The linear polarized lasing, one of the criteria for high quality laser beam, is important for real application of microlaser in integrated on-chip photonic. Unlike conventional lasers, which can be induced by highly polarized seed light, the bottom-up synthesized microlaser generally possesses low degree of polarization due to unpolarized spontaneous emission. The crucial factor to improve the degree of polarization is the selection of modes with same polarization direction.

The research team led by Shanghai Institute of Optics and Fine Mechanics, together with East China Normal University and Nanjing University of Aeronautics and Astronautics, has recently demonstrated single-mode lasing with low threshold, highly linear polarization degree and good stability at ~531 nm by Vernier effect in coupled perovskite microspheres. The work was published in Nanoscale.

In this study, not only single-mode lasing but also linearly polarized lasing had been achieved in coupled CsPbBr₃ microsphere cavities. By Vernier effect, the degree of polarization improved from ~0.2 (before coupling) to linear polarization 0.78 (after coupling). By the finite element method (FEM), the mode distributions of the individual microsphere and coupled microspheres were analyzed systematically, and the clearly physical diagram of coupling mode was presented.

They found that when the two cavities were aligned with a 30 nm gap, single-mode lasing with low threshold (4.09 μJ/cm²), highly linear polarization degree (~0.78) and good stability (~55 min) at ~531 nm was generated from the coupled microspheres.

The in-depth understanding of mechanism about polarized lasing emission and the improvement of the lasing polarization degree are of the great significance not only for the basic physics of lasing, but also for application expansion of microlaser.

These works were supported by the National Natural Science Foundation of China.

Polarization properties of lasing modes from individual and coupled microspheres. (Image by SIOM)