Plasmonic Gold Nanostar Mediated Self-Photothermal Modulation of Microfiber Bragg Grating

Photothermal actuation that leverages optical fiber and plasmonic materials would not only add a practical function but also spur many important applications for the fiber-optic sensors, for example, the self-temperature governing and fiber-optic photothermal medicine probe. In this paper, we propose and demonstrate a microfiber Bragg grating device that integrates the functionality of self photothermal modulation mediated by the plasmonic gold nanostar (AuNSt). As an excellent plasmnoic nanomaterial, AuNSt stands out due to its tailorable surface plasmon resonance(SPR) spectrum and pronouced “lightning rod” effect. After exploring the optimized AuNSt colodial solution for immobilization on the fiber surface, the AuNSt-functionalized microfiber Bragg grating presented a high pump-heat slope ${\sim }$ 0.06 $^{\circ }$ C/mw and the maximum temperature elevation of 18.5 $^{\circ }$ C in the liquid environment. Furthermore, the enhanced electromagnetic field of AuNSt effectively improves the sensitivity of the microfiber Bragg grating. The functional grating probe also performs good stability and fast on-off switch of the photoheating. The demonstration heralds the potential of the plasmonic microfiber grating for steering the interfacial temperature through the photothermal effect, which will be beneficial for the bio-chemical sensing and medical therapeutics.