Transcript Slide 1

Local Oscillator distribution over
fibre
Roshene McCool
SPDO – Signal Transport & Networks
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
1
Contents
• Distribution of LO signals over fibre
• Merlin L-Band Link (LBL)
• L-Band Link over fibre
• Results of experiments
• Is round trip correction required?
• Interferometry using a fibre LBL
• Results
• Conclusions
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Transfer of Local Oscillator
Signals Over Fibre
• Motivation
– Accurate timing signals to all antenna & data processing stations
– Like to have transmission over fibre to avoid RFI
• Specifications
– Not specified directly, yet…
– Working to ±1 ps in 1 second (driven by astronomy at high frequencies)
and ±10 ps over 10 minutes
• Other LO over fibre systems
– EVLA, 22 km
– ATCA, 4.5 km
• LO over fibre for the SKA & e-MERLIN
– Same specifications, similar distances
– e-MERLIN, 400km (120km longest unrepeatered hop)
– Adapted MERLIN LO distribution equipment for optical transmission
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Merlin L-Band Link (LBL)
1486.3 MHz signal arrives at the antenna with
delay Φone way
Good quartz oscillator locks a 10 MHz local
oscillator signal using the incoming 1486.3
MHzround trip
one way
Φ
/2 = Φ
The LBL equipment switches to transmit
At Jodrell the phase Φround trip
of the incoming 1486.3 MHz
signal is measured.
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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L Band link over fibre
Master L-Band
Link
120 MHz over 30m of RG214
HP 8508A Vector
Voltmeter
1486.3 MHz signal
120MHz over 10m of
RG59
Line stretcher
Master
Laser
Slave
Receiver
SMF28 Fibre Link
(variable length)
B
-23d
1486.3 MHz signal
-40dB
Master Receiver
Slave Laser
Aerial
switch
Slave L-band
Link
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Phase stability of an LBL over fibre link
ᶲround trip /2 - ᶲone way
Back to Back
28.6 km @ 1550 nm
28.6 km @ 1310 nm
110 km no thermal
control
110 km thermal
control
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Phase stability of an LBL over fibre link
Back to Back
28.6 km @ 1550 nm
28.6 km @ 1310 nm
110 km no thermal
control
110 km thermal
control
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Phase stability of an LBL over fibre link
Back to Back
28.6 km @ 1550 nm
28.6 km @ 1310 nm
110 km no thermal
control
110 km thermal
control
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Phase stability of an LBL over fibre link
1 ps r.m.s stability in 1 second,
2 ps r.m.s stability in 10 minutes
5 ps r.m.s stability in 3 hours.
Back to Back
28.6 km @ 1550 nm
28.6 km @ 1310 nm
110 km no thermal
control
110 km thermal
control
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Do we need round trip correction?
Why not use a directly transmitted
frequency standard?
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Do we need round trip
correction?
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Interferometry with a fibre LBL
• Observations of calibrator
sources at 5 GHz
• Used a fibre LBL, distributing LO
signals from Jodrell Bank to
Pickmere (28.6 km)
• Other telescopes remained on a
microwave LBL
• Direct comparison of competing
architectures impossible – only 1
LO connections per antenna!!
•Observations were successful.
•Fibre LBL results impressive
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Link Phase stability, microwave
and fibre
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Astronomy Phase at 5 GHz
(correlated and round trip correction added)
Using a fibre LBL
Using a microwave LBL
** These plots are not direct comparisons and are made, using the same baseline
(Knockin – Pickmere) over 5 hrs at different dates. Changes in Atmosphere will
effect phase stability. However, we can certainly conclude the fibre LBL system is no
worse than the microwave system.
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Conclusions
• LO distribution over fibre is possible
• Over short links it may be possible to distribute phase with
no round trip correction.
‼ Hostage to external temperature changes
• Distribution over long links is possible using thermally
controlled lasers
• Interferometry, performed at 5 GHz, using a fibre distributed
LO was successful
• Further work will address fibre distributed LOs over longer
distances, using repeatered and optically amplified links
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Questions
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Wide area data networks
Roshene McCool
SPDO – Signal Transport and Networks
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Contents
• Defining the problem
• Identifying the risks
• How to approach it
• Questions
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Introduction
• Defining the problem
– 6.5 Peta bits per second total data transport requirements
– In one day SKA will transport 35,000x total internet traffic of the
USA* !!
– Network along arms of 3,000 km length
– To a network of ~ 300 AA stations & 600 dishes
x3 !
* AT&T Analyst Conference 2007 - Stankey
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Technology risks
• Technology risk in wide area networks – relatively low
– 40 Gbps DPQSK systems
– 10 GE SFP+ and XFP transponders commodity & address even
long links
– optical transmission mature technology - EDFAs, DCMs, DWDM,
CWDM
– Many possible suppliers
• Long distance fibre networks (> 500 km)
– Cost of high bit rates over long distance
– Use commercial systems to avoid re-gen at lengths > 480 km
– Availability of commercial dark fibre over long distances
• Interfaces (may be none standard)
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Risks
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Risks related to scale
Cost !!
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
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How do we approach this problem ?
• Use industry & obtain a turn key solution
– Transfer risk from the project to the supplier
– Now we can all go home!

• This option doesn’t let us off the hook!
– Have to produce a contract that will deliver for the SKA
– Don’t know what it will cost
– Evaluate ability of suppliers to deliver
– Need a Plan B
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
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How do we approach this problem ?
• Target development of subsystems to directly address SKA
digital signal processing design block
– Efficient use of development resource
– address interface issues
– power
– Identify cost effective solutions
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
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How do we approach this problem ?
• Critical Analysis of solutions
– Technical risk is low, telecoms industry & pathfinders can provide
solutions – but this can encourage complacency
– Implementation is on a scale not yet conceived in industry
– Hand-crafted designs in pathfinders do not necessarily scale either
– Ask questions, build systems that lead to objective metrics upon
which to base costed designs for implementation.
– Optimisation is required to reduce costs
4th SKADS Workshop, Lisbon, 2-3 October 2008
Phase Transfer & WANs
Roshene McCool
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Questions
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