Engineers Break Speed Barrier with Tiny Plasmonic Modulator

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Design engineers constantly face trade-offs between speed, size, power, and integration when working on next-generation optical systems, especially in areas like data center interconnects, optical transceivers, 6G wireless, and advanced sensing.

These trade-offs arise as engineers push for faster, smaller, and more efficient components. For example, faster modulators often require higher voltages, which increases power consumption and generates more heat. Modulators, which map high-speed electrical data signals onto an optical signal, are needed to translate electrical signals into the optical domain in order to propagate them over an optical fiber cable. Smaller components, such as modulators, can produce signal integrity issues or require complex fabrication techniques. Integrating new photonic technologies into complementary metal-oxide-semiconductor (CMOS)-compatible platforms typically requires major system design shifts.

However, a recent development by a team from Eidgenössische Technische Hochschule (ETH) Zurich may challenge those assumptions.

A Solution to Four Significant Challenges

Researchers at the institution have developed a plasmonic modulator that is not only significantly smaller than silicon-based alternatives but also achieves ten times the bandwidth, all while using less power and integrating with standard CMOS processes.[i]

The breakthrough modulator operates at terahertz frequencies while occupying just a few square micrometers of space (Figure 1).

Figure 1: The modulator (in gold) transfers information from an electrical wave to an optical one (Source: Christian Haffner, Nature Photonics 2015)

"If you think about state-of-the-art modulators in silicon that take several square millimeters of space, you're talking here about the modulator that takes several square micrometers in space, which means we have a footprint reduction at least in three orders of magnitude," said Professor Juerg Leuthold, Head of the Department of Information Technology and Electrical Engineering at ETH Zurich.

Along with the size reduction, the device also features a 10-fold performance improvement. Most commercial optical modulators top out at 100GHz, but the ETH design demonstrated a capability of 1000GHz.

The ETH team has also shown a broad operating range from 10MHz to 1.14THz, which is a rare feat for any modulator. This wide frequency coverage means a single component can handle multiple roles across communication and sensing platforms, which simplifies system design and reduces the need for multiple specialized parts.

The device also manages impressive efficiency. It runs on approximately 2V peak-to-peak, compared to the 4V typically required, which reduces power consumption significantly due to the squared relationship between voltage and power.

"Now we have a technology that integrates into everything," Leuthold said. "So, I think with this technology, we can solve four of the most important challenges in our [photonics] industry."

The new device relies on plasmonics, which is a method that manipulates light at the nanoscale using metals like gold. While gold is not an industry standard for large-scale production, it was a reliable test material in the lab.

What Is a Plasmonic Modulator?

Unlike traditional silicon photonics, which routes light through waveguides, plasmonic modulators manipulate surface plasmon polaritons (SPPs)—electromagnetic waves that travel along the interface of a conductor and dielectric. These waves allow for extremely compact light-matter interaction, creating fast signal modulation in a much smaller footprint.

Plasmonics does come with challenges, such as optical losses, but this ETH Zurich design bypasses some of those by minimizing path lengths and leveraging gold's natural conductivity.

Why This Matters

The plasmonic modulator’s flat frequency response is one of its most appealing characteristics for engineers. As bandwidth increases, most modulators exhibit gain roll-off, forcing them to compensate with equalization filters, digital signal processing (DSP) overhead, or even redesign link budgets.

"In digital signal processing and in optical communications, people undo this drop of response at higher frequency with an equalizer. They put in calculation power," Leuthold explained. "Now you have a device where you don't need this calculation anymore … the signal processing is getting easier … you can perform experiments at frequencies that were simply not accessible before. So, there's a huge new world that opens up with this device."

For design engineers, this flat frequency could reduce system complexity, power budgets, and even bill of materials (BOM) costs. It also improves impedance matching and signal fidelity at the transceiver level.

Integration Without the Headache

This plasmonic modulator does not just promise standalone performance. It was designed with CMOS compatibility in mind, meaning it can be embedded into existing silicon architectures with fewer process changes, creating potential use in mainstream transceiver production lines.

In fact, Polariton Technologies AG, a startup founded by Leuthold's PhD students, is already offering commercial versions of this modulator.

While gold was used in the lab for ease of prototyping, Leuthold confirmed that copper or aluminum would likely be used in commercial production for cost and compatibility.

New Applications in Terahertz and Beyond

The ETH Zurich modulator opens up opportunities for new applications beyond data centers.

In addition to optical transceivers, it is a promising option for spectroscopy, medical imaging, and airport security systems. These areas typically require high-frequency operation, small size, and low power consumption.

The modulator also opens new possibilities for 6G wireless, advanced sensing, and quantum communications.

"The opportunities are in 6G, just to name one application area, which is bound to go to higher frequencies, and in the sensing area, where all of a sudden you have access to frequencies that so far were not accessible," said Leuthold.

With gold's excellent thermal conductivity, the device can move heat away rapidly, even in high-frequency switching conditions, ensuring reliable performance.

Looking Ahead to a Complete Transceiver

The team isn't stopping at modulators. They're already working on a high-speed photodetector to match.

"We have the modulator, and now we make the photodetector happen. We would like to have both ends of the transceiver," Leuthold said.

[1]https://ethz.ch/en/news-and-events/eth-news/news/2025/03/tiny-component-for-record-breaking-bandwidth.html