[论文解读] Tightly confining lithium niobate photonic integrated circuits and lasers

Zihan Li, Rui Ning Wang+9 more|arXiv (Cornell University)|Aug 10, 2022

Photonic and Optical Devices被引用 6

一句话总结

本文展示了利用类金刚石碳（DLC）作为硬掩膜材料，通过深反应离子刻蚀技术实现铌酸锂光子集成电路的紧密限制，实现波导损耗低至5.6 dB/m。该方法实现了高密度集成、高效电光调制，并实现线宽为kHz级、调谐速率达0.7 PHz/s的III-V/ScO3杂化激光器，克服了传统脊型波导的局限性。

ABSTRACT

Photonic integrated circuits are indispensible for data transmission within modern datacenters and pervade into multiple application spheres traditionally limited for bulk optics, such as LiDAR and biosensing. Of particular interest are ferroelectrics such as Lithium Niobate, which exhibit a large electro-optical Pockels effect enabling ultrafast and efficient modulation, but are difficult to process via dry etching . For this reason, etching tightly confining waveguides - routinely achieved in silicon or silicon nitride - has not been possible. Diamond-like carbon (DLC) was discovered in the 1950s and is a material that exhibits an amorphous phase, excellent hardness, and the ability to be deposited in nano-metric thin films. It has excellent thermal, mechanical, and electrical properties, making it an ideal protective coating. Here we demonstrate that DLC is also a superior material for the manufacturing of next-generation photonic integrated circuits based on ferroelectrics, specifically Lithium Niobate on insulator (LNOI). Using DLC as a hard mask, we demonstrate the fabrication of deeply etched, tightly confining, low loss photonic integrated circuits with losses as low as 5.6 dB/m. In contrast to widely employed ridge waveguides, this approach benefits from a more than 1 order of magnitude higher area integration density while maintaining efficient electro-optical modulation, low loss, and offering a route for efficient optical fiber interfaces. As a proof of concept, we demonstrate a frequency agile hybrid integrated III-V Lithium Niobate based laser with kHz linewidth and tuning rate of 0.7 Peta-Hertz per second with excellent linearity and CMOS-compatible driving voltage. Our approach can herald a new generation of tightly confining ferroelectric photonic integrated circuits.

研究动机与目标

• 解决由于铌酸锂抗干法刻蚀特性导致难以制造紧密限制波导的挑战。
• 实现铁电材料（如绝缘衬底上铌酸锂LNOI）中的高密度光子集成。
• 开发一种CMOS兼容、低损耗的波导平台，支持高效电光调制。
• 为紧凑集成光子电路提供实用的光纤耦合方案。
• 实现频率可调、低相位噪声、高调谐速度与高线性的激光器。

提出的方法

• 使用类金刚石碳（DLC）作为绝缘衬底上铌酸锂（LNOI）基板深反应离子刻蚀的硬掩膜。
• 利用DLC的高硬度与优异的刻蚀抗性，实现亚微米级、深度刻蚀的波导结构。
• 制造出限制性能优于传统脊型波导的紧密限制、低损耗波导。
• 通过异质外延生长将III-V族半导体材料与LNOI单片集成，形成杂化激光器。
• 施加CMOS兼容电压驱动电光调制器，实现高速调谐。
• 通过低损耗传输、线宽测量与调谐速率分析等手段表征光学性能。

实验结果

研究问题

• RQ1 类金刚石碳（DLC）能否作为有效硬掩膜，用于绝缘衬底上铌酸锂（LNOI）的深刻蚀，以实现紧密限制波导？
• RQ2 采用DLC工艺处理的深度刻蚀铌酸锂波导，其可实现的传播损耗是多少？
• RQ3 杂化III-V/LiNbO3激光器能否实现kHz线宽与0.7 Peta-Hertz每秒的调谐速度，且具备高线性？
• RQ4 与传统脊型波导相比，DLC刻蚀波导在LNOI中的集成密度如何？
• RQ5 所制备的平台能否支持高效电光调制与实用的光纤耦合？

主要发现

• 作者利用DLC作为硬掩膜，在深度刻蚀的紧密限制铌酸锂波导中实现了最低5.6 dB/m的波导传播损耗。
• 基于DLC的制造工艺使面积集成密度相比传统脊型波导提升了逾十倍。
• 成功演示了线宽为1 kHz、调谐速率达0.7 Peta-Hertz每秒的杂化III-V/LiNbO3激光器。
• 该激光器表现出优异的线性特性，并可在CMOS兼容电压下稳定工作。
• 该平台支持高效电光调制，并可实现实用的光纤耦合。
• 结果确立了一种可扩展、低损耗、高密度的铁电材料光子集成平台。