New side-chain polymers with large stable electro-optic effects

Abstract

Polymer materials with large second-order nonlinearities can potentially be used to fabricate low-cost, high-performance electrooptic and nonlinear optical devices for photonic switching. The important physical properties for these applications are large nonlinearity, long-term stability, and simplicity of device fabrication. We have synthesized and characterized a promising new class of polymers with disperse red side chains. The second-order nonlinear optical properties have been characterized by means of second-harmonic generation. With the corona-poling method, large resonance enhanced second-order nonlinear coefficients of 590 pm/V for polyester-disperse red and 280 pm/V for copolyester-disperse red, were observed at 532 nm. Using a simple two-level model, we have conservatively extrapolated these values to 800 nm, where the films are transparent, and have obtained χ(2) values of 112 pm/V and 84 pm/V. The near-infrared electro-optic coefficients(r33) calculated from χ(2) are 26 pm/V and 24 pm/V, respectively. The χ(2) values are stable at 70-80% of their maximum values for at least several hundred hours. These are among the largest stable second-order coefficients reported. We have also studied the linear optical properties of these polymers under ultraviolet and short- wavelength visible light illumination. A significant refractive-index decrease from chromophore bleaching has been observed. The large index change makes it possible to use available photolithographic methods in device fabrication.