How topological protection enables robust nanophotonic device fabrication

Nanoimprint lithography (NIL) offers two major advantages: (1) it requires no etching during patterning, making it more cost‑effective than traditional methods such as electron‑beam lithography and focused‑ion‑beam etching; (2) it is well-suited for large‑area, high‑volume fabrication. However, practical visible‑band nanodevices still face stringent fabrication‑tolerance requirements, as defects are difficult to avoid during demolding. This issue is especially pronounced for solution‑processed functional materials, such as organic dyes and colloidal semiconductor nanocrystals (NCs). Topological photonics provides a potential pathway to address these fabrication challenges. Originating from mathematics, topology describes the properties of objects that remain invariant under continuous deformations. This has motivated researchers to combine NIL with topological photonics to develop low‑cost, scalable topological photonic devices, including topological lasers.

This work reports a room‑temperature nanoimprinted topological laser operating at 523 nm. The device is fabricated by a single, hand‑made imprint step with all‑inorganic cesium lead halide (CsPbBr₃) perovskite nanocrystals as the gain medium. Based on tight‑binding modeling and finite‑element simulations, the authors designed a specialized two‑dimensional Kagome lattice that supports multiple higher‑order topological corner states (HOTCS), which they characterized using stimulated‑emission spectroscopy. Beyond the conventional type‑I and type‑II corner states, the study achieved the first observation and lasing demonstration of type‑III corner states in the visible band. The device exhibits strong robustness against fabrication defects introduced during nanoimprinting. The results highlight the potential of NIL for the large‑scale fabrication of topological photonic devices using low‑index materials, extend HOTCS research into the visible spectrum, and provide important insights into how topological design can enhance the functionality and robustness of conventional NIL processes.

The team notes that further studies are needed, but this work represents the first step toward imparting functional robustness to conventional NIL fabrication strategies. “In light of these results, a systematic and exhaustive quantification of the defect tolerance upper bound across all possible disorder configurations in topological design will be necessary,” says Duan.