  We demonstrate that important information about linear optical circuits can
be obtained through the phase shift induced by integrated optical resonators.
As a proof of principle, the phase of an unbalanced Mach-Zehnder interferometer
is determined. Then the method is applied to a complex optical circuit designed
for linear optical quantum computation. In this controlled-NOT gate with qubit
initialization and tomography stages, the relative phases are determined as
well as the coupling ratios of its directional couplers.
