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 chrom ophore-containing polymers is opposed by molecular-shape-dependent intermol ecular electrostatic interactions. Modification of chromophore structure (s hape) to minimize the deleterious effect of such interactions leads to sign ificant improvement in electro-optic activity. Drive voltage requirements f or polymeric modulator devices are reduced to values ranging from 0.7 to 5 V. Optical loss of electro-optic polymer materials, at the communication wa velengths 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 ma terial. The former are significantly reduced by partial deuteration and hal ogenation to values slightly less than 1 dB/cm. A major source of optical l oss encountered in the utilization of polymeric electro-optic modulator dev ices is coupling losses associated with the mode mismatch between silica fi ber waveguides and polymeric modulator waveguides. Recently, alternative co upling strategies based on utilization of tapered transitions and Vertical transitions have dramatically reduced coupling losses. Total insertion loss es comparable to those for lithium niobate devices are realized. Finally, a phototrimming technique is developed that enables fine-tuning of the perfo rmance of circuit elements such as power splitters. (C) 2000 Society of Pho to-Optical Instrumentation Engineers. [S0091 -3286(00)00203-8].