Optical materials, nonlinear crystal engineering

Recently, a second-order nonlinear photonic crystal has been realized.38 In this nonlinear optical bandgap material, there is a periodicity in the nonlinear optical properties of the engineered material. With this definition, a periodically poled second-order nonlinear optical material could be called a nonlinear photonic crystal. However, its linear optical properties do not show a periodicity, except for the (small and useless for bireffingent phase-matching) poling-induced birefringence. Here, the material is the same in the complete structure. It is only periodically made into a non-centrosymmetric structure for second-order nonlinear and phase-matching... 

The applicable fundamental concepts of nonlinear integrated optics for SHG were outlined decades ago and can be found in a number of review papers [6-8]. The basic theory as applied to organic materials and polymers is of course unchanged from that for dielectric materials and these papers are still very useful. Some twenty plus years ago, nonlinear integrated optical experiments started to be conducted, but mostly on inorganics and crystals. The specific field of amorphous and semi-ordered organics came when the chemical engineering of nonlinear chromophores was developed. 

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