  We examine different methods to implement coherent detection in the
subcarrier wave quantum key distribution (SCW QKD) systems. For classical
wavefields, we present the models describing homodyne-type and heterodyne-type
coherent detection schemes needed to extract information from the quadrature
phase-coded multimode signals used in SCW QKD. Practical feasibility of the
proposed schemes is corroborated by the experiments.
