Abstract

Nonlinear optical (NLO) and electrooptic (EO) processes are events that take place in transparent materials where refractive indexes can vary with electric field intensity. The field elicits a polarization response in which terms dependent on second and higher orders of the field intensity become significant contributions to the overall polarization response. As light propagates through a transparent solid, liquid, or gas, it encounters the electric fields associated with the valence electrons, polarizing them and creating oscillating electric dipoles. These oscillators in turn act as antennas to broadcast or propagate the electric field through the medium.

NLO materials possess a high degree of optical nonlinearity, physical durability and chemical inertness, and high threshold to optical damage. In addition, it must be possible to process the materials into the form required by the intended application.

Optically nonlinear ceramics all contain highly polarizable bonds. In the case of oxide ceramics, such polarizable bonds are often found between oxygen and early transition metals, eg, BaTiO₃, SrNb₂O₆. Nonoxide NLO ceramics include Si and compound semiconductors having the silicon structure, eg, GaAs, InP, and InSb, as well as ferrelectrics such as SbSI. All-optical wavemixing applications generally require single crystals.

Electrooptic (EO) materials are optical media in which birefringence can be readily induced or altered by an externally applied electric field. As with NLO ceramics, good EO materials tend to be ferroelectrics. EO materials are generally used as either bulk optical elements or guided wave devices.