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The dielectric constant, magnetic permeability, and refractive index are the fundamental optical parameters of a material. To investigate these optical parameters, a mixed-type common-path heterodyne interferometer is developed in this paper. By using this interferometer to detect the amplitudes and phases of both the transmission and reflection coefficients, the complex dielectric constant, magnetic permeability, and refractive index can be obtained using the algorithm discussed here. The validity of the mixed-type common-path heterodyne interferometer is demonstrated for visible lights, such as red, green, and blue, using lasers as light sources. Furthermore, the specifications for characterizing the optical properties of samples using the mixed-type common-path heterodyne interferometer are investigated. For example, dielectric constant epsiv, magnetic permeability mu, and the refractive index n of 2.161 + i0.002, 0.9997 - i0.0009, and 1.4699 - i3.4 times10-7 with low uncertainties of 0.003 + i0.002, 0.0003 + i0.0009, and 0.0007 + i8 times10-8, respectively, for a fused quartz measuring 632.8 nm are investigated. It also demonstrated that, in the case of the investigation in visible ranges, the measurement procedure is performed by only the common-path transmission type heterodyne interferometer.