Measuring absolute spectral radiance using an erbium-doped fiber amplifier

We describe a method to measure the spectral radiance of a source in an absolute way without the need of a reference. Here we give the necessary detail to allow for the device to be reproduced from standard fiber-optic components. The device is suited for fiber-optic applications at telecom wavelengths and calibration of power meters and spectrometers at light levels from 1 nW to 1 $\ensuremath{\mu}$W.