Broadband unidirectional transverse light scattering in a V-shaped silicon nanoantenna

Abstract

The efficient manipulation of light-matter interactions in subwavelength all-dielectric nanostructures offers a unique opportunity for the design of novel low-loss visible- and telecom-range nanoantennas for light routing applications. Several studies have achieved longitudinal and transverse light scattering with a proper amplitude and phase balance among the multipole moments excited in dielectric nanoantennas. However, they only involve the interaction between electric dipole, magnetic dipole, and up to the electric quadrupole. Here, we extend and demonstrate a unidirectional transverse light scattering in a V-shaped silicon nanoantenna that involves the balance up to the magnetic quadrupole moment. Based on the long-wavelength approximation and exact multipole decomposition analysis, we find the interference conditions needed for near-unity unidirectional transverse light scattering along with near-zero scattering in the opposite direction. These interference conditions involve relative amplitude and phases of the electromagnetic dipoles and quadrupoles supported by the silicon nanoantenna. The conditions can be applied for the development of either polarization- or wavelength- dependent light routing on a V-shaped silicon and plasmonic nanoantennas.

Unidirectional Transverse Light Scattering in Notched Silicon Nanosphere

“…Therefore, the situation is more complicated than the simple model shown in Figure 1a. Figure 3c,d shows the vector diagram of the complex multipole coefficients [21,22,31] at 𝜆 = 650 nm for the pristine Si NS and the notched Si NS, respectively. Not only the amplitudes, but also the phases are strongly modified by the formation of the notch.…”

“…These values are comparable to that of the V-shaped Si nanoantenna (6.4 dB). [22] One of the important aspects of unidirectional transverse scattering is the generation of lateral optical forces (F x ) as a recoil of scattering. [10,29] We calculate the optical force on a notched Si NS from the Maxwell stress tensor.…”

“…[25,27,28] In contrast, the experimental research for plane wave illumination is scarce, although there have been a few theoretical studies, e.g., on V-shaped Si nanoantennas. [21,22] In this work, we develop an asymmetric dielectric nanoantenna, namely a notched Si nanosphere (Si NS), that exhibits unidirectional transverse scattering under plane wave excitation. We first discuss necessary conditions for transverse unidirectional scattering of a plane-wave by a nanoparticle.…”

“…[ 25,27,28 ] In contrast, the experimental research for plane wave illumination is scarce, although there have been a few theoretical studies, e.g., on V‐shaped Si nanoantennas. [ 21,22 ]…”

“…[12,[16][17][18] More interestingly, by using designed structures such as nanocubes [19] and nanoplates, [20] "bidirectional" transverse scattering can be achieved through the interference between a series of Mie modes (e.g., ED, MD, electric quadrupole (EQ), and magnetic quadrupole (MQ)) with different phases. Similarly, "unidirectional" transverse light scattering has been studied for optical routing, [21,22] optical coupling, [23,24] position sensing, [25][26][27][28] and optically actuated nanomotors. [10,29] Many of these previous studies on unidirectional transverse light scattering use vector beams such as radially or azimuthally polarized light.…”