Optical waveguiding in thin films of polyelectrolytes

Planar waveguides were prepared by spin-coating of polyelectrolytes, a class of polymers that is also called ionenes, to characterize their linear optical properties. A prism-coupler experiment was used to evaluate the refractive index n at different wavelengths. The dispersion of n was calculated from the absorption spectrum by means of the Kramers-Kronig relations. Adjusting the parameters of the Kramers-Kronig analysis to the measured n allows the determination of the influence of the polymer backbone and its separation from contributions of the counterions. Using different combinations of polymers and counterions, a range of n between 1.57 and 1.72 with Abbe numbers nu _D between nu _D=13 and nu =65 can be achieved. The birefringence of these films was found to be less than 0.001 as derived from comparison of TE and TM modes. The waveguide losses were measured by monitoring the stray light of the films with a diode array. The attenuation coefficients were studied at various laser wavelengths and waveguide modes. Attenuation coefficients in the region of 1 dB cm^-1 were achieved.