Whispering gallery mode laser enhanced by amplified spontaneous emission coupling in semiconducting polymer solutions

Evanescent-wave-coupled gain microresonators suffer from inherent low efficiency under transversal pumping because they are based on the gain only in the evanescent field region of the whispering gallery modes (WGMs) of the resonator. In this paper we demonstrate a new coupling scheme that remarkably enhances the efficiency of the WGM laser. A glass fiber is used as the microresonator and semiconducting polymer solutions as the gain media. A single pump beam is used to produce a WGM laser and an optically induced liquid waveguide, which confines the amplified spontaneous emission (ASE) of the gain media. Both WGM lasing and ASE occur simultaneously in the sample. Despite the fact that only a small fraction of the pump beam directly excites the evanescent field volume around the microresonator, almost 97% of the output signal is due to the WGM laser, at the highest pump power. The liquid waveguide also serves to out-couple the WGM lasing. This simple one-step all-optical optofluidic circuit might improve the applications of WGMs in optoelectronics and optofluidics.