Non-linear optical (NLO) polymers have potential application in ultra-fast electro-optic modulators.Although physical doping of NLO chromophores into a matrix polymer appears to be efficient in the preparation of NLO polymers and electric poling

it suffers from low chromophore loading and poor temporal stability.In this paper

a new approach of preparation towards highly efficient NLO materials was demonstrated by doping a novel type of zwitterionic chromophore (BPIPP-DEMI) into an acid-containing matrix polyimide (API) and fabrication via alternate spin-coating of polymeric multilayer films comprising layers of the resulting NLO polymer and layers of a spacing tertiary amine-containing polyimide (BPI).The individual polymer layers had a thickness in the range of 100～200 nm

which can be readily controlled by adjusting the concentration of polymer solutions and the spin speed.Investigation of the UV-Vis absorption and the growth in the thickness of the multilayer films indicated a uniform growth of multilayer films.A five bi-layer NLO multilayer film (1.6 μm) was thus fabricated

with each API layer containing 10 wt% of the NLO chromophore BPIPPDEMI.In contrast to API films containing 10 wt% of BPIPPDEMI

which showed significant phase separation

NLO multilayer films containing the same amount of BPIPP-DEMI exhibited no obvious phase separation under optical microscope

indicating a better host for NLO chromophores.