Abstract
Abstract Second-order nonlinear optical sol-gel polymers are extensively applied in photonic devices, such as frequency doubling and electro-optical（EO）modulation, because of their large optical non-linearity, excellent processibility, low dielectric constants, and high laser damage thresholds. In addition, sol-gel reactions can be operated in lower temperatures, which prevent dyes from thermal degradation during polymer fabrication processes. Thermal degradation of dyes may cause the decrease of non-linear optical constants and higher optical loss. Polymer materials derived from sol-gel reactions have balanced cross-linking density and excellent optical transparency. In this study, two NLO polymer systems are compared by identification of chemical structures, thermal analyses and measurement of optical properties. The first NLO polymer system is organic reactive sol-gel NLO polymers prepared by condensing azo dye DO3 and 2,4-diamino-4’-nitroazobenzene with the cross-linking network of the (Hydroxymethyl) Benzoquanamine polymer, respectively. The other NLO polymer system is guest-host NLO polymers which was prepared by blending 2,4-diamino-4’-nitroazobenzen, DRI, N,N-Diethylaniline and N,N-Dimethylaniline with the cross-linking network of the (Hydroxymethyl) Benzoquanamine polymer, respectively. These two systems were oriented by Corona poling at 150℃ for 2 hours. The second-order nonlinear optical coefficient (d33) of up to 40 pm/V has been determined. The time-dependent of the decay was found to be well represented by the Kohlrausch-Williams-Watts stretched exponential equation. With the data, the two NLO polymer systems both have good stability at room temperature. Besides, the organic reactive sol-gel NLO polymer system is much more stable than the guest-host NLO polymer system at high temperature due to the covalent bonding. The molecular motion of the organic sol- gel NLO polymer is restricted by the covalent bonding, therefore the dye would not be reoriented to original state easily. This can also be proved form Arrhenius that the organic reactive sol-gel NLO polymer has a higher activation energy (Ea), namely the orientation of the organic sol-gel NLO polymer is more stable than guest-host NLO polymer.