A microring multimode laser using hollow polymer optical fibre

We report the observation of multimode laser operation at wavelengths corresponding to whispering-gallery modes from a freestanding microring cavity based on rhodamine B dye-doped PMMA hollow optical fibre. Cylindrical microcavities with diameters 155, 340 and 615 mu m were fabricated from a dye-doped hollow polymer optical fibre preform. An average mode spacing of 0.17 nm was observed for the 340 mu m cavity. This shows that the laser mode intensity distribution is concentrated on the outer edge of the cavity.