Abstract

We carried out photobleaching experiments on thin films of azo chromophore functionalized side chain polymers at different wavelengths in the UV and visible sprectral regions. Photobleaching alters the polymer layer due to two different mechanisms: In the first place, bleaching results in lowering of the index of refraction by destruction of the highly polari­zable NLO chromophore electronic π system and thus shifting the absorption band. Secondly, as a result of outgassing of molecular fragments and ablation, the polymer layer thickness is significantly reduced. Both effects strongly depend on the wavelength spectrum of the bleaching source and in addition exhibit remarkably different time responses. Limiting the wavelength spectrum the proper way we were able to either concentrate on chromophor modification alone or on both chromophor modification and thickness modification. This allows us to tailor the resulting geometrical profile of channel waveguides as well as the index difference to the surrounding cladding. Figure 1 (left) shows an AFM-micrograph of the geometrical dimensions of the top surface of a channel waveguide photobleached in a NLO-sidechain polymer as described. A very smooth profile (Figure 1 right side) is realized with a rms-value of the surface roughness of only 0.3 nm. In addition to the modification of the surface topography, the refractive index in the bleached region of the polymer is shifted by up to 10^-2.

© 1995 Optical Society of America