Synthesis and characterization of a thermally curable second-order nonlinear optical polymer

To stabilize the dipole alignments induced by an electric field in A second-order nonlinear optical (NLO) polymer, especially at elevated temperatures, we have synthesized a thermally cross-linkable, second-order nonlinear optical polymer containing ethynyl groups. The ethynyl groups in the polymer backbone can undergo thermal intramolecular reactions with amide groups to form heterocyclic structures and/or undergo intermolecular reactions with amide groups on other polymer chains to form cross-linkages. The thermal curing of the polymer can be effected during electric poling and therefore the device elements (planar waveguide, channelized waveguide) can be easily prepared by using this polymer. Second harmonic generation measurements indicated that the cured polymer indeed exhibits a high stability in the dipole orientation: no obvious decay at room temperature for more than 1000 h. Long-term stability of second harmonic coefficients was observed even at 90 degree C, at least for 500 h.