Use of spiro compounds as materials in non-linear optics

The non-linearly optical structural element, selected from the group consisting of opto-optical couplers, Mach-Zehnder interferometers, mode selective couplers and prism couplers, which comprises an optical waveguide comprising a spiro compound of the formula (I)

• in which ψ is C, Si, Ge or Sn, and K1 and K2 independently of one another are conjugated systems or a conjugated polymer, comprising repeating units of the formula (VI),
• in which the symbols and indices have the following meanings:
• m and n are 0, 1, 2, or 3;
• ψ is Sn, Ge, Si or C;
• D, E, F and G are identical or different and are —CR1R2—, —O—, —S—, —NR3— or a chemical bond;
• in which R1, R2 and R3 are C1-C20-alkyl or H, and in which R1 and R2 together can form an optionally substituted cycloalkyl ring;
• U is —CR4═CR5— or a chemical bond;
• V has the meaning of U or is —CR1R2—, —O—, —S—, —NR3—, —SiR1R2—, —SO2—, —SO— or —CO—, in which R1, R2 and R3 have the above-mentioned meaning and R4 and R5 have the meaning of R1, R2 and R3 or are fluorine or CF3;
• A is hydrogen, C1-C20—, alkyl, which can also contain heteroatoms;
• R6 and R7 are hydrogen or a C1-C20-hydrocarbon radical, which can be aliphatic, aromatic, linear, branched or alicyclic, in which R6 together with R7 can form a ring,
• T is —O—, —S—, —NR3—, —CR1R2—, —CH═N—, —CA═CA—, —CH═CA—, —CH═CF— or —CF═CF—, in which R1, R2, R3 and A have the above-mentioned meaning,
• K, L, M and Q are identical or different hydrocarbon radicals which contain conjugated electron systems and can contain heteroatoms, where K, L, M and Q, with the particular groups A in the ortho-position, can also be closed together to form a ring, which is saturated, partly unsaturated or unsaturated to the maximum degree, L, M can also be H, a non-conjugated hydrocarbon radical, preferably containing 1 to 20 carbon atoms, which can contain hetero atoms, halogen, CN, NO2, an amino, alkylamino or dialkylamino group.