Rational Design of Organic Electro-Optic Materials
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Rational Design of Organic Electro-Optic Materials Alex Jen1, Robert Neilsen2, Bruce Robinson2, William H. Steier3, and Larry Dalton2 1 Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195-2120. 2 Department of Chemistry, University of Washington, Seattle, WA, 98195-1700, U.S.A. 3 Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089-0483 ABSTRACT A number of material properties must be optimized before organic electro-optic materials can be used for practical device applications. These include electro-optic activity, optical transparency, and stability including both thermal and photochemical stability. Exploiting an improved understanding of the structure/function relationships, we have recently prepared materials exhibiting electro-optic coefficients of greater than 50 pm/V and optical loss values of less than 0.7 dB/cm at the telecommunication wavelengths of 1.3 and 1.55 microns. When oxygen is excluded to a reasonable extent, long-term photostability to optical power levels of 20 mW has been observed. Photostability is further improved by addition of scavengers and by lattice hardening. Long-term (greater than 1000 hours) thermal stability of poling-induced electro-optic activity is also observed at elevated temperatures (greater than 80°C) when appropriate lattice hardening is used. The successful improvement of organic electro-optic materials rests upon (1) attention to the design of chromophore structure including design to inhibit unwanted intermolecular electrostatic interactions and to improve chromophore instability and (2) attention to processing conditions including those involved in spin casting, electric field poling, and lattice hardening. A particularly attractive new direction has been the exploitation of dendrimer structures and particularly of multi-chromophore containing dendrimer structures. This approach has permitted the simultaneous improvement of all material properties. Development of new materials has facilitated the fabrication of a number of prototype devices and most recently has permitted investigation of the incorporation of electro-optic materials into photonic bandgap and microresonator structures. The latter are relevant to active wavelength division multiplexing (WDM). Significant quality factors (greater than 10,000) have been realized for such devices permitting wavelength discrimination at telecommunication wavelengths of 0.01 nm. INTRODUCTION Advantages of electro-optic devices fabricated from second-order nonlinear optical chromophore-containing polymeric materials include low (e.g., one volt or less) drive voltage (Vπ) requirements [1,2], large (e.g., greater than 100 GHz) bandwidths [3-8], and ease of integration with semiconductor electronics, diode lasers, and silica transmission fibers [9-12]. Because of the low and relatively frequency-independent dielectric constants, ε, and refractive indices, n, of organic materials, large bandwidths have been easily realized [3-8]. Devices with bandwi
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