an optical demultiplexer includes an electrooptic modulator which modulates a beam of light in response to frequency - multiplexed radio - frequency information signals , to produce diverging beamlets of light . the diverging beamlets are separated by a spatial separator arrangement , and each beamlet , including the information of its rf carrier , is coupled to a separate optical detector . the detector can extract amplitude modulation from the signal . in order to reconstruct the rf signal as well as the amplitude modulator , an optical &# 34 ; local oscillator &# 34 ; signal is coupled to each detector together with its information signal . signal loss due to vibration or misalignment is avoided , and heterodyne mixing efficiency is maximized in an embodiment of the invention , by propagating the olo and information signals through a single - mode optical fiber to the detector . in a particular embodiment of the invention , the olo signal is applied to a first fiber , the information signal is applied to a second fiber , and the first and second fibers are coupled together by a fiber - optic coupler . in another embodiment of the invention , the olo signal results from generating an rf l . o . signal , and combining the rf l . o . local signal with the information signals before application to the electrooptic modulator , to generate an olo beamlet which is subject to the same vibration and misalignment as the signal beamlets .