Nonlinear Optical Material Made of Tellurium Nanorods

Tellurium nanorods – produced by naturally occurring bacteria – is an effective nonlinear optical material. (Source: USGS)

An inter­national team of researchers has reported a new way to safeguard drones, surveil­lance cameras and other equipment against laser attacks, which can disable or destroy the equipment. The capability is known as optical limiting. The work also describes a superior manner of telecom switching without the use of electronics; instead, they use an all-optical method that could improve the speed and capacity of internet communi­cations. That could remove a roadblock in moving from 4GLTE to 5G networks.

The team reported that a material created using tel­lurium nanorods – produced by naturally occurring bacteria – is an effective nonlinear optical material, capable of protecting electronic devices against high-intensity bursts of light, including those emitted by inex­pensive household lasers targeted at aircraft, drones or other critical systems. The researchers describe the material and its performance as a material of choice for next-generation opto­electronic and photonic devices.

Seamus Curran, a physics professor at the University of Houston, said while most optical materials are chemically synthesized, using a bio­logically-based nano­material proved less expensive and less toxic. “We found a cheaper, easier, simpler way to manufacture the material,” he said. “We let Mother Nature do it.” The new findings grew out of earlier work by Curran and his team, working in colla­boration with Werner Blau of Trinity College Dublin and Ron Oremland with the US Geological Survey. Curran initially synthesized the nano­composites to examine their potential in the photonics world. He holds a US and inter­national series of patents for that work.

The researchers noted that using bacteria to create the nano­crystals suggests an environ­mentally friendly route of synthesis, while generating impressive results. “Nonlinear optical measurements of this material reveal the strong saturable absorp­tion and nonlinear optical extinc­tions induced by Mie scattering overbroad temporal and wave­length ranges,” they reported. “In both cases, Te [tellurium] particles exhibit superior optical non­linearity compared to graphene.”

Light at very high intensity, such as that emitted by a laser, can have unpre­dictable polarizing effects on certain materials, Curran said, and physicists have been searching for suitable nonlinear materials that can withstand the effects. One goal, he said, is a material that can effec­tively reduce the light intensity, allowing for a device to be developed that could prevent damage by that light. The researchers used the nano­composite, made up of bio­logically generated elemental tellurium nano­crystals and a polymer to build an electro-optic switch that is immune to damage from a laser, he said.

Oremland noted that the current work grew out of thirty years of basic research, stemming from their initial discovery of selenite-respiring bacteria and the fact that the bacteria form discrete packets of elemental selenium. “From there, it was a step down the Periodic Table to learn that the same could be done with tellurium oxyanions,” he said. “The fact that tellurium had potential appli­cation in the realm of nano­photonics came as a serendipitous surprise.”

Blau said the bio­logically generated tellurium nanorods are especially suitable for photonic device appli­cations in the mid-infrared range. “This wavelength region is becoming a hot technological topic as it is useful for biomedical, environ­mental and security-related sensing, as well as laser processing and for opening up new windows for fiber optical and free-space communi­cations.” Work will continue to expand the material’s potential for use in all-optical telecom switches, which Curran said is critical in expanding broadband capacity. “We need a massive investment in optical fiber,” he said. “We need greater bandwidth and switching speeds. We need all-optical switches to do that.” (Source: U. Houston)

Reference: K. Wang et al.: Bacterially synthesized tellurium nanostructures for broadband ultrafast nonlinear optical applications, Nat. Commun. 10, 3985 (2019); DOI: https://doi.org/10.1038/s41467-019-11898-z

Link:Institute for NanoEnergy, Dept. of Physics, University of Houston, Houston, USA

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