  A recent experiment performed by S. S. Afshar et al. has been interpreted as
a violation of Bohr's complementarity principle between interference visibility
and which-path information in a two-path interferometer. We have reproduced
this experiment, using true single-photon pulses propagating in a two-path
wavefront- splitting interferometer realized with a Fresnel's biprism, and
followed by a grating with adjustable transmitting slits. The measured values
of interference visibility V and which-path information, characterized by the
distinguishability parameter D, are found to obey the complementarity relation
V^2+D^2=<1. This result demonstrates that the experiment can be perfectly
explained by the Copenhagen interpretation of quantum mechanics.
