Smallest photodetector for optical data transmission

2nd August 2016
Nat Bowers

Data traffic is growing worldwide. Glass-fibre cables transmit vast amounts of information over long distances at the speed of light. Once they have reached their destination, however, these optical signals have to be converted into electrical signals for subsequent processing. KIT researchers have now developed a novel type of photodetector that needs far less space than conventional ones.

The phototdetector has a base area of less than one millionth of a square millimetre without the data transmission rate being affected adversely.

The newly developed photodetectors, claimed to be the smallest photodetectors worldwide for optical data transmission, can be used for integrated optical circuits that significantly enhance the performance of optical communication systems. Due to the small space needed, many detectors can be assembled on optical chips. In experiments, the researchers reached a data rate of up to 40Gb/s.

Sascha Mühlbrandt, Physicist, KIT, commented: “This component can transmit the contents of a complete DVD within a fraction of a second."

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, who conducted his studies at the Institute of Microstructure Technology and the Institute of Photonics and Quantum Electronics, KIT, emphasises. The high-speed photodetector, called PIPED (Plasmonic Internal PhotoEmission Detector), is now presented by Mühlbrandt as first author, together with colleagues from KIT and ETH Zurich, in the Optica journal, titled Silicon-Plasmonic Internal-Photoemission Detector for 40 Gbit/s Data Reception.

The reduced size enables the photodetector to 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,” said project coordinator Professor Manfred Kohl, Institute of Microstructure Technology, KIT. 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 added. 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 metre apart.

The researchers consider the PIPED concept to be essential not only for future optical data transmission systems, but also for wireless data transmission. “This novel approach to detecting optical signals allows for the generation and detection of electromagnetic signals with bandwidths in the terahertz range,” said Professor Christian Koos of KIT, Spokesperson of the Helmholtz International Research School for Teratronics (HIRST) that focuses on the combination of photonic and electronic processes for ultra-rapid signal processing. “Plasmonic components might be used in wireless high-speed communication and allow for transmission rates of up to 1Tb/s. “Research related to PIPED was also supported by the EnTeraPIC Starting Grant of the European Research Council, the HIRST at KIT, at which the disciplines of physics, electrical engineering, computer science and mechanical engineering cooperate, as well as by KIT’s Karlsruhe Nano-Micro Facility (KNMF) platform.

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