A device-quality second-order nonlinear optical (NLO) polymer prepared by post-functionalization of an epoxy-based precursor polymer exhibits an improved processability, such as good solubility in common organic solvents and excellent film-forming property. Toluene-2,4-diisocyanate as a cross-linking agent was used to cross-link the NLO polymer to create a three-dimensional (3D) network of polyurethane during poling. Using this thermosetting polyurethane, an electro-optic (EO) modulator based on attenuated-total-reflection (ATR) technology was fabricated successfully, and its performance was discussed. The highest EO coefficient of 16 pm/V for this modulator measured at a wavelength of 832 nm was obtained by an improved ATR method, and a high temporal stability of the poling-induced order was observed at elevated temperature up to 100 degrees C. (C) 2005 Elsevier B.V. All rights reserved.