A new Mueller matrix ellipsometer (MME) is presented. It provides the simultaneous measurement of the 16 Mueller matrix coefficients in four modulation periods (80 mu s under the present conditions). This system is accurate (error less than or equal to 1%), robust since there are no moving parts, enables low-light-level measurements without a chopper and lock-in amplifier and can be easily used for real time measurements. The setup is based on the polarization modulator-sample-polarization detector configuration. The polarization modulation is provided by a coupled-phase-modulator (CPM) which uses two identical phase-locked electro-optic phase modulators operating at 50 KHz. With the introduction of a coupling object between the two phase modulators, the four Stokes parameters of the light beam, including the intensity, are independently modulated on the basis of the first and second complex harmonics of the modulation signal. The polarization of light, after interaction with the sample, is measured with a multichannel division of amplitude polarimeter (DOAP). This DOAP is based on a slightly beveled amorphous-silicon (a-Si) coated glass plate. The high index of refraction contrast between a-Si and SiO2, provides an efficient polarimeter, less sensitive to the angle of incidence than usual dielectric-coated ones. The spectroscopic capability of the MME is illustrated by preliminary measurements of depolarization effects at two laser wavelengths : He-Ne at 632.8 nm and Ar at 488 nm.