Christian Remmersmann

Phase noise optimization in temporal phase-shifting digital holography with partial coherence light sources and its application in quantitative cell imaging

In temporal phase-shifting-based digital holographic microscopy, high-resolution phase contrast imaging requires optimized conditions for hologram recording and phase retrieval. To optimize the phase resolution, for the example of a variable three-step algorithm, a theoretical analysis on statistical errors, digitalization errors, uncorrelated errors, and errors due to a misaligned temporal phase shift is carried out. In a second step the theoretically predicted results are compared to the measured phase noise obtained from comparative experimental investigations with several coherent and partially coherent light sources. Finally, the applicability for noise reduction is demonstrated by quantitative phase contrast imaging of pancreas tumor cells.

Application of 3D tracking, LED illumination and multi-wavelength techniques for quantitative cell analysis in digital holographic microscopy

Digital Holographic Microscopy (DHM) allows quantitative multi-focus phase contrast imaging that has been found suitable for technical inspection and quantitative live cell imaging. The combination of DHM with fast and robust autofocus algorithms and a calibrated imaging system enables the determination of axial sample displacements. The evaluation of quantitative DHM phase contrast images permits also an effective detection of lateral object movements. Thus, data for 3D tracking is provided. Partially coherent light sources and multi-wavelength techniques open up prospects for an increased phase resolution in DHM by reduction of parasitic interference effects due to multiple reflections within the measurement setup. For this purpose, the utilization of light emitting diodes (LEDs) as well as the generation of short coherence properties by tunable laser light has been investigated for application in DHM. Results from investigations on sedimenting erythrocytes in suspension demonstrate that DHM enables (automated) quantitative dynamic 3D tracking of multiple cells without mechanical focus adjustment. Furthermore, it is shown that LEDs and multi-wavelength techniques enhance the axial resolution in inspection of reflective surfaces and quantitative digital holographic cell imaging.

Optical Filter-Based Mitigation of Group Delay Ripple- and PMD-Related Penalties for High-Capacity Metro Networks

In high-capacity metro networks, fiber Bragg gratings (FBGs) offer a potentially cost-effective solution for compensation of chromatic dispersion (CD). However, FBGs suffer from stochastic variations of their group delay, the so-called group delay ripple (GDR). We propose a novel statistical model to describe the effects of stochastic variations of GDR. The statistical properties of our model are verified by comparison to measurement data and Monte Carlo simulations as well as Multicanonical Monte Carlo (MMC) simulations. Results indicate that without further measures to counteract the GDR distortions, very large penalties (>; 10 dB) for the optical signal-to-noise ratio (OSNR) occur frequently at a bitrate of 112 Gbit/s. Thus, we investigated the performance of short and cost-effective optical finite and infinite impulse response equalizer structures to mitigate the GDR distortions and to enhance the signal quality. With the use of optical equalizers (which can be realized as planar lightwave circuits) we were able to reduce the mean OSNR penalty due to the GDR to less than 0.1 dB. We also demonstrate that the same filter structures can efficiently be used to mitigate all-order PMD distortions as well.

Fast parallelized simulation of 112 Gb/s CP-QPSK transmission systems using stratified Monte-Carlo sampling

A novel parallelized implementation of the split-step Fourier method on graphics processing units was developed. The combination of Monte-Carlo simulations with single and double precision yields a speedup of up to 180 compared to CPUs.

Application of light emitting diodes in digital holographic microscopy

Digital holographic microscopy permits quantitative phase contrast imaging of reflective and (partially) transparent samples. The utilization of low coherent light sources opens up prospects for a reduced phase noise by avoiding multiple reflections in the experimental setup. Thus, light emitting diodes (LEDs) have been investigated for applicability as low cost light sources in digital holographic microscopy. The LEDs were characterized for the spectral properties and the resulting coherence length. Furthermore, dispersion effects and their influences on the interferogram formation have been analyzed. Since the interference fringe number of off-axis holograms is limited by the coherence length of the LEDs (few micrometers) in addition to spatial phase shifting digital holographic reconstruction techniques, temporal phase shifting procedures were applied. The characterization of the lateral and axial resolution has been performed for both temporal and spatial phase shifting techniques by investigations on technical specimen. Finally, the application on biological samples is demonstrated by investigations on pancreas tumor cells.

Optical Equalization of PMD-Induced Penalties in 112 Gbit/s Metro Networks

We investigate the performance of optical equalization of distortions induced by polarization mode dispersion (PMD) in 112 Gbit/s metro networks using FIR filters. The PMD-induced mean OSNR penalties are reduced to < 0.1 dB.