Park Kyong-Tae, Kim Kyoung-Ho, Min Byung-Ju, No You-Shin
Department of Physics, Konkuk University, Seoul, 05029, Republic of Korea.
Department of Physics, Chungbuk National University, Cheongju, 28644, Republic of Korea.
Sci Rep. 2023 Oct 16;13(1):17510. doi: 10.1038/s41598-023-44809-w.
Coupled optical cavities are an attractive on-chip optical platform for realizing quantum mechanical concepts in electrodynamics and further developing non-Hermitian photonics. In such systems, an intercavity interaction is often considered as a key parameter to understand the system's behaviors but its estimation/calculation is typically limited for some simplified systems owing to extended complexities. For example, multi-coupled photonic crystal (PhC) nanocavities exhibiting strong resonances with a large free spectral range can serve as an excellent test-bed to study non-Hermitian optical properties when spatially non-uniform gain is introduced. However, the detailed quantitative analysis such as spectral tracing of cavity normal modes is often limited in commercially available numerical tools because of the required massive computation resources. Herein, we report on a concept of spatial overlap integrals (SOIs) between the eigenmodes in non-coupled PhC nanocavities and utilize them to obtain the intercavity interactions in passively coupled PhC nanocavity systems. With the help of coupling strength factors calculated from SOIs, we were able to fully exploit the coupled mode theory (CMT) and readily trace the detailed spectral behaviors of normal modes in various multi-coupled PhC nanocavities. Full-wave numerical simulation results verified the proposed method, revealing that the characteristics of original eigenmodes from non-coupled PhC nanocavities can act as key building blocks for analyzing the normal modes of multi-coupled PhC nanocavities. We further applied this SOI method to various multi-coupled PhC nanocavities with non-symmetric optical gain/loss distributions and successfully observed the unusual spectral evolution of normal modes and the correspondingly occurring unique non-Hermitian behaviors.
耦合光学腔是一种极具吸引力的片上光学平台，可用于实现电动力学中的量子力学概念，并进一步发展非厄米特光子学。在这类系统中，腔间相互作用通常被视为理解系统行为的关键参数，但其估计/计算通常因复杂性增加而仅限于一些简化系统。例如，当引入空间非均匀增益时，具有大自由光谱范围且表现出强共振的多耦合光子晶体（PhC）纳米腔可作为研究非厄米特光学性质的理想测试平台。然而，由于需要大量计算资源，诸如腔正常模式的光谱追踪等详细定量分析在商业可用的数值工具中往往受到限制。在此，我们报告了非耦合PhC纳米腔本征模式之间的空间重叠积分（SOI）概念，并利用它们来获得被动耦合PhC纳米腔系统中的腔间相互作用。借助从SOI计算出的耦合强度因子，我们能够充分利用耦合模理论（CMT），并轻松追踪各种多耦合PhC纳米腔中正常模式的详细光谱行为。全波数值模拟结果验证了所提出的方法，表明非耦合PhC纳米腔的原始本征模式特征可作为分析多耦合PhC纳米腔正常模式的关键构建块。我们进一步将这种SOI方法应用于具有非对称光学增益/损耗分布的各种多耦合PhC纳米腔，并成功观察到正常模式的异常光谱演化以及相应出现的独特非厄米特行为。
