We propose and demonstrate two new techniques based on the hybrid-interferometer, composed of optical low-coherence
interferometer and confocal optics to simultaneously measure the phase index (np), group index (ng) and
geometrical thickness (t) of optically transparent materials. In the first method, we utilize the interference signal
measured with several laser sources having different center wavelength and calculate the square of dispersion parameter
τc2) of a glass plate from the interference signals. By analyzing the dispersion effect of interference signals, we can
successfully separate the three parameters. In the second method, we approximate the derivative term of phase index in
the definition of group index, by using the confocal signals measured with the laser sources having different center
wavelength. From this approximation, we can also separate the parameters.
The average measurement errors of first and second method are ~0.123 %, ~0.061 % in geometrical thickness,
~0.133 %, ~0.066 % in phase index, and ~0.106 %, ~0.057 % in group index, respectively, for eight different samples
which are B270, CaF2, two of BK7, two of fused silica, cover glass and cigarette cover film. We are currently
attempting to improve the accuracy and this technique will be extended to index measurement for biomedical tissues.