298 Time and Distance Metrology base on free-space laser Communication link

Job title:

298 Time and Distance Metrology base on free-space laser Communication link

Company:

Centre National d’Etudes Spatiales

Job description

25-298 Time and Distance Metrology base on free-space laser Communication linkPostuler25-298 Time and Distance Metrology base on free-space laser Communication link

• Doctorat, 36 mois
• Temps plein
• Indifférent
• Maitrise, IEP, IUP, Bac+4
• Telecommunications

PostulerMissionThe proposed thesis is in the field of free-Space Optical (FSO) telecom links, particularly dedicated to ground-space links. It consists in development and demonstration of a metrology system that carries out time & frequency (or distance) measurements based on a high-debit FSO telecom link. The thesis objectives are to identify the elementary bricks needed for the implementation of this new metrology technique and to demonstrate metrology performance on a real 10Gbps FSO telecom link at 1550nm. The expected performances are a few tens of femtosecond in time measurement stability (or a few tens of microns in distance) over an integration time of a few seconds. This performance allows us to achieve frequency transfer with an accuracy ~10^(-17) at 1000 seconds, time transfer accuracy better than 100 ps, and sub-millimeter distance accuracy with tens microns resolution.Rapid improvement on optical power of modulated laser source allows us to integrate laser communication terminal (LCT) in a small satellite for bidirectional space-ground high data-rate transmission. Several satellites for 10 Gbps downlink LaserComm demonstrations are planned to be launched in 2020 – 2021: OSIRISv3 developed by Germany and HICALI developed by Japan. The Grasse station, part of the ILRS network (ID7845) with forty stations, participates to various laser applications including Satellite Laser Ranging, Lunar Laser Ranging [Chabe 2019], Time Transfer by Laser Link (T2L2) [Samain 2018], high-resolution imagery, and debris detection. Since 2014, the France Space Agency (CNES) has identified LaserComm as key technologies for future high data rate transmissions. In addition, in collaboration with Geoazur, CNES is investigating the use of optics both for high data rate between satellites and ground and for future telecommunications applications (Feeder link relay network). Several campaigns have been performed successfully and planned since 2015 between Grasse station and LaserComm terminal at low Earth orbit, SOTA onboard SOCRATES, OPALS integrated on ISS, DLR’s OSIRIS mission [Samain 2015], [Phung 2019 ILRS, PhungIcso2021, Giggen2022]. In the context of a first funding from CNES and Labex First-TF in 2017, we have been able to perform the first experiment between Grasse station and a ground target to evaluate the possibility to use LaserComm for metrology. We have also demonstrated that a tens-femtoseconds level on timing detection can be reached from a simple OOK LaserComm configuration [Phung 2020 – submitted]. We directly exploit the phase of high data-rate modulated signal at several GHz by using coherent heterodyne detection with a high-speed and high-resolution phasemeter. The first experiment result shows a propagation delay uncertainty of 80 fs (25 µm in distance) at 5 ms and better than 350 fs from 5 ms to 5 seconds.During a first thesis on the subject, Geoazur laboratory and Sigmaworks have developed a low phase noise telecom signal generator with a stability of about 50 fs at 27 µs. This stability is more than 10 times better than telecom based commercial system (BER tester type). Then, a calibration process has been realized in order to keep this stability up to 10000 s. Current investigations are focused on errors source identification. Experimental results show the importance of the detection, and particularly the dependency of time walk on injection position on APD detectors. The thesis has identified some mitigation strategies of this effect and they are currently tested.Another perspective application of high-resolution timing measurement (80 fs ~ 25 µm in distance) is to enable sub-millimetric accuracy on free-space long distance measurement. Note that, SLR actual performance is millimetric precision and centimetric accuracy limited by laser pulse width (several tens of picoseconds), detector performance, SLR repetition rate and accurate models for removing systematic errors caused by Earth’s atmosphere [Luceri 2019], reaching mm accuracy still poses some challenges, particularly for long horizontal distance. Multi-wave length and tens fs timing performance features of LaserComm system may be attractive for SLR community in order to achieve sub-millimetric accuracy level on ground-satellite distance measurement by two-colors ranging technique [Wijaya 2011].The new objectives of this thesis proposal are to implement an absolute distance measurement using a pseudo-random telecom signal (time of flight measurement) and to combine this measurement with the high resolution phase measurement already available. To this purpose the telecom signal generator is going to be upgraded in collaboration with Sigmaworks. The PhD student will have to test this new system in the laboratory and in a free space link using a remote target located at 2,5km from our Optical Ground Station. We expect to compare the performances of this system with high accuracy ranging methods used for Satellite Laser Ranging.For more Information about the topics and the co-financial partner (found by the lab !);contact Directeur de thèse –Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online before March 14th, 2025 Midnight Paris time !

Expected salary

Location

Valbonne, Alpes-Maritimes

Job date

Wed, 05 Feb 2025 06:53:53 GMT

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