Nonlinear Optical Properties

Abstract

Photonic technologies operate by the optical processing and transmission of information and require a variety of materials with appropriate properties to facilitate the modulation of light. Polymers containing organic nonlinear optical (NLO) chromophores allow the modulation of the phase, the state of polarization, and/or the frequency of light beams, as required for the optical encoding, transmission, and routing of information. Both secondand third-order NLO effects are potentially useful [1]. Materials with large secondand third-order nonlinearities can be useful for the doubling and tripling, respectively, of the frequency of optical signals. They can also be used for routing and switching applications in which NLO effects involving the ability to vary the refractive indices of the materials using an applied electric field are important. The refractive index of second-order NLO materials is dependent on electric field; this effect is known as the linear electro-optic (EO) or Pockels effect. Materials with large EO coefficients can be used for the fabrication of ultrafast low-power EO modulators that can be integrated with electronics. In third-order NLO materials, the refractive index is dependent on the intensity of light and so can bemodulated with an optical control pulse, negating the need to integrate electronics directly with the NLO material and facilitating all-optical modulation, which holds promise for ultrafast signal processing, potentially enabling much higher bandwidth communications. In organic materials with large secondor third-order nonlinearities, these nonlinearities are largely due to the interaction of light with conjugated p-systems. Here a simple model is described that has helped to provide design strategies for the optimization of second-order and third-order nonlinear optical effects in quasi-linear organic molecules.