Spectrally-resolved interferometry (SRI) is a very useful technique to measure distances and surface profiles based on
the analysis of the spectral interferogram. The most attractive feature of SRI is to obtain the spectral phase to extract the
measuring distance at once without any scanning mechanism opposed to the low coherence scanning interferometry
although phase shifting techniques can be involved in SRI to improve the measurement accuracy in some cases.
However, the measurement range of SRI is relatively small because of the fundamental measuring range limitations such
as the maximum measurable range and the minimum measurable range. Moreover, the important issue in SRI is the
direction ambiguity because it always provides the positive values, regardless of the direction. In case of measuring
optical path difference (OPD) when the reference path is longer than the measurement path, the measurement result of
SRI is the same as the distance in the opposite case. Then, SRI only uses one direction to measure distances or surface
profiles for the linearity of the measurement results due to these fundamental characteristics although its whole
measuring range is two times longer. In this investigation, we propose a very simple and effective technique to eliminate
the direction ambiguity and the dead zone, which limit the measurable range in SRI. By using a dispersive material, the
nonlinear spectral phase caused by the dispersion can provide useful information and determine the direction of
measuring distances. In addition, the dead zone can be successfully removed by two complementary measurement results
in dichroic SRI.