Optical Time Transfer (OTT): PoC Results and Next Steps

Transcription

1 AGH University of Science and Technology Department of Electronics, Krakow, Poland Physikalisch-Technische Bundesanstalt (PTB) Braunschweig, Germany Deutsche Telekom Technik GmbH Bremen, Germany Deutsche Telekom together with AGH and ITSF 2016 Optical Time Transfer (OTT): PoC Results and Next Steps Helmut Imlau et. al., November, 3 rd 2016 ITSF 2016: OPTICAL TIME TRANSFER, AGH, PTB, Deutsche Telekom Helmut Imlau et. al. 1

2 Optical Time Transfer Agenda Partners and participants Hierarchical network synchronization and supervision OTT ELSTAB: The method Proof-of-Concept (PoC): Purpose and setup PoC Step 1: Latest results Future: PoC Step 2 & UTC(k) measurements.. 6. Summary and outlook.. 2

3 Optical Time Transfer: Participants: Tasks: For OTT PoC: Schnatz H., Bauch A., Piester D. Physikalisch-Technische Bundesanstalt (PTB) Braunschweig, Germany National Metrology Institute, realization and dissemination of UTC(PTB) and German legal time Clock and time transfer development UTC(PTB) provision T&F domain measurements Partners and participants Śliwczyński Ł., Krehlik P. AGH University of Science and Technology Department of Electronics, Krakow, Poland OTT ELSTAB development (Electronically STABilized fiber optic time and frequency distribution system [1] ) System installation System supervision System repair Link calibration Imlau H., Ender H., Deutsche Telekom Technik GmbH Fixed and Mobile Engineering Bremen, Germany Helmut.Imlau@telekom.de Network operation including synchronization network Obtains traceability to UTC via its UTC(DTAG) time scale Fiber link and remote access planning and provisioning Telecommunication domain and GNSS Common view measurements The measurement data evaluation was supported by Lee Cosart of Microsemi with Time Monitor software 3

4 Optical Time Transfer 1. Hierarchical network synchronization solutions by ITU-T & more Synchronization supply solutions for network operation can be based on: (1) Ethernet Physical Layer Synchronization (SyncE acc. to ITU-T G.826x series) (2) Precision Time Protocol (PTP) with Full Timing Support from the network acc. to ITU-T G.8275.x (3) Clock functions as specified in ITU-T G.81x, G.826x, G.827x A hierarchical synchronization network consists of several levels A separate layer is recommended for synchronization network supervision (in yellow). For 24/7 synchronization dissemination: Based on the needed maximum time error of end-application, a hierarchical synchronization network is needed (in gray) Supervision level 24/7 service Architectural level Optical Time Transfer GNSS based Common View Network core level Aggregation level Base station level max TE <±1ns <±10 ns **) <±30 ns <±100 ns <±1.1 s No. of Locations *) For eprtc / cnprtc please refer [2] [3], **) averaged values /20 10/ n* Methods, Systems OTT GNSS CV e/cnprtc*) T-BC, PRTC T-TSC 4

5 Optical Time Transfer: 2. The method: OTT/ELSTAB (1/3) The fundamental time transfer problem over optical fibers: Delay variation (e. g. wander in a order of 40ps/km/K due to temperature effects over the year) to be compensated (as it is done by time stamp calculation like NTP/PTP method at a lower accuracy level) The ELectronic STABilization (ESTAB) solution: Round-trip delay kept constant Active frequency propagation delay (electronic) stabilization of the of the optical link Phase detector measures the phase difference between the input and feedback signal (Round-trip including variable delay lines (blue) in both directions) Variable delay lines in forward and return path (same values for both direction) Modified delay due to phase measurements. to keep the delay constant 10 MHz IN LP A = Local module 1549,32 nm 10 MHz OUT LP 1548,52 nm B = Remote module 5

6 Optical Time Transfer: 2. The method: OTT/ELSTAB (2/3) Assumptions: Same delay fluctuations (wander) effects in both directions due to same fiber and more or less similar wave length (Only chromatic dispersion and Sagnac effect to be compensated) Same values of variable delay compensation in both directions t DF + t L->R + t R->L + t DB = const t DF + t L->R + t R->L + t DB = 0 The stabilization solution: t DF + t L->R = 0 DLL (Delay Locked Loop) with variable delay modules keeps round trip delay constant Forward local module t DF Delay local to remote module t L->R 10 MHz IN t DF = LP t DB t L->R = t R->L LP 10 MHz OUT Backward local module t DB Delay remote to local module t R->L 6

7 Optical Time Transfer: 2. The method (3/3) Extension for 1PPS transfer At A: Every second, specific phase modulation is applied on frequency signal at PPS embedder De-embedder extracts the 1PPS Round-trip delay measured between 1PPS ref out and 1PPS return out At B: 1PPS out calculation with ½ round trip delay + corrections due to chromatic dispersion, + Sagnac effect 1ns/100 km east-west correction currently manually performed, may be implemented into the OTT ELSTAB system 1PPS in 10 MHz in 1MHz 1PPS ref out PPS embedder LP 1549,32 nm 1548,52 nm LP 1PPS out 10 MHz out DLL E/O Circulator Circulator O/E 1PPS return out A = local module B = remote module 7

8 Optical Time Transfer: 3. Proof-of-Concept: Purpose and setup Feasibility of OTT over an existing fiber network to transfer frequency and phase/time synchronization over around 450 km. Use of optical mono-mode fiber cables laid between 2000 (14%) and 2015 (2%) Use optical fiber type: ITU-T G.652 acc. to valid specification at installation year 2015/16 Setup 10 MHz 1 PPS 10 MHz 1 PPS Local Module Braunschweig Remote Module 77 km 53 km 48 km 46 km Peine Hannover Nienburg 77 km 53 km 48 km 46 km Tap Module Bremen 10 MHz 1 PPS 2016/17 Setup 10 MHz 1 PPS Local Module 77 km 53 km 48 km 46 km Remote Module 10 MHz 1 PPS 8

9 Optical Time Transfer 4. Proof-of-Concept Step1: Latest measurement results Time Error 10 MHz 1 PPS UTC(PTB) Atomic clock ensamble Braunschweig (PTB) 10 MHz 1 PPS Local Module Remote Module Peine Han- Niennover burg 77 km 53 km 48 km 46 km Bremen Tap Module 10 MHz 1 PPS UTC (TCB) 100 psec Counter: Keysight 53230, Counter Control:& Evaluation: Microsemi Time Monitor Diagram shows all 1PPS values as dots only 20 psec /div -80 psec 0,0 days Start: days/div 74 days 9

10 MTIE Optical Time Transfer 4. Proof-of-Concept Step1: Latest measurement results - MTIE 1 s 100 ns 10 ns 1 ns 100 ps 10 ps 1 sec Network Mask PRTC Mask eprtc Mask (Class A) 10 MHz over OTT ELSTAB 1 PPS over OTT ELSTAB 100 sec 10 ksec Observation Window (Tau) 6.4 Msec 10

11 TDEV Optical Time Transfer 4. Proof-of-Concept Step1: Latest measurement results - TDEV 100 ns 10 ns 1 ns 100 ps 10 ps 1 ps 10 MHz over OTT ELSTAB 1 PPS over OTT ELSTAB PRTC Mask eprtc Mask (Class A) 100 fs 1 sec 10 sec 100 sec 1 ksec 10 ksec 100 ksec Observation Window (Tau) 1 Msec 11

12 Optical Time Transfer: 5. Future Proof-of-Concept Step 2 Objective: More complex evaluation scenario to see time error variation depending on different systems, cables and fibers as final OTT system evaluation prior to UTC(DTAG)-UTC(PTB) setup (next step) Braunschweig (PTB) Hannover (Telekom) Bremen (Telekom) UTC(PTB) TCB Atomic clock ensemble (1) New PoC Step 2 links (2) Atomic clock ensemble (3) PoC Step 1 link (modified) (4) Planned result evaluation: (1)-(2) - Same cable, different fibers, different OTT modules (3) - Different cables, different OTT setup, L/R module vs. amplifier (2)-(4) - like (3) 12

13 Optical Time Transfer: 5. Future UTC(k) comparison Objective: UTC(DTAG)-UTC(PTB) measurement at Braunschweig and Frankfurt Results to be delivered for BIPM to allow permanent plausibility check Test Center Bremen (TCB) supplied for testing (PRTC, eprtc) UTC hub Hannover for future options: Uni Hannover, UTC(DLR) Oberpfaffenhofen, UTC(BKG) Wetzell Braunschweig (PTB) Hannover (Telekom) Frankfurt (Telekom) UTC(PTB) UTC(DTAG) Atomic clock ensemble Bremen (Telekom) TCB Atomic clock ensemble Atomic clock ensemble 13

14 Optical Time Transfer 6. Summary and outlook Currently, OTT can be used for time dissemination and /or to measure primary clocks remotely allows better primary clock comparison than GNSS CV as used for TAI/UTC performs well for telecommunication synchronization supervision (< 1 ns) over existing (including older) fibers requires specific operational attendance needs a specific separate optical ( dark ) fiber Improvements for PoC Step 2 improved 1PPS resolution, improved operational procedures 1PPS + 10 MHz squelch extended control range with less operational attendance SNMP interface 4 instead of 2 1PPS outputs In future, OTT to be developed as carrier grade solution to be sufficient for synchronization network production layer to be part of a commercial WDM/OTN system solution, e. g. via OSC (Optical Supervisory Channel) 14

15 Optical Time Transfer Thank you Questions? References: [1] P. Krehlik; L. Sliwczynski; L. Buczek; J. Kolodziej; M. Lipinski, "ELSTAB - fiber optic time and frequency distribution technology - a general characterization and fundamental limits, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Year: 2015, Volume: PP, Issue: 99, DOI: /TUFFC [2] Ł. Śliwczyński., P. Krehlik., H. Schnatz H., D. Piester, A. Bauch, H. Imlau, H. Ender: Towards sub-nanosecond synchronization of a telecom network by fiber optic distribution of UTC(k) EFTF 2016, York/U.K., [3] H. Imlau, "Primary Reference Clocks in Telecommunication Networks: PR(T)C, eprtc and cnprtc" WSTS 2015, San Jose / U.S., [4] G. Zampetti: Coherent Network Primary Reference Time Clocks, (cnprtc) Simulation and Test Results ITSF2015, Edinburgh/ U.K [5] ITU-T G /Y Timing characteristics of enhanced primary reference time clocks (eprtc), Consented September 2016 at SG15 plenary meeting 15

16 Optical Time Transfer Backup: 1pps 16