Ion implantation may be used to change the optical properties of insulators, either because of the chemical presence of the dopant ions, or more generally because of the radiation damage caused during their implantation. The latter effect produces a significant change in the refractive indices of most materials, and consequently He+ implantation has been used to define optical waveguides in a wide variety of substrates. These include electro-optic, non-linear and laser host materials, with key successes in quartz, LiNbO3, KNbO3, KTiOPO4 (KTP), Bi4Ge3O12 (BGO), garnets such as Y3Al5O12 (YAG), and amorphous glasses such as silica and lead germanate.

Although this technique has wide applicability, the refractive index profiles vary considerably between materials, and even between different indices of the same material. The index change may vary in degree, and even in sign, for both the nuclear collision and the electronic ionisation regions. These effects are discussed in this chapter, together with their applicability in the formation of optical waveguides, and more complex structures. Of particular interest are the three detailed examples of quartz, LiNbO3 and Bi4Ge3O12 since between them they embody most of the features so far observed in ion implanted waveguides in insulating materials. The performance of the implanted waveguides is considered in terms of their thermal stability and their attenuation due to absorption, scattering and tunnelling losses. The He+ guides are first compared with those produced by conventional chemical diffusion methods. At the end of the chapter, waveguides formed by implantation of chemically active components are discussed.