Graphene sheet with one-way light flow

One-Way Street for Light: Graphene's Revolutionary Trick to Bend Light

Beau Callahan in Tech & Innovation December 2025 • 4 min read.

"Scientists discover how drift-induced graphene plasmons can revolutionize optical devices, creating 'one-way' light flow without magnets."

For years, scientists have dreamed of creating optical systems where light flows in only one direction. In conventional photonics, light travels both ways, constrained by a fundamental principle called Lorentz reciprocity. This principle, related to the time-reversal symmetry of Maxwell's equations, makes it challenging to build devices like optical isolators and circulators that dictate the direction of light.

The increasing demand for highly integrated all-photonic systems has spurred a search for ways to break this reciprocity. Traditional methods involve using static magnetic fields to create a gyrotropic response, but this approach is bulky and hard to integrate into nanoscale devices. Other methods, such as using nonlinear effects or opto-mechanical interactions, have limitations like high power requirements or weak responses.

Now, a team of researchers is exploring a novel solution: using a graphene sheet biased with a drift electric current. Their theoretical model shows that this method creates a strong nonreciprocal response, allowing for 'one-way' propagation of surface plasmon polaritons. This approach not only enables unidirectional light flow but also significantly enhances the propagation length of graphene plasmons, opening new doors for optical technology.

Graphene's 'One-Way' Light Trick

The key to this breakthrough lies in graphene's unique properties. Graphene, a single layer of carbon atoms, boasts ultrahigh electron mobility, allowing electrons to drift at significant velocities when an electric current is applied. This drift current interacts with light in a way that breaks the symmetry of light propagation, enabling light to travel in one direction while being blocked or attenuated in the opposite direction.

Researchers have created a model using quantum mechanical methods to accurately describe how the drift current affects the graphene's conductivity. The model reveals that the drift current introduces a frequency Doppler shift, leading to a nonreciprocal electromagnetic response. This means that the way graphene interacts with light is different depending on the direction the light is traveling relative to the current.

This approach offers several potential advantages:

Subwavelength Control: Enables light manipulation at scales smaller than the wavelength of light.
Magnetic-Free: Eliminates the need for bulky magnets, simplifying device integration.
Enhanced Propagation: Boosts the distance light can travel through graphene.
Tunable Response: The 'one-way' effect can be adjusted by changing the drift velocity or the chemical potential of the graphene.

To illustrate the potential of this method, the researchers simulated a scenario where a graphene sheet with a drift current is illuminated by a near-field emitter. The simulations showed that the light propagates unidirectionally, guided by the graphene plasmons. Moreover, when obstacles or defects are placed in the path of the light, the unidirectional propagation ensures that the light flows around these imperfections, minimizing backscattering. This demonstrates that graphene plasmons are protected by a drift-current, analogous to topological systems.

A New Dawn for Optical Circuits

This breakthrough offers a promising route toward building advanced optical circuits, such as optical isolators and circulators, which are essential components in modern communication systems. By harnessing the unique properties of graphene and electric currents, scientists can create compact, efficient, and tunable devices that control light at the nanoscale. This research opens new avenues for innovation in nanophotonics, paving the way for faster, more efficient, and more integrated optical technologies.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1021/acsphotonics.8b00987, Alternate LINK

Title: Drift-Induced Unidirectional Graphene Plasmons

Subject: Electrical and Electronic Engineering

Journal: ACS Photonics

Publisher: American Chemical Society (ACS)

Authors: Tiago A. Morgado, Mário G. Silveirinha

Published: 2018-10-23

Everything You Need To Know

What fundamental principle makes it challenging to achieve one-way light flow in conventional photonics, and what limitations do traditional methods face when trying to overcome this?

The conventional flow of light, as governed by Lorentz reciprocity which is related to the time-reversal symmetry of Maxwell's equations, dictates that light travels in both directions. This principle poses a significant hurdle in creating optical isolators and circulators, essential for directing light flow in only one way. Traditional solutions often involve bulky static magnetic fields to induce a gyrotropic effect which is hard to integrate into nanoscale devices. Other methods, such as employing nonlinear effects or opto-mechanical interactions, suffer from limitations like high power demands or weak responses.

How does using a graphene sheet biased with a drift electric current enable 'one-way' light propagation, and what benefits does this approach offer over traditional methods?

This innovative technique leverages the unique properties of graphene and electric currents. By applying a drift electric current to a graphene sheet, scientists can induce a strong nonreciprocal response. This enables 'one-way' propagation of surface plasmon polaritons, which means light can travel in one direction while being blocked or attenuated in the opposite direction. This method not only achieves unidirectional light flow but also extends the propagation length of graphene plasmons, offering new possibilities for optical technology.

What property of graphene is critical to achieving one-way light flow, and how does the drift current influence the electromagnetic response of graphene?

The ultrahigh electron mobility of graphene allows electrons to drift at substantial velocities when an electric current is applied. This drift current interacts with light in a manner that breaks the symmetry of light propagation. Quantum mechanical models reveal that the drift current introduces a frequency Doppler shift, resulting in a nonreciprocal electromagnetic response. Consequently, graphene interacts with light differently based on the light's direction relative to the current, facilitating the 'one-way' light flow.

What are the key advantages of using drift-induced graphene plasmons for controlling light, and how do these benefits contribute to the advancement of optical technologies?

This technique offers several advantages. First, it provides subwavelength control, allowing for light manipulation at scales smaller than the wavelength of light. Second, it eliminates the need for bulky magnets, simplifying device integration. Third, it enhances the propagation distance of light through graphene. Finally, the 'one-way' effect is tunable by adjusting the drift velocity or the chemical potential of the graphene, offering greater flexibility in device design.

How do simulations demonstrate the effectiveness of using drift current to protect graphene plasmons from imperfections, and what does this imply for building advanced optical circuits?

The simulations showed that when a graphene sheet with a drift current is illuminated by a near-field emitter, light propagates unidirectionally, guided by the graphene plasmons. The unidirectional propagation ensures that the light flows around these imperfections, minimizing backscattering. Graphene plasmons are protected by a drift-current, analogous to topological systems, which indicates their robustness and reliability in complex optical circuits. This enables the creation of compact, efficient, and tunable devices for advanced communication systems.