Abstract

A DPSK communication system employs an optical signal which comprises plural, coherent, optical frequencies, each optical frequency positioned within a range of frequencies (i.e., a "frequency slot"). The optical signal comprises plural frequency slots, with the wavefront in each time segment of each frequency slot being phase modulated in accordance with data signals. Plural frequency slots are transmitted "in parallel", in each of a plurality of succeeding time segments. A demodulator includes first and second optical paths, the first component of the optical signal directed onto the first optical path and a second component directed onto the second optical path. A modulator is positioned in at least one of the optical paths and is responsive, during a time segment, to a first applied control signal, to alter the phase, and thus the frequency, of the first component by approximately one frequency slot. At the output of the first and second optical paths, an optical coupler interferes the first component and the second component so as to enable constructive and destructive interference therebetween in accordance with respective phase modulations thereof.