Abstract

Nonlinear optical materials are the building blocks of the emerging technologies of optoelectronics and photonics (photonics uses light to acquire, process, transmit, and store information). These materials perform functions such as modulation, switching, rectification, frequency generation, limiting, and amplification, all of which are typically performed by semiconductors in electronic technology. Nonlinear optical materials and phenomena can be classified as second or third-order, reflecting the order of electric field interactions involved. Second-order phenomena are typically observed only for noncentrosymmetric materials. Such phenomena include electrooptic modulation, spatial light modulation, and second harmonic generation. Electrooptic modulation may play a critical role in electric-to-optical signal transduction and in switching in local area networks and can be used for specialized applications as diverse as phased array radar and optical gyroscopes. Third-order phenomena include the dynamic Kerr effect, degenerate four-wave mixing, third harmonic generation, saturable absorption, reverse saturable absorption, etc. The dynamic Kerr effect can be exploited for all-optical switching and also for beam focusing, such as in mode-locking of the Ti:sapphire laser. Reverse saturable absorption can be exploited for sensor protection. Both organic and inorganic materials have been observed to exhibit relatively large optical nonlinearities. Material morphologies ranging from crystalline to polymeric to photonic bandgap have been considered for nonlinear optical applications; examples of materials are given.