Realization of Large, Stable Second Order Optical Nonlinearities Through Double-End Crosslinkable Chromophores
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Abstract We have developed a novel class of double-end crosslinkable (DEC) chromophores. Processible side-chain nonlinear optical (NLO) polymers with crosslinkable groups at the ends of chromophore pendants were synthesized from DEC monomers. The polymers were processed into good quality films, which were subsequently poled with a corona setup and thermally cured to attain stable noncentrosymmetric order. Using this DEC approach, we have realized large optical nonlinearities (X(2) = 90-220 prm/V) with long term stability at 125 °C.
Introduction Polymeric NLO materials are promising candidates for the fabrication of electrooptic devices such as electrooptic light modulators. The major advantages of polymer materials, as opposed to inorganic crystals, are their large optical nonlinearities, low dielectric constants (leading to large modulation bandwidth and high modulation efficiency) and excellent processibility. The polymers can be spin cast onto semiconductor substrates and processed into optical waveguiding structures and modulators that are compatible with semiconductor electronics. Electrooptic device applications require long term stability of large optical nonlinearities of materials in the working temperature range 60-125 'C. This requirement currently limits the application of poled NLO polymers. In the absence of a poling electric field, the poling-induced asymmetric dipole orientation in poled polymers tends to relax through polymer chain segmental motions and pendant rotations, leading to decay of NLO effects. Therefore, stabilizing the polinginduced noncentrosymmetric lattice is a challenging and critical undertaking. A number of approaches have been explored to realize stabilization of the poling-induced dipole alignment 4 through utilization of crosslinkable polymers.l- These include thermosetting prepolymers,"-3 9 8 side-chain polymers,4- main-chain polymers, and guest-host composites.10 - 3 Other methods of stabilizing the poling-induced order include doping NLO chromophores into polymer matrices with high glass transition temperatures (Tg) and attaching the chromophores covalently onto the backbone of high-Tg polymers, such as polyimides. 14 1 6 All of these approaches are somewhat successful in improving the temporal stability of optical nonlinearity. So far, however, there has not been a polymer material prepared that meets the aforementioned requirements. Most of the materials still do not possess enough NLO stability, especially at elevated temperatures (e.g., 90 'C to 125 °C), and some materials gain the stability at the sacrifice of optical nonlinearity. To 461 Mat. Res. Soc. Symp. Proc. Vol. 328. @1994 Materials Research Society
realize an acceptable NLO stability without sacrificing the optical nonlinearity, we have developed a novel class of double-end crosslinkable (DEC) chromophores. 6 In this paper, we present the design of NLO materials using DEC chromophores as well as synthesis and NLO properties of several polymers with crosslinkable chromophore ends. OH
///-A-1 NLO it-conjugati
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