A laser ranging method dedicated to path lengths equalization in diluted telescopes

International audienceWhen implementing a diluted telescope with large dimensions, one has to reach the equal path condition to the different segments of the primary mirror. In this work we suggest a way to implement a fast laser ranging method able to provide the error signal, using phase detection of the microwave modulation of a laser beam

Elimination of systematic errors in two-mode laser telemetry

4p.International audienceWe present a simple two-mode telemetry procedure which eliminates cyclic errors, to allow accurate absolute distance measurements. We show that phase drifts and cyclic errors are suppressed using a fast polarization switch that exchanges the roles of the reference and measurement paths. Preliminary measurements obtained using this novel design show a measurement stability better than 1 micron. Sources of residual noise and systematic errors are identified, and we expect that an improved but still simple version of the apparatus will allow accuracies in the nanometre range for absolute measurements of kilometre-scale distances

IMPLEMENTATION OF TWO TELEMETER DESIGNS FOR HIGH ACCURACY LASER RANGING OF KILOMETER SCALE DISTANCES IN SPACE

We present two different laser ranging systems under development, both based on the use of a high frequency modulated beam. The first range meter makes no use of interferometry: only the phase of the return beam is detected, in a way that rejects cyclic errors due to optical and electronic crosstalk. An Allan deviation slightly better than 10nm has been obtained with this simple system. The other range meter should provide better resolution, at the expense of a somewhat more sophisticated procedure, as it involves both time-of-flight and interferometry measurements

ABSOLUTE DISTANCE MEASUREMENTS USING TWO-MODE LASER TELEMETRY

A novel laser ranging method is described that uses a two-mode laser source, and detection of the phase of the return beam. The design eliminates the cyclic error usually associated with phase measurements and provides unambiguous, absolute distance determination. Measurements of an 8m path are obtained at a beat frequency of 13 GHz. We analyse the 1µm stability of the data obtained with this preliminary implementation, and expect that an improved version will allow accuracies well below 1 µm, for the kilometer-scale distances involved in satellite formation flight

Nanometer-scale absolute laser ranging: exploiting a two-mode interference signal for high accuracy distance measurements

International audienceAbsolute distance measurement with accuracy below the micron scale is important in astronomical optical interferometry. We present here an absolute laser rangefinder which relies on the detection of a two mode interference signal. We exploit the specific signature of the signal to extract both the interferometric and synthetic phase measurements, leading to distance measurement with nanometric accuracy. A resolution of 100 pm has been achieved in 75 μs with a relatively simple laser source. Amplitude to phase coupling in the detection chains turns out to be the largest source of systematic errors. A specific detection scheme is implemented, using optical demodulation of the microwave optical signal, to reduce amplitude-to-phase related systematic errors to below the required level

Long distance absolute laser ranging at the nanometer precision level: the two-mode interference measurement in the Iliade rangemeter

International audienceSome measurement schemes have been proposed and realized for the absolute measurement of long distances with an accuracy better than 10 nm. Published measurement setups use one or even two laser frequency combs. But significant engineering will be required to space qualify such a system. Simple methods, less technology-demanding would be valuable in the perspective of embedded instrumentation. We have designed and implemented a two-mode interference measurement scheme that allows sub-nanometer scale resolution in long distance measurement. The two-mode interference signal contains both - (sub-µm) interferometric information: the scale is the optical wavelength - (sub-15mm) modulation phase information: the scale is the "synthetic wavelength" corresponding to the frequency of the beat-note of the two modes. With the addition of a time-of-flight (ToF) measurement, the method allows to combine the three data (ToF, synthetic wavelength and interferometric) in a single, high-resolution, high accuracy length measurement, obtained every 50 ms. A measurement update rate of 100 µs is possible, but may rely on the availability of significantly higher data processing rates in the FPGA phase-meter. Implementation of this scheme has required that systematic errors on the phase and amplitude of the microwave optical signal be kept at a level well below 10^-4 cycle and 10^-4 respectively. One consequence of this requirement is the replacement of any parallel optics in the optical setup by wedged optics, so that multiple reflections do not interfere with the measurement and reference beams to better than 10^-8 in optical power. Systematic errors of electronic origin are more difficult to deal with because the amplitude-to-phase (AM-to-PM) couplings effects at 20 GHz appear to have, not only an instantaneous contribution, but also a transient contribution. This contribution, related to the heating of the photodiode junction under the dissipated Joule power, exceeds the limit of 10^-4 cycle by roughly two orders of magnitude. This thermal behaviour is not purely exponential with time and cannot be accurately corrected for. We will present the implementation of the setup, and the way we have suppressed, by 3 orders of magnitude, the AM-to-PM coupling effect by modifying the detection scheme of the 20 GHz beatnote. This last point is important, not only for the range meter presented, but also for in high accuracy and low phase noise microwave optical links

GENESIS: Co-location of Geodetic Techniques in Space

Improving and homogenizing time and space reference systems on Earth and, more directly, realizing the Terrestrial Reference Frame (TRF) with an accuracy of 1mm and a long-term stability of 0.1mm/year are relevant for many scientific and societal endeavors. The knowledge of the TRF is fundamental for Earth and navigation sciences. For instance, quantifying sea level change strongly depends on an accurate determination of the geocenter motion but also of the positions of continental and island reference stations, as well as the ground stations of tracking networks. Also, numerous applications in geophysics require absolute millimeter precision from the reference frame, as for example monitoring tectonic motion or crustal deformation for predicting natural hazards. The TRF accuracy to be achieved represents the consensus of various authorities which has enunciated geodesy requirements for Earth sciences. Today we are still far from these ambitious accuracy and stability goals for the realization of the TRF. However, a combination and co-location of all four space geodetic techniques on one satellite platform can significantly contribute to achieving these goals. This is the purpose of the GENESIS mission, proposed as a component of the FutureNAV program of the European Space Agency. The GENESIS platform will be a dynamic space geodetic observatory carrying all the geodetic instruments referenced to one another through carefully calibrated space ties. The co-location of the techniques in space will solve the inconsistencies and biases between the different geodetic techniques in order to reach the TRF accuracy and stability goals endorsed by the various international authorities and the scientific community. The purpose of this white paper is to review the state-of-the-art and explain the benefits of the GENESIS mission in Earth sciences, navigation sciences and metrology.Comment: 31 pages, 9 figures, submitted to Earth, Planets and Space (EPS

Développement de télémètres laser de haute exactitude et de haute résolution pour applications spatiales

Improving the angular resolution of telescopes implies an increase of their size. Spacecrafts in formation flying are more and more investigated for future space telescope projects. Operation of such systems requires absolute distance measurement between two spacecrafts with an accuracy of few tens of microns. The absolute distance measurement with high precision is also at the centre of fundamental physic experiments. My thesis work has consisted in the development of two rangefinders, T2M and Iliade which could be used for these projects. The difficulty is to combine a great measurement range with high sensitivity in a simple set-up for being eventually embedded instruments. Our goal is to measure a distance of one kilometre with an accuracy better than one micron. The difference between T2M and Iliade resides in their designs but also in their complexity and their resolution. The T2M rangefinder uses the phase difference of a beam modulated in amplitude and split in a measurement path and a reference path. The target resolution with this system is in the tens of nanometres. T2M is able to reach a high accuracy because the distance is obtained from frequency measurements. Cyclic errors linked to the use of phase comparison are suppressed using an optical switching system which exchanges the beams of the two paths with respect to the two detection chains. After having stabilized the frequency of the beatnote between the two laser, I have worked on the improvement of the resolution. I have also worked on the suppression of different errors which affect the accuracy of T2M. Objectives seem to be reached and the results are very encouraging for the future tests and developments. The Iliade rangefinder combines a time of flight measurement between optical pulses and a two-wavelength interferometric measurement. This sophisticated system compared to T2M, is expected to have a resolution below one nanometer. I have characterised the 20 GHz pulse source and shown that the 65 fs timing jitter is mainly limited by the phase noise of the initial two-mode beat-note. I have worked on a fibered Fabry Perot cavity for single-mode laser frequency pre-stabilization and demonstrated a scheme for obtaining a dispersive-shaped error signal without any modulation. I have studied a numerical method based on harmonic analysis in order to measure phase difference with an accuracy better than 10-5 radian. The Iliade rangefinder is presently under development.Si les performances des instruments d'exploration de l'Univers continuent de s'améliorer, c'est souvent au prix d'une augmentation de leurs dimensions. Pour le développement de nouveaux télescopes spatiaux, le vol en formation de satellites est une solution technique de plus en plus envisagée. La mesure absolue des distances entre satellites avec une exactitude de l'ordre de quelques dizaines de microns est alors une nécessité pour l'exploitation des données obtenues avec de tels systèmes. Elle est aussi au cœur d'expériences de physique fondamentale. Mon travail de thèse a porté sur le développement de deux télémètres, T2M et Iliade pouvant répondre à ces besoins. La difficulté dans le développement de ces deux systèmes est de concilier un grand intervalle de mesure de distances avec une grande sensibilité tout en gardant une certaine simplicité et ainsi permettre que ces instruments puissent être embarqués. La performance visée est une mesure de distance de l'ordre du kilomètre exacte à mieux d'un micron. La différence entre T2M et Iliade réside dans leurs conceptions mais aussi dans leurs complexités et les performances visées en termes de résolution. Le télémètre T2M exploite la différence de phase d'une onde modulée en amplitude séparée entre une voie de mesure et une voie de référence. La résolution visée avec ce système est la dizaine de nanomètres. Ce système est capable d'atteindre une grande exactitude du fait que la mesure de distance est déduite d'une mesure de fréquence. Les problèmes d'erreurs cycliques inhérentes à l'utilisation de ce type de techniques sont éliminés par un système d'aiguillage optique permettant d'échanger les faisceaux propres aux deux voies de télémétrie en regard des deux voies de détection. Après la stabilisation du battement de fréquences des deux lasers, mon travail a porté sur l'amélioration de la résolution et sur l'élimination des diverses sources d'erreurs affectant l'exactitude. Les objectifs fixés semblent être atteints et les résultats obtenus sont très encourageants pour les futurs tests et développements à réaliser. Le télémètre Iliade combine une mesure de temps de vol d'impulsions laser et une mesure interférométrique à deux longueurs d'onde. Au prix d'une sophistication un peu plus importante que T2M, la résolution visée est inférieure au nanomètre. La caractérisation de la source d'impulsions d'Iliade présentant un taux de répétition de 20 GHz, a permis de montrer que la gigue temporelle de 65 fs à sa sortie est principalement due au bruit de phase du battement initial de deux lasers monomodes. J'ai travaillé sur une cavité Fabry Perot fibrée pour pré-stabiliser le rayonnement d'un laser monomode. J'ai démontré une technique permettant d'obtenir un signal d'erreur de type dispersif, sans recourir à une modulation. Enfin j'ai étudié une méthode numérique basée sur l'analyse harmonique permettant d'assurer une mesure de différence de phase avec une exactitude de 10-5 radian. Le télémètre Iliade est actuellement en cours de développement

Développement de télémètres laser de haute exactitude et de haute résolution pour applications spatiales

Si les performances des instruments d exploration de l Univers continuent de s améliorer, c est souvent au prix d une augmentation de leurs dimensions. Pour le développement de nouveaux télescopes spatiaux, le vol en formation de satellites avec une exactitude de l ordre de quelques dizaines de microns est alors une nécessité pour l exploitation des données obtenues avec de tels systèmes. Elle est aussi au cœur d expériences de physique fondamentale. Mon travail de thèse a porté sur le développement de deux télémètres, T2M et Iliade pouvant répondre à ces besoins. La difficulté dans le développement de ces deux systèmes est de concilier un grand intervalle de mesure de distances avec une grande sensibilité tout en gardant une certaine simplicité et ainsi permettre que ces instruments puissent être embarqués. La performance visée est une mesure de distance de l ordre du kilomètre exacte à mieux d un micron. La différence entre T2M et Iliade réside dans leurs conceptions mais aussi dans leurs complexités et les performances visées en termes de résolution. Le télémètre T2M exploite la différence de phase d une onde modulée en amplitude séparée entre une voie de mesure et une voie de référence. La résolution visée avec ce système est la dizaine de nanomètres. Ce système est capable d atteindre une grande exactitude du fait que la mesure de distance est déduite d une mesure de fréquence. Les problèmes d erreurs cycliques inhérentes à l utilisation de ce type de techniques sont éliminés par un système d aiguillage optique permettant d échanger les faisceaux propres aux deux voies de télémétrie en regard des deux voies de détection. Après la stabilisation du battement de fréquences des deux lasers, mon travail a porté sur l amélioration de la résolution et sur l élimination des diverses sources d erreurs affectant l exactitude. Les objectifs fixés semblent être atteints et les résultats obtenus sont très encourageants pour les futurs tests et développement à réaliser. Le télémètre Iliade combine une mesure de temps de vol d impulsions laser et une mesure interférométrique à deux longueurs d onde. Au prix d une sophistication un peu plus importante que T2M, la résolution visée est inférieure au nanomètre. La caractérisation de la source d impulsions d Iliade présentant un taux de répétition de 20 GHz, a permis de montrer que la gigue temporelle de 65 fs à sa sortie est principalement due au bruit de phase du battement initial de deux lasers monomodes. J ai travaillé sur une cavité Fabry Perot fibrée pour pré-stabiliser le rayonnement d un laser monomode. J ai démontré une technique permettent d obtenir un signal d erreur de type dispersif, sans recourir à une modulation. Enfin, j ai étudie une méthode numérique basée sur l analyse harmonique permettant d assurer une mesure de différence de phase avec une exactitude de 10 [puissance]-5 radian, Le télémètre Iliade est actuellement en cours de développement.Improving the angular resolutions of telescopes implies an increase of their size. Spacecrafts in formation flying are more and more investigated for future space telescope projects. Operation of such systems requires absolute distance measurement between two spacecrafts with an accuracy of few tens of microns. The absolute distance measurement with high precision is also at the centre of fundamental physic experiments. My thesis work has consisted in the development of two rangefinders, T2M and Iliade which could be used for these projects. The difficulty is to combine a great measurement range with high sensitivity in a simple set-up for being eventually embedded instruments. Our goal is to measure a distance of one kilometre with an accuracy better than one micron. The difference between T2M and Iliade resides in their designs but also in their complexity and their resolution. The T2M rangefinder uses the phase difference of a beam modulated in amplitude and split in a measurement path and a reference path. The target resolution with this system is in, the tens frequency measurements. Cyclic errors linked to the use of phase comparison are suppressed using an optical switching system which exchanges the beams of the two paths with respect to the two detection chains. After having stabilized the frequency of the beat-note between the two laser, I have worked on the improvement of the resolution. I have also worked on the suppression of different errors which affect the accuracy of T2M. Objectives seem to be reached and the results are very encouraging for the future tests and developments. The Iliade rangefinder combines a time of flight measurement between optical pulses and a two-wavelength interferometric measurement. This sophisticated system compared to T2M, is expected to have a resolution below one nanometer. I have characterised the 20 GHz pulse source and shown that the 65 fs timing jitter is mainly limited by the phase noise of the initial two-mode beat-note. I have worked on a fibered Fabry Perot cavity for single-mode laser frequency pre-stabilization and demonstrated a scheme for obtaining a dispersive-shaped error signal without any modulation. I have studied a numerical method based on harmonic analysis in order to measure phase difference with an accuracy better than 10 [puissance]-5 radian. The Iliade rangefinder is presently under development.NICE-BU Sciences (060882101) / SudocSudocFranceF