▎ 摘　　要

In this work, actively tunable and enhanced optical properties are investigated elaborately with graphene metamaterials, which consists of a pi-shaped resonator and a hollow rectangular resonator. The unit cell is periodically arranged on the dielectric substrate. An obvious plasmon-induced transparency (PIT) effect is achieved through destructive interference between these two resonators. The tunable transparency window can be well regulated with the Fermi energy and polarization angle. Specifically, padding a gain medium onto the graphene metamaterials, the intrinsic loss of the system can be greatly compensated, and the resonant intensity gets amplified to achieve a dramatic stimulated emission of radiation with a low gain threshold. Meanwhile, tunable radiation emission is also realized by adjusting the polarization angle. This gain-assisted double-resonant amplification is intensively investigated to compensate the system loss and demonstrate the brilliant performance of the lasing spaser. To the best of our knowledge, these bifunctional plasmonic metamaterial-enabled tunable and enhanced optical properties are rarely investigated. This work demonstrates a novel modulation strategy to get tunable PIT resonance and paves the way toward designing adjustable lasing spasers with metamaterials.