3 Artificial materials

In our study, we will call ˜artificial materials the structures which have particular optical properties ( absorption , reflex ion, transmission) that a natural material could not have. These properties are due at the same time to the properties of the materials which constitute the structure and the geometrical parameters of these [Yablonovitch 87, John 87, Yeh 94, Joannopoulos 95]. Thus, while structuring the matter, one manages to create specific and particular optical properties, these properties not being able to be obtained for a homogeneous material.

Namely, we will consider a new family of artificial materials: photonic crystals. The photonic crystals are periodic structures with a periodicity of one, two or three dimensions [Yablonovitch 87, John 87, Yeh 94, Joannopoulos 95].

Figure 17.2: Examples of artificial structures of photonic crystal, one, two and three dimensions

Since their appearance, photonic crystals have seen a number of applications growing in an extremely strong way, in very varied directions. The field of application of photonic crystals opens new prospects, namely for example the inhibition of spontaneous emission, the control of electron -hole recombination in the materials [Yablonovitch 91, Ozbay 95, Russel 95, Gerard 02]. The applications of photonic crystals exist now in the field of microwaves or millimeter-wavelength as well as in the optical region. One can quote: perfectly reflective mirrors, filters, polarisers, modulators, substrates for millimeter wavelength antennas, switches, high efficiency light emitting diodes LED and finally lasers without threshold.

These enthralling applications open a new prospect in all the branches of physics such as atomic physics, optoelectronics, telecommunications and optical interconnections. Moreover, the nonlinear effects in such photonic crystals contribute to the development of powerful machines such as the optical computer. Thus, electronic switches and transistors will be replaced in the more or less long term by their optical parents.

Motivated by these significant applications, technologists for their part provide an enormous efforts in order to create other structures which meet future needs. For example the Yablonovite [Yablonovitch 91] was fabricated to operate in the millimeter-wavelength, structure "layer by layer" [Ozbay 95], two-dimensional structures of parallel cylinders etc The manufacture of photonic crystal operating in the optical region proves to be a real challenge which currently puts into competition different laboratories at international level such as MIT, Corning, the University of Southampton, the University of Glasgow, and in France: Alcatel, the LETI, the LEOM, the IEF, etc [Russel 95, Gerard 02].