in the area of semiconductors, such as hetero­ structures based on III-V compounds or mesoscopic structures at the nanometer scale such as quantum weHs, quantum wires and quantum dots, have found robust applications in the generation, modulation, detection and processing of light. Major developments in glass techniques have also dramaticaHy improved the performance of optoelectronic devices based on optical fibers. The optical fiber doped with rare-earth materials has aHowed the amplification of propagating light, compensating its own los ses and even generating coherent light in fiber lasers. The UV irradiation of fibers has been used to inscribe gratings of hundreds of nanometer size inside the fiber, generating a large class of devices used for modulation, wavelength selection and other applications.