Coupled photonic systems exhibit intriguing optical responses attracting intensive attention, but available theoretical tools either cannot reveal the underlying physics or are empirical in nature. Here, we derive a rigorous theoretical framework from first principles (i.e., Maxwell’s equations), with all parameters directly computable via wave function integrations, to study coupled photonic systems containing multiple resonators. Benchmark calculations against Mie theory reveal the physical meanings of the parameters defined in our theory and their mutual relations. After testing our theory numerically and experimentally on a realistic plasmonic system, we show how to utilize it to freely tailor the lineshape of a coupled system, involving two plasmonic resonators exhibiting arbitrary radiative losses, particularly how to create a completely “dark” mode with vanishing radiative loss (e.g., a bound state in continuum). All theoretical predictions are quantitatively verified by our experiments at near-infrared frequencies. Our results not only help understand the profound physics in such coupled photonic systems, but also offer a powerful tool for fast designing functional devices to meet diversified application requests.

耦合光子系统表现出有趣的光学响应，引起了人们的广泛关注，但现有的理论工具要么无法揭示潜在的物理现象，要么本质上是经验性的。在这里，我们从第一原理（即麦克斯韦方程组）推导出严格的理论框架，所有参数都可以通过波函数积分直接计算，以研究包含多个谐振器的耦合光子系统。针对米氏理论的基准计算揭示了我们理论中定义的参数的物理意义及其相互关系。在现实的等离激元系统上对我们的理论进行数值和实验测试后，我们展示了如何利用它来自由定制耦合系统的线形，其中涉及两个表现出任意辐射损耗的等离激元谐振器，特别是如何创建具有消失的完全“暗”模式辐射损失（例如，连续体中的束缚态）。所有理论预测均通过我们在近红外频率下的实验定量验证。我们的研究结果不仅有助于理解此类耦合光子系统中的深刻物理原理，而且还为快速设计功能器件以满足多样化的应用需求提供了强大的工具。