Single-mode lasing via loss engineering in fiber-taper-coupled polymer bottle microresonators

Abstract

Due to the lack of mode selection capability, single whispering-gallery-mode (WGM) lasing is a challenge to achieve. In bottle microresonators, the highly nondegenerated WGMs are spatially well-separated along the long-axis direction and provide mode selection according to their axial mode numbers. In this work, we use a loss-engineering approach to suppress the higher-order WGMs and demonstrate single-mode lasing emission in small polymer bottle microresonators. The fiber tapers are not only used to couple pump light into the bottle microresonators to excite the WGMs but also to bring optical losses that are induced from the diameter mismatch between fiber tapers and microresonators. By adjusting the coupling positions, the diameters of fiber tapers, and the coupling angles, single fundamental-mode lasing is efficiently generated with side-mode suppression factors over 15 dB. Our loss-engineering approach is convenient just by moving the fiber taper and may find promising applications in miniature tunable single-mode lasers and sensors.

Optical bottle microresonators

“…Lasing microresonators can be fabricated of an active material or fabricated of a passive material and post-processed by coating with an active material. The BMR lasers [61][62][63][64][65][66][67][68] have certain advantages compared to other microlasers. In fact, their elongated geometry and fabrication simplicity allows one to fabricate active BMR with predetermined spectrum and facilitate mode selection by patterned pumping much easier than for active microresonators having other geometries.…”

“…In Refs. [62,64,65,67,68], active BMRs were fabricated by depositing polymer droplets doped with active materials onto the optical fiber followed by the UV and/or heat curing. In Ref.…”

“…In Ref. [65] Brillouin lasing and Brillouin-coupled four-wavemixing in an ultra-high-Q silica BMR was demonstrated. In Ref.…”

“…(a) -Lasing spectra and corresponding microscope images and electric field-intensity distributions of a polymer BMR under the action of a uniform and a spatially modulated laser beam [64]. (b) -Lasing spectra and corresponding microscope images of a polymer BMR pumped by the uniform radiation and by the radiation from a microfiber contacting BMR at different positions along the BMR axis [65]. (c) -Single mode lasing at different frequencies for different positions of a coupled microfiber along the BMRs and the corresponding optical microscope images of the lasing mode field distribution [67].…”

“…(c) -Single mode lasing at different frequencies for different positions of a coupled microfiber along the BMRs and the corresponding optical microscope images of the lasing mode field distribution [67]. (Reproduced with permission from Refs [64,65,67]).…”