HARMONIC-GENERATION, INDUCED NONLINEARITY, AND OPTICAL BISTABILITY IN NONLINEAR COMPOSITES

We investigate the dielectric response of composite materials containing a quadratically nonlinear component. The bulk effective second order nonlinearity coefficients of a few simple microgeometries are calculated, and found to diverge in the vicinity of a quasistatic resonance of the composite. It is shown that second and third harmonic generation can be much enhanced in such composites, compared to bulk samples of the nonlinear component. An induced cubic nonlinearity (ICN), which also diverges near a resonance, is generated in the composite, even though none of its components possess it intrinsically. This ICN may be much larger than the effective nonlinearity of a composite with the same microgeometry and a cubic nonlinear component. Finally, such composites are shown to exhibit optical bistability. Such bistability is shown to be theoretically possible far away from a quasistatic resonance, even when all the components have real, positive dielectric constants. This is in contrast to bistability in composites containing a cubic nonlinear component, in which at least one metallic component and a close approach to a resonance are needed. However, tuning to the vicinity of a resonance is still needed in order to obtain bistability at reasonable levels of the applied held. Thresholds in the order of 10(4) W/cm(2) are predicted for a particular layered microgeometry with three components.