Graphene plasmons are waves formed by electrons moving together in a synchronized way across a sheet of graphene. They're special, because they can work at very high frequencies, called terahertz (THz), which are faster than those used in most electronics.
Plasmon Problems
Until now, however, getting plasmons to deliver practical applications hasn't been easy. Traditionally, they have been based on metals and this causes them to lose a lot of energy. Newer techniques using graphene, on the other hand, rely on light-based methods that are inefficient and hard to control.
Generate, Control and Detect
That's why NTT, partnering with the University of Tokyo and the Japanese National Institute for Materials Science (NIMS), has been working on ways to generate, control, and detect graphene plasmons in the THz range. Doing this enables precise adjustment of signal strength and timing, which then brings interesting possibilities for THz devices that could be faster and more efficient than today's technology.
What are Plasmons?
First of all, though, let's see if we can imagine what a plasmon actually is. Think of it as a ripple of electrons moving together across the surface of a material, like ripples in a pond when you toss in a stone. In metals, plasmons create unique optical effects useful in areas like imaging, but they lose energy and can't easily be adjusted on the fly. Graphene plasmons, on the other hand, are much easier to control. In graphene-a single layer of carbon atoms-these electron waves move with less energy loss, and scientists can tweak their speed and direction by applying an electric field, adjusting the "ripple" to suit different needs.
That kind of control is extremely valuable in the THz frequency range, which could be key for a number of future technologies, including ultra-fast wireless communication and advanced imaging. Graphene's plasmons work well at THz frequencies, making it one of the few materials able to support new types of ultra-fast electronics in this range.
Terahertz Electrical Frequencies
For graphene plasmons to be useful in THz circuits, researchers need a way to create a plasmon at one point, guide it through a circuit, and measure it accurately at another point. Traditional methods often use THz light waves traveling through open space to create plasmons, but this approach wastes a lot of energy and is hard to control instantly. NTT and its partners have developed a simpler, more direct way to do this. Instead of using light, they use electrical pulses at THz frequencies to make plasmons right on the chip. It's like flicking one end of a string to send a wave through it, rather than waiting for the wind to create one. This direct approach lets researchers create precise waves in graphene that can travel far without losing much energy.
The new method also integrates graphene devices onto a single chip, allowing them to control the wave's strength and timing as it moves-important for making adjustments in real time. This combination of direct generation and on-chip control means that THz signals can be processed with high accuracy, laying the foundation for ultra-fast data processing.
The World's Shortest Wave Packets
Another major achievement in developing graphene plasmons was creating super-short "wave packets," which last only 1.2 picoseconds-or a trillionth of a second. These very brief pulses are perfect for sending THz signals accurately without losing their shape, which is key for processing data at high speeds. By applying an external voltage, the research team can also adjust the signal's strength and timing, essential for basic functions like filtering, amplifying, and modifying signals in circuits.
Zinc Oxide for Efficiency
Researchers were able to improve efficiency by adding a zinc oxide (ZnO) layer on the graphene device, which helps convert electrical pulses into graphene plasmons with about 35% efficiency-much higher than older light-based methods. This improvement makes graphene plasmons practical for THz circuits, potentially enabling devices like ultra-sensitive sensors and rapid data processors.
Next-Gen High-Speed Communication
Graphene plasmons could soon support devices capable of processing data at THz frequencies, far faster than today's GHz-range technology. Because graphene plasmons can be triggered by both electrical signals and light, they could be used in hybrid devices that blend the speed of light-based technology with the precision of electronic control. This could lead to even faster, more efficient devices for applications across communication and data processing.
For further information, please see this link:
https://group.ntt/en/newsrelease/2024/07/22/240722a.html
NTT-Innovating the Future
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NTT - Nippon Telegraph & Telephone Corporation published this content on January 24, 2025, and is solely responsible for the information contained herein. Distributed by Public, unedited and unaltered, on January 24, 2025 at 03:44:03.080.