Abstract
We introduce a family of complex modulation signals that are generated as patterns over the real and
imaginary plane for characterization of coherent optical receivers. The properties of the complex signals can be
predicted from first principles, enabling quantitative comparisons between measurement and theory. An optical
heterodyne technique with phase-locked loops for frequency control and narrow-band lasers was used to create the known
signals, providing temporal stability and ease of operation. The modulation patterns could be made arbitrarily
intricate simply by selection of the heterodyne frequencies, with no hardware modifications. The technique is capable
of generating signals with frequencies of more than 100 GHz. A real-time optical modulation analyzer was used to
visualize the modulation patterns and illustrate their properties. In turn, we used the modulation patterns to
characterize the coherent receiver within the modulation analyzer, thereby examining its demodulation algorithm,
software processing, digital filtering, and detector gain balance. By working with known modulation patterns, we were
able to create an error vector waveform to allow quantitative evaluation of measured signals as they spanned the
complex plane.
© 2013 USGov
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