Waveguide Coupled Polymer Micro-Ring Resonator in a D-Shaped Fiber

We proposed and demonstrated a waveguide coupled fiber optic polymer micro-ring whispering-gallery mode (WGM) resonator side-coupled to a bended nanoscale polymer waveguide in a D-shaped single mode fiber (SMF). The flat region of the D-shaped fiber fabricated by femtosecond (FS) laser ablation was etched over the core, which could be regarded as a substrate with natural light input and output ports, creating a flexible platform for integrated photonics. The resonator and waveguide were printed by FS micro-ring laser-induced two-photon polymerization (TPP) on the 'substrate'. The design of angled side walls of the D-shape fiber and tapered polymer waveguide reduces mode mismatch, which the simulated power transmission is enhanced from 0.215 to 0.835, and backscattering power is reduced from 0.025 to 7 × 10-6. The fabricated resonator obtains a Q factor of 4.86 × 103 at the resonant wavelength of 1508.14 nm. Furthermore, the temperature sensing performance of the resonator was investigated with the sensitivity of -193 pm/°C. The resonator is suitable for developing optical biochemical sensors, and our methodology has the potential in integrating multiple photonic components all in a SMF.