ABSTRACT
Active optical waveguides are the light guiding structures that contain a material possessing optical gain and/or optical nonlinearity that leads to various active functionalities. Stimulated emission of light is a process whereby an atom or a molecule undergoes a transition from higher to lower energy states as a result of the presence of external stimulating photons and is key to the functionalities of both laser emission and optical gain devices. Nonlinearity can lead to establishing active functionalities in waveguide photonic devices such as all-optical switching or optical bistability. Optical gain is a property that a material acquires by exciting its molecules, atoms, or carriers in large densities into higher energy states, resulting in amplification of incident optical power through stimulated emissions. When a semiconductor optical amplifier as an active optical waveguide is used in an optical cavity, lasing takes place as a result of the positive feedback and optical gain.
