Spatially shifted beam approach to subwavelength focusing.

Lensless focusing with subwavelength resolution by direct synthesis of the angular spectrum

We consider the coherent superposition of unfocused wave fronts for lensless focusing of electromagnetic waves with subwavelength resolution. Near the focal point, intensity distributions generated using the approach approximate those generated using lenses. Far from the focal point, discretization of spatial frequencies results in a trade-off between the number of wave fronts and the accuracy ...

Highly efficient and ultra-broadband graphene oxide ultrathin lenses with three-dimensional subwavelength focusing

Nanometric flat lenses with three-dimensional subwavelength focusing are indispensable in miniaturized optical systems. However, they are fundamentally challenging to achieve because of the difficulties in accurately controlling the optical wavefront by a film with nanometric thickness. Based on the unique and giant refractive index and absorption modulations of the sprayable graphene oxide thi...

Machine learning based compact photonic structure design for strong light confinement

We present a novel approach based on machine learning for designing photonic structures. In particular, we focus on strong light confinement that allows the design of an efficient free-space-to-waveguide coupler which is made of Sislab overlying on the top of silica substrate. The learning algorithm is implemented using bitwise square Sicells and the whole optimized device has a footprint of 2μ...

Shaping a Subwavelength Needle with Ultra-long Focal Length by Focusing Azimuthally Polarized Light

Flat optics, which could planarize and miniaturize the traditional optical elements, possesses the features of extremely low profile and high integration for advanced manipulation of light. Here we proposed and experimentally demonstrated a planar metalens to realize an ultra-long focal length of ~240λ with a large depth of focus (DOF) of ~12λ, under the illumination of azimuthally polarized be...

Subwavelength beam focusing by multiple-metal slits surrounded by chirped dielectric surface gratings