A passive optical network (PON) device and method for optical power measurement along an optical transmission path supporting bidirectional propagation of downstream light and upstream light between two network elements of a PON is provided. The device includes an optical power splitter assembly extracting respective portions of the upstream and downstream light, and an upstream wavelength analyzer determining, from the extracted upstream light, an upstream spectral characteristic of the upstream light. The device also includes a processing unit determining, based on the upstream spectral characteristic, a downstream spectral characteristic of a downstream signal of interest among a plurality of downstream signals of the downstream light, and a downstream filter assembly filtering the extracted downstream light to select a portion of the downstream signal of interest. The device further includes a downstream optical power meter assembly measuring an optical power parameter of the selected portion of the downstream signal of interest.