The ACES Microwave Link: Instrument Design and Test Results

Phase-coherent frequency comparison of optical clocks using a telecommunication fiber link

“…The observed fractional instability [given by the allan standard deviation σ y (τ )] of laser frequency transmission using the 146-km PTBlUH-PTB link according to [18] compared with that of a state-of-the art single-ion optical clock [1] and to the estimated instability of a link of 1000-km length (see text). For comparison, we include state-of-the-art frequency comparisons by satellite and the predicted instability of the carrier-phase TWsTFT technique and other advanced in-orbit methods [28], [29]. The dashed line corresponds to the modified allan standard deviation using time deviation data from [29].…”

“…5, the estimated instability of a 1000-km link (black line) becomes smaller than that of the presently best optical clocks [1] for an averaging time τ > 1000 s. after an averaging time of 3 h, the contribution of the optical link to the total instability would be negligible. Even with the assumed fairly high noise level of the link, a clock comparison by optical fiber could exceed the predicted capability of the atomic clock Ensemble in space (acEs) microwave link [28], the Time Transfer by laser link (T2l2) experiment on the Jason 2 satellite [29], or that of satellite-based comparisons using an advanced carrier-phase two way satellite time and frequency transfer (TWsTFT) technique [30] by at least a factor of 5. note, both acEs or the advanced carrier-phase TWsTFT require assuring the phase traceability over an uninterrupted measurement time on the order of a day to reach the instability of the optical clock. For T2l2, phase traceability over a full orbit is not implemented and a comparison of ground clocks will be limited by the stability of the link on all time scales because of the small time of visibility (several minutes) compared with the orbit period of 1.5 to 2 h.…”

Phase-coherent frequency comparison of optical clocks using a telecommunication fiber link

“…5, the estimated instability of a 1000 km link (black line) becomes smaller than that of the presently best optical clocks [1] for an averaging time τ > 1000 s. After an averaging time of 3 hours, the contribution of the optical link to the total instability would be negligible. Even with the assumed fairly high noise level of the link, a clock comparison by optical fiber could exceed the predicted capability of the ACES 2 microwave link [28], the T2L2 3 experiment on the Jason 2 satellite [29], or that of satellitebased comparisons using an advanced carrier-phase TWSTFT 4 technique [30] by at least a factor of 5. Note, both ACES or the advanced carrier-phase TWSTFT require to assure the phase traceability over an uninterrupted measurement time of the order of a day to reach the instability of the optical clock.…”

“…The observed fractional instability (given by the Allan standard deviation σy(τ )) of laser frequency transmission using the 146 km PTB-LUH-PTB link (red squares ) according to [18] compared to that of a state-of-the art single-ion optical clock [1] and to the estimated instability of a link of 1000 km length (black line) (see text). For comparison we include state-of-the-art frequency comparisons by satellite (grey line) and the predicted instability of the carrier-phase TWSTFT technique (green line) and other advanced inorbit methods [28,29]. The dashed line corresponds to the modified Allan standard deviation using time deviation data from [29].…”

STE-QUEST mission and system design

“…Similarly, the links allow to compare distant ground clocks to one another using the on-board segment as a relay. The microwave link (MWL) is designed based on re-use and further development of existing MWL technology for the ACES mission [29,30], while implementing lessons learned from ACES. This applies to the flight segment and the ground terminals, as well as for science data post-processing issues down to the principles and concept for deploying and operating a network of ground terminals and associated ground clocks.…”