Dispersion-tolerant all-optical subcarrier modulator for broad-band BPSK transmissions

We introduce a novel all-optical binary phase-shift keying (BPSK) subcarrier modulator based on commercial Mach-Zehnder electrooptic modulators (MZ-EOMs) that provides a dispersion-tolerant output signal with enhanced optical modulation depth. The design exploits the nonlinear transfer function of MZ-EOM to halve the frequency of the electrical signal required to generate a given subcarrier. Moreover, the bit rate of the data imposed on the subcarrier is shown to be constrained only by the bandwidth of the deployed MZ-EOM; hence, in principle, current commercial technology could provide BPSK modulation of microwave/millimeter-wave subcarriers at up to 40 Gb/s. The operation of the BPSK subcarrier modulator and its tolerance to chromatic dispersion impairments are experimentally demonstrated transmitting a 15-GHz subcarrier with 2.5-Gb/s BPSK modulation over a 25-km standard single-mode fiber link.