Nanostructures enable on-chip mixer of electronic frequencies and light waves

Imagine how a phone call works: Your voice is converted into electronic signals, shifted to higher frequencies, transmitted over long distances, and then brought back down to be heard clearly on the other end of the line. The process of shifting signal frequencies is called frequency mixing, and it’s essential for communications technologies like radio and Wi-Fi. Frequency mixers are essential components of many electronic devices and typically operate using frequencies that oscillate billions (GHz, gigahertz) to billions (THz, terahertz) times per second.

Now imagine a frequency mixer that operates at a frequency of one quadrillion times (PHz, petahertz) per second, up to a million times faster. This frequency range corresponds to the oscillations of the electric and magnetic fields that make up light waves.

Petahertz frequency mixers would allow us to shift signals to optical frequencies and then back to more conventional electronic frequencies, allowing the transmission and processing of much larger amounts of information at much higher speeds. This leap forward doesn’t just speed things up; it also enables new capabilities.

Lightwave electronics (or petahertz electronics) is an emerging field that aims to integrate optical and electronic systems at incredibly high speeds, by exploiting ultrafast oscillations of light fields. The key idea is to exploit the electric field of light waves, which oscillate at sub-femtosecond speeds (10^-15 time scales of a few seconds, to directly control electronic processes.

This allows information to be processed and manipulated at speeds far beyond those possible with current electronic technologies. Combined with other petahertz electronic circuits, a petahertz electronic mixer would allow us to process and analyze vast amounts of information in real time and transfer larger amounts of data over the air at unprecedented speeds.

The MIT team’s demonstration of a lightwave electronic mixer at petahertz frequencies is a first step toward faster communications technology and advances research toward developing new miniaturized lightwave electronic circuits capable of handling optical signals directly at the nanoscale.

In the 1970s, scientists began exploring ways to extend electronic frequency mixing into the terahertz range using diodes. While these early efforts showed promise, progress stalled for decades. Recently, however, advances in nanotechnology have revived this field of research. Researchers have discovered that tiny structures like nanometer-sized needle tips and plasmonic antennas can operate similarly to these early diodes, but at much higher frequencies.

A recent study published in Scientific progress A significant breakthrough has been made by the work of Matthew Yeung, Lu-Ting Chou, Marco Turchetti, Felix Ritzkowsky, Karl K. Berggren, and Phillip D. Keathley at MIT. They have developed an electronic frequency mixer for signal detection that operates beyond 0.350 PHz using tiny nanoantennas. These nanoantennas can mix different frequencies of light, making it possible to analyze signals that oscillate orders of magnitude faster than the fastest signals accessible to conventional electronics.

Such petahertz electronic devices could enable developments that would ultimately revolutionize fields that require precise analysis of extremely fast optical signals, such as spectroscopy and imaging, where capturing dynamics at the femtosecond timescale is crucial (a femtosecond is one millionth of a billionth of a second).

The team’s study highlights the use of nanoantenna arrays to create an on-chip, wideband electronic optical frequency mixer. This innovative approach enables precise readout of optical waveforms spanning more than an octave of bandwidth. Importantly, this process worked using a commercial, off-the-shelf laser that can be purchased off-the-shelf, rather than a highly customized laser.

Although optical frequency mixing is possible using nonlinear materials, the process is purely optical (i.e., it converts light input to light output at a new frequency). In addition, the materials must be several wavelengths thick, which limits the size of the device to the micrometer scale (a micrometer is one millionth of a meter).

In contrast, the lightwave electronic method demonstrated by the authors uses a light-driven tunneling mechanism that offers high nonlinearities for frequency mixing and direct electronic output using nanoscale devices (a nanometer is one billionth of a meter).

Although this study focused on characterizing light pulses of different frequencies, the researchers envision that similar devices will enable circuits to be built using light waves. This device, which has a bandwidth spanning several octaves, could provide new ways to study ultrafast interactions between light and matter, accelerating progress in ultrafast source technologies.

This work not only pushes the boundaries of what is possible in optical signal processing, but also bridges the gap between the fields of electronics and optics. By connecting these two important research areas, this study opens the door to new technologies and applications in areas such as spectroscopy, imaging, and communications, thereby advancing our ability to explore and manipulate the ultrafast dynamics of light.

This article is republished with kind permission from MIT News (web.mit.edu/newsoffice/), a popular site covering the latest research, innovation, and teaching at MIT.