Blue line: measured null depth, when the wavelength is fixed (laser diode) and the piston of the cells on the SDM is scanned to maintain a nulling phase pattern at each step for the reference wavelength, as indicated on the horizontal axis. The bandpass at a null depth level of 10^-2 is indicated by the horizontal straight line. Solid black line: null depth in a perfect case. Dotted line: nulling depth for a perfect Bracewell interferometer.