Ye Han, Wang Yanrong, Zhang Shuhe, Wang Danshi, Liu Yumin, Wang Mingchao, Zhang Qiming
State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications Beijing 100876 China
Centre for Theoretical and Computational Molecular Science, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland St Lucia QLD 4072 Australia
Nanoscale Adv. 2021 Jun 25;3(15):4579-4588. doi: 10.1039/d1na00198a. eCollection 2021 Jul 27.
Precise manipulation of mode order in silicon waveguides plays a fundamental role in the on-chip all-optical interconnections and is still a tough task in design when the functional region is confined to a subwavelength footprint. In this paper, digital metamaterials consisting of silicon and air pixels are topologically designed by an efficient method combining 2D finite element method for optical simulations, density method for material description and method of moving asymptotes for optimization. Only around 150 iterations are required for searching satisfactory solutions. Six high-quality and efficient conversions between four TE-polarized modes are achieved in a functional region with footprint 0.645 (center wavelength = 1550 nm). Based on asymmetric mode conversion, a reciprocal optical diode with high contrast ratio is further obtained with the optimization starting from TE0-to-TE1 mode converter. Moreover, we successfully design a 1 × 2 demultiplexer with footprint 1.0 and demonstrate a simple mode division multiplexing system with satisfactory performances. Finally, by changing the refractive index to an equivalent value, quasi-3D designs are obtained and the functionalities are validated in 3D simulations for both free-standing and SOI configurations.
硅波导中模式阶次的精确操控在片上全光互连中起着基础性作用，而当功能区域被限制在亚波长尺寸时，其设计仍然是一项艰巨的任务。本文通过一种高效方法对由硅和空气像素组成的数字超材料进行拓扑设计，该方法结合了用于光学模拟的二维有限元方法、用于材料描述的密度方法以及用于优化的移动渐近线方法。搜索满意解仅需约150次迭代。在尺寸为0.645 （中心波长 = 1550 nm）的功能区域内实现了四种TE偏振模式之间的六个高质量且高效的转换。基于非对称模式转换，从TE0到TE1模式转换器开始优化，进一步获得了具有高对比度的互易光学二极管。此外，我们成功设计了尺寸为1.0 的1×2解复用器，并展示了一个性能良好的简单模式分复用系统。最后，通过将折射率改变为等效值，获得了准三维设计，并在三维模拟中对独立配置和绝缘体上硅配置的功能进行了验证。
