Abstract
Designing various nanostructures to achieve narrowband light reflection resonances is desirable for optical sensing applications. In this work, we theoretically demonstrate two narrowband light reflection resonances resulting from the excitations of the zero-order transverse magnetic (TM) and transverse electric (TE) waveguide modes, in a waveguide structure consisting of an Au sphere array on an indium tin oxide (ITO) spacer on a silica (SiO2) substrate. The positions of the light reflection resonances can be tuned easily, by varying the array periods of gold (Au) spheres or by changing the thickness of the ITO film. More importantly, the light reflection resonances have a very narrow bandwidth, the full width at half maximum (FWHM) of which can be reduced to only several nanometers for the zero-order TM and TE waveguide modes. The conventionally defined performance parameters of sensors, sensitivity (S) and figure of merit (FOM), have quite high values of about 80 nm/RIU and 32, respectively, in the visible wavelength range.
Highlights
Exploring different approaches to achieve high-quality refractive-index sensors has been drawing more and more of the attention of researchers in recent years, due to their great realistic significance and broad application prospect in the field of sensing detection
Because of the process of electromagnetic radiation decay and the Joule heat produced by Ohmic loss in metal materials, surface plasmon resonances usually have a relatively broad bandwidth, and the electromagnetic field enhancement associated with surface plasmon resonances is limited, which is very detrimental to improving the sensing performances of refractive-index sensors [7,8]
We theoretically study narrowband light reflection resonances in a waveguide structure consisting of an Au sphere array on an indium-tin oxide glass (ITO) spacer on a SiO2 substrate
Summary
Exploring different approaches to achieve high-quality refractive-index sensors has been drawing more and more of the attention of researchers in recent years, due to their great realistic significance and broad application prospect in the field of sensing detection. The plasmonic Fano resonance has an extremely narrow bandwidth associated with the great enhancement of electromagnetic fields, and is very sensitive to very small changes in the refractive index of the surrounding medium [19]. In a recent work [30], the interactions between waveguide modes and localized surface plasmon resonances in ellipsoidal Au nanoparticles are investigated theoretically to produce a sharp Fano resonance for refractive index sensors with good performance. We mainly focus on narrowband light reflection resonances resulting from the excitations of both TE and TM waveguide modes, not considering Fano-like resonances due to the interactions between waveguide modes and localized surface plasmon resonances [30]. With the help of waveguide theory, we can satisfactorily predict the positions of the narrowband light reflection resonances
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