Tailored Light Coupling for High-Q Microbottle Polymer Resonators Using a GRIN-Capillary Optical Fiber Structure

In this work, we propose an optical fiber coupling structure for the excitation of whispering gallery mode (WGM) resonances in polymer microbottle resonators (MBR). The MBRs were fabricated using a UV-curable polymer deposited over micro-optical fiber tapers (∼5 µm waist). These MBRs were subsequently integrated into a spliced SMF–GRIN–capillary fiber assembly without the need for tapering or etching processes. Three configurations were tested using two MBRs (∼17 µm and ∼16 µm in diameter), where resonances were excited via antiresonant reflecting optical waveguide and interference mechanisms. These structures have high Q-factors of up to 12,000 and notable signal-to-noise ratios of 7 dB. Fourier analysis confirmed the geometry-dependent WGM behavior.