5 - Ion implanted waveguide analysis
Summary
Characteristics of ion implanted waveguides
A waveguide is characterised by a region of high refractive index bounded by regions of lower index. The confinement of the light, as well as the spatial distribution of optical energy inside the guiding layer depends on the refractive index profile. There are several conventional techniques for fabricating optical waveguides. These techniques, including epitaxial growth, metal diffusion and ion exchange, increase the refractive index of the surface layer for a few microns (Figure 5.1), and this high index layer is surrounded by the low index of air and substrate to form an optical waveguide. Ion implantation, as a surface modification technique, can modify the optical properties of an insulator surface. However, when light ions are used, particularly when dealing with crystals, instead of changing the refractive index of the surface layer, a low index optical barrier is built up at the end of the ions' track due to elastic energy deposition from ions to the lattice. Therefore, the surface layer, ideally the same as the substrate, is surrounded by the low index of air and this optical barrier (Figure 5.1(c)). During the ion implantation, some point defects may be produced in the surface layer due to ionisation and excitation when the ions are travelling fast. These simple defects will change the properties of the material, and induce absorption and scattering loss. In practice, it has been found that post-implant annealing at a moderate temperature can either reduce or aggregate these defects depending on the material in question. In many materials, a low loss optical waveguide (∼0.5dB/cm) can be produced by ion implantation and subsequent annealing.
- Type
- Chapter
- Information
- Optical Effects of Ion Implantation , pp. 151 - 195Publisher: Cambridge University PressPrint publication year: 1994
- 2
- Cited by