High Efficiency Photorefractive Polymers

Abstract

The processibility and structural flexibility of photorefractive polymers give them an important technological potential and have driven intensive research efforts to improve the performance of this new class of PR materials. Since the first proof of principle of photorefractivity in a polymer [1], numerous PR polymeric materials have been synthesized by using different approaches [2], but significant performance improvement was obtained by using the photoconductive polymer poly(N-vinylcarbazole) (PVK) as the composite host and by doping it with nonlinear optical molecules referred to as chromophores [3,4]. In plasticized PVK-based polymer composites doped with the chromophore 2,5-dimethyl-4-(p-nitrophenylazo)anisole) (DMNPAA) [4], we recently demonstrated [5] that PR polymeric materials can exhibit light-induced refractive index modulation amplitudes as high as Δn = 7 × 10-3 at 1 W/cm2 writing intensity, and applied field of 90 V/µm. As shown in Fig. 1, such a high index modulation leads to complete diffraction and periodic energy transfer between the probe and diffracted beams in four-wave mixing (FWM) experiments and also, to net gain coefficients in excess of 200 cm-1 in two-beam coupling (TBC) experiments [5]. These results demonstrate that PR polymeric materials can reach performance levels that are competing with those of the best inorganic crystals, but with better processing capabilities.