Hybrid gap modes induced by fiber taper waveguides: application in spectroscopy of single solid-state emitters deposited on thin films

摘要

We show, via simulations, that an optical fiber taper waveguide can be anefficient tool for photoluminescence and resonant, extinction spectroscopy ofsingle emitters, such as molecules or colloidal quantum dots, deposited on thesurface of a thin dielectric membrane. Placed over a high refractive indexmembrane, a tapered fiber waveguide induces the formation of hybrid mode waves,akin to dielectric slotted waveguide modes, that provide strong fieldconfinement in the low index gap region. The availability of such gap-confinedwaves yields potentially high spontaneous emission enhancement factors($\approx20$), fluorescence collection efficiencies ($\approx 23%$), andtransmission extinction ($\approx 20%$) levels. A factor of two improvement influorescence and extinction levels is predicted if the membrane is insteadreplaced with a suspended channel waveguide. Two configurations, for operationin the visible ($\approx 600 \nm$) and near-infrared ($\approx 1300 \nm$)spectral ranges are evaluated, presenting similar performances.