Optofluidic fluorescence resonance energy transfer lasing in a polydimethylsiloxane microfluidic channel

Abstract

A bare quartz fiber with single refractive index is implanted into a polydimethylsiloxane (PDMS) microfluidic channel. The lasing gain medium consists of fluorescence resonance energy transfer (FRET) donor-acceptor dye pair Rhodamine B (RhB)-LDS821 mixture solution, which has a lower refractive index than that of the optical fiber and flows in the PDMS microfluidic channel. The circular cross section of the optical fiber forms a ring resonator and hosts high-quality (<i>Q</i>) whispering gallery modes (WGMs). Pumping along the optical fiber axis, the FRET characteristic parameters, i.e., the FRET efficiency <inline-formula><tex-math id="M1000">\begin{document}$\eta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181696_M1000.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181696_M1000.png"/></alternatives></inline-formula> and the Förster distance <i>R</i>₀ of donor-acceptor dye pair, are firstly studied by using a continuous wave laser as a pump light source with a wavelength of 532 nm. The excited states are thencreated in the donor (RhB) by using a pulse laser with a wavelength of 532 nm and whose energy is transferred into the adjacent acceptor (LDS821) through the non-radiative FRET mechanism. Finaly, the emission of LDS821 iscoupled into the WGM of the ring resonator to lase. Due to the high energy transfer efficiency and high <i>Q</i>-factor, the acceptor shows a lasing threshold as low as 1.26 <inline-formula><tex-math id="M1002">\begin{document}${\text{μ}}{\rm J}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181696_M1002.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181696_M1002.png"/></alternatives></inline-formula>/mm².