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Session T2b: Updates and Insights from Metrology Institutions and Broader Scientific/Regulatory Communities

Ultrastable Transfers Over Large Telecom Networks
Josef Vojtech(a), Raimena Veisllari(e), Guy Roberts(f), Jan Radil(a), Michal Spacek(a,c), Jaromir Sima(a), Tomas Novak(a,b), Vladimir Smotlacha(a), Ondrej Havlis(a), Michal Hazlinsky(a), David Verner(a), Tomas Horvath(a,d), Elisabeth Andriantsarazo(a,c), Rudolf Vohnout(a), Martin Slapak(a),, Lada Altmannova(a), Radek Velc(a), Petr Pospisil(a) a CESNET z.s.p.o., Prague, Czechia b Faculty of Nuclear Science and Physical Engineering, Czech Technical University, Prague, Czechia c Faculty of Electrical Engineering, Czech Technical University, Prague, Czechia d Faculty of Electrical Engineering and Communication, Technical University Brno, Czechia e SIKT, Trondheim, Norway f GEANT, Cambridge, UK
Location: Imperial Room
Date/Time: Wednesday, Jan. 28, 11:48 a.m.

Time and frequency transfer over optical fiber may bring some challenges, especially when transmitting in one fiber together with data signals. Frequency is not so critical in this aspect because it is a continuous wave (CW) unmodulated laser. However its power level in fibre must be kept below Brillouin scattering threshold which not complicated in standard telecom fibers. However precise time is transmitted by means of the simplest modulation scheme - on off keying (OOK). This situation has been encountered in the last 15 years or so, from the time when the first generation of coherent system became available on the market. Legacy OOK data signals may affect the high speed coherent data signals, which are phase (and now also amplitude) modulated, with modulations ranging from quadrature phase shift keying (QPSK) to multilevel quadrature amplitude modulations (QAM) via nonlinear effects, especially cross phase modulation (XPM). Coherent systems have become much more resilient to such nonlinear cross talks, but the exact rules how to transmit OOK and coherent signals in one fiber, vary significantly. This is interesting topic because shared fiber infrastructures should be used to transmit not only huge amount of data, but also new applications like precise time - GNSS alternatives.

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