Reciprocity of propagation in optical fiber links demonstrated to 10⁻²¹

Abstract

We present a study of the fundamental limit of fiber links using dedicated link architecture. We use an experimental arrangement that enables us to detect the forward and backward propagation noise independently and simultaneously in optical fiber and where the optical phase evolution is expected to be driven by the only contribution of the reference arms of the Michelson interferometer ensemble. In this article, we demonstrate indeed the high correlation between the optical phase evolution and the temperature variation of the interferometer ensemble, leading to a frequency offset of (4.4 ± 2.3) × 10 −21 . Using a simple temperature model and a Bayesian analysis to evaluate the model parameters, we show that the temperature effect can be compensated with post-processing, removing the frequency offset down to (0.5 ± 2.0) × 10 −21 . The residual slope of the optical phase evolution over 33 days is 350 yoctosecond/s. Using a global temperature parameter, we divide these 33 days dataset in four subsets and analyse their uncertainties. We show that they are self-consistent when the temperature is taken into account. This provides an alternative method to evaluate the accuracy of a fiber link, especially when the dataset includes large dead times. The result is finally interpreted as a test of the reciprocity of the propagation delay in an optical fiber. This unprecedented transfer capability could enable the comparisons of future optical clocks with expected performance at 10 −20 level and open new possibilities for stringent tests of special and general relativity.

Free-space point-to-multiplepoint optical frequency transfer with lens assisted integrated beam steering

“…Beyond 4,000 s, the value starts to decrease again thanks to the high performance of the two-layer temperature stabilization system with the better long-term stability [58]. Similar fractional frequency instability trends have been reported in the previous experimental results with the similar temperature stabilization performance [57], [76]. The results for the short 1 m freespace link and fiber interferometer as the down and up triangle markers illustrated in Fig.…”

Polarization Scramblers to Solve Practical Limitations of Frequency Transfer

“…Our system is schematically shown in Fig. 1 and is intended to analyse propagation delay fluctuations properties in singlemode fibers [27], [28]. The laser source located in Lab1 is a narrow bandwidth laser emitting at 1542.14 nm, phase and frequency locked to an ultra-stable laser with a bandwidth of about 100 kHz.…”

“…This set-up allows us to measure simultaneously frequency fluctuations for light that travels either bidirectionaly or uni-directionaly, only in spool 1, only in spool2, or any combination of both. More details and performances assessment and noise floor limits were reported in [28]. For this experiment we will focus on two beat notes we denote RT1 (Round-Trip1, at 152 MHz) and LP1 (Loop1, at 34 MHz) on photo-diode PD1.…”

GENESIS: co-location of geodetic techniques in space

“…Optical frequency standards at the leading national metrology institutes today show relative frequency inaccuracies in the 10 −18 range (corresponding to 1 cm in height) and beyond (Brewer et al 2019;Bothwell et al 2019;Beloy et al 2021). Long-distance optical frequency transfer using phasestabilized optical fibers has been demonstrated with a relative frequency inaccuracy at the 10 −19 level (Lisdat et al 2016), and even 10 −21 on shorter distances (Xu et al 2019). Free-space laser links already realized common view time transfer over thousands of kilometers at the picosecond level (e.g., with T2L2, see Exertier et al 2017), and reach on shorter distances the femtosecond level for time transfer (Sinclair et al 2019) and 10 −21 level for frequency transfer (Gozzard et al 2022).…”