Characterization of Complex Optical Modulation Formats at 100 Gb/s and Beyond by Coherent Optical Sampling

Optical fiber communication systems are migrating toward the use of sophisticated, nonbinary, modulation formats. It is thus important to develop measurement techniques and solutions capable of unambiguously quantifying such signals and associated hardware. Although one can adapt certain techniques developed for wireless signal characterization, significant differences exist between optical and RF wireless implementations of advanced modulation formats. To meet this measurement demand we present a method for characterizing high symbol rate multilevel modulation optical signals with high fidelity, based on coherent optical sampling, as a complement to the standard real-time electrical sampling approach. The technique enables constellation- and waveform monitoring, bit-error rate and error-vector magnitude analysis, which makes it suitable for transmitter characterization.