Monitoring of optical signals from constellation diagrams measured with linear optical sampling

Linear optical sampling detects samples of the electric field of an optical waveform using its interference with a train of sampling pulses. This unique ability allows statistical electric-field characterization, for example, the measurement of a constellation diagram in the complex plane. From such information, one can directly track impairments that affect the phase and, more generally, the electric field of a data-encoded telecommunication channel. Constellation diagrams of 10-Gb/s phase-shift-keyed (PSK) signals are measured using a waveguide implementation of linear optical sampling. The intensity and phase fluctuations of these signals are quantified in various situations typically met in optical networks. The properties of various data-modulation schemes for phase-shift keying are investigated, and the noise induced by amplified spontaneous emission (ASE) on the electric field is directly quantified. Finally, a direct measurement of the Gordon-Mollenauer nonlinear phase noise is performed.