Novel second-order nonlinear optical polymers via chemical cross-linking-induced vitrification under electric field

Abstract

We present a novel method of preparing highly efficient and stable second-order nonlinear optical (NLO) polymers via chemical cross-linking induced vitrification under electric field. In this method a soluble prepolymer is first prepared that contains cross-linking sites attached to the NLO-active groups. Upon preparing samples of desired thicknesses, the prepolymer is heated (precured) to enable some chemical cross-linking and thus to increase the glass transition temperature (Tg) to an optimum for poling. The precured polymer is then heated above its Tg and subjected to a high electric field to obtain the desired alignment of NLO moieties. Subsequent chemical cross-linking (curing) under electric field continues to advance the Tg and hence leads to in situ vitrification of the polymer that stabilizes the electric-field-induced orientation of the NLO moieties. Detailed results of thermal, linear optical, poling kinetics, and NLO properties are described for the polymer system prepared from tetrafunctional 4-nitro 1,2-phenylenediamine and bifunctional Bisphenol-A diglycidylether as the starting monomers. The polymer which has been cured finally at 140 °C under a very high corona field exhibits d33≂14 and d31≂3 pm/V, determined from the Maker-fringe experiments. Most significant, however, is the fact that this polymer shows no detectable decay in second harmonic generation for over 500 h under ambient conditions and no tendency of relaxation even at 85 °C.

Novel Crosslinked Guest-Host System with Stable Second Order Nonlinearity

“…The curing time for this system is relatively short (i.e. 2 hours) compared to a typical thermally-crosslinked epoxy [2] (approximately 16 hours). Highly stable second order nonlinearity at 1000C has been achieved through this crosslinked guest-host polymer.…”

“…Enhanced temporal stability of second-order NLO properties in a poled polymer system can be obtained when a certain degree of crosslinking is introduced [1][2][3][4]. In the crosslinked polymer, the NLO moieties are covalently bound into a rigid polymer network and are, therefore, much less likely to relax to random orientation.…”

Nonlinear Optical Polymers Derived From Organic/Inorganic Composites

“…This is due to the fact that the molecular motions of NLO chromophores are closely associated with the Tg of the polymer [4]. Further, enhanced temporal stability of second-order NLO properties in a poled polymer can be obtained when a certain degree of crosslinking is introduced [5][6][7][8][9][10]. Long term stability of second-order nonlinearities in a number of different crosslinked polymeric systems at temperatures higher than 100 'C has been reported earlier [6,9,10].…”

Novel Crosslinked Guest-Host System with Stable Second-Order Nonlinearity

“…In the crosslinked polymer, the NLO moieties are covalently bound into a rigid polymer network and are, therefore, much less likely to relax to random orientation. Such an approach was first reported by Eich et al [2] in an epoxy system in which the NLO moieties are incorporated either in the multifunctional epoxy or amine components.…”