A phase coherent optical link through the turbulent atmosphere

Transcription

1 A phase coherent optical link through the turbulent atmosphere Mini-DOLL : Deep Space Optical Laser Link Presented by : Khelifa DJERROUD people involved : Acef Ouali (SYRTE) Clairon André(SYRTE) Lemonde Pierre (SYRTE) Man Nary Catherine (ARTEMIS/OCA) Samain Etienne (Géo-Azur/OCA) Wolf Peter (SYRTE) 1

2 Outline Context and interests of coherent laser links Mini-DOLL : project progress (3 steps) 1. First step: Mini-DOLL ground/ground link: Turbulence noise Experimental setup Latest results Applications of the satellite/ground coherent optical links Satellite Laser Ranging (SLR) Frequency comparison of distant clocks Ex : SAGAS project Perspectives 2

3 Context : Context and interests Distribution of optical clock signals : inter comparison of clocks, navigation of satellites, time dissemination, broadband communication, Other applications : space geodesy, space oceanography, Earth and solar system gravity, Fundamental physics : Future missions require optical links (SAGAS, ODYSSEY, LATOR, BEACON,...) Interest of a coherent laser link vs. pulsed link? Optical phase measurements potentially allows an improvement 4 orders of magnitude (pulse duration /optical period), implemented in the fiber links. Advantages: high accuracy, low sensitivity to intensity fluctuations, insensitive to parasitical light (cf. AM FM Radio) Disadvantages: sensitive to the atmospheric turbulence (transverse and temporal coherence), power requirements. 3

4 3 essential steps: Project progress 1.Mini-DOLL ground / ground with a stationary target (CCR : corner cube reflector): study of the turbulence effects for an horizontal propagation. 2.Achieving an experimental setup at SYRTE planned for the ground-satellite link (high power laser, freq. stabilization, Doppler shift ± 10 GHz...) 3.Mini-DOLL satellite /ground : Install setup at the OCA on MeOtelescopes, first tests on existing satellites equipped with a CCR (JASON 1 and 2, TerraSAR-X,...). Objectives: - Demonstrate the feasibility - Study the turbulence limitations - Study the potential limitations of laser power - Study the optimal size of the telescope (adaptive optics?) - Study the potential for data transmission by phase modulation

5 Mini-DOLL ground/ground link: Turbulence noise Turbulence noise (model) Laser noise f 0 f 1 Laser noise and turbulence noise for an horizontal path of 5 km (roundtrip time, T = 16,6 µs) f 0 = 0.05 Hz et f 1 = 1x10 4 Hz (correspond to L 0 = 100 m, l 0 = 3 mm, v = 5 m/s) 5

6 Mini-DOLL ground/ground link: Experimental setup Counter /4 VCO φ lock BW = 0.1 à 100 khz Ampli. -30 dbm, 200 MHz Pol. 700 mw Laser λ/2 λ/4 Ι 200 MHz AOM λ/2 to telescope 6

7 Mini-DOLL ground/ground link: Experimental setup M 3 M 4 Some characteristics of MeO Telescope: M 1 Øoftelescope1,5 m Grandissement : 50 Øat the entrance of the telescope: 76 mm Øat the exit of the telescope: 38 cm M 6 M 5 2 m M 7 Some characteristics of MeO Telescope: Telescope diameter : 1.5 m Beam Øat the entrance : 76 mm Beam Øat the exit : 380 mm CCR 5 m 2.5 km MeO (LLR) Telescope T = 16.6 µs target 7

8 Mini-DOLL ground/ground link: Last results (1) CCR on the Calern km) One cycle/ms 1 mm Data rate : 1 khz Total recorded points Fraction of deleted points min 8

9 Mini-DOLL ground/ground link: Last results (2) Atmosphere Mechanical vibration Amplitude to phase noise conversion? White Phase τ > 1/f 0 Noise floor σ x (1 ms) = 2 x s = 45 nm 9

10 Applications (1): Satellite Laser Ranging (SLR) and Frequency clocks comparison y d (t 4 ) y (clocks) Doppler Atmosphere y u (t 2 ) y r is sensitive to Doppler and troposphere, but less sensitive to clock noise y t is sensitive to clock frequency difference but less sensitive to Doppler and troposphere 10

11 Applications (2): Satellite Laser Ranging (SLR) and Frequency Clocks Comparison SLR: Short term (1 ms) noise 23 nm, but unknown offset (velocity measurement) On longer term limited by troposphere models ( 1 mm), but good potential for intersatellite links (formation flying). Frequency comparison estimation: set t 2 = t 3 cancellation of satellite Doppler Example: geostationary satellite (round trip time t 4 -t 1 = 250 ms). Calculate (y t =y(t) y(t+250 ms))/2 and look at its satistics: Estimated noise on space to ground clock comparison

12 Applications (3): SAGAS (Search for anomalous Gravitation using Atomic Sensors) SAGAS specs. on one way noise Accelerometer Turbulence Turbulence contribution should be OK! 12

13 (Very) Long-term perspectives Two-way comparison with noise compensation Optical Doppler Satellite Telemetry (Geodesy,...) Intercontinental comparison of frequencies (frequency metrology,...) => Geostationary satellite with laser on board Optical clocks embedded in satellite in the solar system => Fundamental Physics, Optical Communications ground / ground and ground / satellite (Collaboration with DLR?) Adaptive Optics at the OCA (collaboration with ONERA, DGA) 13

14 Thanks Albanesse Dominique (OCA) Bize Sébastien(SYRTE) Lours Michel (SYRTE) Santarelli Giorgio (SYRTE) Torre Jean Marrie(OCA) CNES and PPF-GRAVITE (Université Paris VI) for financing 14