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A photonic approach to generating square waveforms using a single dual-parallel Mach-Zehnder modulator driven by a single-tone radio frequency signal is proposed and demonstrated. The two sub MZM are set to be biased at the minimum transmission point and the maximum transmission point, respectively. By simply adjusting the modulation index to have a proper value, optical intensity with expression corresponding to the Fourier expansion of a square waveform is obtained, and square waveforms will be generated. Neither an optical filter nor an electrical component of frequency multiplier or hybrid is needed to guarantee the simplicity and the wide working frequency range. A proof-of-concept experiment is taken. Both 1- and 4-GHz square waveforms fitting well with the ideal ones are successfully generated. [ABSTRACT FROM AUTHOR]

We propose a technique for the generation of optical frequency comb from a single source, which reduces the costs of optical access networks. Two Mach-Zehnder modulators are cascaded with one phase modulator driven by radiofrequency signals. With 10-GHz frequency spacing, the generated 40 optical multi-carriers have good tone-to-noise ratio with least excursions in their comb lines. The laser array at the optical line terminal of the conventional wavelength division multiplexed passive optical network (WDM-PON) system has been replaced with optical frequency comb generator (OFCG), which may result in cost-effective optical line terminal (OLT) supporting a large-capacity WDM-PON system. Of 40 carriers generated, each carrier carries 10 Gbps data based on differential phase-shift keying. Four hundred Gbps multiplexed data from all channels are successfully transmitted through a fiber span of 25 km with negligible power penalties. Part of the downlink signal is used in uplink transmission at optical network unit where intensity-modulated on-off keying is deployed for remodulation. Theoretical analysis of the proposed WDM-PON system based on OFCG are in good agreement with simulation results. The metrics considered for the analysis of the proposed OFCG in a WDM-PON system are power penalties of the full-duplex transmission, eye diagrams, and bit error rate. [ABSTRACT FROM AUTHOR]