Coupled nanoscale antennas pave the way for lightwave electronics

Integrated lightwave electronic circuits allow the absolute phase of a light wave to be determined

nanoscale antennas

Interaction of laser pulses with an array of nanoscale antennas. The direction of the current in the electronic circuit depends on the phase of the laser light (Credit (Author): Yujia Yang).

A research team from the Massachusetts Institute of Technology (MIT) in Boston (US), DESY and the University of Hamburg has succeeded for the first time in building nanoscale integrated electronic circuits that can capture light with the help of tiny antennas and determine the absolute phase of the light wave – a measurement that was previously restricted to extremely complex and large vacuum equipment. The team presented its findings, which could provide the basis for a new type of light-controlled high-speed electronics, in the journal Nature Communications.

Visible light is part of the electromagnetic spectrum, which ranges from radio waves through thermal or infrared radiation to ultraviolet and gamma radiation. According to quantum mechanics, introduced more than 100 years ago, all these phenomena can be described both in terms of waves and in terms of particles, known as photons. The only difference as you cross the spectrum is the energy of the photons or the frequency of the wave, which are directly related to one another. In the past, the absence of suitable technologies meant that for the most part it was only the wave characteristics of low-frequency radiation, such as radio or microwaves, that could be exploited and used in everyday electronic devices, such as radios (megahertz frequencies) or Wi-Fi (gigahertz frequencies). Visible light (whose frequency lies in the terahertz range) and ultraviolet light (having petahertz frequencies) were only considered in terms of their particle characteristics: solar cells, for example, absorb individual photons and convert them into an electric current. Conventional electronic circuits were too slow to follow the teraherz frequencies. Recently, however, it has become possible to operate electronics on the fundamental timescale of visible and ultraviolet light, by reducing circuit sizes and using tiny antennas. At frequencies of around a petahertz, i.e. one billion million oscillations per second, a time resolution of the order of femtoseconds (10-15 seconds) is required.

By using so-called plasmonic antennas which are a few 100 nanometres across, light waves can be efficiently captured and antennas can be made to oscillate at the frequency of the light. As a result of this oscillation, charge is transferred between the two halves of the antenna. Although this allows short light pulses to be detected and measured, the currents produced only consist of individual electrons and are therefore too small to be used in electronic devices.

The research team from MIT, DESY and the University of Hamburg has now succeeded in taking an important step towards using this principle for technical applications. They managed to combine hundreds of these antennas to form an array, a detector in which the currents from all the antennas add up and produce an easily measurable signal. Using this antenna array, the team even managed to measure the absolute phase of short laser pulses, i.e. the position of the wave crests in a light wave. In the past, this called for extremely complex and large vacuum equipment, which can now be replaced by a small microchip operating at room temperature as well as in air. At the same time, the experiments are an important advance in the use of light waves for the next generation of ultrafast electronics potentially outstripping the operating frequency of today’s electronics, which lies in the gigahertz range, by a factor of 100 000.

The research was partly funded by the Air Force Office of Scientific Research, the European Research Council, the Hamburg Centre for Ultrafast Imaging CUI and by the MIT – Hamburg PIER programme. The MIT – Hamburg PIER programme promotes the lively exchange between scientists in Hamburg and at MIT, thus enabling a close scientific collaboration between them.

(from DESY news)


Light phase detection with on-chip petahertz electronic networks; Yujia Yang, Marco Turchetti, Praful Vasireddi, William P. Putnam, Oliver Karnbach, Alberto Nardi, Franz X Kärtner, Karl K. Berggren, Phillip D. Keathley; Nature Communications.