Addressing the need to be able to sense the subtle details of light fields themselves, rather than just the total energy they deliver, the researchers have demonstrated a microchip with nanometer-length-scale circuit elements that act like antennas to collect the electric field of light oscillating at nearly 1 quadrillion times per second. Previously, say the researchers, the apparatus and expense required for such femtosecond timing precision has been "huge" and limited to a few specialized research laboratories.
Their chip, however, is small, self-contained, and requires only inexpensive electronics for readout. Their work, say the researchers, has the potential to enable new applications in "lightwave electronics" for high-speed signal processing using the electric field waveforms of few-cycle optical pulses.
"We see a wide range of new optical and electronic devices that could be based on this technology," says Karl Berggren, MIT professor of electrical engineering and co-author of the work. "For example, this technique could have future impact on applications such as determining the distance to remote astronomical objects, optical clocks critical to GPS technology, and chemical analysis of gases."
To demonstrate operation of the device, the researchers first generated optical pulses using a specialized laser system, designed to make light pulses consisting of just a few optical cycles. They shined the light onto a microchip on which they had fabricated hundreds of tiny plasmonic "bow-tie" nanoantennas patterned out of an ultrathin gold film.
To get a strong enough electrical signal, the antennas had to have small gaps between them, each gap only 10 billionths of a meter wide. When the light passed through these narrow gaps, it created huge electric fields that ripped electrons out of one antenna, pulled them through the air, and deposited them on the next antenna. While each antenna on its own contributed only a tiny electrical current, say the researchers, the total signal across the array was substantial, and could easily be measured.