Metallic nanowires can lead to wavelength-scale microlenses and microlens arrays

Abstract

We theoretically and experimentally demonstrate that the diffraction of microstructures based on silver nanowires leads to very efficient microfocusing effects. Pairs of parallel nanowires act as ultrasmall cylindrical microlenses with diffraction-limited resolution in the Fresnel region. This is a new diffraction scheme to make micron-sized optical lenses with higher transmittance than plasmonic microlens based on nano-aperture arrays. Calculations based on the scalar Rayleigh-Sommerfeld integral highlights the pure scalar diffractive contribution. Thus, the plasmon contribution is negligible in such micron-sized metallic geometry. We demonstrate that two-dimensional grids of nanowires can be used to fabricate dense arrays of microlenses, i.e. 10000x10000 DPI (dots per inch).

Cylindrical planar microlens based on diffraction of parallel metallic nanowires

“…The experimental values Z f ∕λ shown in Fig. 9(b) by stars are obtained with the use of two silver nanowires with a width of about 300 nm [12]. The excellent agreement with our calculations shows clearly that the plasmon contribution is negligible in our microsized geometry, with respect to pure diffraction effects.…”

“…We present in this section the experimental results performed with silver nanowires fabricated by a photoreduction process using the two-photon absorption technique [12,15]. The setup is based on a TeemPhotonics tridimensional microfabrication module [16] coupled to a Zeiss Axiovert 200 inverted microscope, including a Q-switched Nd:YAG microlaser (NP-15010 TeemPhotonics) operating at λ 1064 nm, and a three-dimensional (3D) piezo-nanopositioning system (PI nanocube) with a scanning range of 100 μm × 100 μm× 100 μm.…”

“…In a previous work [12], we have demonstrated that the diffraction of a pair of metallic nanowires clearly shows constructive interferences that lead to a focusing process in the near field region. We have shown that such microlenses can lead to high transmitted intensity at the focal point.…”

“…The stars in Fig. 14 correspond to the experimental transversal extensions for a pair of silver nanowires separated by D 2 μm [12].…”

“…The calculated optical properties are compared to the experimental results obtained for silver nanowires. These metallic structures are fabricated by a photoreduction process using a two-photon absorption technique [12].…”