Researchers have made a significant advancement by merging two key areas of photonics to create a tiny object with remarkable optical properties. This object, which measures a thousand times thinner than a human hair but boasts remarkable power, holds tremendous promise for the creation of efficient and compact nonlinear optical devices.
At Chalmers University of Technology in Sweden, researchers have successfully combined two critical fields within photonics for the first time by developing a nanoobject with exceptional optical characteristics. Due to its impressive power despite being a thousand times thinner than a human hair, this development could lead to the creation of highly efficient and compact nonlinear optical devices. “I believe this discovery holds immense potential,” states Professor Timur Shegai, who led the research at Chalmers.
Photonic applications use light-matter interactions to create fascinating phenomena, which have propelled advancements in fields such as communication, medicine, and spectroscopy, as well as in laser and quantum technologies. Now, researchers at the Department of Physics at Chalmers University of Technology have successfully unified two key research areas—nonlinear and high-index nanophotonics—within a single disk-like nanoobject.
“We were both surprised and delighted by our achievement. The disk-shaped object is much smaller than the wavelength of light, yet it functions as a highly efficient light frequency converter. It is also 10,000 times more efficient, and possibly even more, than similar unstructured materials, confirming that nanoscale structuring is essential for enhancing efficiency,” explains Dr. Georgii Zograf, the lead author of the study published in Nature Photonics.
A new fabrication method with preserved properties
In simpler terms, the researchers merged material and optical resonances with light frequency conversion capability through the crystal’s non-linearity in their nanodisk design. They utilized transition metal dichalcogenide (TMD), specifically molybdenum disulfide, which is an atomically thin material displaying exceptional optical properties at room temperature. However, a challenge arises as it is challenging to stack this material without compromising its nonlinear characteristics due to constraints posed by its crystalline lattice symmetry.
“For the first time, we have successfully created a specifically stacked molybdenum disulfide nanodisk that retains its broken inverse symmetry throughout its volume, thus maintaining the optical nonlinearity. This nanodisk can uphold the nonlinear optical properties of each individual layer, resulting in both retention and enhancement of the material’s effects,” states Georgii Zograf.
The material possesses a high refractive index, allowing for more efficient light compression within it. Additionally, it can be easily transferred onto any substrate without needing to align the atomic lattice with the underlying material. The nanostructure is also highly effective in localizing the electromagnetic field and generating light at double frequency, a phenomenon known as second-harmonic generation. This is a nonlinear optical effect akin to those utilized in high-energy pulsed laser systems.
Consequently, this nanodisk integrates extreme nonlinearity and high refractive index into a single, compact structure.
A significant advancement in optics research
“Our proposed material and design represent cutting-edge technology due to their exceptionally high inherent nonlinear optical properties and notable linear optical characteristics—a refractive index of 4.5 within the visible spectrum. These attributes make our research highly novel and potentially appealing to different industries,” says Georgii Zograf.
“This is truly a groundbreaking achievement, especially considering the tiny size of the disk. Although second harmonic generation and other non-linearities are routinely applied in lasers, the platforms that utilize them usually measure in centimeters. In contrast, our object is approximately 50 nanometers in size, making it about 100,000 times smaller,” adds research leader Professor Timur Shegai.
The researchers are optimistic that the nanodisk’s capabilities will advance photonics research. In the long run, the incredibly compact dimensions of TMD materials, combined with their unique qualities, could be utilized in sophisticated optical and photonic applications. For instance, these structures could find applications in various types of optical circuits or in the miniaturization of photonic devices.
“We believe this could facilitate future nonlinear nanophotonics experiments of all kinds, both classical and quantum. By effectively nanostructuring this remarkable material, we could significantly reduce the size and boost the efficiency of optical devices like nanodisk arrays and metasurfaces. These innovations might be beneficial in nonlinear optics and the generation of entangled photon pairs. While this is just a small initial step, it is nonetheless a significant one. We are only beginning to explore the possibilities,” concludes Timur Shegai.
