An incoming DPSK optical signal is first split into two beams with equal intensities, in which one beam is delayed in space by an optical path difference that introduces a time delay corresponding to one bit. The two beams in the two paths are then coherently recombined to interfere each other constructively or destructively.
In the context of DPSK signal processing, an incoming optical signal is first split into two equal-intensity beams, with one beam being delayed by an optical path difference that corresponds to a single bit period. These beams are then recombined coherently to produce either constructive or destructive interference.