For the first time, a research team led by the Technical University of Munich in Germany has successfully used a plasmon micro-antenna with a size of only a few nanometers to generate ultra-short electrical pulses with a frequency of 10THz on a chip, and then run these electrical pulses through the chip, and generate a read them in a controlled manner.
The frequency of traditional Electronic devices can generally reach about 100GHz. Optoelectronic devices employ electromagnetic waves starting at 10 THz. Electromagnetic waves in this frequency range (100GHz ~ 10THz) are also known as “terahertz waves”.
Terahertz wave technology has a wide range of uses, such as: radio astronomy, medicine, communications, radar, electronic countermeasures, electromagnetic weapons, non-destructive testing, military and many other fields. In order to give you a more direct understanding of the application of terahertz technology, let us first review the two typical cases that the author has introduced in the past:
1) Researchers at the Massachusetts Institute of Technology used terahertz technology to image the contents of the pages of a closed book. This way, you can read the contents of the book without opening it.
(Image credit: Barmak Heshmat)
2) Scientists at the Moscow Institute of Physics and Technology (MIPT) in Russia, together with their German and Dutch colleagues, have developed a technology that uses electromagnetic pulses in the terahertz frequency band to switch the memory states of computer memory cells thousands of times faster than magnetic induction switches.
(Image credit: Moscow Institute of Physics and Technology)
However, components that generate, convert, and detect signals in the terahertz frequency range are very difficult to implement.
Recently, a scientific research team led by the Technical University of Munich in Germany has successfully used metal antennas only a few nanometers in size to generate ultra-short electrical pulses on a chip, and then run the signal a few millimeters above the surface, in a controllable manner. way to read them.
The experiments were funded by the European Research Council (ERC) project “NanoREAL” and the “Nanosystems Innovation Cluster Munich” (NIM).
Pictured below: Femtosecond pulses emitted from a pump laser (left) generate on-chip electrical pulses at terahertz frequencies. With the laser on the right, the information is read again.
(Image credit: Christoph Hohmann/NIM, Holleitner/TUM)
TUM physicists Alexander Holleitner and Reinhard Kienberger succeeded in using plasmonic micro-antennas to generate electrical pulses at frequencies up to 10THz and run them through a chip. The researchers call them “plasmonic” antennas because of their shape. They increase light intensity on metal surfaces.
The shape of the antenna is important. They are asymmetrical: one side of the nano-sized metal structures is more pointed than the other. When a laser pulse focused by the lens excites the antenna, the antenna emits more electrons on the sharper side than on the flat side. An electrical current is generated between the two contact points, but only if the antenna is excited by the laser.
Shown below: Electron micrograph of a chip with an asymmetric plasmonic antenna made of gold on sapphire.
(Image credit: A. Holleitner/TUM)
“In the photoelectric effect, light pulses induce electrons from a metal into a vacuum,” said lead author Christoph Karnetzky. “All lighting effects are stronger on the sharper side, including the photoelectric effect we use to generate a small amount of current.”
Light pulses last only a few femtoseconds (a femtosecond is only one quadrillionth of a second), and correspondingly, the electrical pulses in the antenna are short. This structure is particularly interesting from a technical point of view because nanoantennas can be integrated into terahertz circuits that are only a few millimeters in size.
In this way, femtosecond laser pulses with a frequency of 200THz can generate ultra-short terahertz signals at frequencies of up to 10THz in circuits on a chip, Karnetzky said.
The researchers used sapphire as the chip material because it is not optically stimulated and therefore does not interfere. Considering future practical applications, they also adopted a laser with a wavelength of 1.5 microns used in traditional Internet fibers.
Holleitner and colleagues made another surprising discovery: Both electrical and terahertz pulses are nonlinearly related to the excitation power used by the laser. This suggests that the photoelectric effect in the antenna is triggered by multiphoton absorption in each light pulse.
This technology will facilitate the development of powerful new terahertz components. In addition, “Such fast, nonlinear on-chip pulses have not existed before,” says Alexander Holleitner. He hopes to use this effect to explore faster tunnelling effects in antennas and apply them to chips.