The T2L2 Metrological Test Bed

The new generation of optical time transfer (T2L2 [1]> [2] -Time Transfer by Laser Link) under development at OCA and CNES will allow the synchronization of remote ultra stable clocks and the determination of their performances over intercontinental distances. The principle is based on the propagation of light pulses between laser telemetry stations connected to the clocks that have to be synchronized. Expected T2L2 performances are in the 100 ps range for accuracy, with an ultimate stability better than 1 ps over 1,000 s and than 10 ps over one day and will thus allow an improvement of one to two orders of magnitude with respect to the performances of existing time transfer systems. In this paper we report on a test facility designed to derive the metrological performances of the T2L2 space instrument and to perform calibrations of electronics and optics. This test bed is capable of subjecting the flight instrument to the experimental conditions it will meet in orbit. For this purpose, the test bed consists of several subsystems: an optical subsystem in order to illuminate T2L2´s optics with faint laser pulses (simulating laser stations) and background illumination, an electronic subsystem including a high performance timing system for reference timing and a mechanical subsystem for simulation of different angles of incidence (corresponding to the elevation of the satellite with respect to a laser station). The experimental setup also includes a DORIS space clock engineering model in order to simulate the conditions on the satellite Jason 2, and alternatively a Rubidium and H-Maser for stability measurements. With this instrumentation it is possible to simulate the experimental conditions of operation of the space instrument and thus derive their impact on the metrological performances and therefore the quality of the time transfer. After a short review of the instrument architecture we give a detailed description of the metrological test bed and its subsystem- s. We then outline the calibration and performance tests that were carried out on the T2L2 flight model and conclude.