Reconstructable Low‐Threshold Quasi‐BIC Lasers via a Tunable Polymer Coating

ABSTRACT Reconstructable and sustainable microcavity lasers are highly desirable for next‐generation integrated photonics. Here, we report a reconstructable, low‐threshold quasi bound state in the continuum (quasi‐BIC) laser fabricated via low‐cost, high‐throughput interference lithography. By introducing a polyvinyl alcohol (PVA) coating on a dye‐doped photonic crystal, we suppress out‐of‐plane symmetry breaking, which reinforces optical confinement and reduces the lasing threshold. The quasi‐BIC modes are further tuned through tailoring the refractive‐index of the PVA layer by using Kramers–Kronig (K–K) relation via Rhodamine 6G doping, demonstrating a wavelength shift of 7.14 nm and a sensitivity of 215 nm RIU − 1 as a sensing prob. More importantly, lasing modes are reversibly tuned via precisely controlling the coating thickness. Exploiting the dissolving and re‐coating process, the laser is repeatedly reconstructed while maintaining performance. This work provides a sustainable and adaptive platform for sensing and reconstructable photonic devices.