A new electro-optical device just 29 µm long can convert signals at a rate of about 40 Gb/s, making it the world’s most compact high-speed phase modulator. The converter device, developed at Karlsruhe Institute of Technology (KIT), demonstrates high modulation speeds and energy efficiency, and can be produced by already established CMOS fabrication processes, enabling future integration into current chip architectures. Also possible is the use of plasmonic devices for signal processing in the terahertz range. “Conversion of electrical into optical signals happens closer to the processor,” said Juerg Leuthold, coordinator of the research project and a professor at 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.” A beam of light is modulated by the digital bits of the converter when voltage is applied. This converts an electrical signal into an optical signal. Courtesy of Karlsruhe Institute of Technology. The electro-optical converter consists of two parallel gold electrodes that are one-third the diameter of a human hair and separated by a gap of about one-tenth of a micron in width. The voltage applied to the electrodes is synchronized with the digital data, and the gap filled with an electro-optical polymer whose refraction index changes as a function of the applied voltage. The device uses IR light with a wavelength of 1480 to 1600 nm, which is usually encountered in a broadband glass fiber network. “A continuous beam of light from the silicon waveguide excites electromagnetic surface waves, so-called surface plasmons (SP), in the gap,” said Argishti Melikyan, a professor at 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.” The research project is funded by the 7th Research Framework Programme of the European Commission and is part of the Nano Scale Disruptive Silicon-Plasmonic Platform for Chip-to-Chip Interconnection project (NAVOLCHI). The work was published in Nature Photonics. For more information, visit www.kit.edu/english.