Plasmonic Antennas Could Deliver Ultrafast Pulses for THz Electronics

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MUNICH, Germany, June 28, 2018 — In an experiment that combined the advantages of femtosecond nanophotonics with on-chip communications, researchers generated ultrashort electric pulses on a chip using metal structures (i.e., antennas) only a few nanometers in size, then ran the signals a few millimeters above the surface. The signals were then read out in a controlled manner. The researchers demonstrated that femtosecond optical pulses in the NIR could drive electronic on-chip circuits with a prospective bandwidth of up to 10 THz.

Physicists from the Technical University of Munich (TUM) exploited femotsecond photoswitches based on the nanoscale metal structures to drive the pulses. The nonlinear ultrafast response was based on a plasmonically enhanced, multiphoton absorption, resulting in a field emission of ballistic hot electrons propagating across the nanoscale structures.

Generating ultrashort electric pulses on a chip using plasmonic antennas, TUM.
A team headed by physicists Alexander Holleitner and Reinhard Kienberger from the Technical University of Munich (TUM) has generated ultrashort electric pulses on a chip using metal antennas only a few nanometers in size. Pulses of femtosecond length from the pump laser (left) generate on-chip electric pulses in the terahertz frequency range. With the laser on the right, the information is read out again. Courtesy of Christoph Hohmann/NIM, A. Holleitner/TUM.

One side of the nanometer-size metal structures was more pointed than the other, giving the metal structures (antennas) an asymmetrical shape.

When a lens-focused laser pulse excited the antennas, they emitted more electrons on the side that was more pointed.

An electric current flowed between the contacts as long as the antennas were excited. The light pulses lasted only a few femtoseconds, and the electrical pulses in the antennas were correspondingly short. Researchers said that all the lighting effects were stronger on the pointed side, including the photoemission that was used to generate the current.

According to researchers, a femtosecond laser pulse with a frequency of 200 THz could generate an ultrashort terahertz signal with a frequency of up to 10 THz in the circuits on the chip.

Researchers used sapphire as the chip material because sapphire cannot be stimulated optically and would therefore cause no interference. Lasers with a 1.5-μ wavelength were used in traditional internet fiber optic cables.

Generating ultrashort electric pulses on a chip using plasmonic nanoantennas made from gold on sapphire, TUM.
An electron-microscopic image of the chip with asymmetric plasmonic antennas made from gold on sapphire. Courtesy of A. Holleitner/TUM.

Researchers further discovered that the electrical and THz pulses both were nonlinearly dependent on the excitation power of the laser used, indicating that the photoemission in the antennas could be triggered by the absorption of multiple photons per light pulse.

“Such fast, nonlinear on-chip pulses did not exist hitherto,” said professor Alexander Holleitner.

The team believes that these results could pave the way toward femtosecond electronics integrated in wafer-scale terahertz circuits. By further exploring the nonlinearity effect, the team hopes to discover even faster tunnel emission effects in the antennas for possible use in on-chip applications.

The research was published in Nature Communications (doi:10.1038/s41467-018-04666-y).

Published: June 2018
Optoelectronics is a branch of electronics that focuses on the study and application of devices and systems that use light and its interactions with different materials. The term "optoelectronics" is a combination of "optics" and "electronics," reflecting the interdisciplinary nature of this field. Optoelectronic devices convert electrical signals into optical signals or vice versa, making them crucial in various technologies. Some key components and applications of optoelectronics include: ...
Plasmonics is a field of science and technology that focuses on the interaction between electromagnetic radiation and free electrons in a metal or semiconductor at the nanoscale. Specifically, plasmonics deals with the collective oscillations of these free electrons, known as surface plasmons, which can confine and manipulate light on the nanometer scale. Surface plasmons are formed when incident photons couple with the conduction electrons at the interface between a metal or semiconductor...
Nanophotonics is a branch of science and technology that explores the behavior of light on the nanometer scale, typically at dimensions smaller than the wavelength of light. It involves the study and manipulation of light using nanoscale structures and materials, often at dimensions comparable to or smaller than the wavelength of the light being manipulated. Aspects and applications of nanophotonics include: Nanoscale optical components: Nanophotonics involves the design and fabrication of...
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
Terahertz (THz) refers to a unit of frequency in the electromagnetic spectrum, denoting waves with frequencies between 0.1 and 10 terahertz. One terahertz is equivalent to one trillion hertz, or cycles per second. The terahertz frequency range falls between the microwave and infrared regions of the electromagnetic spectrum. Key points about terahertz include: Frequency range: The terahertz range spans from approximately 0.1 terahertz (100 gigahertz) to 10 terahertz. This corresponds to...
Research & TechnologyeducationEuropeLasersOpticsoptoelectronicspulsed lasersCommunicationson-chip communicationsplasmonicsnano-opticsnanophotonicsnanoterahertzultrafast photonics

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