Metalens has emerged as an important optical block in free-space optical systems, which shows excellent performance. Even the metalens based on gradient index (GRIN) profiles can be implemented for on-chip beam focusing behavior. However, for most previous schemes, the GRIN metalenses can only achieve on-chip beam focusing behavior in one dimension, which limits their applications in low-loss waveguide interconnecting or fiber-to-chip coupling. In this paper, an on-chip half Maxwell’s fisheye lens based on GRIN profiles with subwavelength features, integrated with silicon waveguides, is experimentally demonstrated. Benefitting from the index distribution and beam focusing characteristics of the half Maxwell’s fisheye lens, an on-chip beam transforming can be achieved for transverse electric (TE) fundamental mode in two waveguides with different heights and widths. The simulated 1 dB bandwidth can reach 1100 nm, which exhibits great prospects in integrated photonic circuits. The measured insertion loss of an on-chip 5.4 μm-length lens is less than 1 dB to connect a 220 nm-height, 8 μm-wide waveguide, and a 60 nm-height, 0.5 μm-wide waveguide in the wavelength range of 1280–1620 nm.

中文翻译：

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GRIN 元透镜在绝缘体上硅平台上实现超宽带片上光束聚焦

Metalens已成为自由空间光学系统中重要的光学模块，表现出优异的性能。甚至基于梯度指数 (GRIN) 轮廓的元透镜也可以用于片上光束聚焦行为。然而，对于大多数先前的方案，GRIN 元透镜只能在一维上实现片上光束聚焦行为，这限制了它们在低损耗波导互连或光纤到芯片耦合中的应用。在本文中，实验演示了一种基于具有亚波长特征的 GRIN 轮廓的片上半麦克斯韦鱼眼镜头，并与硅波导集成。受益于半麦克斯韦鱼眼镜头的折射率分布和光束聚焦特性，可以在具有不同高度和宽度的两个波导中实现横向电 (TE) 基模的片上光束变换。模拟的1 dB带宽可以达到1100 nm，在集成光子电路中展现出巨大的前景。片上 5.4 μm 长透镜的测量插入损耗小于 1 dB，以连接 220 nm 高、8 μm 宽的波导和 60 nm 高、0.5 μm 宽的波导，波长范围为1280–1620 纳米。