Design engineers constantly face trade-offs between speed, size, power, and integration when developing next-generation optical systems.

These trade-offs are particularly evident in areas such as data center interconnect, optical transceivers, 6G wireless, and advanced sensing.

These trade-offs arise as engineers strive to create faster, smaller, and more efficient components.

For example, faster modulators typically require higher voltages, which increases power consumption and heat generation.

A modulator is a device that maps high-speed electrical data signals to optical signals, and is essential for converting electrical signals into the optical domain that can be transmitted through fiber optic cables.

Small components such as modulators can cause signal integrity issues or require complex manufacturing processes.

Additionally, integrating new photonic technologies into CMOS (complementary metal-oxide semiconductor)-compatible platforms requires major changes to the overall system design.

However, ETH Zurich (A recent study by a research team at ETH Zurich is shaking up these existing assumptions.

Researchers at the university have developed a plasmonic modulator that is significantly smaller than silicon-based alternatives, yet offers a tenfold increase in bandwidth, reduces power consumption, and can be integrated into existing standard CMOS processes.

This innovative modulator operates in the terahertz (GHz) frequency range while occupying an extremely small area of only a few square micrometers (㎛²).


“Current state-of-the-art silicon-based modulators occupy an area of a few square millimeters (㎟), but the modulator developed this time is only a few square micrometers (㎛²),” said Professor Juerg Leuthold, who heads the Department of Information Technology and Electrical Engineering at ETH Zurich. “That is, we have achieved an area reduction of at least 1,000 times,” he explained.

In addition to the size reduction, the performance improvement is also notable.

While most commercial optical modulators have their limits at around 100 GHz, the ETH team's design has demonstrated performance that can operate up to 1,000 GHz (1 terahertz).

The ETH research team also demonstrated that this modulator has a very wide operating range, from 10 MHz to 1.14 MHz.

This is a rare achievement for any modulator, and this wide frequency coverage means that a single component can perform multiple roles across communications and sensing platforms.

As a result, system design is simplified and the need for multiple specialized components is reduced.

The device also showed excellent performance in terms of efficiency. Unlike conventional modulators, which typically require around 4V, this device operates at around 2V peak-to-peak, and power consumption is significantly reduced because power is proportional to the square of the voltage.

“We now have a technology that can be integrated into any system,” said Professor Roithold. “We believe this technology will address four key challenges in the photonics industry.”

This new device is based on a technology called 'plasmonics'.

This is a way to control light at the nanoscale using metals such as gold. Gold is not an industrial standard material used in large-scale production, but it has been used as a very stable test material in the laboratory.

While traditional silicon photonics transmits light waves through waveguides, plasmonic modulators control surface plasmon polaritons (SPPs), electromagnetic waves that travel along the interface between a conductor and a dielectric.

These waves enable light-matter interactions in extremely small areas, realizing fast signal modulation even in much smaller areas.

Of course, plasmonics presents technical challenges such as optical losses, but the ETH Zurich research team's design largely overcomes these loss issues by minimizing the propagation path and leveraging the high conductivity of gold.

One of the most attractive features of plasmonic modulators is that they maintain a flat frequency response across the entire frequency band. Most modulators exhibit gain roll-off as the bandwidth increases, requiring equalizer filters, digital signal processing (DSP) operations, or link budget redesign to compensate.

Professor Roithold explained, "In digital signal processing and optical communications, additional computational resources are typically needed to compensate for the drop in response at high frequencies using equalizers. However, this device eliminates such computational effort. Signal processing becomes much simpler, and experiments in previously inaccessible frequency ranges become possible. This device opens up a whole new world."

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

This plasmonic modulator is not simply aimed at excellent standalone performance.

Designed with compatibility with CMOS processes in mind, it can be integrated into existing silicon architectures with minimal process changes.

This opens up the possibility of easy application to mainstream optical transceiver production lines.

In fact, Polariton Technologies AG, a startup founded by Professor Leuthold's PhD students, is already bringing a commercial version of this modulator to market.

While gold was used in the lab for ease of prototyping, Professor Roithold said copper or aluminum would likely be used for commercialization due to cost and compatibility reasons.

ETH Zurich's new modulator opens up new application possibilities beyond data centers.

This modulator is considered a promising choice not only for optical transceivers but also for spectroscopy, medical imaging, and airport security systems.

These fields generally require high-frequency operation, miniaturization, and low-power characteristics.

It also presents new possibilities in next-generation fields such as 6G wireless communications, advanced sensing, and quantum communications.

“To give just one example of an application area, 6G will inevitably require a move to higher frequencies, and in sensing, it will allow us to utilize frequency bands that were previously inaccessible,” said Professor Roithold.

Additionally, thanks to gold's excellent thermal conductivity, the device dissipates heat quickly even in high-frequency switching environments, maintaining stable and reliable performance.

The research team did not stop at developing a modulator. We have also started developing a corresponding high-speed photodetector.

"We've already completed the modulator, and now we're working on implementing the photodetector. Our goal is to create a complete system with both ends of the transceiver," said Professor Roithold.

※ About the author
Nicolette Emmino is the content strategist and co-lead at ReBoot eMedia. Combining over a decade of industry experience and a passion for content creation, she transforms complex technical concepts into accessible content for electronics professionals. Her goal is not only to help manufacturers and distributors stay abreast of industry trends, but also to establish them as leaders in their respective fields.