Linearly polarized lasing based on coupled perovskite microspheres.

The polarization of lasing, as a fundamental property related to the emission coherence of microlasers, is one of the criteria for a high quality laser beam but has been rarely investigated. Unlike conventional lasers which can be induced by highly polarized seed light or by using a polarizing film, the microlaser for on-chip integrated photonic circuits generally possesses a low degree of polarization due to unpolarized spontaneous emission. Here, we firstly demonstrate that the Vernier effect can be used to improve the degree of polarization from ∼0.2 to 0.78 based on metal halide perovskite microspheres. After coupling, linearly polarized single-mode lasing with a low threshold and high quality can be achieved. In addition, by using the finite element method, the mode distributions of CsPbBr microspheres before and after coupling are analyzed systematically and a clear physical diagram of coupled resonances is obtained. Our work clearly suggests that a coupled linearly polarized single-mode microlaser by the Vernier effect would offer a real step closer to the platform for on-chip integrated photonics.