An inexpensive broadband source such as an ASE source, used for erbium amplifier measurements, compares well with the use of a prior art ITU grid. Deltas are less than 0.4 and 0.3 dB for gain and noise figure respectively. The spectral loading used to test erbium amplifiers needs to closely resemble conditions seen in the field. Use of an ITU grid is a good way of achieving this, however it is a costly solution and may restrict the spectral resolution. Use of a high power amplified spontaneous emission source gives a cost-effective alternative, which compares well with ITU grid measurements. In addition the spectral resolution of the measurement is then only limited by the spectral resolution of the optical spectrum analyzer.