A class of molecules whose size, structure and chemical composition have been optimized for photonic use could provide the demanding combination of properties needed to serve as the foundation for low-power, high-speed all-optical signal processing.
All-optical switching could allow dramatic speed increases in telecommunications by eliminating the need to convert photonic signals to electronic signals – and back – for switching. All-optical processing could also facilitate photonic computers with similar speed advances
Switching of optical signals carried in telecommunications networks currently requires conversion to electrical signals, which must be switched and then converted back to optical format. Existing electro-optical technology may ultimately be able to provide transmission speeds of up to 100 gigabits-per-second. However, all-optical processing could theoretically transmit data at speeds as high as 2,000 gigabits-per-second, allowing download of high-definition movies in minutes rather than hours.
“This work provides proof that at least from a molecular point of view, we can identify and produce materials that have the right properties for all-optical processing,” said Seth Marder, a professor in the Georgia Tech School of Chemistry and Biochemistry and co-author of the paper. “This opens the door for looking at this issue in an entirely different way.”
The polymethine organic dye materials developed by the Georgia Tech team combine large nonlinear properties, low nonlinear optical losses, and low linear losses. Materials with these properties are essential if optical engineers are to develop a new generation of devices for low-power and high-contrast optical switching of signals at telecommunications wavelengths. Keeping data all-optical would greatly facilitate the rapid transmission of detailed medical images, development of new telepresence applications, high-speed image recognition – and even the fast download of high-definition movies.
But favorable optical properties these new materials developed at Georgia Tech have only been demonstrated in solution. For their materials to have practical value, the researchers will have to incorporate them in a solid phase for use in optical waveguides – and address a long list of other challenges.
“We have developed high-performing materials by starting with optimized molecules and getting the molecular properties right,” said co-author Joseph Perry, also a professor in the Georgia Tech School of Chemistry and Biochemistry. “Now we have to figure out how to pack them together so they have a high density and useful physical forms that would be stable under operation.”
All-optical switching applications require materials with large third-order nonlinearities and low nonlinear optical losses. We present a design approach that involves enhancing the real part of the third-order polarizability () of cyanine-like molecules through incorporation of polarizable chalcogen atoms into terminal groups, while controlling the molecular length to obtain favorable one- and two-photon absorption resonances that lead to suitably low optical loss and appreciable dispersion enhancement of Re(). We implement this strategy in a soluble bis(selenopyrylium) heptamethine dye that exhibits a real part of that is exceptionally large throughout the wavelength range used for telecommunications, and an imaginary part of , a measure of nonlinear loss, that is two orders-of-magnitude smaller. This combination is critical in enabling low-power and high-contrast optical switching.
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