Photoisomerization Activated Intramolecular Charge-Transfer Process for Broadband Tunable Single-Mode Microlasers.

Miniaturized lasers with high spectral purity and wide wavelength tunability are crucial for various photonic applications. Here we propose a strategy to realize broadband tunable single-mode lasing based on photoisomerization activated intramolecular charge-transfer (ICT) process in coupled polymer microdisk cavities. The photoisomerizable molecules doped in the polymer microdisks can be quantitatively transformed into a kind of laser dyes with strong ICT characters by photoexcitation. The gain region was tailored over a wide range through the self-modulation of the optically activated ICT isomers. Meanwhile, the resonant modes shifted with the photoisomerization due to an effective refractive index change of the polymer microdisk cavity. Based on the synergetic modulation of optical gain and microcavity, we realized the broadband tuning of the single-mode laser. These results advance the fundamental understanding of the excited-state processes in tunable organic gain materials and offer a promising route to fabricate broadband tunable microlasers towards practical photonic integrations.