Linear optical sampling capable of characterizing advanced modulation formats with high fidelity can satisfy the demand as the rapid development of fiber optical communications.

We demonstrate on-field measurement trial of commercial four-channel 128 Gbps polarization division multiplexing quadrature phase shift keying (PDM-QPSK) signals with truly random characteristics by self-developed equipment using linear optical sampling.

We carry out performance comparison with the Agilent modulation format analyzer (N4391A), and verify that the prototype has almost the same capability for on-site measurement.