团队张永老师的工作--Ultra-broadband mode size converter using on-chip metamaterial-based Luneburg lens（基于片上龙柏透镜的超宽带模斑转换器）相关成果近期被ACS Photonics期刊接收发表，该工作得到了国家重点研发计划（2019YFB2203601）、国家自然科学基金（61975115/61835008/62035016）、上海市科学技术委员会（2017SHZDZX03）的部分资助。作者在提出了一种集成并基于龙柏（Luneburg）透镜的超宽带模斑转换器，用于以极低损耗将TE/TM模斑尺寸在不同宽度大小的光波导中进行转换。这项工作不仅完成了单个器件1.5 dB的极低损耗，还解决了以往模斑转换器带宽较小的问题，在740 nm的超宽带范围内实现模斑尺寸大小的转换。这为超宽带波导交叉、端面耦合等集成器件以及大规模集成应用提供一个有前景的方案。
摘要：A Luneburg lens with a gradient index distribution is an aberration-free and coma-free spherical lens. It has wide applications ranging from invisibility cloaks, illusion optics, and superlensing. However, it is challenging to realize an on-chip Luneburg lens with superior performance. In this paper, an on-chip Luneburg lens is implemented through the integration of gradient metamaterial structures and silicon waveguides. The filling ratio mapping of silicon nanorods is used to achieve the gradient index distribution. As an example of the application, a general and scalable approach for a mode size converter is demonstrated to match two waveguide modes with arbitrary widths. Benefiting from the aberration-free property, a 740 nm bandwidth is achieved in simulation. Limited by our measurement setup, the measured device bandwidth is 220 nm, covering the wavelengths of 1.26–1.36 and 1.507–1.627 μm. To the best of our knowledge, this silicon mode size converter exhibits the largest bandwidth.