Integrated Optical Circuits (IOCs) have been under development for over three decades. In an analogy to electronic integrated circuits, developers of IOCs envision the possibility of combining several or many optical processing functions on a single miniature platform, such as a semiconductor chip, fabricated using processes similar to those used for electronic chip production. Also called Planar Lightwave Circuits (PLCs) or Planar Optical Chips (POCs), these devices incorporate functional optical components such as linear or curved waveguides to conduct light from one location to another, filters fabricated from specially shaped waveguides that control the spectral characteristics of the light, and lenses and mirrors embedded in waveguides to alter the shape of the light. The PLCs may be interfaced to other optical components and devices via optical fibers or other interconnecting devices such as the mode converters described below.