Phase sensitive parametric fiber amplifier for the 2 µm wavelength range.

A widely tunable phase sensitive parametric fiber amplifier employing a three fiber stages configuration and operating in the 2 µm wavelength region is demonstrated. Phase sensitive gain levels of 30 dB and a gain variation of 20 dB were measured for a pulsed pump by determining the conversion efficiency near 2 µm when a signal at 1.281 µm was applied. The amplifier operates in the wavelength range of 1952 nm to 2098 nm, with its bandwidth being around 0.1 nm. The bandwidth can be controlled by the fiber lengths and their dispersion properties.

Nonlinear pulse propagation in a quantum dot laser.

We investigate the nonlinear propagation of an ultra-short, 150 fs, optical pulse along the waveguide of a quantum dot (QD) laser operating above threshold. We demonstrate that among the various nonlinear processes experienced by the propagating pulse, four-wave mixing (FWM) between the pulse and the two oscillating counter-propagating cw fields of the laser is the dominant one. FWM has two important consequences. One is the creation of a spectral hole located in the vicinity of the cw oscillating frequency. The width of the spectral hole is determined by an effective carrier and gain relaxation time. The second is a modification of the shape of the trailing edge of the pulse. The wave mixing involves first and second order processes which result in a complicated interaction among several fields inside the cavity, some of which are cw while the others are time varying, all propagating in both directions. The nonlinear pulse propagation is analyzed using two complementary theoretical approaches. One is a semi-analytical model which considers only the wave mixing interaction between six field components, three of which propagate in each direction (two cw fields and four time-varying signals). This model predicts the deformation of the tail of the output signal by a secondary idler wave, produced in a cascaded FWM process, which co-propagates with the original injected pulse. The second approach is a finite-difference time-domain simulation, which considers also additional nonlinear effects, such as gain saturation and self-phase modulation. The theoretical results are confirmed by a series of experiments in which the time dependent amplitude and phase of the pulse after propagation are measured using the cross-frequency-resolved optical gating technique.

Spontaneous emission study on 1.3 µm InAs/InGaAs/GaAs quantum dot lasers.

True spontaneous emission (TSE) measurements on InAs/InGaAs/GaAs quantum dot (QD) lasers have been performed as a function of injection current and cavity length. For each laser, TSE from both the ground state (GS) transition and the excited state (ES) transition has been analyzed. It is found that Auger processes are the major nonradiative recombination (NR) processes for both the GS and ES transitions. In particular, for the first time, the existence of Auger like NR features in ES transitions has been experimentally demonstrated. In addition, obvious competition for carriers between the ES transition and the GS transition has been observed in TSE analysis. Furthermore, the QD laser's cavity length has a strong effect on the NR process in GS transitions, due to GS gain saturation. Therefore, when analyzing the NR processes in operating QD lasers, gain saturation due to cavity length limits should be properly considered.

Cell cultures in microsystems: biocompatibility aspects.

Bio-Micro-Electro-Mechanical Systems (BioMEMS) are a new tool in life sciences, supporting cell biology research by providing reproducible and miniaturized experimental platforms. In order to cultivate cells in such systems, appropriate microenvironmental conditions are required. Due to the multitude and variety of microbioreactors and cultivated cell types available, standardized cell handling methods and comprehensive biocompatibility data are sparse. The bioreactor developed at Ilmenau University of Technology features BioMEMS consisting of silicon, glass, and polymers, supplied by peripheral components. To verify the system's suitability for cell cultivation, it was necessary to prove whether materials and surfaces are biocompatible. Custom-tailored biocompatibility test procedures along with adequate cell seeding and handling methods had to be developed. According to this, proper positive and negative control samples had to be identified. The cultivation procedures were carried out using osteoblast-like murine fibroblasts (MC3T3-E1) and primary human osteoblasts (hOB). We could provide evidence that cultivation of these cells in our BioMEMS is feasible. In this context the relevant materials and the system's structure can be regarded as to be biocompatible. We could show that cell seeding and handling methods possess a strong impact on growth, development, and cellular activity of cell cultures in BioMEMS. Statistical biocompatibility data for the materials used is given.