Estimating the phase in groundbased interferometry: performance comparison between singlemode and multimode schemes

Aims. In this paper we compare the performance of multi and single-mode interferometry for the estimation of the phase of the complex visibility. Methods. We provide a theoretical description of the interferometric signal which enables to derive the phase error in presence of detector, photon and atmospheric noises, for both multi and single-mode cases. Results. We show that, despite the loss of ux occurring when injecting the light in the single-mode component (i.e. single-mode bers, integrated optics), the spatial ltering properties of such single-mode devices often enable higher performance than multimode concepts. In the high ux regime speckle noise dominated, single-mode interferometry is always more ecient, and its performance is signicantly better when the correction provided by adaptive optics becomes poor, by a factor of 2 and more when the Strehl ratio is lower than 10%. In low light level cases (detector noise regime), multimode interferometry reaches better performance, yet the gain never exceeds 20%, which corresponds to the percentage of photon loss due to the injection in the guides. Besides, we demonstrate that single-mode interferometry is also more robust to the turbulence in both cases of fringe tracking and phase referencing, at the exception of narrow eld of views ( < 1 00 ). Conclusions. Our conclusion is therefore that, from a theoretical point of view and contrarily to a widespread opinion, fringe trackers built using single-mode optics should be considered as a solution both practical and competitive.