Fig. 1. (a) Schematic diagram of the fabrication process of the freestanding gold nanomembrane. Photographs of the (b) HCF and (c) freestanding gold nanomembrane on HCF. The dashed circles indicate the profile of the HCF beneath the gold nanomembrane. Scale bars, 50 μm; inset, SEM image of the gold nanomembrane (scale bar, 1 μm).

Fig. 2. (a) Simulated transmission spectra of the gold nanohole arrays with different configurations in air; insets, simulated electrical field |E| distributions overlaid with the Poynting vectors at 500 nm in the x−z plane (left) and transmission spectrum of a nanohole described by classical aperture theory (right); (b) calculated (dashed lines) and simulated (2D mapping) dispersion relations of the freestanding nanomembrane in air.

Fig. 3. (a) Simulated electrical field |E| distribution at 653 nm in the x−y plane; (b) field distributions overlaid with the Poynting vectors (top) and z component of the corresponding electrical field |Ez| (bottom) at 576 and 653 nm [transmission minimum and maximum in Fig. 2(a), respectively] in the x−z plane, and (c) field distribution of the cross section [x=−0.1  μm, dashed line in (b)] along z at 653 nm of the freestanding nanomembrane in air; (d) simulated electrical field |E| distributions overlaid with the Poynting vectors at 627 nm (top) and 841 nm (bottom) in the x−z plane of the gold nanomembrane on SiO2 in air.

Fig. 4. (a) Simulated transmission spectra of the gold nanohole arrays with different configurations in water; (b) calculated (dashed lines) and simulated (2D mapping) dispersion relations of the freestanding nanomembrane in water.

Fig. 5. (a) Simulated electrical field |E| distributions overlaid with the Poynting vectors (top) and z component of the corresponding electrical field |Ez| (bottom) at 610, 742, and 837 nm in the x−z plane; (b) field distribution at 742 and 837 nm in the x−y plane, and (c) field distributions of the cross section [x=−0.1  μm, dashed lines in (a)] along z at 742 and 837 nm of the freestanding gold nanomembrane in water. The resonance at 837 nm corresponds to the maximum transmission in Fig. 4(a).

Fig. 6. Experimental (a) spectral evolution, (b) wavelength shifts and corresponding simulated (c) spectra, (d) wavelengths of the freestanding gold nanomembrane to varied refractive index. Experimental (e) spectral evolution, (f) wavelength shifts and corresponding simulated (g) spectra, (h) wavelengths of a gold nanomembrane on a solid silica fiber end face to varied refractive index.

Fig. 7. (a) Reflection spectra of the freestanding gold nanomembranes based on various configurations. The red dots and open circles indicate the corresponding resonance modes in experiments and simulations, respectively. (b) Evolution of the reflection spectra and (c) resonance wavelength shifts of the freestanding gold nanomembrane on the 125 μm hollow ferrule to varied refractive index; (d) simulated refractive index response of the freestanding gold nanomembrane.

Table 1. Comparison of Performances among Various Plasmonic Sensors Based on Nanohole Arrays