Whispering gallery modes of dye-doped polymer microspheres in microtube

A micro-system including a silica micro-tube (inner diameter≈6.2 µm) and dye-doped microspheres (diameter≈6 µm) was pumped by a 532 nm laser. The whispering gallery modes (WGMs) of fluorescence resonance were observed. Free Spectral Range (FSR) of single-sphere with diameters of 40 μm was 3.1 nm and with diameters of 6 μm was 5.4 nm. Two size-matched microspheres were coupled using a bi-sphere micro-system. Resonances from each sphere's evanescent field were coupled, which leads to resonance splitting. The measured resonance splitting in the spectra of the two coupled spheres is about ∆λ≈0.8 nm. The scheme would be a promising component in future micro-photonic devices.