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International audience; The Grasse Satellite Laser Ranging (SLR) station (ID7845), part of the International Laser Ranging Service (ILRS) network, participates to various laser applications including SLR, Lunar Laser Ranging (LLR), Time Transfer by Laser Link (T2L2), high-resolution imagery, and debris detection. Since 2014, in collaboration with the France Space Agency (CNES), the Grasse station has been upgrading in order to be able to take part in laser communication (lasercom) experiments. The main challenges of these experiments are the implementation of a complete laser communication chain from space to ground and the characterization of the turbulent atmosphere during the optical data transfer. Several campaigns have been successfully performed and planned since 2015 between Grasse station and lasercom terminal at low Earth orbit, SOTA onboard SOCRATES [5], OPALS integrated on ISS [6], and recently DLR's OSIRIS mission [7]. To prepare for possible higher data-rate lasercom campaigns in the near future (OSIRISv1 at 40 Mbps, OSIRISv2 and Optelµ at 1 Gbps, OSIRISv3 at 10 Gbps) Grasse SLR station is upgrading on lasercom optical bench, with a fine auto-tracking system and a high sensitivity telecom detector. In the proceeding, we will describe the architecture of our optical bench for high data-rate lasercom link and some primary results of the lasercom link between OSIRISv1 [14] (onboard FlyingLaptop satellite) and the station.

International audience; Based on a fully passive space segment, the lunar laser ranging experiment is the last of the Apollo Lunar Surface Experiments Package to operate. Observations from the Grasse lunar laser ranging station have been made on a daily basis since the first echoes obtained in 1981. In this paper, first, we review the principle and the technical aspects of lunar laser ranging. We then give a brief summary of the progress made at the Grasse laser ranging facility (Observatoire de la Côte d'Azur, Calern Plateau on the French Riviera) since the first echoes. The current performance, driven by the use of an infrared wavelength laser, is presented in the last section for the year 2018.

ICSO 2016 conference, paper 163; International audience; Distributed feedback (DFB) diode lasers are convenient, small footprint and robust single mode laser sources. Control of the diode forward current allows for the control the frequency of the emitted laser beam. Locking the laser frequency to some optical frequency discriminator, such as an optical interferometer or an atomic or molecular line, can easily be achieved. Such a lock, with a moderate (< kHz) bandwidth can prevent long term drifts of the laser optical frequency. On the other hand, reaching high lock bandwidth (> MHz) can lead to laser line narrowing. DFB lasers have an emission linewidth in the MHz to several MHz range, which may be too large for some applications, such as cold atom physics, optical clocks, laser ranging, lidar or gas sensing...We have tried to achieve a high bandwidth in the lock of a DFB diode laser with a feedback loop using both the laser diode forward current and an optoelectronic external modulator. A lock bandwidth in the MHz range has been obtained, and the optical spectrum shows narrowing. But a significant fraction (15-20%) of the optical power remains broadband. By contrast, much more efficient and convenient operation has been found when the external electro-optical modulator is not in a feed-back loop but in a feed-forward configuration. The optical spectrum shows a half width at half maximum of 3 to 4 kHz, with about 1% of residual broadband optical power. The system allows implementation at any wavelength, if the frequency discriminator is obtained from a Michelson interferometer with gold-coated mirrors.

International audience; For satellite to ground laser links, atmospheric turbulence is a major cause of impairments. The induced phase perturbations along the propagation path cause beam scintillation in the receiver plane and they can also severely compromise the coupling of the flux into a receiver of limited size. To address these impairments, dedicated mitigation strategies must be developed. This requires accurate understanding of the perturbation origin. Beam propagation models have demonstrated their ability to reproduce statistical characteristics of optical perturbations on a satellite to ground laser link for elevations as low as 20°. For smaller elevations, measurements performed on stars illustrated the limits of analytical approaches and the interest for end-to-end models. We report here the first propagation channel measurements performed on a LEO microsatellite with a Shack-Hartmann wavefront sensor (WFS). The laser beam at 976 nm provided by SOTA optical terminal have been analyzed with a Shack- Hartmann wavefront sensor located at Coudé focus of the French ground station (1,55 m MéO telescope) in July 2015. Wavefront characteristics and scintillation patterns recorded with the WFS are analyzed and compared to atmospheric turbulence perturbations model fed with in situ measurements of atmospheric parameters retrieved from GDIMM.; La turbulence atmosphérique est la principale cause de dégradation des liens laser sol satellite. Les perturbations de phase induites le long du cana de propagation conduisent à de la scintillation dans le plan du récepteur et peuvent sévèrement compromettre le couplage du flux dans un récepteur de petite dimension. Pour résoudre ces problèmes, différentes stratégies dédiées doivent être développées. Cela nécessite une compréhension précise de l'origine des perturbations. Les modèles de propagation de faisceau ont démontré leur capacité à reproduire les caractéristiques statistiques des perturbations optiques affectant un lien laser satellite sol pour des élévations descendant à 20°. Pour des élévations plus petites des mesures réalisées sur étoiles ont démontrées toutefois les limites de ces approches analytiques et l'intérêt de modèles de type Monte-Carlo. Nous faisons état ici des premières mesures sur un canal de propagation établi avec un microsatellite LEO grâce à un analyseur de Shack Hartmann. Le faisceau laser à 976nm est fourni par le terminal optique SOTA et analysé grâce à un Shack Hartmann situé au foyer coudé d'une station française (télescope MéO de 1.55m) en juillet 2015. Les caractéristiques du front d'onde et les structures de scintillation enregistrées avec l'analyseur sont analysées et comparées aux modèles de perturbation de la turbulence atmosphérique alimentés par les mesures in situ des paramètres atmosphériques tels que fournis par un GDIMM.

International audience; For satellite to ground laser links, atmospheric turbulence is a major cause of impairments. The induced phase perturbations along the propagation path cause beam scintillation in the receiver plane and they can also severely compromise the coupling of the flux into a receiver of limited size. To address these impairments, dedicated mitigation strategies must be developed. This requires accurate understanding of the perturbation origin. Beam propagation models have demonstrated their ability to reproduce statistical characteristics of optical perturbations on a satellite to ground laser link for elevations as low as 20°. For smaller elevations, measurements performed on stars illustrated the limits of analytical approaches and the interest for end-to-end models. We report here the first propagation channel measurements performed on a LEO microsatellite with a Shack-Hartmann wavefront sensor (WFS). The laser beam at 976 nm provided by SOTA optical terminal have been analyzed with a Shack- Hartmann wavefront sensor located at Coudé focus of the French ground station (1,55 m MéO telescope) in July 2015. Wavefront characteristics and scintillation patterns recorded with the WFS are analyzed and compared to atmospheric turbulence perturbations model fed with in situ measurements of atmospheric parameters retrieved from GDIMM.; La turbulence atmosphérique est la principale cause de dégradation des liens laser sol satellite. Les perturbations de phase induites le long du cana de propagation conduisent à de la scintillation dans le plan du récepteur et peuvent sévèrement compromettre le couplage du flux dans un récepteur de petite dimension. Pour résoudre ces problèmes, différentes stratégies dédiées doivent être développées. Cela nécessite une compréhension précise de l'origine des perturbations. Les modèles de propagation de faisceau ont démontré leur capacité à reproduire les caractéristiques statistiques des perturbations optiques affectant un lien laser satellite sol pour des élévations descendant à 20°. Pour des élévations plus petites des mesures réalisées sur étoiles ont démontrées toutefois les limites de ces approches analytiques et l'intérêt de modèles de type Monte-Carlo. Nous faisons état ici des premières mesures sur un canal de propagation établi avec un microsatellite LEO grâce à un analyseur de Shack Hartmann. Le faisceau laser à 976nm est fourni par le terminal optique SOTA et analysé grâce à un Shack Hartmann situé au foyer coudé d'une station française (télescope MéO de 1.55m) en juillet 2015. Les caractéristiques du front d'onde et les structures de scintillation enregistrées avec l'analyseur sont analysées et comparées aux modèles de perturbation de la turbulence atmosphérique alimentés par les mesures in situ des paramètres atmosphériques tels que fournis par un GDIMM.

En attente de publication papier; Lien vers l'éditeur: http://ieeexplore.ieee.org/xpl/articleDetails.jsp? arnumber=6775285&sortType%3Dasc_p_Sequence% 26filter%3DAND%28p_IS_Number%3A4357488%29; International audience; High accuracy and low noise measurement of the phase of a microwave signal requires that spurious contributions are adequately dealt with. In this paper we investigate the power-to-phase coupling in two commercial high bandwidth P-I-N, near-IR photodetectors. We observe that a sudden change of the optical power induces a transient of the phase of the 20 GHz signal, at different time scales. The temperature rise of the photodetector junction is likely to be involved in this dynamical behaviour. The value of the bias voltage applied to the photodetector appears to control the size of the phase transients, as well as the optical power for which the slope of the amplitude-to-phase coupling cancels. The most efficient way to reduce amplitude to phase couplings consists in implementing optical demodulation, instead of electrical demodulation, of the microwave signal.

International audience; We demonstrate a laser ranging scheme that uses a high-frequency modulated beam to achieve subnanometer precision by the combined use of interferometric and time-of-flight measurements. We first describe how the absolute distance is extracted from a two-mode interference signal. In particular, we show that the signal, which presents both optical and synthetic wavelength scales, allows one to achieve nanometer-scale accuracy, despite the significant long-term phase drifts in the 20 GHz detection chains. We present results obtained with the telemeter implemented for a distance of about four meters, obtained by folding the laser beam path to the target.

International audience; We present a laser ranging system, under development, that uses a high frequency modulated beam to achieve sub-nm resolution by the combined use of interferometric and time-of-flight measurements. We first describe how the absolute distance is extracted from a two-mode interference signal. In particular we show that the signal, which presents both optical and synthetic wavelength scales, is essential to achieve nm-scale accuracy, despite the significant long-term phase drifts in the 20 GHz detection chains. Then we present results obtained with the telemeter implemented on an optical table, for a distance of about four meters, implemented by folding the laser beam path to the target. The challenge here is to achieve a phase and amplitude measurement of two 20 GHz signals with a resolution well below 10-4 cycle and 10-4, respectively, despite the fact that the signal undergoes very strong (×3 ) amplitude changes.