Optical Waveguiding in Poled NLO Polymers
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OPTICAL WAVEGUIDING IN POLED NLO POLYMERS
J. D. SWALEN, W. FLEMING, M. JURICH, W. E. MOERNER, B. A. SMITH, S. HERMINGHAUS, and G. C. BJORKLUND IBM Research Division, San Jose, CA 95120.
ABSTRACT For potential optoelectronic applications, new polymeric thin films containing nonlinear optical chromophores aligned by electric field poling for a X(2) nonlinear optical response have been prepared and studied. Spectroscopic and optical waveguiding techniques, as well as second harmonic generation and electrooptic measurements, are being used to characterize these thin film materials. Here we optimize the chromophores in spectral response, nonlinearity, concentration and degree of alignment. Stability in the nonlinearity has been improved considerably by attaching the chromophores to crosslinked epoxy polymers. Some applications of these materials for electrooptic phase modulators will be presented. INTRODUCTION An increase in research and development activity in optoelectronics has occurred because of the good prospects for utilizing optical methods in information storage and communications. This application, however, requires good nonlinear optical materials. A number of research groups have initiated investigations into the properties and behavior of organic polymeric nonlinear optical materials, because they may have potential advantages over inorganic crystals. Molecules containing charge transfer donors and acceptors connected by a conjugated chain can exhibit large optical nonlinearity and as such offer promise. The major problem, however, has been their long term stability: the oriented chromophores, necessary for second order nonlinearity, tend to randomize under thermal processes. Significant progress has recently been made in improving the longevity of these materials. We wish to report on some of our recent results on (1) the optimization of the properties of some new materials made in our laboratories, (2) linear and nonlinear optical measurements on these systems, and (3) some waveguide device designs involving polymeric thin layer configurations. There are, at this meeting, three reports of work being done at the IBM Almaden Research Center and they are closely related and connected in a logical manner with only a minimum overlap and duplication. The paper by Twieg et al1 covers some the new chromophores and their incorporation into polymer systems. We describe some of the measurements done on these materials and their design and fabrication into waveguide devices. The third in the series by Smith et a12 describes electrooptic measurements and results by waveguide measurements on one of the better polymer systems. Hence a rather complete picture evolves by combining all these results together. MATERIAL PARAMETERS The microscopic second order 4nonlinear molecular polarizability and the 3 macroscopic polarizability are related ' Mat. Res. Soc. Symp. Proc. Vol. 228. m1992 Materials Research Society
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Z(2)= Nf,2,f < o0
>,
1
where N is the number of molecules, the f's are the local field factors, fl is
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