Azo dye polymers useful in nonlinear optics contain as characteristic monomer units radicals of the formulae I, II, III and IV ##STR1## where D is the radical of a heterocyclic diazo component,R.sup.1 and R.sup.2 are each hydrogen, C.sub.1 -C.sub.6 -alkyl or substituted or unsubstituted C.sub.1 -C.sub.6 -alkoxy, and R.sup.2 may also be C.sub.1 -C.sub.4 -alkanoylamino,R.sup.3 is hydrogen, C.sub.1 -C.sub.6 -alkyl, C.sub.5 -C.sub.7 -cycloalkyl or C.sub.3 -C.sub.4 -alkenyl,R.sup.4 is hydrogen, deuterium, methyl, trideuterated methyl or chlorine,R.sup.5 is hydrogen or deuterium,Y.sup.1 and Y.sup.2 are each substituted or unsubstituted C.sub.2 -C.sub.10 -alkylene,W is oxygen, imino or C.sub.1 -C.sub.4 -alkylimino, andX is hydroxyl, substituted or unsubstituted C.sub.1 -C.sub.6 -alkoxy, phenoxy, amino or mono- or di(C.sub.1 -C.sub.4 -alkyl)amino,and have an average molecular weight of from 1,000 to 100,000.