Efficient directional beaming from small apertures using surface-plasmon diffraction gratings

Abstract

We demonstrate efficient optical directional beaming using an array of sub-wavelength patterns on a metallic surface. Specifically, a sub-wavelength sized slit placed next to a periodic grating is designed and optimized to realize maximum coupling efficiency and directional radiation into a leaky-wave plasmonic mode. Collective scattering from the corrugations forming the grating is synthesized to radiate towards the desired direction, and efficient beaming is achieved through tailoring the design parameters with a simple analytical model. We also prove that directivity can be further enhanced by improving the slit-grating coupling efficiency through efficient plasmon generation, showing improved angular response in far-field radiation. V

Patterned Plasmonic Surfaces—Theory, Fabrication, and Applications in Biosensing

“…Zhang’s group in [26] has exhibited a unidirectional optical beaming obtained via an array of sub-wavelength nano-slits on a metallic surface. The proposed geometry contains a subwavelength size slit with an array of periodic gratings (bumps) on its left-hand side which are patterned on a 250 nm Ag film as shown in Fig.…”

“…Considering the phasor form, Eq. (38) can be written as $$E_i^S=true\iint k_0^{2}false[{\epsilon }_{P}false({\mathrm{x}}^{\prime },{\mathrm{z}}^{\prime }false)-{\epsilon }_{U}false({\mathrm{z}}^{\prime }false)false]E_i^{U}false({\mathrm{x}}^{\prime },{\mathrm{z}}^{\prime }false)d{{\mathrm{normal\Lambda }}^{\prime }}_i\times \text{exp}false(-j{\mathrm{k}}_0\rho +\mathrm{normalj}{\psi }_0-{\text{jk}}_{SP}{d}_i^{SE}false)$$ where ε P and ε U are the perturbed and unperturbed dielectric constants of the nanograting corresponding to $E_i^P$ and $E_i^U$ [26]. A phase matching condition has been used to obtain a collimated directional beam using $$k_{SP}{d}_i^{SE}=\{\begin{array}{c}{d}_i^{SE}{k}_0\text{sin}\theta +2\pi m_i,i=\mathit{odd}\\ d_i^{SE}{k}_0\text{sin}\theta +2\pi m_i-\pi ,i=\mathit{even},\end{array}$$ where m i is the diffraction order at the i th edge.…”

“…Zhang’s group used EBL to experimentally demonstrate tunable plasmonic radiation from a periodic array of plasmonic nano-scatterers [26, 50]. The proposed structure can be tailored to convert surface plasmon polaritons into directional, high gain leaky modes.…”

Beam Collimation Using an Anisotropic Metamaterial Slab Without Any Nanometer-Sized Aperture

“…For example, plasmonic alternatives with SP wave excited on metallic nanostructures can manipulate light in subwavelength scale, enabling the miniaturization of conventional devices. SP has attracted intensive attention and has already been applied in many areas, such as beam shaping [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], signal sensing [24,25], design of absorbers [26,27], waveguide optics [28,29], photovoltaic and light emission devices [30][31][32], etc.…”

“…The optimized beaming effect along the on-axis direction requires that the excited SPs from the slit and the textured grooves in the exit plane must be approximately in phase [8]. Beaming will perform along off-axis directions when asymmetric factors are applied during the excitation of SPs [10,19,21,23]. Later, this miniaturized beaming system was introduced into semiconductor lasers aiming for reducing the divergence angle of emission [11,14,16].…”