Metamaterials can produce astounding effects. They possess quite different electromagnetic properties from conventional materials that allow them—among other things—to make objects appear invisible. Physics as magic, if you will.
If you manipulate the structure of a metamaterial, it will change how it interacts with electromagnetic waves. Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have taken advantage of this phenomenon at the nanoscale to create “the world’s smallest three-dimensional optical cavities with the potential to generate the world’s most intense nanolaser beams.”
The development of the “world’s smallest optical cavities” should have applications across a number of optical fields, including LEDs, optical sensing, nonlinear optics, quantum optics and photonic integrated circuits. It seems that metamaterials are on a bit of a roll when it comes to optoelectronics applications as evidenced by research coming out of the UK and Spain earlier this year.
Key to this technology’s operation is the optical property known as negative refraction, which makes it possible for some kinds of metamaterials to bend light in the opposite direction from what we would expect based on typical refraction. Achieving this negative refraction involves reversing the electrical component (permittivity) and the magnetic component (permeability) of a material’s refractive index. This is accomplished by constructing the material so that it has structures with dimensions smaller than the wavelengths of the light it is intended to refract.
“Due to the unnaturally high refractive index supported in the metamaterials, our 3D cavities can be smaller than one tenth of the optical wavelength,” says Xiaodong Yang, lead author of the Nature Photonics paper, in a Berkeley Lab press release. “At these nanoscale dimensions, optical cavities compress the optical mode into a tiny space, increasing the photon density of states and thereby enhancing the interactions between light and matter.”
Xiang Zhang, a principal investigator with Berkeley Lab’s Materials Sciences Division and director of UC Berkeley’s Nano-scale Science and Engineering Center (SINAM), believes this research should make possible a new generation of high-performance photonic devices.
“Our work opens up a new approach for designing a truly nano-scale optical cavity,” Zhang says in the Berkeley Lab press release. “By using metamaterials, we show intriguing cavity physics that counters conventional wisdom. For example, the quality factor of our optical mode rapidly increases with the decrease of cavity size. The results of this study provide us with a tremendous opportunity to develop high performance photonic devices for communications.”