GaAs Komponenten der Integrierten Optik für die externe Modulation in optischen Kommunikationssystemen

The improvements of the optical single-mode fiber and the progress in semiconduetor technology, especially in the domain of diode lasers with emission wavelengths in the near IR (1.3/rni 1.6um) allow for the rapidly growing data transmission rates in optical communication Systems. High demands are made on the transmitters, the reeeivers and the transmitting media at data rates of several Gbit/s and for medium to large area networks from several km to more than 100km. The single-mode fiber is the only interconnection that exhibits low attenuation and avoids mode dispersion. Photodetectors with high sensitivity at large bandwidth have been developed and are, to some extent, commercially available, already integrated with amplifier circuits. It seems that the realization of a fast coherent optical transmitter represents a much more difficult problem. Laser diodes in III-V semiconduetors with only a single transverse and longitudinal optical mode have been demonstrated. At high modulation bandwidths, however, mode fluetuations appear which broaden the laser spectrum and reduee the system bandwidth as a consequence of fiber dispersion. The realization of transmission rates of up to about 4Gbit/s is possible when using costly mode stabilization techniques or dynamic single-mode lasers such as DBR and DFB lasers. An alternative that allows still higher system bandwidths is the use of an external modulator at de Operation of a common single-mode laser. In this thesis investigations on external modulators based on the linear electro-optic effect are reported. Applicability of these components in practical optical communication Systems requires a compact construction, the possibility of integration with electronic and optoelectronic circuits, low