Polarization effects in light-tunable Fano resonance in metal-dielectric multilayer structures

Abstract

A planar metal-dielectric multilayer structure containing a waveguide layer doped with azo-dye molecules exhibits a sharp Fano resonance that can be shifted by pump light irradiation owing to a photoinduced change of the refractive index of the waveguide layer by photoisomerization of the azo-dye molecules. Azo-dye-containing materials are polarization sensitive and the photoinduced shift of the Fano resonance is expected to depend on the pump polarization. Previous pump-probe attenuated-total-reflection measurements performed with a normal incidence of pump light exhibited intriguingly no dependence on the pump polarization. In this work, we extend our measurements to an oblique incidence, to optimize the overlap between the pump and probe polarizations, and we demonstrate a strong dependence on the pump polarization. To analyze the experimental results for both the normal and oblique pump conditions, we introduce phenomenological equations, based on the angular hole burning model of the photoisomerization of the azo-dye molecules. The equations allow us to describe the dependence of the refractive index changes in the waveguide layer on the pump angle and polarization. Using the equations, we could obtain good theoretical fits to the experimental data. The results of fitting suggest that the overlap between the pump and probe polarizations plays an important role in determining the amount of the photoinduced shift of the Fano resonance.

Line shape engineering of sharp Fano resonance in Al-based metal-dielectric multilayer structure

“…26 Furthermore, we have demonstrated the light-tuning of the Fano resonance using a PMMA waveguide layer doped with photofunctional molecules (disperse red 1). 27,28 Very recently, Zheng et al 29 reported the results of experimental and numerical studies on the Fano resonance in a multilayer structure consisting of an Au layer, a SiO 2 layer, and a ZrO 2 layer surrounded by water.…”

Plasmonic Sensing and Modulation Based on Fano Resonances

“…Therefore, the sharp Fano resonances provide a platform for achieving the high‐performance and ultrasmall optical modulators and switches. In the past decades, various tuning methods, such as the mechanical, thermal, magnetic, electrical, and optical tuning schemes, were utilized to improve the performance of the Fano modulators. All of these modulation approaches have applications in active plasmonic devices .…”

“…However, because of the weak nonlinear light–matter interactions in natural materials and the short propagation distances of nanoscale‐confined SPP modes, the achievement of the all‐optical modulation with a large modulation depth in a small metallic nanostructure is an enormous challenge. The Fano resonances with sharp asymmetric profiles and strong field enhancements are extremely sensitive to the variations of the refractive index, and thus they provide an effective solution to this problem . By placing a photorefractive polymer on the metallic hole arrays, the Fano resonance (linewidth of Δλ ≈ 80 nm and spectral contrast of C ≈ 0.93) around λ = 750 nm was tuned based on the photorefractive effect under the pump beam of λ = 387 nm, as shown in Figure a .…”

“…It is noticed that the photorefractive effect and third‐order nonlinear Kerr effect can only bring a small index variation (|Δ n | ≤ 0.05) because of the weak light–matter interaction. This small index variation in the tuning process significantly limits the dynamic tuning ranges of the all‐optical plasmonic modulators.…”

Fano Resonance in Artificial Photonic Molecules

“…Fano resonance, a fundamentally interesting feature resulting from the interference between a discrete narrow localized state and the background broadband continuum, exhibits an asymmetric line shape with a high quality factor, which can sustain significantly enhanced modal fields, [ 1–5 ] and enable numerous photonic applications, such as optical switching, [ 6–9 ] sensing, [ 10–15 ] nonreciprocal propagation, [ 16–21 ] modulation, [ 22–26 ] optical logic gates, [ 27–29 ] and light buffering and storage. [ 3,30–35 ]…”