Reversible transition between FP lasing and WGM lasing in CH3NH3PbBr3 perovskite microwires

Semiconductor microwires have attracted much current attention due to their excellent geometric uniformities, inherent optical gain, relatively high refractive index, making them potential candidates for microscale electronic and optoelectronic building blocks, especially as the next frontier in miniaturization of semiconductor lasers. Recently, organic-lead halide perovskite semiconductors (CH
3
NH
3
PbX
3
with X = Cl, Br, I), with high optical absorption coefficient, optimal direct band gap, and long electron/hole diffusion lengths, good optical properties and long electron hole diffusion length, which ensure adequate gain and efficient optical feedback, have become a research hotspot to achieve semiconductor lasers. Up to now, both Fabry-Perot (FP) lasing and Whispering Gallery Mode (WGM) lasing have been observed in perovskite micro-cavities, such as microwires, hexagonal microplates and square microdisks. However, the lasing mechanism is fixed once the perovskite microcavity is synthesized. Here the transition between FP lasing and WGM lasing is demonstrated in perovskite microwires and moreover, the transition is reversible without any damage to the samples. The CH
3
NH
3
PbBr
3
perovskite microwires are synthesized with one-step solution based self-assembled method and the typical lengths are tens of microns with an aspect ratio about 1 in the transverse plane. When perovskite microwire on glass substrate is pumped uniformly above threshold, FP lasing action can be observed which oscillates between the two end facets along the microwire axial direction. By repositioning the microwire on a perovskite block with one end suspending in the air or placing a perovskite block on one end of the microwire via micromanipulation, the FP lasing mode can be suppressed. In such case, single mode lasing can be excited when the suspending end of the microwire is pumped. After transferring the microwire to glass substrate again, FP lasing can be observed when pumped uniformly. Numerical simulations show that the perovskite block induces huge leaky loss to the microwire, which suppresses the FP lasing mode. As the lasing modes corresponds to the high quality (Q) modes, WGM modes exhibit larger Q factor than the FP modes in the transverse plane. Therefore, the single mode lasing originates from WGM mode in the transverse plane when the FP modes are suppressed. By introducing perovskite blocks, transition between FP lasing in the microwire axial direction and WGM lasing in the transverse plane can be achieved without any damage to the sample. The proposed mechanism provides a simple and flexible way to tailor the perovskite lasing actions, exhibiting potential applications in integrated photonic circuits and light sources.