A Novel Hybrid Plasmonic Resonator With High Quality Factor and Large Free Spectral Range

Abstract

Whispering gallery (WG) mode resonators are experiencing a surge in the application of biosensing, attributing to high speed, flexibility, low cost, multi-analyte detection and compatibility with extra optical elements. The decoration of localized surface plasmon nanostructures to a dielectric WG mode resonator offers unprecedented sensitivity compared with a pure dielectric resonator. However, at the moment, the experimental quality (Q) factors of dielectric micro rings always achieve the value of 104 to 106, whereas the only reported hybrid counterpart possesses the Q factor of 300 and most studies are focused on the theoretical design. The resulting experimental detection limits (DLs) are in the range of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> RIU, which is one order of magnitude lower than the best value of hybrid resonators. The hybrid resonator should possess the experimental Q factor of 5000 to 10000 so as to match their purely dielectric rivals. We demonstrated a novel hybrid plasmonic WG mode resonator working on the multimode resonance mechanism. Under the condition of the multimode resonance, predominant field was distributed on the waveguide surface resulting in an improved bulk sensitivity. The multimode resonance promoted satisfied resonance frequency reduced and thus a high Q factor and a low value of DL could be achieved in the experiment. Afterwards, the resonator was made via micro-and nanofabrication. It was shown that the experimental Q factor of 5685 and the free spectral range larger than 35 nm, which were superior to the previously reported value to our best knowledge. Hypoglycemia and Hyperglycemia will produce noticeable organ damage over time. Early detection of glucose concentration is crucial for clinical diagnosis. The proposed resonator was used for the detection of glucose solution. The experimental sensitivity was 428 nm/RIU and the DL was 1.31 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> RIU. The device with a footprint of 1500 μm × 12.7 μm, is able to integrate with other optical elements and developed as a commodity in the future.