  The very recent years have seen a promising start in scientific publications
making use of images produced by near-infrared long-baseline interferometry.
The technique has reached, at last, a technical maturity level that opens new
avenues for numerous astrophysical topics requiring milli-arcsecond
model-independent imaging. The Very Large Telescope Interferometer (VLTI) is on
the path to be equipped with instruments capable to combine between four to six
telescopes. In the framework of the VLTI second generation instruments Gravity
and VSI, we propose a new beam combining concept using Integrated Optics (IO)
technologies with a novel ABCD-like fringe encoding scheme. Our goal is to
demonstrate that IO-based combination brings considerable advantages in terms
of instrumental design and performance. We therefore aim at giving a full
characterization of an IO beam combiner to establish its performances and check
its compliance with the specifications of an imaging instrument. Laboratory
measurements were made in the H band with a dedicated testbed. We studied the
beam combiners through the analysis of throughput, instrumental visibilities,
phases and closure phases in wide band as well as with spectral dispersion.
Study of the polarization properties is also done. We obtain competitive
throughput, high and stable instrumental contrasts, stable but non-zero closure
phases which we attribute to internal well calibrable optical path differences.
We validate a new static and achromatic phase shifting IO function close to the
nominal 90deg value. All these observables show limited chromaticity over the H
band range. Our results demonstrate that such ABCD-like beam combiners are
particularly well suited to achieve aperture synthesis imaging. This opens the
way to extend to all near infrared wavelengths and in particular, the K band.
