Electrically-driven optical antennas

Abstract: Unlike radiowave antennas, optical nanoantennas so far cannot be fed by electrical generators. Instead, they are driven by light or via optically active materials in their proximity. Here, we demonstrate direct electrical driving of an optical nanoantenna featuring an atomic-scale feed gap. Upon applying a voltage, quantum tunneling of electrons across the feed gap creates broadband quantum shot noise. Its optical frequency components are efficiently converted into photons by the antenna. We demonstrate that the properties of the emitted photons are fully controlled by the antenna architecture, and that the antenna improves the quantum efficiency by up to two orders of magnitude with respect to a non-resonant reference system. Our work represents a new paradigm for interfacing electrons and photons at the nanometer scale, e.g. for on-chip wireless data communication, electrically driven single- and multiphoton sources, as well as for background-free linear and nonlinear spectroscopy and sensing with nanometer resolution.

• The paper introduces electrically-driven optical nanoantennas that use quantum tunneling to enable direct and efficient photon generation.
• The method employs lateral tunnel junctions in single-crystalline gold antennas, with advanced ion beam and AFM fabrication achieving up to 100-fold efficiency improvements.
• Electroluminescence characterization reveals voltage-dependent blue shifts and polarized emission, indicating promising applications in on-chip communications and spectral sensing.

Electrically-Driven Optical Antennas: A Novel Paradigm in Nanophotonics

The paper, Electrically-driven optical antennas by Johannes Kern et al., presents an innovative approach to activating optical nanoantennas electrically, uniquely distinct from traditional radiowave antennas. Historically, optical antennas have been driven by light, due to difficulties in generating optical frequencies (around 300 THz) using conventional electrical circuits. This study marks a significant advancement as it successfully demonstrates the direct electrical driving of an optical nanoantenna via quantum tunneling at atomic scales. This is achieved by inducing quantum shot noise in electrons across a nano-fabricated feed gap, converting high-frequency components into photon emissions.

The central focus of this research is the design and implementation of a lateral tunnel junction within the feed gap of single-crystalline gold antennas on transparent substrates. The methodology incorporates a combination of focused ion beam structuring and advanced nano-manipulation techniques with atomic force microscopy to achieve this structure. The quantum tunneling effect serves as a fundamental mechanism directing electron flow and photon emission at optical frequencies. The efficiency of this emission is optimized through precise control over antenna architecture, leading to a reported quantum efficiency improvement by up to two orders of magnitude over non-resonant references.

One of the study's highlights is its unique electroluminescence (EL) characterization. The EL spectra exhibit a voltage-dependent blue shift, a direct consequence of modulating antenna resonance. Through elaborate experimental setups, including dark-field scattering spectroscopy, the study meticulously measures and correlates the far-field scattering and electroluminescence spectra with varying antenna geometries. Such measures are vital for understanding the tunability of the spectral response concerning antenna designs. Additionally, the polarization of emitted light exhibited a dominant orientation along the antenna axis, further reinforcing the controlled resonance response.

The implications of such electrically-driven photonic devices are significant and wide-ranging. Practically, these antennas hold promise for applications in on-chip wireless communication, providing a feasible alternative for multi-photon sources and highly sensitive spectral sensing. Theoretically, this work opens new avenues in studying light-matter interaction at nanoscales through the development of optoelectronic devices powered by quantum tunneling. The integration of such antennas with molecular switches could herald advances in photonic switching and optical transistor applications.

Future prospects in this area could involve improving device stability and efficiency, which are tied to the atomic configuration of tunneling junctions. By exploring different molecular spacer designs for stabilizing the conduction pathway, we can further refine the operational parameters and enhance the performance of these photonic systems. Moreover, such endeavors will be instrumental in increasing the bandwidth and tunability of optoelectronic devices in hybrid electronic-photonic circuits.

In summary, the electrically-driven optical nanoantenna described in this study represents an essential step in bridging electronic and photonic domains, providing a viable and efficient method of optical radiation generation at nanoscale dimensions. By leveraging advanced nano-fabrication techniques and harnessing quantum shot noise, the research delineates a new paradigm in nanophotonic interfacing with potential applications across a spectrum of scientific and industrial fields.