KIT develops 'ultra-small, ultra–fast' electro-optic modulator

19 Feb 2014

Measuring just 29µm, novel modulator converts data at 40Gbits/s.

Thanks to optical communictions, data can be transmitted rapidly around the globe. But to accelerate the exchange of digital information between electronic chips and to improve conversion efficiency requires simple methods to switch from electrical to optical signals.

Now researchers at the Karlsruhe Institute of Technology, Germany, have developed such a device that measures just 29 µm in length, which converts signals at a rate of about 40 Gbits/s. The KIT team say this is the most compact high-speed phase modulator developed so far and they have reported their work this week in the journal Nature Photonics.

Cutting the electricity bill

KIT research coordinator Juerg Leuthold (who has since moved to the ETH Zurich) commented, “Conversion of electrical into optical signals happens closer to the processor. As a result, speed gains are achieved and conduction losses can be prevented. This could significantly reduce energy consumption of the growing information technology sector.”

The KIT electro-optical converter consists of two parallel gold electrodes of about 29µm in length. The electrodes are separated by a gap of about 0.1µm. The voltage applied to the electrodes is synchronized with the digital data. The gap is filled with an electro-optical polymer, whose refraction index changes as a function of the applied voltage.

“A continuous beam of light from the silicon waveguide excites electromagnetic surface waves, so-called surface plasmons (SP), in the gap,” Argishti Melikyan, KIT, first author of the publication, added. “As a result of the voltage applied to the polymer, the phase of the SP is modulated. At the end of the device, the modulated SP enters the exit silicon waveguide in the form of a modulated beam of light. In this way, the data bits are encoded in the phase of the light.”

The recent KIT results have shown that the electro-optic modulator reliably converts data flows of about 40 gigabits per second. It uses the infrared light of 1480 – 1600nm in wavelength usually encountered in broadband optical fiber networks. Even temperatures of up to 85°C do not cause any operational failures. The device is the most compact high-speed phase modulator in the world, the developers claim. It can be produced by well-established CMOS fabrication processes. Integration into current chip architectures is hence possible.

“The device combines many advantages of other systems, such as a high modulation speed, compact design, and energy efficiency. In the future, plasmonic devices might be used for signal processing in the terahertz range,” says Christian Koos, spokesperson of KIT’s Helmholtz International Research School of Teratronics (HIRST), which focuses on merging photonic and electronic techniques for high-speed signal processing. "Hundreds of plasmonic modulators might fit on a chip and data rates in the range of terabits per second might be reached.”

Presently, information and communication systems consume about 10 percent of the electricity demand in Germany. This includes computers and smartphones of individual users as well as servers at large computing centers. As data traffic grows exponentially, new approaches are required to increasing the capacity of such systems and reducing their energy consumption at the same time. Plasmonic components might be of decisive importance in this respect.

The Nature Photonics paper is part of the EU project NAVOLCHI - Nano Scale Disruptive Silicon-Plasmonic Platform for Chip-to-Chip Interconnection. This project is aimed at using the interaction of light and electrons in metal surfaces for the development of novel components for data transmission between chips, which is funded under the 7th Research Framework Programme of the EU and has a budget of €3.4 million.

About the Author

Matthew Peach is a contributing editor to optics.org.