National reference standards for determining optical-fibre power maintained by the National Institute of Standards and Technology (NIST, USA) and the All-Russian Research Institute for Optophysical Measurements (VNIIOFI, Russian Federation) were compared at wavelengths near 1300 nm and 1550 nm at a power level of 0.5 mW. Instruments from both laboratories are based on thermal detectors capable of electrical calibration. The comparisons indicate relative differences of 2 parts in 10 3 or less, which is easily within the combined uncertainty of the two laboratories.

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