Nano-sized photo detector can be integrated on CMOS chip

Glass fibers may become the information superhighways of the information age. Researchers from the Karlsruhe Institute of Technology (KIT) succeeded in developing an innovative photo detector for optical data paths—the central component at the receiver side of the glass fibers—that sets new standards as to their size: The researchers claim a footprint of less than 100 square micrometer, ideal for integration on an integrated circuit. Even more impressing is its data rate.

The new photo detector, according to the research team around Sascha Mühlbrandt the smallest worldwide for optical data transmission, permit a significant performance increase of optical communications systems, because they can be integrated on optical semiconductors in large quantities. In their experiments, the researchers reached a throughput up to 40 Gbps—enough to transfer the entire content of a video DVD within a fraction of a second, explains Sascha Mühlbrandt who carried out the related research activities at the Institutes for Microstructure Technology and Institute for Photonics and Quantum Electronics, both subsidiaries of the KIT.

Mühlbrandt is convinced that the throughput of still has upside potential. “This plasmonic internal photoemission detector (PIPED) is the smallest detector ever to reach this data rate”, the researcher said. The devices is 100 times smaller than a conventional photo detector.

A benefit of this extremely small size lies in the possibility that the photo detector can be integrated along with downstream preprocessing circuitry on a single CMOS chip. The introduction of novel plasmonic components for high-speed data exchange between integrated circuits in computers opens the possibility to combine the advantages of electronic and optical components at the same or higher data throughput as with electronic-only components, said project coordinator Manfred Kohl from the KIT Institute for Microstructure Technology.

The detector has been developed within the project NAVOLCHI (Nano Scale Disruptive Silicon-Plasmonic Platform for Chip-to-Chip Interconnection which has been funded from the 7th EU Research Frame Program.

CMOS Photonics Yole

A plasmonic detector, which is coupled directly to a silicon optical waveguide and less than one micrometer in size, was developed at KIT. (Graphic: KIT).

To combine the optics and electronics within very small spaces, the photo detector makes use of surface plasmon polaritons—highly concentrated electromagnetic waves on metallic-dielectric boundary surfaces. “This new class of plasmonic converters is based on the driect signal conversion at metallic surfaces at optical wavelengths, known as photo emission. To efficiently control the absorption of light and its conversion into electric signals, the researchers generated charge carriers in a titanium-silicon junction and recombined in another gold-silicon junction. The high speed of the detector is achieved through its specific geometry—between the two metal-silicon junctions there is a distance of less than 100 nanometers.

The researchers regard the PIPED concept only as essential for future optical data transmission systems but also as key component for wireless data communications. “This approach makes it possible generating electromagnetic signals at bandwidths in the terahertz range”, said professor Christian Koos from the Helmholtz International Research School of Teratronics (HIRST) that investigates the fusion of photonic and electronic means of ultra-fast signal processing at the KIT. “Plasmonic components could be used in wireless high-speed data communications and enable data rates up to 1 terabit per second”, he said.

Along with several colleagues from KIT and the ETH Zurich university, Mühlbrandt introduced the PIPED in the magazine Optica under the title “Silicon-Plasmonic Internal Photoemission Detector for 40 Gbps Data Reception” (