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

Abstract

Larry R. DaltonUniversity of WashingtonDepartment of ChemistrySeattle, Washington 98195-1700andUniversity of Southern CaliforniaLoker Hydrocarbon Research InstituteLos Angeles, California 90089-1661E-mail: dalton@chem.washington.eduE-mail: ldalton@methyl.usc.eduAbstract. Translation of the large molecular hyperpolarizability of chro-mophores into large macroscopic electro-optic activity by electric fieldpoling of chromophore-containing polymers is opposed by molecular-shape-dependent intermolecular electrostatic interactions. Modificationof chromophore structure (shape) to minimize the deleterious effect ofsuch interactions leads to significant improvement in electro-optic activ-ity. Drive voltage requirements for polymeric modulator devices are re-duced to values ranging from 0.7 to 5 V. Optical loss of electro-opticpolymer materials, at the communication wavelengths of 1.3 and 1.55mm, is defined by C–H, O–H, and N–H vibrational absorptions and byscattering from index of refraction gradients in the material. The formerare significantly reduced by partial deuteration and halogenation to val-ues slightly less than 1 dB/cm. A major source of optical loss encoun-tered in the utilization of polymeric electro-optic modulator devices iscoupling losses associated with the mode mismatch between silica fiberwaveguides and polymeric modulator waveguides. Recently, alternativecoupling strategies based on utilization of tapered transitions and verticaltransitions have dramatically reduced coupling losses. Total insertionlosses comparable to those for lithium niobate devices are realized. Fi-nally, a phototrimming technique is developed that enables fine-tuning ofthe performance of circuit elements such as power splitters.