Spatiotemporal light control with frequency-gradient metasurfaces

Abstract

The capability of on-chip wavefront modulation has the potential to revolutionize many optical device technologies. However, the realization of power-efficient phase-gradient metasurfaces that offer full-phase modulation (0 to 2π) and high operation speeds remains elusive. We present an approach to continuously steer light that is based on creating a virtual frequency-gradient metasurface by combining a passive metasurface with an advanced frequency-comb source. Spatiotemporal redirection of light naturally occurs as optical phase-fronts reorient at a speed controlled by the frequency gradient across the virtual metasurface. An experimental realization of laser beam steering with a continuously changing steering angle is demonstrated with a single metasurface over an angle of 25° in just 8 picoseconds. This work can support integrated-on-chip solutions for spatiotemporal optical control, directly affecting emerging applications such as solid-state light detection and ranging (LIDAR), three-dimensional imaging, and augmented or virtual systems.

A Dynamically Modulated All‐Dielectric Metasurface Doublet for Directional Harmonic Generation and Manipulation in Transmission

“…As the most prominent example, we consider implementation of a frequency diverse transmitarray. The concept of frequency diverse arrays was proposed for the first time in the RF array antennas and it has been recently extended to the passive and active optical metasurfaces . Unlike the conventional phased transmitarrays which use a progressive phase delay to transmit the light toward a specific direction by imparting a spatial phase gradient to the wavefront, a frequency diverse transmitarray implements a progressive frequency shift between the elements to impart a “spatiotemporal” phase gradient to the wavefront of light.…”

“…Due to the pure frequency mixing functionality of the constituent elements, such a time‐modulated metasurface acts as a frequency comb whose output spectrum consists of discrete and equally spaced frequencies. Due to the negligible modulation‐induced dispersion effects in the adiabatic regime of modulation, all the generated frequency harmonics are in‐phase at the metasurface plane at t = 0 s. The spatiotemporal phase gradient imprinted across the metasurface as a result of the frequency offset between the elements in the timeframe of | t | < τ/2 can be simply obtained as ϕ( x , t ) = ( x /λ)2πΔ ft which will yield a directional dynamic beam in transmission whose direction is time‐dependent and can be expressed as …”

Octave bandwidth photonic fishnet-achromatic-metalens

“…They are subwavelength nanostructured interfaces, capable of controlling optical waves. A large variety of components has been reported, including lenses [9][10][11][12][13][14][15][16] , holograms, quarter-wave plates, half-wave plates, vortex plates, carpet cloaks, concentrators, polarizers, thin absorbers, or sensors [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] . Despite exciting findings, achieving simultaneously high efficiencies and large bandwidths has remained a challenge.…”

Metasurfaces: Subwavelength nanostructure arrays for ultrathin flat optics and photonics

“…115 Spatiotemporal beam scanning using metasurfaces was achieved using laterally resolved spectrally modulated metasurfaces, which control the wavefront using a frequency gradient as opposed to using a conventional phase gradient. 21,116 Integrated with quantum emitters, metasurfaces could be used as a platform for quantum photon sources. In a weak coupling regime, Purcell enhancement of quantum emitters, or their enhancement of spontaneous emission rates, could enable the development of efficient single-photon sources for quantum optics.…”