This part of IEC 60793 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)
Methods A and B can be performed using one of two launches: an overfilled launch (OFL)
condition or a restricted mode launch (RML) condition. Method C is only defined for A1a.2
(and A1a.3 in preparation) multimode fibre and uses a weighted summation of DMD launch
responses with the weights corresponding to an overfilled launch condition. The relevant test
method and launch condition should be chosen according to the type of fibre.