Comparison of integrated optics concepts for a near-infrared multi-telescope beam combiner

Second generation VLTI instruments will be able to use of the array full imaging capability with up to 8 telescopes. Such an instrument will allow astronomers to measure 28 visibilities and 21 independent closure-phases at the same time, providing therefore rapidly imaging abilities with a spatial resolution of one milliarcsecond in the near infrared range. The VITRUV project is a proposition to achieve the VLTI interferometric combination thanks to single-mode planar optics (the so-called integrated optics, IO). IO technologies allow to design integrated combiners with remarkable stability and self allignement properties. In addition, modal filtering associated with photometric calibration will lead to accurate visibility and closure-phase measurements. In this paper we present a detailed analysis of beam combination concepts that takes into account several constraints: throughput, signal to noise ratio, interferometric efficiency, integrated optics circuit design constrains and astrophysical requirements for imaging mode.