  The crossed-sine wavefront sensor (WFS) is a pupil plane wavefront sensor
that measures the first derivatives of the wavefront. It is made by three main
components: a gradient transmission filter (GTF) built from a product of sine
functions rotated by 45 degrees around the optical axis, a 2x2 mini-lens array
(MLA) at the focus of the tested optical system and a detector array located on
a plane conjugated to the pupil. The basic principle consists in acquiring four
pupil images simultaneously, each image being observed from different points
located behind the GTF. After the simulation work which demonstrated the
wavefront reconstruction capability, we are now in the phase of implementation
of the prototype in the lab. The crossed-sine WFS could achieve a simultaneous
high spatial resolution at the pupil of the tested optics and absolute
measurement accuracy comparable to that attained by laser-interferometers. In
this paper we introduce seven customized phase masks and make measurements of
them.First tests and resultsare demonstrated, based on which we explore the
performance of our crossed-sine WFS and make comparisons with that of the
laser-interferomete
