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For the optical system of the telescope, with the increase in telescope size, the manufacture of monolithic primary
becomes increasingly difficult. Instead, the use of segmented mirrors, where many individual mirrors (the segments)
work together to provide an image quality and an aperture equivalent to that of a large monolithic mirror, is considered a
more appropriate strategy. But with the introduction of the large telescope mirror comprised of many individual
segments, the problem of insuring a smooth continuous mirror surface (co-phased mirrors) becomes critical. One of the
main problems is the measurement of the vertical displacement between the individual segments (piston error), for such
mirrors, the segment vertical misalignment (piston error) between the segments must be reduced to a small fraction of
the wavelength (<100nm) of the incoming light. The measurements become especially complicated when the piston error
is in order of wavelength fractions. To meet the performance capabilities, a novel method for phasing the segmented
mirrors optics system is described. The phasing method is based on a high-aperture Michelson interferometer. The use of
an interferometric technique allows the measuring of segment misalignment during the daytime with high accuracy,
which is a major design guideline. The innovation introduced in the optical design of the interferometer is the
simultaneous use of monochromatic light and multiwavelength combination white-light source in a direct method for
improving the central fringe identification in the white-light interferometric phasing system. With theoretic analysis, we
find that this multiwavelength combination technique can greatly increase the visibility difference between the central
fringe and its adjacent side fringes, and thus it offers an increased signal resolution. So make the central fringe
identification become easier, and enhance the measure precision of the segment phasing error. Consequently, it is
suitable for high-precision measurement purpose and application in the segment piston error phasing system. The
description about the expected interferograms and the feasibility of the phasing method are presented here.
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