  Injection of mode-filtered electrons into a phase-sensitive four-terminal
waveguide Aharonov-Bohm (AB) ring is studied. An individually tuneable quantum
point contact (QPC) in a waveguide lead of the GaAs/AlGaAs-ring allows to
selectively couple to one-dimensional modes in the ring. Thus, we demonstrate
single-mode transport in a multi-mode waveguide structure. Coherent
mode-filtering by the lowest QPC subband is verified by non-local bend
resistance and phase-sensitive AB interference measurements.
