20 research outputs found
Plasmonic silicon Schottky photodetectors: the physics behind graphene enhanced internal photoemission
Recent experiments have shown that the plasmonic assisted internal photoemission from a metal to
silicon can be
significantly enhanced by introducing a monolayer of graphene between the two media. This is despite the limited
absorption in a monolayer of undoped graphene (
∼
π
α
=
2.3
%
). Here we propose a physical model where surface plasmon polaritons
enhance the absorption in a single-layer graphene by enhancing the field along the interface. The
relatively long relaxation time in graphene allows for multiple attempts for the carrier to overcome the
Schottky barrier
and penetrate into the semiconductor. Interface disorder is crucial to overcome the momentum
mismatch in the internal photoemission process. Our results show that quantum efficiencies in
the range of few tens of percent are obtainable under reasonable experimental assumptions.
This insight may pave the way for the implementation of compact, high efficiency
silicon based
detectors for the telecom range and beyond
Array-scale inverse design of active metasurfaces
We develop an inverse design approach to optimize array architectures of reconfigurable metasurfaces and report dramatically improved beam steering performances with non-ideal antenna components. The versatility is enhanced by enabling continuous steering up to 70°
Array-Level Inverse Design of Beam Steering Active Metasurfaces
We report an array-level inverse design approach to optimize the beam steering performance of active metasurfaces, thus overcoming the limitations posed by nonideal metasurface phase and amplitude tuning. In contrast to device-level topology optimization of passive metasurfaces, the outlined system-level optimization framework relies on the electrical tunability of geometrically identical nanoantennas, enabling the design of active antenna arrays with variable spatial phase and amplitude profiles. Based on this method, we demonstrate high-directivity, continuous beam steering up to 70° for phased arrays with realistic tunable antenna designs, despite nonidealities such as strong covariation of scattered light amplitude with phase. Nonintuitive array phase and amplitude profiles further facilitate beam steering with a phase modulation range as low as 180°. Furthermore, we use the device geometries presented in this work for experimental validation of the system-level inverse design approach of active beam steering metasurfaces. The proposed method offers a framework to optimize nanophotonic structures at the array level that is potentially applicable to a wide variety of objective functions and actively tunable metasurface antenna array platforms
All-dielectric multiple quantum well active metasurfaces
We report a design of an all-dielectric Mie-resonant active metasurface, which exhibits a high reflectance (>45%) and a broad tunable phase shift at an operation wavelength of 1550 nm. The proposed design can be used for the realization of two-dimensional active metasurfaces
Emitter-Metasurface Interface for Manipulating Emission Characteristics of Quantum Defects
We demonstrate a chip-scale quantum emitter-metamaterial device that emits highly directional photons. Our device opens the door for quantum imaging of yveak sources by adding photon(s) to manipulate the photon statistics for improved signal-to-noise ratio
Tunable intraband optical conductivity and polarization-dependent epsilon-near-zero behavior in black phosphorus
Black phosphorus (BP) offers considerable promise for infrared and visible photonics. Efficient tuning of the bandgap and higher subbands in BP by modulation of the Fermi level or application of vertical electric fields has been previously demonstrated, allowing electrical control of its above-bandgap optical properties. Here, we report modulation of the optical conductivity below the bandgap (5 to 15 μm) by tuning the charge density in a two-dimensional electron gas induced in BP, thereby modifying its free carrier–dominated intraband response. With a moderate doping density of 7 × 10¹² cm⁻², we were able to observe a polarization-dependent epsilon-near-zero behavior in the dielectric permittivity of BP. The intraband polarization sensitivity is intimately linked to the difference in effective fermionic masses along the two crystallographic directions, as confirmed by our measurements. Our results suggest the potential of multilayer BP to allow new optical functions for emerging photonics applications
Emitter-Metasurface Interface for Manipulating Emission Characteristics of Quantum Defects
We demonstrate a chip-scale quantum emitter-metamaterial device that emits highly directional photons. Our device opens the door for quantum imaging of yveak sources by adding photon(s) to manipulate the photon statistics for improved signal-to-noise ratio