Researchers at Karlsruhe Institute of Technology (KIT), Germany, have developed a novel type of photodetector that occupies far less space than conventional devices. The component has a base area of less than one millionth of a square millimeter without the data transmission rate being affected adversely. The corresponding article is published in the Optica journal. (Reference: DOI:10.1364/OPTICA.3.000741)
The newly developed photodetectors can be used for integrated optical circuits that significantly enhance the performance of optical communication systems. Due to the small space required, many detectors can be assembled on optical chips. In experiments, the researchers reached a data rate of up to 40 gigabits per second. “This component can transmit the contents of a complete DVD within a fraction of a second,” physicist Sascha Mühlbrandt of KIT explained.
He conducted his studies at the Institute of Microstructure Technology and the Institute of Photonics and Quantum Electronics of KIT. This rate can be even further increased. “It is the so far smallest detector reaching this data rate. It is one hundred times smaller than a conventional photodetector,” Mühlbrandt emphasized.
The high-speed photodetector, called PIPED (Plasmonic Internal Photoemission Detector), is now presented by Mühlbrandt as first author, together with colleagues of KIT and ETH Zurich, in the Optica journal under the heading “Silicon-Plasmonic Internal-Photoemission Detector for 40 Gbit/s Data Reception.”
A special advantage of the reduced size is that the photodetector can be integrated with electronic components on the same CMOS chip. “Introduction of novel plasmonic components for high-speed transmission of information between electronic chips in the computer combines the advantages of electronic and optical components, while the transmission rate is comparable or even improved,” says project coordinator Professor Manfred Kohl of KIT’s Institute of Microstructure Technology.
The photodetector was developed under the NAVOLCHI (Nano Scale Disruptive Silicon-Plasmonic Platform for Chip-to-Chip Interconnection) project. Under the 7th EU Research Framework Programme, the KIT project of three years’ duration in the area of information and communication technologies was funded with about €500,000.
The high-performance photodetector uses so-called surface plasmon polaritons, highly concentrated electromagnetic waves at metallic-dielectric interfaces, to combine optics and electronics on smallest space. “This new class of plasmonic transceivers is based on the mechanism generating photocurrent, i.e. direct signal conversion at metallic interfaces with optical frequencies.
This process is known as internal photoemission,” Mühlbrandt says. For enhancing the efficiency of light absorption and light conversion into electrical signals, charge carriers are generated at a titanium-silicon transition and taken up at another gold-silicon transition. The high rate is due to the special detector geometry: Both metal-silicon transitions are located less than one hundred billionth of a meter apart.