本论文主要对光子集成中激光器的抗反射问题以及无源波导的损耗表征问题展开了研究。研究内容包括：分布反馈（Distributed Feedback, DFB）激光器在反馈下的动态特性以及关于抗反射性能的参数仿真优化； DFB激光器的设计制作与抗反射测试；提出并验证了基于法布里 - 珀罗（Fabry-Perot, F-P）腔反射谱精细度的波导损耗测量方法。本论文的主要研究内容和创新成果如下：

1.      从DFB激光器的耦合波方程出发，阐述了外界反馈对激光器动态特性的影响。通过对DFB激光器的非稳态阈值的计算，从理论上得到了提高DFB激光器抗反射性能的优化方向。

2.      通过商用软件搭建了DFB激光器在反馈下的静态和动态仿真模型。针对1310nm的DFB激光器进行了仿真优化，仿真研究了端面反射率、光栅结构等参数对DFB激光器抗反射性能的影响。提出了基于相对强度噪声谱的Bessel积分用于表征激光器的非稳态阈值。

3.      制作了DFB激光器，并对其抗反射性能进行了系统测试。包括变温反馈下的光谱特性、眼图以及误码曲线等。通过实验测量，验证了理论计算和仿真中激光器在反馈下的动态行为。

4.      对F-P干涉的反射谱进行了理论计算，通过对F-P干涉反射谱的精细度提取，解决了F-P腔内反射谱中首次反射光（the Initially Reflected Launching Optical Filed, IRLOF）不确定性导致的反射谱误差问题，并且从理论上论证了反射谱精细度可以用于表征谐振腔内波导损耗的可行性。首次提出了基于F-P反射谱精细度的波导损耗测量方法。实验验证了基于F-P反射谱精细度的波导损耗测量方法的可行性与准确性。

With the development of integration technology, highly reliable, low-cost photonic integrated chips will be crucial to future optical fiber networks. As the core component in transmitters, the laser source is a key factor influencing the performance of the entire photonic integrated chip. Since there is still no on-chip optical available for photonic integrated chips, the reflections from inside and outside of the chip will have great influence on the performance of the entire photonic integrated device. On the other hand, in order to reduce the cost of the transmitters in the optical access network, it is also desirable to remove the isolator in the optical module. Therefore, a laser with a certain reflection-resistant capability will be beneficial to achieving high reliability, high performance, and low-cost photonic integrated chips.

The passive waveguide loss is also a key factor affecting the performance of the integrated devices. At present, the waveguide loss measurements mainly rely on double end fiber coupling, resulting in a complex and time-consuming coupling procedure. Finding an accurate and simple waveguide loss characterization method is an important issue in photonic integration research.

This thesis focuses on reflection resistant laser sources in photonics integration chips and the loss characterization of passive waveguides. The research includes the dynamic characteristics of DFB lasers under feedback, the simulation, and optimization of reflection-resistant DFB lasers; the characterization of DFB lasers under feedback; the waveguide loss measurement method based on the F-P cavity reflection spectrum fineness. The main research and innovation in this paper include:

1.      Starting from the coupled-wave equation of the DFB laser, the influence of external feedback on the dynamic characteristics of the laser is described. By calculating the unsteady threshold of the DFB laser, the reflection-resistant optimization of the DFB laser is theoretically obtained.

2.      The static and dynamic simulation model of a DFB laser under feedback is built through commercial software. The influence of the parameters such as facet reflectivity and grating structure on the reflection-resistant performance of the DFB laser was studied. A Bessel integral based on relative intensity noise (RIN) spectrum was proposed to characterize the laser's unsteady threshold.

3.      A 1310-nm DFB laser was fabricated and its reflection-resistant performance was systematically tested, including the spectral characteristics under different temperature and feedback levels, eye diagrams and bit error rate curves.

4.      A theoretical calculation of the reflection spectrum of Fabry-Perot (F-P) interference is performed. Through the fineness extraction of the F-P interference reflection spectrum, the problem caused by the uncertainty of the initially reflected launching optical filed (IRLOF) in the F-P cavity reflection spectrum is solved. A waveguide loss measurement method based on the fineness of the F-P reflection spectrum is proposed. The experiment verifies the feasibility and accuracy of the waveguide loss measurement method based on the fineness of the F-P reflection spectrum.