Photonic integrated circuits play an increasingly important role in several emerging technologies. Their functionality arises from a combination of integrated components, e.g., couplers, splitters, polarization rotators, and wavelength selective filters. Efficient and accurate simulation of these components is crucial for circuit design and optimization. In dielectric systems, design procedures typically rely on coupled-mode theory (CMT) methods, which then guide subsequent refined full-wave calculations. Miniaturization to deep sub-wavelength scales requires the inclusion of lossy plasmonic (metal) components, making optimization more complicated by the interplay between coupling and absorption. Even though CMT is well developed, there is no consensus as to how to rigorously and quantitatively implement it for lossy systems. Here we present an intuitive coupled-mode theory framework for quantitative analysis of dielectric–plasmonic directional and adiabatic couplers, whose large-scale implementation in 3D is prohibitively slow with full-wave methods. This framework relies on adapting existing coupled mode theory approaches by including loss as a perturbation. This approach will be useful in designing dielectric–plasmonic circuits, providing a first reference point for anyone using techniques such as inverse design and deep learning optimization methods.

中文翻译：

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等离子体耦合器的耦合模式理论

光子集成电路在多种新兴技术中发挥着越来越重要的作用。它们的功能源自集成组件的组合，例如耦合器、分光器、偏振旋转器和波长选择滤波器。这些组件的高效、准确的仿真对于电路设计和优化至关重要。在介电系统中，设计过程通常依赖于耦合模式理论 (CMT) 方法，然后指导后续的精细全波计算。深亚波长尺度的小型化需要包含有损等离子体（金属）组件，耦合和吸收之间的相互作用使得优化变得更加复杂。尽管 CMT 已经很成熟，但对于如何在有损系统上严格、定量地实施它，还没有达成共识。在这里，我们提出了一种直观的耦合模式理论框架，用于定量分析介电-等离子体定向和绝热耦合器，其在 3D 中的大规模实现采用全波方法的速度非常慢。该框架依赖于通过将损耗作为扰动来适应现有的耦合模式理论方法。这种方法将有助于设计介电等离子体电路，为使用逆向设计和深度学习优化方法等技术的任何人提供第一个参考点。