Emory Achieves 500% Intensity Control of Nanoscale Light

Emory University physicists have achieved 500% intensity control of light generated within a nanoscale device, a level of brightness tuning previously unattainable in such a small component. The integrated component, exceeding 100 times smaller than the width of a human hair at just over 200 nanometers, utilizes second harmonic generation to produce light, but with a crucial new capability. “Nobody had previously shown that you can tune second harmonic generation with an electric knob in such a small device,” says Hayk Harutyunyan, Emory professor of physics and senior author of the work published in Optica. With an active light-generating area spanning only two to six nanometers, the team’s innovation promises more flexible and efficient photonic technologies for communications, sensing, and potentially, quantum computing.

Second Harmonic Generation Enables Tunable Nanoscale Light Control

A device no wider than a virus has achieved an unprecedented 500% control over light intensity, opening new avenues for miniaturized photonic technologies. Researchers at Emory University, in collaboration with teams from the University of Cambridge, the National University of Singapore, and the Air Force Research Laboratory, have demonstrated a nanoscale light source capable of being switched on, off, and tuned across a remarkably broad range of brightness levels using an electrical signal. This level of dynamic control, previously unattainable in devices of this scale, promises advancements in fields ranging from telecommunications to quantum computing. The innovation centers on second harmonic generation, or SHG, a nonlinear optical process where photons combine to create new light at twice the original frequency. This extreme miniaturization is crucial, as Harutyunyan emphasizes. Achieving this level of control required overcoming significant materials science challenges.

The team initially struggled with the stability of the tunneling junction, a semi-permeable barrier essential to the device’s function, with early iterations short-circuiting under voltage. A breakthrough came through collaboration with specialists at the National University of Singapore, who suggested using lutetium oxide, known for its high melting point and stability, for the tunnel junction. “While we are experts in working with nonlinear light, they are the experts when it comes to fabricating thin oxide films,” Harutyunyan notes, highlighting the importance of interdisciplinary expertise. The resulting device not only functioned reliably but also demonstrated the ability to modulate light intensity across a 500% range. “We can switch on our device, completely shut it off, and raise or lower its intensity within a range of 500%,” Harutyunyan says, outlining the device’s versatility for both fundamental research and practical applications.

Plasmonic-EFISH Device Design Utilizing Tunneling Junctions

Current approaches to manipulating light on the nanoscale often rely on plasmonic electric-field-induced second harmonic (plasmonic-EFISH) devices, intended as bridges between electronic and photonic systems for faster optical switching. However, many existing designs suffer from limited tunability and relatively large footprints, hindering their integration into truly miniaturized systems. Researchers are actively seeking methods to overcome these limitations and create more versatile, controllable nanoscale light sources. The Emory University team addressed this challenge by focusing on the tunneling junction, a semi-permeable barrier within optoelectronic components, and optimizing its material composition for stability and performance. A significant hurdle in the development process involved creating a tunneling junction robust enough to withstand applied voltage while remaining thin enough to facilitate electron flow.

Initial attempts using indium tin oxide and silicon dioxide repeatedly resulted in device failure; “It wasn’t stable enough to hold the charge for more than a few minutes,” explained Yuankai Tang, a PhD student at Emory, detailing the initial short-circuiting issues. After over a year of unsuccessful iterations, the team broadened its expertise, collaborating with the Ariando group at the National University of Singapore, specialists in ultra-thin quantum materials. This collaboration proved pivotal, leading to the selection of lutetium oxide for the tunnel junction due to its exceptional thermal stability and resistance to degradation. The resulting device, fabricated using pulsed laser deposition and electron-beam lithography, demonstrated a remarkable level of control over light generation. Experiments confirmed the ability to not only switch the light source on and off but also to modulate its intensity across a 500% range.

This level of dynamic control is achieved within an integrated component measuring just over 200 nanometers in width, exceeding the miniaturization capabilities of many prior second harmonic generation devices. The active light-generating area itself spans only two to six nanometers, further enhancing controllability. “To our knowledge, this is the first demonstration of electrically tunable, second-harmonic generation via a tunnel junction,” Harutyunyan stated, highlighting the novelty of the approach and its potential to advance both fundamental research and integrated photonic circuitry. “If you’re replacing electric currents with photon flows, you need to be able to create photons on demand and control the rate of flow,” he added, emphasizing the broader implications for future photonic technologies.

Lutetium Oxide Stabilizes Nanoscale Component Fabrication

Researchers at Emory University, collaborating with international partners, have overcome a critical materials science hurdle in the fabrication of nanoscale photonic devices, achieving unprecedented stability through the implementation of lutetium oxide. Initial attempts utilizing aluminum oxide consistently resulted in short circuits, frustrating efforts to create a functional, tunable light source. Recognizing the need for combined expertise, the Emory team leveraged the Singapore group’s proficiency in fabricating robust thin films. They ultimately selected lutetium oxide, prized for its high melting point and inherent stability, even under extreme conditions, as the tunneling junction material. Utilizing pulsed laser deposition, the collaborators layered zirconia with indium tin oxide, culminating in an ultra-thin, highly stable layer of lutetium oxide. Tang then integrated precisely crafted gold electrodes, completing the fabrication process. Harutyunyan stated, highlighting the importance of interdisciplinary collaboration.

The resulting device not only demonstrated reliable functionality but also exhibited a remarkable 500% intensity control, allowing for precise manipulation of light emission. Harutyunyan emphasized, “That’s the name of the game in both electronics and photonics. You need to squeeze as many features as you can into a small space.” This innovation promises to advance the development of faster, more energy-efficient photonic chips, potentially paving the way for improvements in communications, sensing, and even quantum computing.