Impact of turbulent phase noise on frequency transfer with asymmetric two-way ground-satellite coherent optical links

Clélia Robert,Peter Wolf,Jean-Marc Conan

doi:10.1088/1742-6596/723/1/012039

Abstract

Bidirectional ground-satellite laser links suffer from turbulence-induced scintillation and phase distortion. We study how turbulence impacts on coherent detection capacity and on the associated phase noise that restricts clock transfer precision. We evaluate the capacity to obtain a two-way cancellation of atmospheric effects despite the asymmetry between up and down link that limits the link reciprocity. For ground-satellite links, the asymmetry is induced by point-ahead angle and possibly the use, for the ground terminal, of different transceiver diameters, in reception and emission. The quantitative analysis is obtained thanks to refined end- to-end simulations under realistic turbulence and wind conditions as well as satellite cinematic. These temporally resolved simulations allow characterizing the coherent detection in terms of time series of heterodyne efficiency for different system parameters. We show that Tip/Tilt correction on ground is mandatory at reception for the down link and as a pre-compensation of the up link. Good correlation between up and down phase noise is obtained even with asymmetric apertures of the ground transceiver and in spite of pointing ahead angle. The reduction to less than 1 rad2 of the two-way differential phase noise is very promising for clock comparisons.

Highlights

Optical bi-directional links between ground stations and spacecraft in Earth or solar system orbits are of interest for a number of applications ranging from telecommunications to navigation, geodesy, time/frequency metrology and fundamental physics [1,2,3,4]
In the presence of a point ahead angle of 63 μrad, the phase noise of the up and down links as well as their difference is plotted for the case where the apertures are symmetric (Dg−emit = Dg−rec = 0.4 m) with tip/tilt correction on the down link and the same tip/tilt correction applied as pre-compensation on the up link
In summary, we show that the down link must be tip/tilt corrected to improve the heterodyne efficiency, avoiding large fluctuations in signal to noise ratio with frequent extinctions

Summary

Introduction

Optical bi-directional links between ground stations and spacecraft in Earth or solar system orbits are of interest for a number of applications ranging from telecommunications to navigation, geodesy, time/frequency metrology and fundamental physics [1,2,3,4]. It is interesting to note that in the particular case where Ɛ = Ɛ⋆ and Ɛ = Ɛ⋆ , symmetry on each terminal between the emission and the local oscillator, is equal to Under these conditions the link reciprocity is perfect, meaning that both sides of the link have strictly identical heterodyne efficiency and phase noise. The fact that one can model the downlink with a downward plane wave propagation, neglecting the Gaussian nature of the beam coming from the satellite, is a usual approximation in ground-space optical links, both for incoherent and coherent detection. The reciprocal expression of shows that, based on the same approximation, the uplink coupling can be calculated from this downward plane wave This is true only when neglecting the point ahead effect mentioned in item 3. There is no need to simulate the upward propagation of a Gaussian beam

Model and methods

Findings

Conclusion