Comparison of optical-power meters between the NIST and the PTB

We describe the results of a comparison of optical-power meters undertaken by the National Institute of Standards and Technology (NIST, USA) and the P hysikalisch-Technische Bundesanstalt (PTB, Germany) at nominal wavelengths of 1300 nm and 1550 nm. Both laboratories used thermal detectors as referen ce standards, which were compared using a germanium trap detector as a tran sfer standard. Measurement results showed differences of less than 1 part i n 10(3), well within the combined uncertainty for both laboratories.