Abstract: A method of and an apparatus for coherently detecting modulated optical signals employing optical mask-generated signals is disclosed. A spatial light modulator modulates a source beam with an information signal composed of one or more frequency components within its frequency bandwidth. The frequency components which are output from the modulator, including the zero frequency component, diverge and become spatially separated. A reference beam is formed from the zero frequency component by a reference beam generator. The reference beam is generated so as to appear to diverge from a reference point located at or near the spatial light modulator. The optical detector performs coherent detection by squaring the sum of the frequency components and the reference beam to provide an output information signal as a function of the input information signal.