Time & Frequency Transfer

Transcription

1 Cold Atoms and Molecules & Applications in Metrology March 2015, Carthage, Tunisia Time & Frequency Transfer Noël Dimarcq SYRTE Systèmes de Référence Temps-Espace, Paris Thanks to Anne Amy-Klein (LPL) for material on fibre links CAMAM 2015, N. Dimarcq, «T/F transfer» 1

2 Effect of the T/F transfer Many applications require different locations for the master T/F clock and the end user clock (time scales, fundamental physics, GNSS, network synchronisation, ) Reference clock Remote clock Need of a T/F link by : - signals conducted in cables or fibres, - signals emitted in longwave(radio), microwave or optical (laser) domains, - sometimes a real clock transportation CAMAM 2015, N. Dimarcq, «T/F transfer» 2

3 Contents T/F links characteristics Satellite links Fibre links Conclusions CAMAM 2015, N. Dimarcq, «T/F transfer» 3

4 Contents T/F links characteristics Satellite links Fibre links Conclusions CAMAM 2015, N. Dimarcq, «T/F transfer» 4

5 Signal distribution / transmission Clock comparison Reference Clock Reference point A Initial signal characteristics : Initial noise : σ clock ϕ clock (t) T/F link T/F link includes signal distribution & propagation effects (cables, electronics, atmosphere, fibres, etc ) + relativistic effects Reference point B Distributed clock characteristics : Remote clock Distributed signal noise : σ clock σ link ( t) + ϕ ( t) CAMAM 2015, N. Dimarcq, «T/F transfer» 5 ϕ clock link

6 Syntonisation - Synchronisation Two kinds of transfer between remote clocks: Frequency transfer / frequency comparison = syntonization (frequency comparisons, tests of fundamental physics, etc ) requirement on the phase / time stability of the link Time transfer / Time comparison = synchronization (ranging, time scales, GNSS, etc ) requirement both on the phase / time stability and on the «time accuracy» ( = absolute delay calibration) CAMAM 2015, N. Dimarcq, «T/F transfer» 6

7 Transmitted signal Pulsed signals Time tagging of the pulse emission and reception Continuous signals Measurement of the phase / frequency difference between the received carrier and the local signal (carrier in microwave or optical domain) Need to remove the phase ambiguity Measurement of the phase difference between the received PRN (Pseudo Random Noise) code and the local code CAMAM 2015, N. Dimarcq, «T/F transfer» 7

8 One way / Two way techniques One-way techniques Require the knowledge of the propagation delay to determine the time difference between the two clocks Two-way techniques (round trip) = Two «One-way» measurements Allow to know and reject the propagation delay Require a good symmetry between the two paths of the round trip CAMAM 2015, N. Dimarcq, «T/F transfer» 8

9 T/F transfer techniques Talking clock 1933 Longwave time transmission (DCF77, France Inter,...) Time transfer : 1-50 ms One-way technique CAMAM 2015, N. Dimarcq, «T/F transfer» 9

10 Contents T/F links characteristics Satellite links Fibre links Conclusions CAMAM 2015, N. Dimarcq, «T/F transfer» 10

11 Clock comparisons with GNSS GNSS : Global Navigation Satellite Systems (GPS, GLONASS, GALILEO, Compass-Beidou) One way technique Access to GPS time Possibility to compare ground clocks in common views T clock A - T clock S T clock B - T clock S T clock A - T clock B CAMAM 2015, N. Dimarcq, «T/F transfer» 11

12 GNSS signals CAMAM 2015, N. Dimarcq, «T/F transfer» 12

13 T/F transfer with GNSS CAMAM 2015, N. Dimarcq, «T/F transfer» 13

14 Influence of ionosphere iono delay TEC 2 f carrier CAMAM 2015, N. Dimarcq, «T/F transfer» 14

15 Influence of ionosphere CAMAM 2015, N. Dimarcq, «T/F transfer» 15

16 Compensation of the ionosphere delay CAMAM 2015, N. Dimarcq, «T/F transfer» 16

17 Influence of troposphere Use of models to compensate for troposphere delay CAMAM 2015, N. Dimarcq, «T/F transfer» 17

18 Relativistic effects Relativistic frequency shift between two identical clocks located in different frames Time dilation effect ( = 2nd order Doppler effect) δυ = υ ( v v A B ) 2 2c 2 Gravitational «red-shift» (sensitivity to the difference between the gravitation potentiels) δυ = υ ( U On ground, a difference of altitude of 1 m frequency shift of δν/ν A U B ) c 2 G. M U = r Earth CAMAM 2015, N. Dimarcq, «T/F transfer» 18

19 Relativistic effects for GNSS Time dilation effect ( = 2nd order Doppler effect) δυ = υ ( v A v B ) 2 2c 2 Time error after one day: -7.2 µs Gravitational «red-shift» (sensitivity to the difference between the gravitation potentiels) δυ = υ ( U A U B ) c Time error after one day: µs 2 Global relativistic time error after one day: µs = 11.6 km CAMAM 2015, N. Dimarcq, «T/F transfer» 19

20 TWSTFT : Two Way Satellite Time & Frequency Transfer CAMAM 2015, N. Dimarcq, «T/F transfer» 20

21 T/F transfer techniques Talking clock 1933 Longwave time transmission (DCF77, France Inter,...) Satellites (GNSS, TWSTFT, ) Time transfer : 1-50 ms 1 ns Frequency transfer : few CAMAM 2015, N. Dimarcq, «T/F transfer» 21

22 Uncertainties : satellite transfer techniques vs clocks Optical clocks Incertitude relativ ve de fréquence SI «atomic» definition of the second day Cold atom fountains fs combs Sr Current uncertainty level (@ 1day) of current microwave links (GNSS, TWSTFT) Date CAMAM 2015, N. Dimarcq, «T/F transfer» 22

23 How to reduce further the uncertainty due to the T/F link? Time stability (for clocks syntonisation and frequency comparisons): More precise measurement of the phase difference: Higher carrier frequency Higher chip rate (= frequency) of the pseudo random modulation More precise correction of the fluctuations of the propagation delays Upgraded Two-way techniques Better atmosphere models Multi-frequency operation for the rejection of the ionosphere delay Time accuracy (for clocks synchronisation and time comparison) : Better calibration of propagation delays: : More precise atmosphere model More precise instrument and cable delays calibration CAMAM 2015, N. Dimarcq, «T/F transfer» 23

24 Space mission ACES Atomic Clock Ensemble in Space A cold Cs atom clock PHARAO + an Hydrogen maser on board ISS in 2017 CAMAM 2015, N. Dimarcq, «T/F transfer» 24

25 T/F microwave link for the ACES mission on-board ISS - 2 way (up and down links) with 2 carrier frequencies in the GHz range and one at ~ 2 GHz (for ionosphere compensation) - Measurements on PRN codes (100 Mbits/s) and on the carrier phase - Possibility to perform common and non-common view comparisons - Time noise < 1 ps - Freq. comparison ~ 1day - Time accuracy: ~ 100 ps CAMAM 2015, N. Dimarcq, «T/F transfer» 25

26 T2L2: an pulsed laser link operating on-board JASON-2-2 way (up and down links) laser link - Time tagging of the laser pulses on ground and in space - Ground clocks comparisons in common-view - Time noise ~ few ps - Time accuracy ~ 100 ps CAMAM 2015, N. Dimarcq, «T/F transfer» 26

27 T/F transfer techniques Talking clock 1933 Longwave time transmission (DCF77, France Inter,...) Satellites (MWL,T2L2) Satellites (GNSS, TWSTFT, ) Time transfer : 1-50 ms 1 ns < 100 ps Frequency transfer : few CAMAM 2015, N. Dimarcq, «T/F transfer» 27

28 Contents T/F links characteristics Satellite links Fibre links Conclusions CAMAM 2015, N. Dimarcq, «T/F transfer» 28

29 Internet protocoles (NTP) Stratum 0 : primary servers synchronized on atomic clocks (about 230 in the world) Strate 1 : secondary servers synchronized on primary servers (about 4500) Two-way technique but not symmetrical Synchronisation uncertainty: ~ ms CAMAM 2015, N. Dimarcq, «T/F transfer» 29

30 Internet protocomes (NTP) Dependence on the internet traffic and server load CAMAM 2015, N. Dimarcq, «T/F transfer» 30

31 Dedicated based T/F optical fibre links CAMAM 2015, N. Dimarcq, «T/F transfer» 31

32 Fluctuation of the propagation delay «Round-trip» method for noise compensation Propagation delay limits noise rejection bandwidth and amplitude Lab 1 Local End Scheme of an optical fiber link Φ C Ultrastable Noise OC µm laser Correction Atomic optical clocks PD FM 2(Φ C + Φ P ) = 0 Accumulated Phase noise Φ P Remote End OC Lab 2 FM Φ C +Φ P = 0 Link instability measurement OC OC Optical coupler CAMAM 2015, N. Dimarcq, «T/F transfer» 32

33 Strategy for a wide metrological T/F fibre network Use either a dedicated fibre or a dedicated channel of an existing scientific network CAMAM 2015, N. Dimarcq, «T/F transfer» 33

34 Ground based T/F fibre links : dark fiber / dark channel - Time noise ~ fs - Freq. comparison ~ 10 4 s ; 1day for ~ 500 km - Time accuracy: realistic target in ps range Clock T/F link CAMAM 2015, N. Dimarcq, «T/F transfer» 34

35 Typical scheme of a multiplex optical link CAMAM 2015, N. Dimarcq, «T/F transfer» 35

36 Long distance optical link Multi-segments approach : Link is divided into a few segments, depending on noise and losses shorter propagation delay larger bandwidth and better noise rejection Repeater stations are needed Repeater station N : send back signal to station N-1, amplify and filter, correct the noise of next link N Local end Repeater Station N-1 Link N Repeater Station N Link N+1 Repeater Station N+1 Remote end CAMAM 2015, N. Dimarcq, «T/F transfer» 36

37 Optical repeater station Station N-1 Station N Laser Lock Link N+1 Lock OC PD FM AOM Link N Polar Control FM PD1 OC Laser Current + Temp. Reg. Local Laser PD2 OC FM AOM Link N+1 Link N Lock Temperature Controlled Box Automated with remote control (IP) Polarization control No stable RF clock required Amplification (optical regeneration) Retrace back signal to station N-1 Correct Link N+1 noise CAMAM 2015, N. Dimarcq, «T/F transfer» 37

38 Cascaded 1100-km LPL-Nancy-LPL link LPL/ Villetaneuse ES ES Reims RS RS Nancy RS Strasbourg Link RS with Germany 2 x 270km 2 x 280km 2 x 200km 4 cascaded links with 2 end stations and 3 repeater stations Transmission on an active telecommunication network: Metrological signal at 1542,14 nm, on ITU 44 Data at & nm, on ITU 43 & OADMs + 12 bidirectional EDFAs CAMAM 2015, N. Dimarcq, «T/F transfer» 38

39 End-to-end phase variation 15.0 Paris-Nancy-Paris 1100 km 12.5 Propagation delay, fs points -2.5 removed over Time, days CAMAM 2015, N. Dimarcq, «T/F transfer» 39

40 End-to-end frequency variation ( Hz) Paris-Nancy-Paris 1100 km 5 Frequency, pp points removed over Time, days CAMAM 2015, N. Dimarcq, «T/F transfer» 40

41 End-to-end stability Modified Allan deviation σ y (τ) LPL-Nancy-LPL km Ushijima et al Sr clock Integration time, τ, s CAMAM 2015, N. Dimarcq, «T/F transfer» 41

42 LPL-Strasbourg-LPL km - Preliminary Modified Allan deviation σ y (τ) End-to-end stability Ushijima et al Sr clock LPL-Nancy-LPL km Integration time, τ, s CAMAM 2015, N. Dimarcq, «T/F transfer» 42

43 Fibre links for T/F metrology In France Refimeve+ PI: C. Chardonnet (LPL) In Europe : NEAT-FT Funded 2012 PI: H. Schnatz (PTB) CAMAM 2015, N. Dimarcq, «T/F transfer» 43

44 T/F transfer techniques Talking clock 1933 Longwave time transmission (DCF77, France Inter,...) Internet (NTP, ) Satellites (MWL,T2L2) Satellites (GNSS, TWSTFT, ) Fibre links Time transfer : 1-50 ms 1 ns < 100 ps Frequency transfer : few < CAMAM 2015, N. Dimarcq, «T/F transfer» 44

45 Contents T/F links characteristics Satellite links Fibre links Conclusions CAMAM 2015, N. Dimarcq, «T/F transfer» 45

46 Conclusions Satellites (GNSS, TWSTFT) links are used for daily operational clock comparisons Comparison capability: 1ns accuracy, frequency uncertainty Upgraded ground to space links (microwave/optical domains) for specific missions Optical fibre links are now mature Comparison capability: <100 ps accuracy, < frequency uncertainty Long distance optical link between Paris and Braunschweig for French and German clocks comparison Also: multi-user dissemination, two-way frequency and time transfer, application to remote laser stabilization Perspective of ultrastable T/F links Remote clock comparison, applications to high-precision experiments, search for fundamental constants variation, relativistic geodesy... CAMAM 2015, N. Dimarcq, «T/F transfer» 46

47 Clocks and relativistic geodesy Direct measurements of optical clock frequency differences to determine the gravitation potential difference ν/ν= U/c² ν = ν / m Clocks and T/F links with an frequency uncertainty of = 1 cm resolution in the gravitation potential CAMAM 2015, N. Dimarcq, «T/F transfer» 47