Published/Posted: July 24, 2019
Authors: Lipkowitz, S. T.; Horton, T. U.; Murphy, T. E.
DOI: 10.1364/OL.44.004710Abstract: We present an electro-optic downconverting mixer with image rejection capabilities. By using a dual-drive Mach–Zehnder modulator (DD-MZM) to modulate an optical carrier with both a signal and a local oscillator, and an asymmetric Mach–Zehnder interferometer (AMZI) to filter the optical spectrum into two separate ports, we generate photocurrents with a phase relationship controlled via direct current (DC) bias voltage applied to the DD-MZM. By choosing these photocurrents to be in quadrature and combining them in a 90-degree electrical hybrid we achieve over 40 dB of image rejection, with a 3 dB bandwidth of approximately 20 GHz limited mainly by the AMZI free spectral range. We demonstrate downconversion of a 1 Gbaud quadrature phase-shift keyed (QPSK) signal even in the presence of a strong interfering image tone.