Laurent Delage

Experimental investigation of the dynamics of a stabilized nonlinear fiber ring resonator

We investigate theoretically and experimentally the nonlinear dynamics of a synchronously pumped all-fiber passive ring cavity. Our study is based on the use of a specially designed stabilization system that allows for interferometric control of the cavity length. With this system we can achieve stable operation and we are able to perform systematic and reproducible measurements for the characterization of the fundamental nonlinear behaviors of the cavity such as optical bistability, period doubling instabilities, and dissipative modulational instabilities. Through the analysis of the output pulse spectra we show that modulational instability plays a crucial role in the dynamics of the cavity (in particular, in the period-doubling route to chaos) even with normal group-velocity dispersion. A theoretical study of modulational instability in the cavity is presented and is successfully compared with experimental results.

Laboratory imaging stellar interferometer with fiber links

We report on the implementation of an end-to-end imaging demonstrator to validate the concept of optical fiber use in high-resolution aperture synthesis in astronomy. As the coherent transport of light has been conclusively investigated, this study is focused primarily on the accuracy and reliability of the experimental data. In the framework of the European Space Agency project Optical Aperture Synthesis Technologies (OAST), the telescope arrays complexity is minimized such that a realistic concept for a future space mission can be proposed. The reconstructed images are obtained by use of a particular self-calibration procedure that was designed to process the visibility contrast and the related weak phase information (one phase closure for each visibility triplet).

Bistable switching induced by modulational instability in a normally dispersive all-fibre ring cavity

We study theoretically and experimentally the switching dynamics of an all-fibre cavity with normal dispersion. This system exhibits modulational instability on the lower branch of its bistable response. We show that, due to the interaction with the homogeneous mode generated by the neighbouring limit point bifurcation, the modulational instability induces premature up-switching and, in this way, truncates the bistable cycle. This instability is identified experimentally through the observation of growing spectral sidebands just before up-switching. The results are successfully compared with numerical simulations.

Kilometric optical fiber interferometer

We report on a preliminary experimental study of an interferometer built with two 500 meters long arms made of polarization maintaining optical fibers. The control of the field polarization state along the single-mode fiber arms enables to measure fringe contrast up to 93% with a laser source emitting a 1290nm carrier wavelength. Tests achieved with broadband spectrum exhibit dispersion differential effect resulting from fiber inhomogeneities. Partial compensation of this effect is achieved introducing additional fiber pieces on one arm.

Analysis and control of polarization effects on phase closure and image acquisition in a fibre-linked three-telescope stellar interferometer

This paper reports the imaging laboratory tests on a fibre-linked telescope array including three interferometric arms. We demonstrate the necessity of using polarization-maintaining fibres to obtain a steady calibration of the phase closure term. The experimental data consist of the complex visibility function acquisitions corresponding to the object Fourier spectrum. The redundant spacing sampling procedure has been selected in order to be robust, leading to full control of the experimental parameters. This work is experimentally illustrated by a one-dimensional object image restoration with 5% accuracy on the intensity.

First results from a laboratory hypertelescope using single-mode fibers

Context. In the future, giant optical interferometric arrays will be developed with kilometric baselines and a large number of telescopes. Such arrays could have direct imaging capabilities if optimized beam combiners are used. Aims. This paper aims at studying the performance of an interferometric beam combiner using single mode fibers and in the frame of a hypertelescope. Methods. A laboratory testbed called SIRIUS was developed. We describe the general concept, the technical specifications and the results obtained. These results are analyzed with the help of a numerical simulator. Results. Direct images were obtained at the densified focus of SIRIUS. We show that the fibers greatly ease the pupil rearrangement. They also greatly improve the quality and the stability of the direct image. The computed images allow us to reproduce the effects of differential photometry and the influence of optical path difference variations. Optical path difference errors less than

An all guided three-arm interferometer for stellar interferometry

\lambda/10

First experimental demonstration of temporal hypertelescope operation with a laboratory prototype

and differential photometries less than 60% are required to keep the quality of the direct image. Conclusions. These results demonstrate the great potential of direct imaging interferometric beam combiners for future optical large arrays. The excellent comparison between experience and simulation clearly shows the simplicity of the fibered pupil densifier. It also gives us a great confidence in the extrapolation of these results and specifications for future arrays with a very large number of apertures.

Test of photonic crystal fiber in broadband interferometry

Following the first demonstration of an all guided two-beam stellar interferometer designed for space missions, we report an experiment recombining the beams coming from three telescopes using only guided optics components. This additional aperture could give us the possibility to achieve an image reconstruction using the phase-closure technique. We focus this calibration experiment on the interference fringe contrast measurements and the evolution of the phase-closure term versus the differential dispersion effects induced by the stretching of fibre delay lines.

Imaging laboratory tests on a fiber linked telescope array

In this paper, we report the first experimental demonstration of a temporal hypertelescope (THT). Our breadboard including eight telescopes is first tested in a manual cophasing configuration on a one-dimensional object. The point-spread function (PSF) is measured and exhibits dynamics in the range of 300. A quantitative analysis of the potential biases demonstrates that this limitation is related to the residual-phase fluctuation on each interferometric arm. Secondly, an unbalanced binary star is imaged, demonstrating the imaging capability of THTs. In addition, a two-dimensional PSF is recorded, even if the telescope array is not optimized for this purpose.