Polymeric electro-optic materials: optimization of electro-optic activity, minimization of optical loss, and fine-tuning of device performance

Translation of the large molecular hyperpolarizability of chromophores into large macroscopic electro-optic activity by electric field poling of chromophore-containing polymers is opposed by molecular-shape-dependent intermolecular electrostatic interactions. Modification of chromophore structure (shape) to minimize the deleterious effect of such interactions leads to significant improvement in electro-optic activity. Drive voltage requirements for polymeric modulator devices are reduced to values ranging from 0.7 to 5 V. Optical loss of electro-optic polymer materials, at the communication wavelengths of 1.3 and 1.55 mu m, is defined by C-H, O-H, and N-H vibrational absorptions and by scattering from index of refraction gradients in the material. The former are significantly reduced by partial deuteration and halogenation to values slightly less than 1 dB/cm. A major source of optical loss encountered in the utilization of polymeric electro-optic modulator devices is coupling losses associated with the mode mismatch between silica fiber waveguides and polymeric modulator waveguides. Recently, alternative coupling strategies based on utilization of tapered transitions and Vertical transitions have dramatically reduced coupling losses. Total insertion losses comparable to those for lithium niobate devices are realized. Finally, a phototrimming technique is developed that enables fine-tuning of the performance of circuit elements such as power splitters. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091 -3286(00)00203-8].