We experimentally investigate interference effects in transport across a single incompressible strip at the edge of the quantum Hall system by using a Fabry-Perot type interferometer. We find the interference oscillations in transport across the incompressible strips with local filling factors $ u_c=1, 4/3, 2/3$ even at high imbalances, exceeding the spectral gaps. In contrast, there is no sign of the interference in transport across the principal Laughlin $ u_c=1/3$ incompressible strip. This indicates, that even at fractional $ u_c$, the interference effects are caused by normal electrons. The oscillations period is determined by the effective interferometer area, which is sensitive to the filling factors because of screening effects.
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