IEC 60793-1-41:2010 describes three methods for determining and measuring the modal bandwidth of multimode optical fibres (see IEC 60793-2-10, IEC 60793-30 series and IEC 60793-40 series). The baseband frequency response is directly measured in the frequency domain by determining the fibre response to a sinusoidaly modulated light source. The baseband response can also be measured by observing the broadening of a narrow pulse of light. The calculated response is determined using differential mode delay (DMD) data. The three methods are: - Method A - Time domain (pulse distortion) measurement - Method B - Frequency-domain measurement - Method C - Overfilled launch modal bandwidth calculated from differential mode delay (OMBc). The main change with respect to the previous edition is the addition of a third method for determining modal bandwidth based on DMD data and to improve measurement procedures for A4 fibres. This standard should be read in conjunction with IEC 60793-1-1 and IEC 60793-1-2, which cover generic specifications.