Anisotropic Refractive Index Dispersion in Polycrystalline PTCDA Waveguides

The dispersion of the inplane and normal refractive index in 3,5,9,10-perylentetracarboxylic dianhydride (PTCDA) waveguides has been determined using the m-line technique. TE and TM mode coupling at excitation wavelengths ranging from 633 to 910 nm has been accomplished by a Rutile prism. The PTCDA waveguides, which were grown by organic molecular beam deposition on Pyrex substrate, reveal a strong optical anisotropy between the inplane and normal refractive index values showing e.g. a birefringence of $\sim $0.8 at a wavelength of 633 nm. Our measurements demonstrate the high optical quality of our PTCDA waveguides as well as their potential for polarization dependent all-optical applications. In particular, the high compressibility of PTCDA waveguides along the soft crystallographic $a$-direction bears potential for pressure sensitive applications.