Edgar Kühn

Polarization-independent and ultra-high bandwidth electroabsorption modulator in multiquantum-well deep-ridge waveguide technology

Electroabsorption modulators with polarization-independence of transmission (TE/TM sensitivity <0.4 dB at 1550 nm) over a wide wavelength range from 1540-1560 nm have been realized using tensile-strained InGaAs and InGaAsP quantum wells. Both designs show 42-GHz modulation bandwidth with a high bandwidth-to-drive-voltage ratio of >23 GHz/V. Polarization insensitivity of modulator transmission and chirp is demonstrated. Technical realization has been done in ridge waveguide technology with low-pressure MOVPE, reactive ion etching (RIE) for semiconductor etching and polyimide for planarization.

Mode-locked laser realized by selective area growth for short pulse generation and optical clock recovery in TDM systems

We report on monolithically integrated active/passive coupled cavity mode locked lasers for 1.55 micrometer realized by selective area growth technology of InGaAs(P) quantum wells. Mode locked FP or DBR lasers are fabricated with an integrated cavity comprising up to three different band gaps. The devices emit short light pulses at around 10 GHz repetition rate with pulse width down to 8.7 ps. A time-bandwidth product of 0.5 is achieved for mode locked DBR lasers. Active/passive integrated mode locked laser is used for generation of optical 10 GHz clock signal from optical 10 Gb/s PRBS RZ data stream injected into the laser cavity.

Monolithic mode locked DBR laser with multiple-bandgap MQW structure realized by selective area growth

The realization of novel monolithically integrated multiple-segment pulse laser sources in InGaAsP MQW technology is reported. The MQW layers for all functional sections of these devices, the modulator, the active (gain) and the passive waveguide, as well as the Bragg section were grown in a single selective area growth (SAG) step by LP-MOVPE on SiO/sub 2/ patterned 2 inch InP substrates. Due to a properly selected pattern geometry 3 different bandgap regions with smooth interfaces are thereby formed along the laser cavity. The more than 4 mm long DBR lasers which exhibit a threshold current as low as 30 mA were mode locked by an intra-cavity electroabsorption modulator applying a sinusoidal voltage at around 10 GHz. In this way an optical pulse train with pulse widths <13 ps (measured with a streak camera) and high extinction ratio was generated. A time-bandwidth product of 0.5 close to the Fourier limit is obtained. This device is very attractive for signal generation in 40 Gb/s OTDM transmission systems at 1.55 /spl mu/m wavelength.

IP based Seamless Mobility Support in Heterogeneous Networks – Evaluation of Handover Mechanisms for Future Heterogeneous 3GPP Networks (IP basierte nahtlose Mobilitätsunterstützung in heterogenen Netzwerken – Evaluierung von Handover-Mechanismen für zukünftige heterogene 3GPP Netzwerke)

Mobile IP (MIP) protocols are candidates for seamless mobility support in heterogeneous networks with different radio access technologies. Handover requirements are analysed by Random-Way-Point mobility simulations. We then simulated packet loss, delay and network load during MIP and Fast MIP handover to identify the main contributions to handover latency. Best performance is found for MIP in Make-Before-Break scenario. Mobil IP (MIP) Protokolle sind Kandidaten für die nahtlose Handover-Unterstüzung in Radio-Zugangsnetzen mit unterschiedlichen Radiotechniken. Die Handover-Anforderungen wurden mit Random-Way-Point-Simulationen analysiert. Danach haben wir Paketverluste, Verzögerungen und die Netzwerklast bei MIP- und FastMIP-Handovern untersucht, um die Hauptursachen für Unterbrechungszeiten zu identifizieren. Das beste Verhalten zeigt MIP mit Make-Before-Break.

High speed low chirp MQW transmitters for standard fibre TDM transmission systems

Details on design, realization and high-speed properties of external and integrated multi-quantum-well electroabsorption modulators (EAM) are reported. 10 Gbit s-1 standard fibre transmission without dispersion penalty over 25.2 km with a low chirp (<0.15 nm) integrated Ea modulator/DFB laser and 100.8 km with a discrete modulator has been demonstrated with a controlled alpha parameter.

Integrated quantum well modulators for very high speed transmission systems

This paper summarises work currently performed within the European program RACE, under contract R2006 WELCOME, Quantum Well Components for High Speed Transmission Systems. The introduction of Integrated Broadband Communication (IBC) services requires solutions that enable high capacity transmission and distribution of information at low cost, including the integration and possible upgrade of existing networks. A currently discussed approach is based on direct detection schemes at very high bit rates on one optical carrier. Optical communication systems based on standard fibres presently achieve data rates of 10 Gbit/s. The most stringent limitation appears to be the dispersion of standard fibres which limits the bridgeable fibre length. Residual chirp which always accompanies intensity modulation has not only to be minimised. For adjustable low negative chirp, however, the maximum fibre length can be even increased above the dispersion limit of chirp-free fibre transmission. In the WELCOME project several approaches for transmission with direct detection and low chirp intensity modulation at bit rates of 10 Gbit/s and above have been successfully demonstrated. Among them, electroabsorption (EA) modulators have shown their potential to fulfil these requirements.<<ETX>>