An optical data signal can be sampled by linearly combining the optical
data signal with optical sampling pulses, and delivering the combination
to first and second balanced detectors. The optical data signal and the
optical sampling pulse are configured to have a first phase difference at
the first balanced detector and a second phase difference at the second
balanced detector. Typically, a difference between the first phase
difference and the second phase difference is configured to be about 90
degrees. In-phase and quadrature balanced detector outputs can be
combined as a sum of squares to produce a linear sampling signal
representative of data signal intensity, and the sample pulses can be
configured to temporally step through the optical data signal so that a
sampled representation of the optical data signal is obtained.