Researchers at the University of Arizona Wyant College of Optical Sciences and Sandia National Laboratories have discovered that by combining highly specialized semiconductor materials and piezoelectric materials not typically used together, they could generate giant nonlinear interactions between photons. Combined with previous innovations demonstrating amplifiers for phonons using the same materials, their work opens up the possibility of making wireless devices such as smartphones or other data transmitters smaller, more efficient, and more powerful. The recent study was published in Nature Materials.
There are approximately 30 filters inside a cell phone, which transform radio waves into sound waves and back. These piezoelectric filters, made on special microchips, cannot be made of the same materials, such as silicon, as the other important chips on the front-end processor.
This makes the size of a device much bigger that it needs to be, and there will be losses from going back and forth between radio waves and sound waves that can degrade the device’s performance, explained the study’s senior author, Matt Eichenfield, who holds a joint appointment at the UArizona College of Optical Sciences and Sandia National Laboratories in Albuquerque, NM, in a news story on University of Arizona’s news site. “Having all the components needed to make a radio frequency front end on a single chip could shrink devices such as cell phones and other wireless communication devices by as much as a factor of a 100,” he explained.
“Normally, phonons behave in a completely linear fashion, meaning they don’t interact with each other,” he said. “It’s a bit like shining one laser pointer beam through another; they just go through each other.”
The synthetic materials produced by the research team caused the phonons to exhibit giant phononic nonlinearities, and they interacted with each much more strongly than in any conventional material, Eichenfield said. “In the laser pointer analogy, this would be like changing the frequency of the photons in the first laser pointer when you turn on the second,” he said. “As a result, you’d see the beam from the first one changing color.”
The team also showed that the components can be made using acoustic wave technologies instead of transistor-based electronics on a single chip. Specifically, they took a silicon wafer with a thin layer of lithium niobate—a synthetic material used extensively in piezoelectronic devices and cell phones—and added an ultrathin layer (fewer than 100 atoms thick) of a semiconductor containing indium gallium arsenide.
While lithium niobate is one of the most nonlinear phononic materials known, its usefulness for technical applications is hindered by the fact that those nonlinearities are very weak when used on its own. By adding the indium-gallium arsenide semiconductor, Eichenfield’s group created an environment in which the acoustic waves traveling through the material influence the distribution of electrical charges in the indium gallium arsenide semiconductor film, causing the acoustic waves to mix in specific ways that can be controlled, opening up the system to various applications.
“The effective nonlinearity you can generate with these materials is hundreds or even thousands of times larger than was possible before, which is crazy,” Eichenfield said. “If you could do the same for nonlinear optics, you would revolutionize the field.”
“Now, you can point to every component in a diagram of a radiofrequency front-end processor and say, ‘Yeah, I can make all of these on one chip with acoustic waves,'” Eichenfield said. “We’re ready to move on to making the whole shebang in the acoustic domain.”
