“Conversion of electrical into optical signals happens closer to the processor,” said Juerg Leuthold who coordinated the research project at the Karlsruhe Institute of Technology and has meanwhile moved to the ETH Zurich. “As a result, speed gains are achieved and conduction losses can be prevented. This might reduce energy consumption of the growing information technology.”
The energy saving electro-optical converter, which is decribed in Nature Photonics magazine, consists of two parallel gold electrodes of about 29 µm in length. The electrodes are separated by a gap of about one tenth of a micrometer in width. 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,” explained Argishti Melikyan, KIT. “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 enter 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.”
Recent results revealed that the electro-optic modulator reliably converts data flows of about 40 gigabits per second. The modulator uses the infrared light of 1480 – 1600 nm in wavelength usually encountered in the broadband glass fiber network. Even temperatures of up to 85°C do not cause any operation failures. The device is claimed to be the most compact high-speed phase modulator in the world and can be produced by CMOS fabrication processes which means integration into current chip architectures is feasible.
“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,” said Christian Koos, spokesperson of KIT’s Helmholtz International Research School of Teratronics (HIRST). ”Hundreds of plasmonic modulators might fit on a chip and data rates in the range of terabits per second might be reached.”
Today information and communication systems consume about 10 percent of the electricity 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 boost the capacity of such systems and reduce their energy consumption at the same time.
The present 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.
“Conventional electric chip-to-chip data transmission reaches its limits,” explained the present project coordinator Manfred Kohl, KIT. “NAVOLCHI is about to overcome those limits using optical technology.” It is funded under the 7th Research Framework Programme of the EU and has a budget of EUR 3.4 million.
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