Precise time transfer on the IPE VUGKT line a detailed analysis

Transcription

1 a detailed analysis Josef Vojtěch,, Pavel Škoda, Vladimír Smotlacha, Radek Velc, Petr Münster, Jan Kundrát, Ondřej Havliš, Lada Altmannová and Michal Altmann Department of Optical networks, CESNET z.s.p.o., Prague 6, Czech Republic TSP 2016

2 Why we need a precise time? Broad range of fields eg.: legal time, sensing, metrology, navigation, astronomy, seismology, fundamental physic... Standards: IEEE1588 Precise time synch for realtime automation applications Optical transfer outperforms radio frequency high carrier frequency (hundreds of THz) shorter propagation paths (vs. GPS) accuracy in order of ps or better no needs for antennas or clear sky view

3 Infrastructure CESNET provides e-infrastructure for R&E in Czech Republic. The 1st fibres were lit-up in 1999 with several EO regenerators. Now the optical amplifiers are widely used on backbone. Currently backbone contains ~6400 km of dark fiber (1510 km with commercial transmission systems and 4890 km CzechLigh). Photonics services Photonic services are end to end connection between two or more sites in network defined by photonic path and allocated bandwidth. Optimaly carried with no or minimal impact to signal. Deployment of multiple applications into a single path is no problem. PSes can share the fibers efficient use of optical paths, sometimes the only one solution (we cannot afford separated fiber).

4 Map of CESNET2 network topology

5 CzechLight R devices Developed and still improved by CESNET. Great monitoring capabilities. ROADM DWDM Reconfigurable Add Drop Multiplexers BiDi CLA bidirectional full optical amplifiers WSS wavelength selective switches TDC tunable dispersion conmensator Used standard chasis.

6 Precise time transmission The first application of T/F infrastructure was made on link IPE BEV (Wiena) 550 km. An one way method has high uncertainty transfer signal from A to B and back. By two way method we eliminate uncertainty of propagation time but we need to ensure that propagation time is the same for both of directions or need to know the difference. (It is better to use the same fiber.) Propagation time depends mainly on refractive index and length of fiber and also on temperature, wavelength and polarization. Pilot link: IPE CESNET VUGKT total 95 km 12 months of observation (2015/ /02) Delay was changed of about 70 ns annual transmission time fluctuation 736 ps/km. Sunny days brings greater day difference ~0.4 ns.

7 Pilot implementation link overview Two spans: IPE CESNET (17 km) and CESNET VUGKT (78 km)

8 Precise time transmission link map

9 Corrections Time corrections for one way time transfer over optical fiber are derived in and lead to formula: t ± = 1 c L 0 ndl ± 1 L v s c 2 l dl + 1 L n(w + v 2 )dl (1) c st term represents influence of refractive index ~5 ms (1000 km) 2nd term describes th Sagnac effect ~±5 ns 3rd term is Shappiro s correction ~3 ps The realworld two way transmission needs different channel s wavelengths time propagation difference: T = (d L + D) λ where: d = chromatic dispersion coefficient, L = fiber length, D = chrom. disp. of passive components for IPE VUGKT line: L =95 km, d =17.5 ps nm 1 km 1, λ = 0.8 nm, D = 200 ps nm 1 T = 1.49 ns 0

10 Sagnac effect The c 2 term in eq. 1 is the Sagnac correction and correct sign from ± depends on direction of tranfer (eastward or westward). t = 2ΩS c 2 (2) where Ω is angular velocity of the Earth numerlicaly 7.292E-5, the variable is S corresponds to area defined projection fiber path.

11 Automated computation Input: GPX file with fiber path (approx.) and some meta information (a real length of fiber).

12 Conclusion The IPE VUGKT line shows directional difference: of 1490 ps based on wavelenght diff, of 79.7±0.004 ps based on Sagnac effect. The main uncertainty 29.8 ps comes from laser wavelength drift, A Polarization Mode Dispersion brings uncertainty of 0.85 ps

13 Contact Josef Vojtěch This slides