Planar optics three-telescope beam combiners for astronomical interferometry

Planar optics technologies allow to design complex single- mode interferometric beam combiners on single miniaturized optical components. Our current collaborations with laboratories and companies allow us to deeply investigate the characteristics of components produced either by silica etching (LETI/CEA technology) or by ion diffusion process (LEMO/ENSERG and GeeO technology). Based on excellent results with 2-telescope beam combiners in the near infrared band (atmospheric H band), the extension to three telescopes has been achieved with both technologies and different combination configurations (co-axial and multi-axial). The specific application of astronomical interferometry requires the full characterization of such components in term of global throughput, identification of photon losses, polarization maintaining properties, interferometric behavior in monochromatic and polychromatic cases.