1. Long haul time distribution in existing telecommunication networks
Jeroen Koelemeij (VU Amsterdam, NL)
Tjeerd Pinkert (VU Amsterdam, NL)
Erik Dierikx (VSL Delft, NL)
Henk Peek (NIKHEF, NL)
Rob Smets (SURFnet, NL)

2. Motivation Scientific motivation:
Astronomy (LOFAR, SKA, CTA, VLBI) needs timing over medium-to-long distance
VU Amsterdam: high-precision frequency measurements of atoms and molecules for tests of fundamental physics
(QED/GR searches for dark matter and higher dimensions, etc.):
Need SI second with highest accuracy!
GPS decimals
Stand-alone Cs 13 decimals
UTC realization at VSL Delft 14 decimals
Fiber-optic WR link VSL-VU (137 km)?
Societal/economical motivation
GPS back-up facitility needed
Integrate accurate time & frequency in fiber-optic telecommunications

3. Fiber-optic T&F links in the Netherlands
Provided by SURFnet
2 x 300 km DWDM unidirectional fiber roundtrip VU-KVI-VU
Time transfer for science: 2 x 137 km WR link from VSL (Delft) to NIKHEF (Amsterdam)
Amplified fiber link to distribute UTC(VSL) via WR
Target performance:
<<10-14 frequency stability
< 1 ns time uncertainty (0.1 ns)
WR link passes three other university campuses, and ESTEC

4. Roundtrip measurements
1470 nm
1470 nm
1490 nm
1490 nm
1490 nm
1490 nm
1470 nm
1470 nm

5. Quasi bi-directional amplifier VU Amsterdam / TU Eindhoven / SURFnet
SOA
MUX OI
Commercially available end of 2014 from OPNT B.V.
Remote control & monitoring
ps-level delay calibration possible
Implementation in DWDM systems also possible

6. WR link VSL- NIKHEF: Results
Stability Rb pps in – pps out…

7. WR link VSL – NIKHEF (Next configuration)

8. Calibration of delay asymmetries
Greg D: thanks for the excellent calibration documentation!
WR + Cs ensemble + TWSTFT + GPS

9. Dealing with dispersion
Use the three-wavelength trick*
Exchange one SFP for another with slightly different l:
l2 l (l1 stays the same)
Two Different RTDs (tAC12, tAC13)
Measure all li
Use formula to find estimated OWD (or, equivalenty, a):
< 10ps/100 km if various l only 1-2 nm apart
~ 200 ps/100 km if l1-l2 ~ 20 nm
*N. Sotiropoulos et al. Optics Express 21, (2013)

10. Delay measurements through fast sampling and cross correlation
40 GS/s DSO
1 Gbps / 10 Gbps pattern generator
DUT
splitter
Differential delay [ns]
XCOR
High resolution (~150 fs / shot)
Works for electrical and optical transmission lines
*N. Sotiropoulos et al. Optics Express 21, (2013)

11. Outlook
Complete methods set for absolute delay calibration of SFPs, WR HW, patches, connectors, etc (under development, Henk Peek, Tjeerd Pinkert, JK)
Use extremely low-noise LO as clean-up oscillator: H-maser stability via WR possible?
VLBI through WR possible? (ASTERICS INFRADEV proposal submitted)
Fiber-optic dissemination of UTC as a service (part of EMPIR proposal SRT-i32, see also talk by P.-E. Pottie)

12. Credits
€€ STW €€ FOM €€ EMRP NEAT-FT €€ SURFnet
Ah.
Hmkay?
Questions?