  In a few years, the second generation instruments of the Very Large Telescope
Interferometer (VLTI) will routinely provide observations with 4 to 6
telescopes simultaneously. To reach their ultimate performance, they will need
a fringe sensor capable to measure in real time the randomly varying optical
paths differences. A collaboration between LAOG (PI institute), IAGL, OCA and
GIPSA-Lab has proposed the Planar Optics Phase Sensor concept to ESO for the
2nd Generation Fringe Tracker. This concept is based on the integrated optics
technologies, enabling the conception of extremely compact interferometric
instruments naturally providing single-mode spatial filtering. It allows
operations with 4 and 6 telescopes by measuring the fringes position thanks to
a spectrally dispersed ABCD method. We present here the main analysis which led
to the current concept as well as the expected on-sky performance and the
proposed design.
