New Solutions of the Electronic Circuits of High Speed Optical Receivers

Introduction The highest growing sectors of the economy in the last two decades are the informatics and telecommunication. Their development is very correlated, due to the fact that the fast and efficient process of information requires transportation of it with extremly high speed as well. The new technical possibilities led to new applications, which are the base of novel industry sectors. They are essential for economical prosperity (high-speed computer networks, Internet). Recently, the Internet became the main information source of professional users in many areas (technical and natural science, research, development, commerce etc.), and on the other hand it is a strong fortress of democracy. One of the main properties of these kind of applications, that due to the demand for higher speed and better quality, they require higher and higher data rate. It can be fullfilled only by fiber optic networks due to the low capacity of coaxial lines and long haul radio links. Beside that, the latter suffers from the lack of free radio channels, bandwidth restrictions and interference or propagation problems. According to this, huge efforts are made to further improve the building parts and circuits of the optical networks. One of the main restriction factors is the bandwidth of the electronic parts and of the E/O and O/E converters of these systems, as the optical fibers have several order higher capacity. Hence, research and development of amplifiers, multiplexers, demultiplexers, optical modulators, photodiodes with extremly high bandwidth became very important. Great efforts are invented to the research of optically feeded mobile radio systems (so called radio over fiber systems). The mobile communication is one of the fastes growing field of telecommunication. Due to the enormous increasing of the user number and the absence of free radio channels, the following tendencies can be observed in the future: • Increasing cell number with decreasing size (picocell systems) • Higher cell capacity • Usage of MMW or higher frequency ranges. According to that, the base stations will be feeded through optical networks, and the MMW carrier will be generated by optical methods or electricaly from an optically transmitted subharmonic reference.