HIGH-SPEED AND COHERENT TRANSMISSION COMPONENTS

This paper focusses on research and development activities for discrete components used either in high speed direct modulation or coherent systems, respectively. By taking full benefit of highly advanced epitaxial growth techniques like LPMOVPE and GSMBE new device structures have been realized. On the transmitter side a SIBH laser structure is reported which is especially designed for extremely low parasitics allowing for a transmission speed in excess of 10 Gbit/s. Results on DFB-MQW lasers are presented. By making use of two dimensional effects these lasers have shown low threshold currents, high output power as well as narrow linewidth, which is of strong interest for both high bit rate and coherent transmission. Wavelength tunable lasers, such as multisection DFB or DBR lasers as well as a YCC-I-3 laser, are investigated. With 3 section DFB-lasers a linewidth of 3.5 MHz has been obtained. A 4-channel FSK transmission experiment at 565 Mbit/s has been successfully performed. The passiv DBR lasers have shown a tuning range of 4.2 nm. With the novel YCC-I-3 laser structure an enormous total tuning range of 22 nm together with a continuous tuning range of 1.15 nm with 20 dB sidemode suppression and a linewidth of 35 MHz has been achieved. Semiconductor travelling wave amplifiers are reported with high average internal gain of 28 dB at bias current of 50 mA. Using 4 cascaded amplifiers a 591 Mbit/s direct detection experiment of 279 km has been performed. Results on pin-photodiodes and APD's are presented. Optimized pin-detectors have been used to detect 20 Gbit/s pattern in a system experiment. Specially designed APD's are reported with a gain-bandwidth product of 70 GHz.