Book excerpt: Ever since the invention of the transistor, semiconductor-based microelec tronics has made a revolutionary impact on the information society, as evi dent from the widespread application of microprocessor-based technology in our modern society. The next wave of modern information technology, after transistors and microelectronics, is that oflasers and micro-optoelectronics. Optoelectronics, or optical electronics, based on lasers and related modern optical technology, has also become a very important field of science and technology in the past 20 years. Electronics or microelectronics deals with (micro)electronic devices and components for generation, transmission, and processing of electronic sig nals. In contrast, in optoelectronics we deal with optoelectronic devices and components for the generation, transmission, and processing of lightwave signals. It is the interaction of lightwaves (photons) with matter that shows the uniqueness of optoelectronic technology; optical absorption and scat tering, optical gain and amplification, material and waveguide dispersion, nonlinear optical effects, etc., are very much dependent on the material's intrinsic properties and the lightwave propagation effects.