This technology could be applied to the development of improved surgical and medical lasers, better laser countermeasures for military use, and more environmentally sensitive lasers, such as those used to measure contaminants and detect the spread of chemical agents in bioterrorism. The team's research will be published in the journal Advanced Materials.
“It’s become a cliché to say that fiber optics are the cornerstone of the modern information age,” Badding said. “These long, thin fibers, which are three times thicker than a human hair, can transmit more than a terabyte of information per second. Still, there are always ways to improve existing technology.” Badding explained that fiber optic technology has always been limited by the use of a glass core. “Glass has a random arrangement of atoms,” Badding said. “In contrast, a crystalline substance like zinc selenide is highly ordered. That allows light to be carried at longer wavelengths, especially in the mid-infrared.”.
Unlike silica crystal, which is traditionally used in optical fibers, zinc selenide is a semiconductor compound. “We’ve known for a long time that zinc selenide is a useful compound, able to manipulate light in ways that silica can’t,” Badding said. “The trick was getting this compound into a fiber structure, something that had never been done before.” Using a novel high-pressure chemical deposition technique developed by Justin Sparks, a graduate student in the Department of Chemistry, Badding and his team deposited zinc selenide guide cores inside silica crystal capillaries to form the new class of optical fibers. “High-pressure deposition is the only method that allows the formation of such long, thin zinc selenide fiber cores in such a confined space,” Badding said.
The scientists discovered that the zinc selenide optical fibers could be useful in two ways. First, it was observed that the new fibers are more efficient at converting light from one color to another. “When traditional optical fibers are used for samples, displays, and art, it’s not always possible to achieve the desired colors,” Badding explained. “Zinc selenide, through a process called nonlinear frequency conversion, is better able to change colors.”
Second, as Badding and his team expected, they found that the new class of fiber provides greater flexibility not only in the visible spectrum but also in the infrared. Existing optical fiber technology is not efficient at transmitting infrared light. However, the zinc selenide optical fibers that Badding's team has developed are capable of transmitting longer wavelengths of infrared light. “Exploiting these wavelengths is very exciting because it represents a step toward manufacturing fibers that can serve as infrared lasers,” Badding explained. “For example, the military currently uses laser-radar technology that can handle near-infrared, or a range of 2 to 2.5 µm. A device capable of handling mid-infrared, or the entire 5 µm range, would be more accurate. The fibers we have created can transmit wavelengths up to 15 µm.”.
Badding also explained that detecting environmental pollutants and toxins could be another application of improved laser-radar technology capable of interacting with light of longer wavelengths.
Furthermore, Badding mentions that zinc selenide optical fiber could also open new avenues of research that could improve laser-assisted surgical techniques, such as corrective eye surgery.
In addition to Badding and Sparks, other researchers who contributed to this study included Rongrui He of the Penn State Research Institute's Department of Chemistry and Materials; Mahesh Krishnamurthi and Venkatraman Gopalan of Penn State's Department of Materials Science and Engineering and the Materials Research Institute; and Pier J.A. Sazio, Anna C. Peacock, and Noel Healy of the University of Southampton's Optoelectronics Research Centre. Technical support for this research was provided by the Engineering and Physical Sciences Research Council, the National Science Foundation, and the Pennsylvania State University Materials Science and Research Center.
