Non-Invasive Groove Engineering Enables External-Cavity-Free Single-Mode Polarized Lasers in Perovskite Microplates

Dynamic modulation of microcavity lasers is crucial for achieving stable single-mode operation with high monochromaticity, compact footprint, and directional emission. However, the emergence of higher-order transverse modes with increasing cavity dimensions has frustrated efforts to scale up cavities while maintaining stable single-mode operation. To date, no suitable physical mechanism has been identified that enables cavity size-independent single-mode lasing. Herein, a breakthrough non-invasive technique is developed for in situ engineering of natural nano-grooves in large-size ( ≥ $ \ge $ 20 × 20 µm) perovskite microplates (MPs) through kinetically controlled vapor-phase epitaxy, achieving unprecedentedly precise mode control for optimal single-mode lasing performance. Critically, these well-defined grooves can alter the lasing resonance modes within the microlasers, enabling the transition from whispering gallery mode (WGM) to Fabry-Pérot (F-P) mode. The optical anisotropy induced by engineered groove structures also achieves polarized lasing emission with a high degree of polarization approaching 0.65. Additionally, numerical simulations elucidate that the external-cavity-free, high-quality (≈2660), and single-mode F-P lasing behavior under large-size conditions arises from the coupling of multiple cleavage cavities, which is induced by broken grooves in perovskite MPs morphology. This study pioneers a mode-selective modulation approach that enables scalable polarization engineering in large-area single-mode microlasers, fundamentally advancing multifunctional integration in photonics and high-density optoelectronic systems.