摘要
归功于硅材料在微电子学上的统治性地位及其在光子学应用上的诸多优势,硅基平台正日渐成为集成光路的主流平台。随着近来硅基有源功能器件的突破,剩下的问题不再是讨论硅基集成光路的可行性,而是如何提高其相比其它方案的竞争力。
首先,随着硅波导尺寸的向下缩放,硅基集成器件与外围光纤的耦合上升为一个严峻的问题,解决该问题的一个方案是采用波导光栅耦合器作为硅集成光路的输入输出接口。本文从提高耦合效率和增加功能两方面来改进波导光栅耦合器的性能。对于前者,本论文利用干法刻蚀工艺中的迟滞效应实现了一个高效的非均匀波导光栅耦合器,它的耦合效率达到了64%,约是普通波导光栅耦合器的两倍。对于后者,本文提出并实验研究了基于一维波导光栅耦合器的新型偏振分束器。新一代的引入了底部布拉格反射层的偏振分束器具有-20 dB的消光比,同时两种偏振光的峰值耦合效率都达到了50%。
其次,硅基兼容技术的引进为在硅基底上实现有源器件提供了可能,但是相关器件的性能与其它方案相比尚有一定差距。混合硅基平台,通过将Ⅲ/Ⅴ族外延片嫁接到绝缘硅基片上,可以实现高性能的硅基有源功能器件。本文引入了一个通用的小信号电吸收光调制器模型,并由此开发了基于混合硅基平台的高速行波电吸收光调制器。实测的混合硅基行波电吸收光调制器的带宽达到了43 GHz,50Gb/s传输速率下,2V的驱动电压摆幅实现了8.8 dB的动态消光比。这是目前世界上速度最快的硅基光调制器。本论文也提出了混合硅基微环电吸收光调制器的构想。它具有增强的消光比、减弱的环境敏感度和改进的光带宽表现。
Nowadays, silicon platform is emerging to be the best candidate of photonic integrated circuits (PICs) due to not only the dominant status of silicon in microelectronics but also the great benefits brought to the photonics. Regarding the recent breakthroughs concerning active devices on silicon substrate, the question left is no longer the feasibility of silicon PIC but the competitiveness of its solution compared with its counterpart.
Firstly, along with the down scaling of the silicon waveguide's cross section, the cou-pling between the silicon PIC and the external fiber becomes a troublesome issue due to the mismatch of the mode and the polarization. One of the promising solution is to use the grating coupler as the input/output interface for the silicon PIC. We have attempted to improve the performance of the grating coupler from two aspects:improve its coupling efficiency and make it being versatile. For the former, a nonuniform grating coupler based on the lag effect in the dry etching process has been developed with a coupling efficiency of 64%, nearly a double of a standard one. For the latter, a polarization beam splitter (PBS) based on a one-dimensional grating coupler has been proposed and experimentally demon-strated. An extinction ratio of around-20 dB, as well as a maximum coupling efficiency of over 50% for both polarizations, is achieved by such a PBS with a bottom Bragg reflector underneath.
Secondly, silicon-compatible techniques make it possible to achieve active function on silicon platform, but more devotion is required in order to catch up with its counterpart. Hybrid silicon platform, where theⅢ/Ⅴmaterial is transplanted to the silicon on insulator wafer, is attractive to realize high performance silicon active devices. We have developed several high speed electroabsorption modulators (EAMs) on the hybrid silicon platform, using a general approach based on the transmission line analysis. A record bandwidth of 43 GHz, as well as a dynamic extinction ratio of 8.8 dB at 50 Gb/s with a 2 V driving voltage swing applied, has been achieved for a hybrid silicon traveling-wave EAM, proving that it is the fastest silicon modulator so far. We have also proposed an efficient hybrid EAM based on a microring. It is able to have an enhanced extinction ratio, a relaxed sensitivity and an improved optical bandwidth.
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