A detector is designed for ground and space based optical experiments for high and ultrahigh energy cosmic ray studies. In this paper a separation method based on the simultaneous light recording from one 'optical pixel' by two or two pairs of silicon photomultipliers (SiPMs) is proposed. The first SiPM detects incoming light flux in the wavelength band of its maximal sensitivity. The second SiPM detects light through an optical UV filter for fluorescent light (FL). If the sensitivity characteristics of the SiPMs, the absorption characteristics of the filter elements, and the spectra of fluorescent and Cherenkov light (CL) are known, one can calculate the contribution of each component to the total light flux. Upon the completion of this work it will be possible to separate fluorescent and Cherenkov light at the stage of on-board primary processing of recorded data. This method will increase methodological accuracy of fluorescent light measurements and thus significantly reduce the impact of simulations for primary cosmic ray characteristics reconstruction.