Experimental studies of fiber phase dynamics in the scope of the LISA backlink @LISAcommunity

Uploaded July 2022 | Updated September 2026, 59 minutes ago

The current baseline design of LISA will utilize telescope pointing to keep the inter spacecraft laser links established over the orbit. This approach requires an intra-spacecraft connection between the two movable optical subassemblies (MOSA), called backlink. It is foreseen to utilize an optical fiber to establish the backlink, making it susceptible to spurious phase dynamics that couple into the measurement over backscattered light from the fiber.
Here, we present the results of experimental studies investigating these phase dynamics of different optical fibers, including the current baseline fiber for LISA. We show that no change in the backscattered amplitude is expected over the mission duration, that the temperature to phase coupling in the fibers is acceptable for the performance, and that the expected motion of the fiber during the actuation of the MOSA is negligibly small. We also present measurement results of backscatter and temperature-coupling measurements for several FIOS that were built for the backlink engineering model.
Lastly, we apply the dynamics to a performance simulation of the backlink and find that the required performance can be achieved depending on the chosen temperature stability of the backlink fiber even without applying balanced detection.

Authors: Johann Max Rohr, Stefan Ast, David Robertson, Katharina-Sophie Isleif, Jens Reiche, Oliver Gerberding, Gerhard Heinzel
Presenter: Johann Max Rohr

Experimental studies of fiber phase dynamics in the scope of the LISA backlink

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$Thermo-elastic and thermo-optical effects on-board LISA Pathfinder Thermal gradients on board the LISA Pathfinder mission induced effects with a potential impact to perturb the main differential acceleration measurement between both free-falling test masses. Temperature gradients across the housing produced forces through three different effects, namely asymmetric outgassing, radiation pressure and radiometer effect. The latter is related to the residual gas pressure around the test mass and, therefore, allows the estimation of the Brownian noise contribution, one of the limiting noise contributions for a future observatory like LISA. In addition to thermal forces arising due to gradients around the proof mass, thermo-optical and thermo-elastic effects can also contribute to instrument noise. There were two places where such distortion could be critical. First, the optical window, i.e. the interface between the optical bench and the test mass. This optical element the only not bonded on the Zerodur optical bench was clamped in a Titanium ring and therefore was susceptible to mechanical stress or changes in the refractive index due to thermal gradients across the glass. The second location were the struts holding the optical bench inside the thermal shield acting as the main thermal link to the outside (thermally noisier) environment. Temperature changes in these structures induced net displacements or tilts of the bench with direct impact on the interferometer read-out. During the LISA Pathfinder mission we have carried out several experiments by which we characterized and quantified the previous effects. The aim of this presentation is to update the results about the impact of thermo-elastic and thermo-optical effects, that we have obtained by analyzing the experiments, on the main differential acceleration measurement. In the same way we want to give an estimate of the impact of these thermal effects for the LISA mission. Authors: PhD Francisco Rivas (Presenting) Universidad Loyola Andalucía, Sevilla, Spain$