Optically pumped cesium enabling ePRC and ePRTC Class B
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Alain Michaud's ITSF 2017 slideshow outlines how new synchronization technology based on optical pumping can deliver major improvements in frequency stability.
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Optically pumped cesium enabling ePRC and ePRTC Class B
- 1. Optically pumped cesium enabling ePRC and ePRTC Class B Alain Michaud, director, R&D and PLM, time and frequency ITSF 2017
- 2. © 2017 ADVA Optical Networking. All rights reserved.2 Cesium clock as time source PRC (G.811) Frequency PRC : Cs or GNSS Sync network SSU SSU NE NE NE PRTC (G.8272) Frequency + phase PRTC : GNSS Sync network Packet slave clock Packet master clock NE NE NE ePRTC (G.8272.1) Frequency + phase GNSS Sync network Packet slave clock Packet master clock NE NE NE CsCombiner Cs as backup
- 3. © 2017 ADVA Optical Networking. All rights reserved.3 ePRTC: enhanced PRTC (ITU-T G.8272.1) What is enhanced? Cesium clock to filter GNSS instabilities: • Atmospheric interference • Solar storms • Equatorial diurnal ionospheric variation 30ns MTIE in GNSS locked mode Cesium clock: resiliency against GNSS outage 100ns MTIE over 14 days in holdover mode MTIE τ(s) 15ns 100ns 1ns 0.1 1 10 100 400k1k 10k 10ns 100k 1M 10M 100M 30ns 4ns 30ns 30ns 100ns 4ns
- 4. © 2017 ADVA Optical Networking. All rights reserved.4 Where is ePRC hiding? ePRTC (G.8272.1) Frequency + phase GNSS Sync network Packet slave clock Packet master clock NE NE NE Cs Combiner ePRTC ePRC (G.811.1) Frequency domain Requires 10-12 frequency accuracy (Achieved with magnetic cesium clocks) Cs
- 5. © 2017 ADVA Optical Networking. All rights reserved.5 ePRTC Class A holdover requirement ePRTC-A holdover spec Free running cesium oscillator Frequency of cesium made coherent to UTC in tracking mode (ePRTC) ePRTC Class A phase/time holdover measurement
- 6. © 2017 ADVA Optical Networking. All rights reserved.6 ePRTC G8272.1 – phase error in holdover Evolution toward Class B holdover Class B: requires a frequency accuracy below 1 x 10-14 ePRTC Class Holdover performance ePRTC-A 100ns over 14 days ePRTC-B 100ns over 80 days (project) Could also be a tighter error budget over a shorter period
- 7. © 2017 ADVA Optical Networking. All rights reserved.7 F=3,4 RFLaser Laser N S N S F=3,4 RF • Weak flux • Strong velocity selection (bent) • Magnetic deflection (atoms kicked off) • Typical performances: ADEV • 2.7 x 10-11 x t-1/2 • High flux (x100) • No velocity selection (straight) • Optical pumping (atoms reused) • Typical performances: ADEV • 3 x 10-12 x t-1/2 Improving frequency stability with optical pumping (versus magnetic deflection)
- 8. © 2017 ADVA Optical Networking. All rights reserved.8 Improving frequency stability with optical pumping (versus magnetic deflection) • Atomic energy states • Ground states (F=3,4) equally populated • Excited states (F’=2,3,4,5) empty • Switching between ground states F by RF interaction 9.192GHz without atomic selection (no useful differential signal) • Atomic preparation by magnetic deflection (loss of atoms) • Atomic preparation by optical pumping with laser tuned to F=4 F’=4 transition (gain of atoms) F’=5 F’=4 F’=3 F’=2 nRF = 9.192GHz F=4 F=3 133Cs atomic energy levels l = 852.1nm or nopt = 352THz Absorption Spontanousemission Cs beam Resonant cavity (Ramsey)
- 9. © 2017 ADVA Optical Networking. All rights reserved.9 Available commercial Cs clock products • Long-life magnetic Cs clock • Stability : 2.7 x 10-11 x t-1/2 • Floor : 5 x 10-14 • Lifetime : 10 years • High-performance magnetic Cs clock • Stability : 8.5 x 10-12 x t-1/2 • Floor : 1 x 10-14 • Lifetime : 5 years • High-performance and long-life optical clock • Stability : 3.0 x 10-12 x t-1/2 • Floor : 5 x 10-15 • Lifetime : 10 years Long-life MAGNETIC High-perf MAGNETIC Super-high-perf long-life OPTICAL ADEV: Allan Deviation Three generations of commercial clocks
- 10. © 2017 ADVA Optical Networking. All rights reserved.10 Decomposition of ePRTC holdover phase error budget Origin of phase error Note Required for ePRTC-B Initial phase error GNSS instabilities + clock stability +/- 30ns as per ePRTC G.8272.1 How to use only ±10ns? High-stab. GNSS+ High-stability clock Random phase excursions (holdover) White frequency noise + flicker frequency noise cesium clock Higher- stability clocks Typ. Φ excursion magnetic Typ. Φexcursion optical (±20ns) (±5ns) Phase drift due to initial clock freq. offset Which is a function of: - Clock stability @Tau > 1d - GNSS stability @Tau >1d Higher-stability GNSS + Higher-stability clock (long term) Required: Freq. error < 5 x 10-14 ePRTC-A Freq. error < 1 x 10-14 ePRTC-B White frequency noise Flicker frequency noise (floor) Initial frequency error + +
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