Two-step refractive index changes by photoisomerization and photobleaching processes in the films of non-linear optical polyurethanes and a urethane–urea copolymer

Photoinduced refractive index and absorption spectrum changes in the films of polyurethanes and a urethane-urea copolymer with large second-order non-linear coefficient d have been studied. These changes were explained by a two-step reaction scheme including a trans–cis photoisomerization followed by a photobleaching reaction. The former process was reversible and the latter was irreversible, so that a thermally stable refractive index was obtained. The changes were accelerated by heating. A channel waveguide was fabricated by the processes and light propagation through the waveguide was observed.