A lattice includes a transmit bus formed of a single mode optical fiber and a return bus formed of a multimode optical fiber. An optical transmitter applies input signals to the transmit bus, and an optical receiver receives the signals guided by the return bus. The return fiber is looped around the couplers so that the signal output from each segment of the lattice passes through all the preceding segments before reaching the receiver. The optical couplers have asymmetric coupling efficiencies so that recirculating light is attenuated.