Metasurface-based Fourier lens fed by compact plasmonic optical antennas for wide-angle beam steering

Compact unidirectional waveguide grating emitter with enhanced wavelength sensitivity based on the hybrid plasmonic mode

Waveguide grating antennas are widely adopted in beam-steering devices, typically enabling the beam steering in longitudinal direction within a two-dimensional scanning optical array by changing the input wavelength. However, traditional waveguide grating antennas suffer from limited tuning range due to low dispersion of the gratings. In this paper, a compact silicon grating waveguide antenna array is proposed with enhanced wavelength sensitivity by introducing a periodically modulated hybrid plasmonic mode. The hybrid plasmonic mode is supported by the hybrid plasmonic waveguides (HPWs) composed of silicon waveguides and periodic subwavelength silver strips. In order to convert the guided waves to the radiated waves, a series of silicon emitting segments are deposited above the HPWs. Additionally, the horizontally arranged array of HPWs also acts as a reflector of the downward radiation, resulting in an effective unidirectional emission. Through the optimization of physical parameters, the proposed antenna array achieves a wavelength-length tuning efficiency up to 0.3°/nm within the wavelength range of 1500∼1600 nm, exhibiting a significant improvement compared with traditional ones. Moreover, an average upward emissivity exceeding 80% with a maximum value of 89% within the 100 nm bandwidth is demonstrated through the numerical simulations. The proposed compact antenna array provides an alternative solution in realizing large-scale integrated high-tuning-efficiency optical beam-steering devices.

Hybrid cubic-chessboard metasurfaces for wideband angle-independent diffusive scattering and enhanced stealth

Because of the shortcomings associated with their scattering patterns, both the chessboard and cubic phased metasurfaces show non-perfect diffusion and hence sub-optimal radar cross section reduction (RCSR) properties. This paper presents a novel and powerful hybrid RCSR design approach for diffusive scattering by combining the unique attributes of cubic phase and chessboard phase profiles. The hybrid phase distribution is achieved by simultaneously imposing two distinct phase profiles (chessboard and cubic) on the hybrid metasurface area with the aid of geometric phase theory to further enhance the diffusive scattering and RCSR. It is shown in this paper that through the integration of cubic and chessboard phase profiles, a metasurface with the hybrid phase mask successfully overcomes all the above issues and shortcomings related to the RCSR of both chessboard and cubic metasurfaces. In addition, the proposed design leverages the unique scattering properties offered by these distinct phase profiles to achieve enhanced stealth capabilities over wide frequency ranges and for large incidence angles. Simulation and measurement results show that the designed hybrid metasurfaces using the proposed strategy achieved RCSR and low-level diffused scattering patterns from 12-28 GHz (80%) for normal incidence of a far-field CP radar plane wave. The hybrid metasurface shows a stable angular diffusion and RCSR performance when the azimuthal and elevation incidence angles are in the range of 0° → ± 75° which is wider than other designs in the literature. Therefore, this work can make objects significantly less detectable in complex radar environments when enhanced stealth is required.

Integrated optical beam steering device using switchable nanoantennas and a reflective metalens

In this paper, an integrated optical device is proposed in which a reflective meta-lens and five switchable nano-antennas are combined to provide optical beam steering at the standard telecommunication wavelength of 1550 nm. For this purpose, a graphene-based switchable power divider is designed and integrated with nano-antennas to control the flow of the light entering the device. To achieve a higher angular accuracy in the radiated beams, a new algorithm is proposed and utilized to optimize the location of feeding nano-antennas in accordance with the reflective meta-lens. In order to achieve a minimum fluctuation in the light intensity when the beams are rotated in the space, an algorithm is developed to select optimum unit cells for the engineered meta-lens. The whole device is numerically analyzed using Electromagnetic full-wave simulations illustrating an optical beam steering with high accuracy (better than 1 degree) in the beam direction, and a low variation (less than 1 dB) in the radiated light intensity. The proposed integrated device can be used for many applications such as inter- and intra-chip optical interconnects, optical wireless communication systems, and advanced integrated LIDARs.