Ultracompact Photodetector

A plasmonic detector that is directly coupled to a silicon optical waveguide and smaller than one micrometer (Source: KIT)

A plasmonic detector that is directly coupled to a silicon optical waveguide and smaller than one micrometer (Source: KIT)

Data traffic is growing worldwide. Glass-fiber cables transmit 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 in the computer. Researchers at Karlsruhe Institute of Techno­logy KIT have now developed a novel type of photo­detector that needs far less space than conven­tional ones. The component has a base area of less than one millionth of a square milli­meter without the data trans­mission rate being affected adversely.

The newly developed photo­detectors, 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 40 gigabits per second. “This component can transmit the contents of a complete DVD within a fraction of a second,” Sascha Mühl­brandt of KIT explains. 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 emphasizes. The high-speed photo­detector, PIPED  for Plasmonic Internal Photo­emission Detector, is now presented by Mühlbrandt together with colleagues of KIT and ETH Zurich.

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 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.

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.

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,” says 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 1 terabit per second. “ (Source: KIT)

Reference: S. Mühlbrandt et al.: Silicon-Plasmonic Internal-Photoemission Detector for 40 Gbit/s Data Reception, Optica 3, 741 (2016); DOI: 10.1364/OPTICA.3.000741

Links: Inst. of Microstructure Technology IMT, Karlsruhe Institute of Technology KIT, Karlsruhe, Germany • NAVOLCHI project

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