Comparison of series and parallel optical modulators for microwave down-conversion

Photonic down-conversion of microwave signals using a pair of broad-band optical modulators is investigated theoretically and experimentally for cascaded and parallel modulator topologies. Improvement of 14 dB, roughly equal to the composite modulator insertion loss, was measured. Low-biasing and balanced detection in parallel links allows a further improvement of over 20 dB through increased laser power without detector saturation.