Low-Loss Switchable Topological Photonic Crystal Enabled by Submicron-Scale Patterning and Phase-Change of Sb ₂ Se ₃

Photonic topological insulators (PTIs) provide robust platforms for light manipulation; however, achieving reconfigurable control of their topological properties without compromising performance remains a significant challenge. Although phase-change materials (PCMs) offer large refractive index modulation and are widely used in commercial applications such as optical data storage, conventional materials like Ge2Sb2Te5 (GST) exhibit significant optical absorption in the crystalline state. This severe absorption limits their applicability in transmissive photonic devices such as PTIs, where high transparency is essential. Here, we address this limitation by integrating the ultralow-loss PCM antimony triselenide (Sb2Se3) with a silicon-based two-dimensional PTI. We demonstrate, for the first time, the submicron-scale selective patterning of Sb2Se3 on a photonic crystal, realizing a topological phase transition triggered by the switching of the material state. Capitalizing on the transparency of Sb2Se3 in both its amorphous and crystalline states, we maintain a high Q-factor on the order of 103, representing an order-of-magnitude improvement over previous GST-based devices. This work resolves the absorption-loss bottleneck in reconfigurable PTIs, paving the way for practical, low-loss, and tunable topological photonic devices.