Silicon technology enabled the miniaturization of computers and other electronic system for information storage, transmission and transformation allowing the development of the Knowledge Based Information Society. Despite the fact that silicon roadmap indicates possibilities for further improvement, already now the speed of electrons and the bandwidth of electronic circuits are not sufficient and photons are commonly utilized for signal transmission through optical fibers and purely photonic circuits promise further improvements. However materials used for these purposes II/V semiconductor compounds, glasses make integration of optoelectronic circuits with silicon complex an expensive. Therefore research on light generation, transformation and transmission in silicon is very active and recently, due to nanotechnology some spectacular results were achieved despite the fact that mechanisms of light generation are still discussed. Three topics will be discussed. Porous silicon was actively investigated due to its relatively efficient electroluminescence enabling its use in light sources. Its index of refraction, differs considerably from the index of silicon, and this allows its utilization for Bragg mirrors, wave guides and photonic crystals. The enormous surface enables several applications on medicine and biotechnology and in particular due to the effective chemo-modulation of its refracting index the design of optical
chemosensors. An effective luminescence of doped and undoped nanocrystalline silicon opened another way for the construction of silicon light sources. Optical amplification was already discovered opening perspectives for the construction of nanosilicon lasers. Luminescences was observed at red, green and blue wavelengths. The used technology of silica and ion implantation are compatible with commonly used CMOS technology. Finally the recently developed and proved idea of optically pumped silicon Raman lasers, using nonlinearity and vibrations in the material to produce optical gain will be described.