Researchers Marry Plasmonics and Electronics on a Single Chip for Record Data Transfer Speeds

July 07, 2020 by Jake Hertz

Researchers from ETH Zürich have successfully combined photonic and electronic elements onto the same chip for the first time. The implications? A brighter future for optical communication networks.

The internet is growing exponentially, and with this growth has come fear that the current optical data networks may reach their limits in the coming years. Events such as the imminent deployment of 5G, the rapid growth of data centers and cloud services, and the development of artificial intelligence have threatened to push the boundaries of existing infrastructure, according to the Optical Networks Group.

Current networks can transmit at gigabit speeds, but researchers estimate that terabit speeds will be necessary to sustain the increased traffic on the internet. 


Global internet device trends and predictions

Global internet device trends and predictions. Image used courtesy of Cisco

The merger of photonic and electronic technologies has long been seen as a route to achieving the necessary transmission rates. Juerg Leuthold, professor of photonics and communications at ETH Zürich, explains, “The rising demand will call for new solutions... The key to this paradigm shift lies in combining electronic and photonic elements on a single chip.”


The History of a Photonic-Electronic Duo

For the past twenty years, researchers at ETH Zürich have been attempting to combine photonic and electronic technology onto a single chip. To understand why this effort has taken so long, it is first important to understand the history of the technologies. 

Historically, photonics chips have been much larger than electronic chips. This size differential has been a major roadblock for combining photonic technologies with CMOS technology. 


Example of a circuit connection photonics and CMOS technology.

Example of a circuit connection photonics and CMOS technology. Image used courtesy of Advanced Micro Foundry

For this reason, electronic and photonic elements have, in the past, been manufactured on separate chips and then connected with wires. However, this technique is limited by the cost of the separate manufacturing of two chips and by the loss of signal quality during conversions between the two chips. The loss in signal quality has fundamentally limited the transmission speeds in fiber optic communication networks. 

The rise of plasmonics has been crucial towards this goal. Plasmonics is a subset of photonics that can be used to squeeze light waves into structures that are much smaller than the wavelength of the light. This technology has allowed photonic chips to scale down to the point where they can finally be integrated with CMOS technology into a single chip.


ETH Zürich's Looks to Plasmonics 

This week, researchers at ETH Zürich were finally able to achieve this goal thanks to some clever design work and years worth of improvements in the field.


The world’s first chip to combine electronic and photonic technology

The world’s first chip to combine electronic and photonic technology. Image used courtesy of ETH Zürich

The researchers achieved this feat by first shrinking the size of a modulator on a chip, which produces light of a certain intensity by turning electrical signals into light waves. 

The researchers placed the electronic and plasmonic components tightly on top of one another on a single substrate and connected them directly to the chip with through-silicon vias (TSVs). By layering the electronics and plasmonics, the transmission path is shortened, leading to smaller losses in terms of signal quality.


Depiction of how this chip is laid out.

Depiction of how this chip is laid out. Image used courtesy of ETH Zürich

The chip also benefits from 4:1 multiplexing to increase speed in the electronic layer. Essentially, the process takes four lower speed signals and combines them into one high-speed electrical signal. In addition, the researchers chose to employ BiCMOS technology over CMOS, allowing the electronics to be even faster.


Lightning Fast Optical Communication

Thanks to the integration of all of these technologies, this chip has been able to transmit data at a speed of over 100 gigabits. According to Ueli Koch, a lead author of the study, this marks the first time that a monolithic chip has achieved these speeds. 

Researchers hope this innovation will lead to a faster infrastructure that will be able to handle the internet’s growth. According to Leuthold: “...this solution can... pave the way for faster data transmission in optical communication networks of the future.”



What technologies do you see as key for the future of optical communications? Share your thoughts in the comments below.