Extinction spectrum of a star by iterative Bracewell nulling uni-axial (Michelson) interferometers of order n = 0,1,...,12. The original Bracewell n = 0 is in black, order 1 in yellow, 2 in red, etc. The x-axis is the wavelength, either Δλ / λ₀ (bottom) or λ in μm for λ₀ = 9.05   μm (top). The integration has been performed over an Airy square of size 2λ₀ / d where d is the size of the mirrors. The maximum bandwidth is indicated between the two dashed vertical lines, and it meets the darwin project nominal bandwidth indicated by the two broken vertical lines. The y-axis is the log  of the integrated extinction factor, 0 means no extinction, and the horizontal line at −5 sets the nominal darwin extinction factor of 10⁵.