Polymeric materials with second order nonlinear optical (NLO) properties are of much interest for applications such as waveguide electrooptic modulation and frequency doubling devices. These NLO properties are presented when the chromophores are aligned in a noncentrosymmetric manner. The alignment of NLO chromophores in the poled polymers must be sufficiently stable at temperatures above 100 deg C in order to use them in practical devices. Several approaches have been adopted to enhance the temporal stability of the poled polymers. Enhanced temporal stability of second order NLO properties in several poled polymer systems has been achieved by crosslinking reactions. The resulting crosslinked network has a higher glass transition temperature and a denser matrix which prevent the aligned NLO chromophores from relaxing to a random orientation. However, slow decay of second order NLO properties at elevated temperatures was still observed in the polymers. Furthermore, the general form of the relaxation curves for the crosslinking polymers do not appear to be distinctly different from those for the guest/host systems. We have selected an interpenetrating polymer network (IPN) containing aligned NLO chromophores to test these issues. An IPN is a structure in which two or more networks are physically combined. The IPN is known to be able to remarkably suppress the creep and flow phenomena in polymers. Permanent entanglement of the two polymer chains restrict their mobility which leads to a significantly more stable NLO material. In this paper, we report on the design, synthesis and characterization of an NLO active IPN ... Interpenetrating polymer network, Nonlinear optical polymer.

There has been a tremendous recent interest in the development of second-order nonlinear optical (NLO) polymeric materials for photonic applications. However, a major drawback of second-order NLO polymers that prevents them from being used in device applications is the instability of their electric field induced dipolar alignment. The randomization of the dipole orientation leads to the decay of second-order optical nonlinearities. Numerous efforts have been made to increase the stability of the second-order NLO properties of polymers. The search for new approaches to develop NLO polymers with optimal properties has been an active research area since the past decade. A novel approach, combining the hybrid properties of high glass transition temperatures, extensively crosslinked networks, and permanent entanglements, based on interpenetrating polymer networks (IPN) is introduced to develop stable second-order NLO materials. Two types of IPN systems are prepared and their properties are investigated. The designing criteria and the rationale for the selection of polymers are discussed. The IPN samples show excellent temporal stability at elevated temperatures. Long term stability of the optical nonlinearity at 100 C has been observed in these materials. Temporal stability of the NLO properties of these IPNs is synergistically enhanced. Relaxation behavior of the optical nonlinearity of an IPN system has been studied and compared with that of a typical guest/host system. The improved temporal stability of the second-order NLO properties of this IPN system is a result of the combination of the high rigidity of the polymer backbones, crosslinked matrices, and permanent entanglements of the polymer networks. A slight modification of the chemical structure resulted in an improvement of the optical quality of the sample.

Nonlinear optical (NLO) polymers have shown increased potential in practical applications, such as frequency doubling and electro-optic modulation, due to their large nonlinearity and ease of processing. A practical NLO polymer will need to possess large second-order nonlinearity, excellent temporal stability at elevated temperatures, and low optical loss. 1 A number of NLO polymers have been developed to exhibit large second-order NLO coefficients comparable to those of the inorganic NLO materials which are currently in use in devices. 2,3 However, the major drawback of NLO polymers is the decay of their electric field induced second-order optical nonlinearities. This decay is a result of the relaxation of the NLO chromophores from the induced noncentrosymmetric alignment to a random configuration. Numerous efforts have been made to minimize this decay through different approaches. 4 Recently, we have reported on an approach to stable second-order NLO polymers using an interpenetrating polymer network (IPN) structure. 5,6 This IPN system, with the hybrid properties of a high glass transition temperature (Tg), an extensively crosslinked network, and permanent entanglements, exhibited excellent temporal stability at elevated temperatures. 6 In this report, a new IPN system, modified from the one reported earlier,5 with higher degree of crosslinking density and larger NLO chromophore density is investigated. Electro-optic modulation, Interpenetrating polymer network, Second-order nonlinearity, Optical loss.

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The linear optical and second order nonlinear optical (NLO) properties of an interpenetrating polymer network (IPN) have been investigated. For the poled and cured IPN samples, large second order NLO coefficients, d33, were measured at 1.064 um and 1.542 um. The linear electrooptic coefficients, r33, were determined at various wavelengths. The poled and cured IPN samples showed no measurable decay of the second-order optical nonlinearity after being treated at 110 deg C for more than 1000 hours. This excellent long-term stability of the NLO property is ascribed to the novel interpenetrating crosslinked molecular structure of the IPN system.