The researchers at Chalmers University of Technology in Sweden have achieved a significant breakthrough by combining two major research fields in photonics. They have created a nanoobject with exceptional optical qualities, which is a thousand times thinner than human hair but remarkably powerful.
This advancement holds promising potential for the development of efficient and compact nonlinear optical devices. Professor Timur Shegai, who led the study at Chalmers, believes that this discovery has immense potential.
The applications of photonics leverage the interactions between light and matter to produce a variety of fascinating phenomena. These applications have driven significant progress in communications, medicine, and spectroscopy, as well as in laser and quantum technologies. The researchers at the Department of Physics at Chalmers University of Technology have successfully integrated two major research fields—nonlinear and high-index nanophotonics—into a single disk-like nanoobject.
“We were amazed and happy by what we managed to achieve. The disk-looking structure is much smaller than the wavelength of light, yet it’s a very efficient light frequency converter. It is also 10,000 times, or maybe even higher, more efficient than the unstructured material of the same kind, proving that nanostructuring is the way to boost efficiency,” says Doctor Georgii Zograf, lead author of the article in Nature Photonics, where the research results are presented.
Researchers have successfully developed a nanostructure that combines material and optical resonances to convert light frequency using crystal nonlinearity. They have utilized a material known as transition metal dichalcogenide (TMD), specifically molybdenum disulfide, which demonstrates remarkable optical properties at room temperature.
However, they have encountered challenges in stacking this material due to its crystalline lattice symmetry constraints, potentially causing a loss of its nonlinear properties.
“We have fabricated for the first time a nanodisk of specifically stacked molybdenum disulfide that preserves the broken inverse symmetry in its volume and, therefore, maintains optical nonlinearity. Such a nanodisk can maintain the nonlinear optical properties of each single layer. This means that the material’s effects are both maintained and enhanced,” says Georgii Zograf.
This extraordinary material possesses a high refractive index, enabling efficient light compression. Additionally, it can be transferred onto any substrate without the need to match the atomic lattice, enhancing its versatility. The nano structure excels in localizing electromagnetic fields and generating doubled frequency light through second-harmonic generation. This nonlinearity, akin to sum- and difference-frequency generation effects in high-energy pulsed laser systems, occurs in a compact nanodisk with exceptional efficiency.
“Our proposed material and design are state-of-the-art due to extremely high inherent nonlinear optical properties and notable linear optical properties – a refractive index of 4.5 in the visible optical range. These two properties make our research so novel and potentially attractive even to the industry,” Georgii Zograf says.
“It really is a milestone, particularly due to the disk’s extremely small size. Second harmonic generation and other nonlinearities are used in lasers every day, but the platforms that utilize them are typically on the centimeter scale. In contrast, the scale of our object is about 50 nanometers, so that’s about a 100,000 times thinner structure,” says research leader Professor Timur Shegai.
The researchers are confident that the work on nanodisks will significantly advance photonics research. Over time, the exceptionally compact dimensions and unique properties of TMD materials could revolutionize advanced optical and photonic applications. Such structures could be seamlessly integrated into a wide range of optical circuits or utilized in the miniaturization of photonics.
“We believe it can contribute towards future nonlinear nanophotonics experiments of various kinds, both quantum and classical. By having the ability to nanostructure this unique material, we could dramatically reduce the size and enhance the efficiency of optical devices, such as nanodisk arrays and metasurfaces. These innovations could be used for applications in nonlinear optics and the generation of entangled photon pairs. This is a first tiny step, but a very important one. We are only just scratching the surface,” says Timur Shegai.
Journal reference:
- George Zograf, Alexander Yu. Polyakov, Maria Bancerek, Tomasz J. Antosiewicz, Betül Küçüköz & Timur O. Shegai. Combining ultrahigh index with exceptional nonlinearity in resonant transition metal dichalcogenide nanodisks. Nature Photonics, 2024; DOI: 10.1038/s41566-024-01444-9