[论文解读] Ultracompact Field Effect Electro-Absorption Plasmonic Modulator

Kaifeng Shi, Zhaolin Lu|arXiv (Cornell University)|Sep 29, 2015

Photonic and Optical Devices参考文献 20被引用 3

一句话总结

本文提出了一种基于氧化铟锡（ITO）掺杂金属-绝缘体-金属（MIM）波导并结合高k电介质与双栅结构实现电场增强的超紧凑电吸收等离子体调制器。器件长度仅为800 nm，在10 MHz时实现2.43 dB的消光比，工作带宽高达500 MHz，展示了面向高速片上光互连的纳米级解决方案。

ABSTRACT

One of the technical barriers impeding the wide applications of integrated photonic circuits is the lack of ultracompact, high speed, broadband electro-optical (EO) modulators, which up-convert electronic signals into high bit-rate photonic data. In addition to direct modulation of lasers, EO modulators can be classified into (i) phase modulation based on EO effect or free-carrier injection, or (ii) absorption modulation based on Franz-Keldysh effect or quantum-confined Stark effect. Due to the poor EO properties of regular materials, a conventional EO modulator has a very large footprint. Based on high-Q resonators, recent efforts have advanced EO modulators into microscale footprints, which have nearly reached their physical limits restricted by the materials. On-chip optical interconnects require ultrafast EO modulators at the nanoscale. The technical barrier may not be well overcome based on conventional approaches and well-known materials. Herein, we report an EO modulator, more specifically electro-absorption (EA) modulator, based on the integration of a novel yet inexpensive active material, indium tin oxide (ITO), in a metal-insulator-metal (MIM) plasmonic waveguide platform, where the field effect is then greatly enhanced by high-k insulator and double capacitor gating scheme. The modulator waveguide length is only 800 nm, which is the smallest recorded dimension according to our knowledge. Preliminary results show that it has extinction ratio of 1.75 (2.43 dB) at 10 MHz, works up to 500 MHz (limited by testing setup for now), and can potentially operate at high speed.

研究动机与目标

• 解决集成光子电路中缺乏超紧凑、高速、宽带电光调制器的问题。
• 克服基于传统材料与结构的常规电光调制器在物理尺寸上的限制。
• 通过等离子体波导与活性材料中的电场效应增强，实现纳米尺度光调制。
• 展示一种实用、低成本且可扩展的片上光互连解决方案，利用氧化铟锡（ITO）在等离子体平台中的应用。

提出的方法

• 在金属-绝缘体-金属（MIM）等离子体波导中集成氧化铟锡（ITO）作为活性材料，以实现电吸收调制。
• 采用高k电介质层以增强电场效应，提高载流子调制效率。
• 实施双电容栅极结构，进一步放大ITO层上的电场。
• 利用等离子体波导结构将光限制在衍射极限以下，实现极端微型化。
• 设计800 nm长的波导，实现迄今报道的电吸收调制器中最小的器件尺寸。
• 利用外加电场下ITO中的Franz-Keldysh效应，调制光学吸收。

实验结果

研究问题

• RQ1 基于ITO的等离子体调制器能否实现亚微米尺度工作，具备高消光比与带宽？
• RQ2 通过高k电介质与双栅结构实现的电场效应增强，如何提升纳米尺度等离子体波导中的电吸收效率？
• RQ3 在MIM结构中使用ITO时，可实现的电吸收调制器最小器件长度是多少？
• RQ4 在等离子体平台中集成ITO在多大程度上可实现适用于片上光互连的高速运行？
• RQ5 像ITO这样低成本、可扩展的材料，能否在超紧凑调制器中替代传统电光材料？

主要发现

• 该调制器实现了创纪录的800 nm波导长度，为迄今报道的电吸收调制器中最小尺寸。
• 在10 MHz时测得1.75（2.43 dB）的消光比，表明实现了有效的光学调制。
• 器件最高工作频率达500 MHz，仅受限于测试设备，表明具备实现更高频率的潜力。
• 采用高k电介质与双栅结构显著增强了电场效应，实现了纳米尺度下的高效调制。
• 在MIM等离子体波导中集成ITO实现了强光-物质相互作用与紧凑的器件尺寸。
• 所提出的结构展示了通往可扩展、低成本、超紧凑电光调制器在片上光互连中应用的可行路径。