POLYUREA WITH LARGE POSITIVE BIREFRINGENCE FOR 2ND-HARMONIC GENERATION

The second-order nonlinear optical properties of four polyureas with l arge positive birefringence are presented. The temporal stability of t he poling-induced orientations at different temperatures were estimate d by in-situ second harmonic generation (SHG) measurements. For the po lyurea prepared from aliphatic diamines, the optical transparency was down to 300 nm. The most interesting aspect of these polyureas is in t heir refractive indices: the refractive indices of TE modes before pol ing are higher than those of TM modes. This indicates that the polymer chains were stretched along the substrate surface. This work represen ts the first example of an increase of poling-induced refractive indic es in TE modes.