Energy losses and fluorescent efficiency of RhB-doped polymer microfibers via optical waveguiding excitation.

We demonstrate the dependencies of energy losses and fluorescent efficiencies on doping concentrations for rhodamine B (RhB)-doped polymer microfibers (PMFs) under optical waveguiding excitation. Compared with the four doping concentration groups (2.0 mg/g, 2.4 mg/g, 2.8 mg/g, and 3.2 mg/g), the 2.4 mg/g concentration group has the largest energy loss rates (∼0.102dB/µm and ∼0.036dB/µm for the excitation light and the fluorescence, respectively) and the highest fluorescence ratio at the coupling point. Further analysis demonstrates that the fluorescent emitting efficiency at the output end is approximately exponentially decaying with the propagation distance. The fluorescent emitting efficiency is also related to the doping concentration, which obtains the optimal fluorescent propagation effect at the doped PMF with a concentration of 2.8 mg/g. This work may provide a helpful reference for waveguiding circuit integration and active device design based on dye-doped micro/nanofibers.

Energy attenuations in single microfiber and double-loop cavity supported by optical substrate.

We report on the characterization of energy losses in single-silica microfiber and double-loop microcavity deposited on MgF2 substrate. When the bending radius is less than ∼37 µm, the bending loss rate of a 1.4 µm diameter microfiber exceeds its propagation loss (∼0.039 dB/µm), which becomes the main source of energy attenuation. Furthermore, we measured the transmission energy losses during the assembling process of a double-loop cavity. The transmission loss in a double-loop cavity varies by adjusting the shape of the cavity. It is also found that a ∼30 µm radius cavity has a similar bending loss to that of a curved microfiber with the two bending radii of ∼60 µm, which demonstrates that the cavity can provide a more compact structure than a curved microfiber in integrated photonic circuits. By further bending the input end of a cavity, the output energy can be greatly attenuated, which indicates that the double-loop cavity is no longer suitable for integration.