We propose and demonstrate a novel optical method to generate multi-level signals with reduced driving voltage through degenerate four-wave mixing processes. With the present approach, it is possible to extend the size of the signal constellations and at the same time reduce the modulator driving voltage without bandwidth degradations. In our experiments, one amplitude shift keying (ASK) signal and one differential phase shift keying (DPSK) signal are used to generate one ASK-DPSK signal with clearly opened eye-diagrams and error-free demodulation results. Our numerical simulations show that the proposed method is applicable for generating several 8-ary and 16-ary quadrature amplitude modulation (QAM) signals with silicon waveguides at a higher modulation baud rate.
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