Giant birefringence in optical antenna arrays with widely tailorable optical anisotropy

Abstract

The manipulation of light by conventional optical components such as lenses, prisms, and waveplates involves engineering of the wavefront as it propagates through an optically thick medium. A unique class of flat optical components with high functionality can be designed by introducing abrupt phase shifts into the optical path, utilizing the resonant response of arrays of scatterers with deeply subwavelength thickness. As an application of this concept, we report a theoretical and experimental study of birefringent arrays of two-dimensional (V-and Y-shaped) optical antennas which support two orthogonal charge-oscillation modes and serve as broadband, anisotropic optical elements that can be used to locally tailor the amplitude, phase, and polarization of light. The degree of optical anisotropy can be designed by controlling the interference between the waves scattered by the antenna modes; in particular, we observe a striking effect in which the anisotropy disappears as a result of destructive interference. These properties are captured by a simple, physical model in which the antenna modes are treated as independent, orthogonally oriented harmonic oscillators.plasmonics | resonance | metasurfaces | scattering T he general function of optical devices consists of the modification of the wavefront of light by altering its phase, amplitude, and polarization in a desired manner. The class of optical components with varying phase retardation includes lenses, waveplates, spiral phase plates (1), axicons (2), and more generally spatial light modulators, which are able to imitate many of these components by means of a dynamically tunable spatial response (3). All of these conventional optical components rely on gradual evolution of phase, amplitude, and polarization as the wave propagates through an optically thick medium. The introduction of abrupt phase changes into the optical path by using the resonant behavior of plasmonic nanostructures allows one to achieve control over the wavefront without relying on gradual phase accumulation (4). This approach is now enabling the design of various optical devices which are thin compared to the wavelength of light (5-7).Our previous work on phase discontinuities involved spatially inhomogeneous configurations of V-shaped optical antennas (4, 5, 7). Here, we report that homogeneous arrays optical antennas supporting two independent and orthogonally oriented current modes operate as highly birefringent meta-surfaces. We consider arrays of V-shaped antennas, creating a connection with our previous work, and Y-shaped antennas in which the anisotropy can be widely tailored or extinguished via interference between the scattered light from the two current modes. A simple, analytical two-oscillator model for such two-dimensional (2D) optical antennas is developed which captures the physics of these antennas and provides an intuitive way to understand how engineering of the amplitude and phase of the scattered light provides control over the optical anisotropy of the resulting meta-sur...

A review of metasurfaces: physics and applications

“…The metasurface creates anomalously refracted and reflected beams satisfying the generalized laws over a wide wavelength range, with negligible spurious beams and optical background, as shown in figure 2(b) and (d). The broadband performance is due to the fact that the two eigenmodes supported by the V-antennas form a broad effective resonance over which the scattering efficiency is nearly constant and the phase response is approximately linear [33,34]. The scalability of metasurfaces allows the extension of this concept to other frequency ranges, e.g., broadband anomalous refraction was also demonstrated at THz frequencies using C-shaped metallic resonators [35] The generalized law of reflection has also [36], (c) and (d) used with permission from [14], (e) and (f) used with permission from [37].…”

Ultra-thin, planar, Babinet-inverted plasmonic metalenses

“…[7][8][9][10][11][12][13][14] An array of such nanoantennas can form a metasurface to bend the light abnormally 7,8 in a fairly broad range of wavelengths and can create, for example, an optical vortex beam. 7,12 In addition, a metasurface arranged of plasmonic nano-antennas can be used as a very efficient coupler between propagating waves and surface waves.…”

Unidirectional Side Scattering of Light by a Single-Element Nanoantenna

“…This simple planar single-element antenna geometry has been used before as a tunable-phase antenna building block in birefringent metasurfaces and aberration-free ultrathin flat lenses at telecom frequencies. 30,31 While these applications rely on diffractive farfield interferences generated by carefully designed arrays, here, the broken mirror symmetry of a single V-antenna allows us to benefit directly from the characteristic phase shifts of an intrinsic Fano interference, arising from the coherent near-field coupling of a dipole and higher order LSPR modeeven at near-infrared and visible frequencies. We use finite difference time domain (FDTD) calculations to analyze the antenna modes and map the three-dimensional far-field scattering intensity distributions.…”