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NPL Management Ltd - Public
Towards an international optical clock
comparison between NPL and SYRTE
using an optical fibre network
1NPL, UK - 2LNE-SYRTE, France - 3LPL, France - 4INRIM, Italy - 5DANTE, UK - 6PTB, Germany
Giuseppe Marra1, Jochen Kronjaeger1, Paul-Eric Pottie2, Anne Amy-Klein3,
Olivier Lopez3, Davide Calonico4, Guy Roberts5 and Harald Schnatz6
NPL Management Ltd - Public
Comparing optical clocks
Caesium
standard
Co-located
Optical
clock
10-15@1d
10-16 acc
10-16@1s
10-17 acc
Two-way satellite
transfer
10-15@1d
Optical fibre
transfer
10-15@1s
10-18@100s
Co-located optical clock: Bloom et al, Nature 506, 72 (2014)
Caesium standard: K Szymaniec, IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT 60, 2475 (2011)
Two-way satellite:P Gill, Phil. Trans. R. Soc. A 369, 4109 (2011)
Optical fibre transfer: Droste et al, PRL 111, 110801 (2013)
NPL
SYRTE
Map based on “English Channel location map.svg”
by NordNordWest/Wikipedia, license CC-BY-SA-3.0-DE
NPL Management Ltd - Public
Optical fibre transfer Transmit optical carrier in telecom C-band (1550nm)
Stabilise optical length of the fibre
Need bi-directional amplifiers (EDFA or Brillouin)
Need bidirectional amplifiers (EDFA or Brillouin)
Temperature and strain
Doppler shift
End marker Frequency
correction
NPL Management Ltd - Public
Bi-directional Amplifiers
Pump
980nm
Signal 1550nm Signal 1550nm
bad splice connector
Rayleigh
scattering
Gain G
Allow signal to propagate both ways
Required by noise cancellation scheme
Refl R1 Refl R2
Laser threshold
E.g. Rayleigh scattering -35dB – occasionally much higher
In practice G = 15…20dB max
NPL Management Ltd - Public
The London-Paris link
~812 km
~210 dB loss
9 or 10 commercial bi-directional EDFAs
Pair of dark fibres
Fibre provided by European research
and education network GÉANT
2 high-gain Brillouin amplifiers (PTB)
NPL Management Ltd - Public
Scheme for clock comparison
Independent
fibres
Compare fibres for real-
time servo monitoring
Transmit ultra-stable light
locked to NPL optical clock
Compare received light
to SYRTE optical clock
NPL Management Ltd - Public
Status of the project
Link established from
NPL to Folkestone
(and back)
Commercial bidirectional EDFA
NPL Management Ltd - Public
Preliminary fibre noise
NPL to Central London
NPL Management Ltd - Public
The future of clock comparison
Challenges of ever longer links
A European network of fibre links?
Residual loss Amplifier gain can’t fully compensate loss
as this would lead to spontaneous
oscillation – e.g. 3dB loss per stretch
Loop bandwidth Detection delay for London-Paris link is
about 8ms – bandwidth of 20Hz
Cost Typical fibre rental cost
~£100k/yr
Court
esy o
f iS
tockphoto
NPL Management Ltd - Public
Thank you for your attention.
The research leading to these results has received funding from the European
Community’s Seventh Framework Programme (FP7 2007-2013) under Grant Agreement
No. 605243 (Gn3plus). It has also received funding from Action Spécifique GRAM.