Abstract
Abstract Mirror-on-mirror nanoplasmonic metamaterials, formed on the basis of voltage-controlled reversible self-assembly of sub-wavelength-sized metallic nanoparticles (NPs) on thin metallic film electrodes, are promising candidates for novel electro-tunable optical devices. Here, we present a new design of electro-tunable Fabry–Perot interferometers (FPIs) in which two parallel mirrors – each composed of a monolayer of NPs self-assembled on a thin metallic electrode – form an optical cavity, which is filled with an aqueous solution. The reflectivity of the cavity mirrors can be electrically adjusted, simultaneously or separately, via a small variation of the electrode potentials, which would alter the inter-NP separation in the monolayers. To investigate optical transmittance from the proposed FPI device, we develop a nine-layer-stack theoretical model, based on our effective medium theory and multi-layer Fresnel reflection scheme, which produces excellent match when verified against full-wave simulations. We show that strong plasmonic coupling among silver NPs forming a monolayer on a thin silver-film substrate makes reflectivity of each cavity mirror highly sensitive to the inter-NP separation. Such a design allows the continuous tuning of the multiple narrow and intense transmission peaks emerging from an FPI cavity via electro-tuning the inter-NP separation in situ – reaping the benefits from both inexpensive bottom-up fabrication and energy-efficient tuning.
Highlights
A Fabry–Perot interferometer (FPI) is an optical cavity comprising two parallel reflective surfaces, which allows only specific wavelengths of incident light to be transmitted – those satisfying the constructive interference condition within the cavity [1, 2]
We present a new design of electro-tunable F abry– Perot interferometers (FPIs) in which two parallel mirrors – each composed of a monolayer of NPs self-assembled on a thin metallic electrode – form an optical cavity, which is filled with an aqueous solution
Three sharp transmission peaks can be observed in the shown spectral window (Figure 3A), which correspond to the resonance states of the cavity where the reflectance is minimal (Figure 3B)
Summary
A Fabry–Perot interferometer (FPI) is an optical cavity comprising two parallel reflective surfaces, which allows only specific wavelengths of incident light to be transmitted – those satisfying the constructive interference condition within the cavity [1, 2]. The proposed design ensures superior transmittance characteristics of an FPI (with narrow, intense, and widely tunable transmission peaks), not achieved in our previous work [31] – involving voltage-controlled self-assembly of gold NPs on transparent electrodes. Those transparent electrodes played no significant role in the cavity’s optical properties. The transmission peaks obtained there were found to be very broad, spectrally overlapping, and reduced in intensity (due to high loss in gold) These drawbacks of the previous design would limit major applications of an FPI. Our theoretical findings demonstrate that mirror-on-mirror nanoplasmonic metamaterials can efficiently function as tunable reflective surfaces for realizing electro-tunable FPIs and could be promising in numerous applications
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