Unidirectional surface plasmon-polariton excitation by a compact slot partially filled with dielectric

Abstract

We propose a new scheme on unidirectional surface plasmon-polariton (SPP) excitation with the following advantages: ultracompact size, working at arbitrary incidence angle and over a wide spectrum. The proposed structure utilizes a partially filled metallic slot with dielectric to realize unidirectional SPP excitation via direct field manipulation. We theoretically and numerically show that unidirectional SPP excitation with a ratio of 93% can be achieved by a structure with a 50 nm slot. The proposed structure keeps its functional capability over incident angles from -80° to 80°, and has a broadband working spectrum of more than 70 nm.

Fabrication and surface plasmon coupling studies on the dielectric/Ag structure for transparent conducting electrode applications

“…The TiO 2 /Ag structure with highest ε d = 6.52 has least SP coupling and hence the highest transmittance in the visible region. The k SP /k 0 ratio can be used as an estimate for SP coupling, where k SP is a wave vector required to excite the surface plasmons at the dielectric/Ag interface [33]. Figure 6 shows the plot of k SP /k 0 as a function of wavelength.…”

Ultra-broadband unidirectional launching of surface plasmon polaritons by a double-slit structure beyond the diffraction limit

“…By adopting the chirped plasmonic gratings with a lateral dimension of about 17 μm 23 or 4 μm, 24 the bandwidths of the unidirectional SPP source reached 190 nm 23 and 210 nm. 24 With a pair of phased nanoslits, 25 the broadband unidirectional SPPs with a bandwidth of about 300 nm were numerically predicted, while the generated SPPs from all of these SPP launchers propagated bulkily along the metal surface, [3][4][5][6][7][8][9][10][12][13][14][15][16][17][18][19][20][21][22][23][24][25] leading to diverging SPP sources or approximate plane-wave SPP sources on the metal surface.…”

“…More importantly, the unidirectional SPPs generated by the ultra-small launcher should be directly and efficiently coupled to a subwavelength plasmonic waveguide rather than bulkily propagating along the metal surface without any confinements. Although some of these unidirectional SPP launchers possessed very small lateral dimensions ( parallel to the SPP propagation direction along the metal surface), which can even be downscaled to subwavelength, [12][13][14]22,23 nearly all of the unidirectional SPP launchers had very large longitudinal dimensions (>10λ, perpendicular to the SPP propagation direction along the metal surface). [3][4][5][6][7][8][9][12][13][14][15][16][17][18][19][20][21][22][23][24][25] This significantly limits the on-chip integration density of the plasmonic devices.…”

“…Moreover, the generated SPPs propagated bulkily along the metal surface without any confinements. [3][4][5][6][7][8][9][10][12][13][14][15][16][17][18][19][20][21][22][23][24][25] This makes it hard to directly couple the generated SPPs to subwavelength plasmonic waveguides. What is worse, the bulky propagation of the SPPs would bring large crosstalk between different plasmonic devices in high-integration plasmonic circuits.…”

“…[20][21][22][23][24][25] Moreover, its broadband and efficient properties are still maintained when the slit length is reduced to a subwavelength scale (<λ/10), which is about one hundred times smaller than that in the previous unidirectional SPP launchers. [3][4][5][6][7][8][9][12][13][14][15][16][17][18][19][20][21][22][23][24][25] This significantly shrinks the occupied area of the SPP launcher on the metal surface to be smaller than λ 2 /10. To avoid the bulky propagation of the SPPs along the metal surface, such a robust unidirectional SPP launcher beyond the diffraction limit is directly coupled to a subwavelength plasmonic waveguide.…”