Krzysztof Czuba ISE, Warszawa, kczuba@elka.pw.pl Matthias Felber

1. Improved fiber-optic link for the phase reference distribution system for the TESLA technology based projects Krzysztof Czuba ISE, Warszawa, kczuba@elka.pw.edu.pl Matthias Felber DESY, Hamburg, matthias.felber@desy.de Krzysztof Czuba

2. OUTLINE • Design requirements • System concept • First system version - summary • Improvements – second system version • Measurement results Krzysztof Czuba

3. DESIGN REQUIREMENTS Synchronize RF devices located along the accelerator with timing jitter (phase) error << 1 ps Distribution distance: • 300 m UVFEL • 3.1 km XFEL • 15 km ILC Distributed RF signal frequency range: 1 MHz to 2.856 GHz 1.3 GHz Krzysztof Czuba

4. LONG TERM PHASE DRIFTS Drifts caused mainly by temperature changes RF signal source ~ Target Device Electrical / optical length change 1.3 GHz signal phase change in 5km of fiber. 10 oC temperature change Reason of drifts: - In fiber: neff change - In cable: physical dimension and dielectric properties change 1400o @ 1.3 GHz corresponds to ~2800 ps!! Feedback on phase required!! Krzysztof Czuba

5. Long Link Simulator 5 km of single mode fiber in temperature controlled oven Mirror Circulator DFB Directional RF Coupler Phase Shifter Laser Signal in FO Tx FO Rx FO Rx Temperature variation B A Controller RF Phase Detector Error voltage RF Phase Detector Output phase check SYSTEM CONCEPT Phase stable signal distribution over long distances (up to 20 km) Feedback on phase suppressing long term drifts Main application of this system is long term phase drifts monitoring / compensation Test system block diagram Krzysztof Czuba

6. FIRST EXPERIMENT System can cover very long distribution distances, up to 20km FIRST SYSTEM TEST IN A CLIMATE CHAMBER DFB laser F.O. receivers Optical phase shifter (oven with 5km of fiber) RF amplifiers F.O. components (circulator, coupler and other) Problems with cabling, vibration and noise Very slow phase shifter response Long link simulator (oven with 20km of fiber) RF phase detectors 1.3 GHz signal source Closed loop - output signal phase Spool with fiber as a phase shifter • Obtained phase stability: • Short term (1 min): 0.8 ps p-p • Long term : 5 ps p-p Krzysztof Czuba

7. SECOND SYSTEM VERSION - ODL • Motorized Optical Delay Line: • Phase shift of 160o at 1.3 GHz – can cover distribution distances up to 500 m • 4.7 fs phase change resolution! • Fast response – possible higher gains in the feedback loop • Digitally controlled – no problems with noise and ambient temperature • Much smaller than the spool inside of the oven Krzysztof Czuba

8. FIBER-OPTIC BOARD, SYSTEM CRATE All components installed on soft foam base Vibration problems removed Easier to handle Shorter connections, semi-rigid for RF signals Improved power supply distribution Shielding System noise reduced significantly Krzysztof Czuba

9. NEW PHASE DETECTOR, CONTROLLER GUI Very low sensitivity to ambient temperature changes: 0.01o/oC Improved interface New functionalities, e.g. automatic measurement data storage and labeling Several important “bugs” removed Krzysztof Czuba

10. F.O. LINK V.2 – MEASUREMENT RESULTS Measurement performed inside of the climate chamber 5 km of fiber used as long link 100 h measurement duration ODL position followed temperature induced phase drifts Output signal phase significantly more stable than in the first system version because of higher feedback loop gain and faster phase shifter Krzysztof Czuba

11. SUMMARY Two system versions tested Significant performance improvements obtained by use of the ODL and proper development of system hardware Result comparison Third system generation is under development. Phase shifter made of the ODL and a spool of fiber connected in series. This will allow to use advantages of both solutions Krzysztof Czuba