Integrated Optics/Electronics Using Electro-Optic Polymers
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Integrated Optics/Electronics Using Electro-Optic Polymers Larry R. Dalton Department of Chemistry, University of Washington Seattle, WA 98195-1700, U.S.A. ABSTRACT Organic electro-optic materials afford the realization of devices with terahertz bandwidths, providing bandwidths are not limited by resistive losses in metal electrodes. Recent realization of electro-optic coefficients (at telecommunication wavelengths) on the order of 200 pm/V permits construction of devices with operating voltage requirements of 1 volt or less. In like manner, substantial progress has been made in both understanding and improving thermal and photostability suggesting that organic electro-optic materials can meet Telacordia standards. However, one of the most intriguing advances afforded by organic materials is their processability including the ability to be integrated with diverse materials. This communication discusses both the systematic improvement, by theoretically-inspired rational design, of relevant material properties and the development of a variety of new processing methodologies, including soft lithography methods, for the fabrication of stripline, cascaded prism, and ring microresonator devices. The fabrication of flexible devices is also discussed.
INTRODUCTION Electro-optic (EO) phenomena involve the interaction of an optical field with an electrical field through the charge distribution of a material. Typically, a low frequency (dc to 30 THz) electrical field is applied to a material resulting in a perturbation of the charge distribution of the material. This, in turn, results in a change of velocity of light propagating in the material, as a consequence of the electric field component of light interacting with the perturbed charge distribution. Another way of viewing this phenomenon is voltage control of the index of refraction or birefringence of the EO material. The most common mechanisms resulting in electro-optic activity involve electric field induced molecular reorientation of liquid crystalline materials, lattice distortion of inorganic crystalline materials such as lithium niobate, or πelectron redistribution in ordered organic chromophore materials. Of course, the time required to respond to changes in the applied electric field will depend upon the mass that must be displaced. Liquid crystalline materials will, in general, be slow responding materials because significant nuclear mass must be moved; this slow response will translate into a limited bandwidth for devices fabricated from such materials. The response of crystalline materials, such as lithium niobate, is defined by the resistance to lattice displacement and will relate to the inverse piezoelectric effect. Elasto-optic effects will also contribute to index of refraction changes for crystalline materials and thus the frequency dependence of devices fabricated from lithium niobate will be more complex. The “effective” electro-optic activity will be a sum of two terms and will decrease with increasing frequency as elasto-optic effects become
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