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High Performance Optically Pumped Cesium Beam Clock

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Meet the world’s best commercial cesium beam clock. Dr. Patrick Berthoud’s ITSF 2015 presentation has the details

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High Performance Optically Pumped Cesium Beam Clock

  1. 1. High performance optically- pumped cesium beam clock Dr. Patrick Berthoud, Chief Scientist Time & Frequency ITSF 2015, Edinburgh, UK, 2nd – 5th November
  2. 2. © 2015 ADVA Optical Networking. All rights reserved. Confidential.2 Outline • Motivation and applications • Cs clock: magnetic vs. optical • Cs clock prototype development • Conclusion
  3. 3. © 2015 ADVA Optical Networking. All rights reserved. Confidential.3 Identified markets • Telecommunication network reference • Telecom operators, railways, utilities, … • Science • Astronomy, nuclear and quantum physics, … • Metrology • Time scale, fund. units measurement • Professional mobile radio • Emergency, fire, police • Defense • Secured telecom, inertial navigation • Space (on-board and ground segments) • Satellite mission tracking, GNSS systems
  4. 4. © 2015 ADVA Optical Networking. All rights reserved. Confidential.4 Available Cs clock commercial products • Long life magnetic Cs clock • Stability : 2.7E-11 t-1/2, floor = 5E-14 • Lifetime : 10 years • Availability : commercial product • High performance magnetic Cs clock • Stability : 8.5E-12 t-1/2 , floor = 5E-15 • Lifetime : 5 years • vailability : commercial product • High perfermance and long life optical Cs clock • Stability : 3.0E-12 t-1/2 , floor = 5E-15 • Lifetime : 10 years • Availability : under development
  5. 5. © 2015 ADVA Optical Networking. All rights reserved. Confidential.5 Timing error prediction • T0 depends on timing reference, meas. resol. and noise • Accuracy depends on reference accuracy, meas. resol. and noise, and flicker frequency noise floor of the DUT • Environmental sensitivities are usually periodic variation of frequency, zero on average • Frequency drift common in quartz and cell stds (Rb, maser), negl. for Cs • Intrinsic noise sources of the DUT (white and flicker FM) Timing error Initial timing calibration Freq accuracy + Env. changes Freq linear drift Noise timing error sx(t)  sy(t) * t
  6. 6. © 2015 ADVA Optical Networking. All rights reserved. Confidential.6 Frequency stability (ADEV) 1E-15 1E-14 1E-13 1E-12 1E-11 1E-10 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 Allanstdfrequencydeviation[Hz/Hz] Averaging time [s] Std. Perf.Magnetic High Perf. Magnetic High Perf. Optical
  7. 7. © 2015 ADVA Optical Networking. All rights reserved. Confidential.7 Timing error prediction 1.E-12 1.E-11 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 Timingerror[s] Averaging time [s] Std. Perf.Magnetic High Perf. Magnetic High Perf. Optical 30 ns 6days 60days
  8. 8. © 2015 ADVA Optical Networking. All rights reserved. Confidential.8 Motivation for an Optical Cs clock • Improved performance (short and long-term stability) for: • ePRTC applications (extended holdover period) • Metrology and time scales • Science (long-term stability of fundamental constants) • Inertial navigation (sub-marine, GNSS) • No compromise between lifetime and performance • Same Cs reservoir capacity • Same Cs oven temperature • Same vacuum pumping capacity • Large improvement of Cs beam efficiency by laser optical pumping
  9. 9. © 2015 ADVA Optical Networking. All rights reserved. Confidential.9 Outline • Motivation and applications • Cs clock: magnetic vs. optical • Cs clock prototype development • Conclusion
  10. 10. © 2015 ADVA Optical Networking. All rights reserved. Confidential.10 Magnetic Cesium clock operation • Cs beam generated in the Cs oven (vacuum operation) • Cs atoms state selection by magnets • Cs clock frequency probing (9.192 GHz) in the Ramsey cavity • Atoms detection and amplification by electron multiplier (vacuum) • RF source servo loop using atomic signal Ramsey cavity Magnetic selectors Magnetic shield + coil FM User 10 MHz Cs Oven Vacuum enclosure Electron multiplier RF source Sync Detect N S N S Cs beam
  11. 11. © 2015 ADVA Optical Networking. All rights reserved. Confidential.11 Optical Cesium clock operation • Cs beam generated in the Cs oven (vacuum operation) • Cs atoms state selection by laser • Cs clock frequency probing (9.192 GHz) in the Ramsey cavity • Atoms detection and amplification by photodetector (air) • Laser and RF sources servo loops using atomic signals Ramsey cavity Light Collectors Magnetic shield + coil FM User 10 MHz Laser Cs Oven Vacuum enclosure Photo- detectors RF source Sync Detect FM Laser source Sync Detect Cs beam
  12. 12. © 2015 ADVA Optical Networking. All rights reserved. Confidential.12 133Cs atomic energy levels • Stable ground states (F=3 and F=4) • Switching between ground states F by RF interaction 9.192 GHz • Unstable excited states (F’=2,3,4,5) • Switching between ground states F and excited states F’ by laser interaction 852 nm (or 351 THz) 6S1/2 nhf = 9.192 GHz F=4 F=3 6P3/2 F’=4 F’=3 F’=2 F’=5
  13. 13. © 2015 ADVA Optical Networking. All rights reserved. Confidential.13 Cesium clock: Magnetic vs. Optical • Weak flux • Strong velocity selection (bent) • Magnetic deflection (atoms kicked off) • Typical performances: • 2.7E-11 t-1/2 • 10 years • Stringent alignment (bent beam) • Critical component under vacuum (electron multiplier) F=3,4 • High flux (x100) • No velocity selection (straight) • Optical pumping (atoms reused) • Typical performances: • 2.7E-12 t-1/2 • 10 years • Relaxed alignment (straight beam) • Critical component outside vacuum (laser) N S N S F=3,4
  14. 14. © 2015 ADVA Optical Networking. All rights reserved. Confidential.14 Outline • Motivation and applications • Cs clock: magnetic vs. optical • Cs clock prototype development • Conclusion
  15. 15. © 2015 ADVA Optical Networking. All rights reserved. Confidential.15 Clock functional bloc diagram • Cs tube • Generate Cs atomic beam in ultra high vacuum enclosure • Electrical and optical feedthoughs for atomic signal generation • Optics • Generate 2 optical beams from 2 lasers modules (cold redundancy) • Electronics • Cs core for driving the Optics and the Cs tube • External modules for power supplies, management, signals outputs Cesium tube Magnetic field and shields Cs Oven Collect CollectRamsey cavity Optics Laser Splitter Mirror Clock electronics RF Source Clock Ctrl Power Supply Photo Detect Photo Detect 4xSyncout(1PPS) Expansion electronics Serial(RS232) Syncin(1PPS) Display 10MHzsine 10MHzsine 10or5MHzsine(option) 10or100MHzsine(option) Metrology Manage ment Remote(TCP/IP) PPS DC/DC AC/DC Battery ExternalDCsupply ExternalACsupply
  16. 16. © 2015 ADVA Optical Networking. All rights reserved. Confidential.16 Cs clock design • 19’’, 3U, 460 mm rack • Cs core is not customizable • Cs clock expansions are customizable: • Sine waves outputs • 1PPS sync In/Out • Local & Remote management • Display • DC/AC power supplies • Internal battery
  17. 17. © 2015 ADVA Optical Networking. All rights reserved. Confidential.17 Cs tube design Photo-detector inserts Pinch-off tubeRF feedth. Laser viewports Electrical feedth. Ion pump Vacuum enclosure
  18. 18. © 2015 ADVA Optical Networking. All rights reserved. Confidential.18 Optics sub-system design Redundant laser modulesDFB laser modules Off-the-shelf optical parts Free space optics Tunable optical mounts
  19. 19. © 2015 ADVA Optical Networking. All rights reserved. Confidential.19 Cs clock prototype
  20. 20. © 2015 ADVA Optical Networking. All rights reserved. Confidential.20 Laser frequency locking • Laser current ramp (yellow) • Atomic fluorescence signal (pink) • FM demodulated atomic signal (green) used as laser frequency error signal • Automatic line identification algorithm • Automatic laser frequency lock
  21. 21. © 2015 ADVA Optical Networking. All rights reserved. Confidential.21 Ramsey fringe • Atomic RF frequency discrimination signal • Inverted fringe (minimum amplitude at resonance) • Fringe amplitude • 700 pA • Signal/Noise • 18’500 Hz1/2 • Fringe linewidth • 740 Hz • Atomic quality factor • 12.4E6
  22. 22. © 2015 ADVA Optical Networking. All rights reserved. Confidential.22 Short-term frequency stability • Measured Allan deviation • 2.7E-12 t-1/2 • Theoretical prediction • 2.4E-12 t-1/2 • Proves proper clock tuning parameters • Performance limitations • Short-term: Spurious light • Long-term: Single servo loop in operation (OCXO) 2.70E-12E t-1/2
  23. 23. © 2015 ADVA Optical Networking. All rights reserved. Confidential.23 Outline • Motivation and applications • Cs clock: magnetic vs. optical • Cs clock prototype development • Conclusion
  24. 24. © 2015 ADVA Optical Networking. All rights reserved. Confidential.24 Conclusion • Development of the world best commercial Cs beam clock • Laser optical pumping technology inside • 10x better frequency stability (<3E-12 t-1/2) • Long lifetime (10 years), no compromise with performance • Standard 19” rack, 3U high, 460 mm deep • Management: serial, remote, display • Signals: 5, 10, 100 MHz, 1 PPS • Acknowledgment: this work is partially financed by the European Space Agency (contract number 21603/08/D/JR and 4000111645/14/NL/CVG)
  25. 25. Thank You IMPORTANT NOTICE The content of this presentation is strictly confidential. ADVA Optical Networking is the exclusive owner or licensee of the content, material, and information in this presentation. Any reproduction, publication or reprint, in whole or in part, is strictly prohibited. The information in this presentation may not be accurate, complete or up to date, and is provided without warranties or representations of any kind, either express or implied. ADVA Optical Networking shall not be responsible for and disclaims any liability for any loss or damages, including without limitation, direct, indirect, incidental, consequential and special damages, alleged to have been caused by or in connection with using and/or relying on the information contained in this presentation. Copyright © for the entire content of this presentation: ADVA Optical Networking.

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