5.1. Introduction

One year after the invention of the lazer [MAI 60], the observation of second harmonic generation [FRA 61] was the starting point for a new field in optics: nonlinear optics. This observation constituted a demonstration of the possibility of changing the wavelength of a lazer via a second order nonlinear process. Since that time, nonlinear optics has grabbed the attention of many researchers and the progress made in this domain can be measured by looking at some of the very important resulting applications. For example, many commercial tunable lazer sources are based on the use of nonlinear processes such as parametric oscillations or parametric amplification. One can also cite the use of the optical Kerr effect, a third order nonlinear effect, in optical fiber communications systems in order to compensate chromatic dispersion and propagate optical solitons. However, breakthroughs are still awaited in nonlinear optics, especially their capability to be used for ultrafast data processing for future optical integrated circuits.

On the other hand, in the domain of nano- and microtechnologies, the tremendous progress achieved in material processing, such as in growing, lithography and etching, are revolutionizing optoelectronics and integrated optics because they enable the fabrication of nano- and microstructures that can be used to manufacture completely new miniaturized optical components [JOA 97].

Using microstructures presenting a periodic modulation of the refractive index was proposed as soon as the first steps were taken in nonlinear optics to obtain greater nonlinear interactions.