Eric Suran

Image reconstruction in segmented femtosecond laser-written waveguide arrays

We present the first experimental realization of image reconstruction in finite femtosecond laser-written waveguide arrays with segmentation. The results show that arbitrary field distributions can be imaged in one-dimensional as well as in two-dimensional geometries.

Coherent femtosecond pulse shaping for the optimization of a non-linear micro-endoscope

A flexible multicore fiber bundle is fed by temporally and spectrally shaped femtosecond pulses allowing for the pre-compensation of both chromatic dispersion and non-linear effects encountered in the bundle. We demonstrate that the pulse duration at the fiber bundle output can be significantly reduced in comparison with linear pre-compensation only. The scheme for femtosecond pulse fiber delivery is applied to the optimization of two-photon fluorescence (TPF) imaging. Experiments and calculations show a five-fold improvement of the TPF signal produced at the end of the fiber bundle in comparison with linear pre-compensation. This is applied to the recording, in real time (12 image/s), of TPF laser-scanning images of human colon cells stained with a fluorescent marker. Further optimizations are discussed.

Coherent combining of 49 laser beams from a multiple core optical fiber by a spatial light modulator

We report co-phasing of 49 beams from a multicore fiber based on a spatial light modulator using a simple feedback loop control. A specific fiber of 7x7 Germanium doped cores was fabricated. The power carried by the far field main lobe of the phased array, in the continuous wave regime, amounts to 96% of its theoretical value. Femtoseconde pulses were also phase-locked with the same device configuration.

Compact direct space-to-time pulse shaping with a phase-only spatial light modulator

A very compact and innovative pulse shaper is proposed and demonstrated. The standard architecture for pulse shaping that is composed of diffraction gratings associated with an amplitude-phase spatial light modulator (SLM) is replaced by a single phase-only SLM. It acts as a pulse stretcher and as an amplitude and phase modulator at the same time. Preliminary experiments demonstrate the accurate control of amplitude and phase of shaped pulses.

Optical limiting and spectral stabilization in segmented photonic lattices.

We demonstrate photonic lattices with segmentation-based linear self imaging as integrated optical limiters. The diffractive propagation between input and output port offers the additional benefit of substantially decreased nonlinear spectral distortions.

Polarization maintaining square lattice multicore fiber

Optical fibers are interesting tools for early diagnostic of various diseases through micro-endoscopy. For this purpose laser scanning imaging with a multicore image guide can be used [1-3]. Easy reconstruction of the image and interfacing with semiconductor detection would however require the cores to be arranged in a square lattice while maintaining the polarization state of the input light.

Self imaging in segmented waveguide arrays

Self-imaging in integrated optical devices is interesting for many applications including image transmission, optical collimation and even reshaping of ultrashort laser pulses. However, in general this relies on boundary-free light propagation, since interaction with boundaries results in a considerable distortion of the self-imaging effect. This problem can be overcome in waveguide arrays by segmentation of particular lattice sites, yielding phase shifts which result in image reconstruction in one- as well as two-dimensional configurations. Here, we demonstrate the first experimental realization of this concept. For the fabrication of the segmented waveguide arrays we used the femtosecond laser direct-writing technique. The total length of the arrays is 50mm with a waveguide spacing of 16 μm and 20μm in the one- and two-dimensional case, respectively. The length of the segmented area was 2.6mm, while the segmentation period was chosen to be 16 μm. This results in a complete inversion of the global phase of the travelling field inside the array, so that the evolution dynamics are reversed and the input field is imaged onto the sample output facet. Accordingly, segmented integrated optical devices provide a new and attractive opportunity for image transmission in finite systems.

Endoscopic Polarization Imaging of Biological Tissues

For the first time polarization images using an endoscopic technique are reported. Images based on the degree of polarization measurement allow to discriminate sound and degraded regions in a type I collagen sample.