Characterization of nonlinear optical polymers and dendrimers for electro-optic applications
Organic second-order nonlinear optical (NLO) polymers have received increasing interest due to their potential for applications in high-speed electro-optic (EO) devices with very broad bandwidth and excellent device performance. Their large EO coefficients and low drive voltages have been demonstrated in prototype EO modulators by using several guest-host poled polymers. Translating the high molecular hyperpolarizabilities (beta) of organic chromophores into large electro-optic coefficient (r33) device-quality polymers is one of the most challenging tasks in electro-optic polymer research. Current research at the University of Washington has implemented several innovative approaches to improve the performance of the nonlinear optical polymers through nanoscale architectural control. The ability to synthetically control several critical design parameters, such as size, shape, surface chemistry, flexibility, and topology, has shaped the exploration of a range of novel materials. UW researchers have extensively studied the effects of increasing the effective conjugation length and/or enhancing the donor and acceptor strengths on the basic rigid rod chromophore guest-host systems. They also have conducted comprehensive research on the effects of manipulating chromophore shape by surrounding it with bulky inert substituents to make the chromophore more spherical. Recent work exploiting smartly controlled chemistry and creative processing/poling procedures has significantly improved poling efficiencies. The typical solubility limit of guest molecules in the host matrix has been pushed to much higher doping levels without an increase in dielectric breakdowns through the site isolation effects contributed by fluorinated dendrons. One of our novel synthetic routes was based on free Diels-Alder chemistry, a very mild catalyst. The Diels-Alder reaction allowed the poling process to occur prior to and separated from the lattice-hardening process and provided materials with high thermal stability and excellent poling efficiency.