We propose a point-to-point or single-ended communications technique based on single-mode optical fibers that uses all-optical pulse multiplexing at the transmitter and coherent optical correlation at the receiver. This technique shows potential for application to secure untappable communications, fiber local-area networks, and optical ranging in the presence of a strong white-light background. The system can employ a low-coherence source, is insensitive to source phase noise and polarization-state rotation in the fiber link, and uses simple electronic threshold detection. Coherent correlation and anticorrelation are demonstrated experimentally, and practical requirements are examined.