Local Oscillator distribution over fibre

1. Local Oscillator distribution over fibre Roshene McCool SPDO – Signal Transport & Networks

2. 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

3. 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

4. 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 MHz Φround trip /2 = Φone way The LBL equipment switches to transmit At Jodrell the phase Φround trip of the incoming 1486.3 MHz signal is measured.

5. L Band link over fibre

6. 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

7. 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

8. 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

9. 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

10. Do we need round trip correction? Why not use a directly transmitted frequency standard?

11. Do we need round trip correction?

12. 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

13. Link Phase stability, microwave and fibre

14. Astronomy Phase at 5 GHz (correlated and round trip correction added) Using a microwave LBL Using a fibre 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.

15. 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

16. Questions

17. Wide area data networks Roshene McCool SPDO – Signal Transport and Networks

18. Contents • Defining the problem • Identifying the risks • How to approach it • Questions

19. 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 * AT&T Analyst Conference 2007 - Stankey x3 !

20. 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)

21. Risks • Radio Antenna environment • RFI requirements • Space • Supply • Continuity of supply • Turning hand-crafted designs into units for efficient manufacture, installation & operation. • Power • V. Hungry in many implementations

22. Risks related to scale Cost !!

23. 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 

24. 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

25. 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

26. Questions