A device for optical power measurement along an optical transmission path between a first network element and a second network element, the optical transmission path supporting bidirectional propagation of downstream light and upstream light, the downstream light comprising a plurality of downstream signals (38, 40) having mutually different central wavelengths, the device comprising: - an optical power splitter assembly configured to extract, from the optical transmission path, a portion of the downstream light and a portion of the upstream light, characterized in that it further comprises - an upstream wavelength analyzer configured to receive the extracted portion of the upstream light and determine therefrom an upstream spectral characteristic of the upstream light, said upstream spectral characteristic of the upstream light being a measured value corresponding to a wavelength of the upstream light or a presence of the upstream light in each of a plurality of distinct upstream spectral bands, the upstream wavelength analyzer generating a detection signal indicative of the upstream spectral characteristic; - a processing unit coupled to the upstream wavelength analyzer and configured to receive the detection signal indicative of the upstream spectral characteristic and to determine therefrom a downstream spectral characteristic of a downstream signal of interest among the plurality of downstream signals (38, 40), said downstream spectral characteristic being an expected value of a wavelength of the downstream signal of interest or a spectral range in which the downstream signal of interest is expected to lie; - a downstream filter assembly configured to receive and filter the extracted portion of the downstream light to select therefrom a portion of the downstream signal of interest according to the determined downstream spectral characteristic; and - a downstream optical power meter assembly configured to measure an optical power parameter of the portion of the downstream signal of interest selected by the downstream filter assembly. - an optical power splitter assembly configured to extract, from the optical transmission path, a portion of the downstream light and a portion of the upstream light, characterized in that it further comprises - an upstream wavelength analyzer configured to receive the extracted portion of the upstream light and determine therefrom an upstream spectral characteristic of the upstream light, said upstream spectral characteristic of the upstream light being a measured value corresponding to a wavelength of the upstream light or a presence of the upstream light in each of a plurality of distinct upstream spectral bands, the upstream wavelength analyzer generating a detection signal indicative of the upstream spectral characteristic; - a processing unit coupled to the upstream wavelength analyzer and configured to receive the detection signal indicative of the upstream spectral characteristic and to determine therefrom a downstream spectral characteristic of a downstream signal of interest among the plurality of downstream signals (38, 40), said downstream spectral characteristic being an expected value of a wavelength of the downstream signal of interest or a spectral range in which the downstream signal of interest is expected to lie; - a downstream filter assembly configured to receive and filter the extracted portion of the downstream light to select therefrom a portion of the downstream signal of interest according to the determined downstream spectral characteristic; and - a downstream optical power meter assembly configured to measure an optical power parameter of the portion of the downstream signal of interest selected by the downstream filter assembly.