Klaus Satzke

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.

Integrated thermo-optic switches in silica/polymer waveguide technology

Thermo-optic 1x2 vertical coupler switches (VCSs) using a hybrid polymer/silica integration technology were designed using finite element method and coupled mode method for different refractive index contrasts. The multilayer structures were optimized by thermal analysis. Based on this design and simulation, hybrid polymer/silica thermo-optic 1x2VSCs exhibiting low insertion loss, low crosstalk, low switching power, and polarization independence were demonstrated. Using this 1x2VCS as the building block, a 1x8VCS has been implemented.

Phase error distribution and spectral response in silica-based AWG multiplexers

PHASARs or Arrayed Waveguide Grating (AWG) multiplexers for application in Dense Wavelength Division Multiplexing optical networks have been realized using silica-waveguide technology. Using waveguide tapers, a flat-top passband characteristic is obtained. Using Fourier transform spectroscopy employing a low coherence interferometer, the power-distribution coefficients and the phase error distribution in such components is evaluated. Because of the coherence length of the used light source being smaller than the optical path length difference in the PHASAR, it is possible to resolve individual waveguides of the array. Thus, the transfer functions of the individual optical paths are accessible to the measurement, enabling the full simulation of the PHASAR transmission spectrum. It is demonstrated that the measured phase error distribution in tapered PHASAR devices consists of contributions from both tapered waveguides and arrayed waveguide grating regions. An evaluation method suitable for investigating both contributions separately is developed. Phase shift introduced by the waveguide tapers is in good agreement with simulation calculations based on the Beam Propagation Method. An analytic transmission calculation based on measured phase and power-distribution coefficients enables a full simulation of PHASARs including insertion loss, bandwidth and crosstalk performance. Excellent agreement with transmission measurements is performed.

Waveguide sidewall roughness measurement on full wafers by SEM-based stereoscopy

We present a technique aiming at sidewall roughness measurement on integrated optical silica waveguides using a scanning electron microscope. The technique uses the principles of stereoscopy to retrieve sidewall topography. Practical implementation details and first results are provided.

Waveguide sidewall roughness estimation via shape-from-shading surface reconstruction of SEM pictures

A shape-from-shading algorithm is applied to topography images of silica waveguide sidewalls coming from a Scanning Electron Microscope. The approach is found appropriate to restitute the sidewall profile. The reconstructed relief obtained is then height calibrated via Line Edge Roughness measurement. The technique enables thereafter roughness measurement at arbitrary positions on the sidewall, with the advantage of providing non-destructive testing on full wafer.

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>>