Beam steering at the nanosecond time scale with an atomically thin reflector

Abstract

Techniques to mold the flow of light on subwavelength scales enable fundamentally new optical systems and device applications. The realization of programmable, active optical systems with fast, tunable components is among the outstanding challenges in the field. Here, we experimentally demonstrate a few-pixel beam steering device based on electrostatic gate control of excitons in an atomically thin semiconductor with strong light-matter interactions. By combining the high reflectivity of a MoSe2 monolayer with a graphene split-gate geometry, we shape the wavefront phase profile to achieve continuously tunable beam deflection with a range of 10°, two-dimensional beam steering, and switching times down to 1.6 nanoseconds. Our approach opens the door for a new class of atomically thin optical systems, such as rapidly switchable beam arrays and quantum metasurfaces operating at their fundamental thickness limit.

Excitonic Beam Steering in an Active van der Waals Metasurface

“…Notably, the two deflected beams are separate from the specular reflection and close to collimated, with an angular divergence of 16°. This is a stark contrast to previous demonstrations, where the deflected beam was highly divergent . The asymmetry in the intensity of the +1 and −1 diffraction order likely is due to an asymmetric alignment of the finite size aperture used in the detection with the applied voltage profile (see Supplementary Note 4).…”

“…38,39 For example, excitonic resonances have been used to demonstrate an intensity-tunable lens with a fixed focal length 40 or to steer a focused beam at an edge of three MoSe 2 flakes. 41 However, despite much progress, the dynamic control thus far has been limited to amplitude modulation or local point control of an edge, and versatile wavefront control of reflected light from a single atomic layer has remained an outstanding challenge.…”

“…Without external enhancement or coupling to optical cavities, excitonic reflectivity of over 80% , and tunability of over 200% in the real and imaginary part of the refractive index have been shown by modifying the radiative and nonradiative rates in MoSe 2 . These rapid advances in understanding exciton resonances have stimulated thinking about active metasurfaces that exploit the excitonic modulation phenomena to enable van der Waals active metasurfaces. , For example, excitonic resonances have been used to demonstrate an intensity-tunable lens with a fixed focal length or to steer a focused beam at an edge of three MoSe 2 flakes . However, despite much progress, the dynamic control thus far has been limited to amplitude modulation or local point control of an edge, and versatile wavefront control of reflected light from a single atomic layer has remained an outstanding challenge.…”

“…This is a stark contrast to previous demonstrations, where the deflected beam was highly divergent. 41 The asymmetry in the intensity of the +1 and −1 diffraction order likely is due to an asymmetric alignment of the finite size aperture used in the detection with the applied voltage profile (see Supplementary Note 4). By applying a voltage gradient to impose a linear phase gradient along the interface, V 1 = 5 V and V 3 = −5 V, we show the asymmetric steering of light into the +1 diffraction order, and the suppression of the −1 order.…”

Active beam steering enabled by photonic crystal surface emitting laser

“…Optical beam steering is an eagerly desired functionality for various optoelectronic applications, such as optical switching 1,2 , displaying [3][4][5] , printing 6 , and light detection and ranging (Lidar) [7][8][9][10] .…”