Second-order photonic topological insulators (SPTIs) featured with topological edge and corner states provide an intriguing way for steering light in integrated optics. However, existing SPTIs have narrow bulk gaps for tightly confining topological edge and corner states. In this paper, we propose a bi-directional evolutionary structural optimization (BESO) method to inversely engineer SPTIs in C₃-symmetric lattices. At first, we maximize the first band gap of a photonic crystal (PC) enforced with C₃ symmetry. Then, the topological phase transition is achieved by inverting the optimized PC. Highly localized topological edge and corner states are formed at the boundary and corner between the optimized PC and its inversion-symmetry partner. The bandwidth of the topological edge state for TE modes achieves 44.9%, exceeding two times of the current record. The robust of the topological corner states is further demonstrated. Our work provides a new route for designing SPTIs, paving the way towards their practical application.

具有拓扑边缘和角状态的二阶光子拓扑绝缘体 (SPTI) 为集成光学中的光导引提供了一种有趣的方式。然而，现有的 SPTI 具有狭窄的体间隙，用于严格限制拓扑边缘和角状态。在本文中，我们提出了一种双向演化结构优化 (BESO) 方法来逆向工程 C ₃对称晶格中的 SPTI。首先，我们最大化用 C ₃强制的光子晶体 (PC) 的第一带隙对称。然后，通过反转优化的 PC 来实现拓扑相变。高度局部化的拓扑边缘和角状态在优化的 PC 与其反演对称伙伴之间的边界和角处形成。TE模式的拓扑边缘状态带宽达到44.9%，超过当前记录的两倍。拓扑角状态的鲁棒性得到进一步证明。我们的工作为设计 SPTI 提供了一条新途径，为其实际应用铺平了道路。