Study on unidirectional-emitting photonic-crystal lasers based on topological photonics

2022年，首先，我继续完善关于单向导引共振(UGRs)的理论。建立了参数空间中UGR的一种新的拓扑解释，它与传统的拓扑电荷图相一致，但可以更好地阐明UGR的物理起源和动态演化。与传统的拓扑电荷图相比，利用这种新的解释可以方便地在参数空间中构造UGR，并讨论了它们与参数空间中的其他辐射奇点的相互作用，如例外点(EPs)和常规的带简并。在此基础上，对arxiv中预印的论文进行了更新，目前已被物理评论信函(Phys.莱特牧师。056401)其次，我发现，这种对UGR的拓扑物理解释实际上也可以应用到光子晶体中的其他振幅奇点。例如，它可以用来描述连续介质(BIC)中的束缚态。遵循同样的策略，我建立了BIC在整个动量空间的通用图景。结果发现，BIC的定义甚至可以扩展到光锥之外，所有可调谐的BIC实际上都是带反转的带间耦合的结果，包括偶然BIC和F-W BIC。

In 2022 year, first, I continued to improve the theory about the unidirectional guided resonances (UGRs). I established a new topological interpretation of UGRs in parameter space, which is consistent with the conventional topological charge picture, but may better clarify the physical origins and dynamic evolution of UGRs. Comparing to conventional topological charges picture, with this new interpretation, it's convenient to construct UGRs in parameter space, and their interplay with other radiation singularities in parameter space, such as exceptional points (EPs) and conventional band degeneracy is also discussed. Based on these, I updated the paper pre-printed in arXiv, and now it has been accepted by Physical Review Letter (Phys. Rev. Lett. 130, 056401)Second, I found that, this topological physical interpretation of UGRs actually can also be applied to other amplitudes singularities in photonic crystals. For example, it can be used to describe the Bound states in continuum (BICs). Following the same strategy, I established a universal picture of BICs in whole momentum space. It is found that the definition of BICs can be extended even outside the lightcone, and all tunable BICs are actually resulted from the interband coupling of band inversion, including the accidental BICs and F-W BICs.