An optical line terminal includes an optical comb generator, N downlink channels Dk, and N uplink-photodetectors PDk. The optical comb generator is configured to generate a carrier signal having an optical-frequency-comb spectrum and including N optical tones Tk and N optical tones Rk, k={1, 2, . . . , N}. Each of the N downlink channels Dk is optically coupled to the optical comb generator and is configured to generate a respective downlink signal DSk that includes optical tone Tk modulated by downlink data. Each of the N uplink-photodetectors PDk is configured to receive a respective one of a plurality of modulated uplink signals USk, having optical tone Rk as a carrier signal.