Researchers advancing use of polymers for nonlinear optical materials
Nonlinear optical (NLO) devices, used in laser systems or for optical information processing, communications and data storage, are made of materials that allow light waves to be manipulated. NLO materials are usually inorganic crystals, which are expensive and difficult to fabricate.
Progress by Virginia Tech researchers on developing NLOs from organic polymers will be reported at the 220th national meeting of the American Chemical Society Aug. 20-24 in Washington, D.C. as part of the symposium on organic thin films for photonic applications.
Polymers are easier to process than crystals and more compatible with modern microelectronic devices. The Virginia Tech researchers in physics, chemistry, and chemical engineering are using ionically self-assembled monolayers (ISAMs) to fabricate optoelectronic devices under ambient conditions without the use of organic solvents, high vacuum chambers or other expensive equipment. One particularly important NLO device, an electro-optic modulator also known as a Mach-Zender interferometer (M-ZI), splits light and then modifies one of the streams of light so that the recombined light streams encode information from an external electrical input. In the modified stream, the light wave is changed by applying an electric field, which changes the refractive index of the material. For the material to change in a predictable manner, its molecules have to have a net orientation (so the dipoles point in the same direction). A significant challenge in creating NLO devices from polymers has been obtaining optical-control characteristics that are stable for months to years. Polymers can be heated in an electric field and then cooled to provide such orientation, but it fades -- usually in hours or days.
Virginia Tech scientists are researching organic, thin film structures to understand the process. Professors Richey M. Davis (chemical engineering), Harry W. Gibson, (chemistry), James R. (Randy) Heflin (physics), and Kevin Van Cott (chemical engineering) and their students have produced ISAM films whose NLO behavior has been stable for years at room temperature. Such materials could be used as conformal coatings on M-ZI devices. The group is looking at how dyes can be oriented by varying conditions and materials.
The papers and authors, and times and places of presentation are: ß PMSE 23 "Second order nonlinear optical properties of ionically self-assembled films containing dianionic chromophores," by physics graduate student Patrick J. Neyman, chemical engineering graduate students Matthew T. Guzy and Smital Shah, chemistry postdoctoral researcher Hong Wang, Gibson, Van Cott and Davis, physics student Charles Figura and Heflin will be presented at 8:50 a.m. Sunday Aug. 20 in the JW Marriottt Hotel Grand Ballroom Salon III. ß PMSE 136 "In situ second harmonic generation measurements of the growth of nonlinear optical ionically self-assembled monolayers," by physics graduate student Charles Brands, Neyman, Guzy, Shah, Wang, Gibson, Van Cott, Davis, Figura, and Heflin, will be presented at 9:20 a.m. Tuesday Aug. 22 in the JW Marriottt Hotel Grand Ballroom Salon III.
ß PMSE 220 "Novel deposition techniques for self-assembled non-linear optic thin films," by Guzy, Shah, Davis, Van Cott, Heflin, Wang, and Gibson, will be presented as a poster at 8 p.m. Monday Aug. 21 in Convention Center Exhibit Hall D.