UNE-EN IEC 60793-1-41:2025

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 60793-2-30 and IEC 60793-2-

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 A1-OM3 to

A1-OM5 multimode fibres 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.

NOTE 1 These test methods are commonly used in production and research facilities and are not easily accomplished in the field.

NOTE 2 OFL has been used for the modal bandwidth value for LED-based applications for many years. However,

no single launch condition is representative of the laser (e.g. VCSEL) sources that are used for gigabit and higher

rate transmission. This fact drove the development of IEC 60793-1-49 for determining the effective modal bandwidth

of laser optimized 50 ¼m fibres. See IEC 60793-2-10:2019 or later and IEC 61280-4-1:2019 or later for more information.