IEC 61300-3-43 pdf download

IEC 61300-3-43 pdf download Fibre optic interconnecting devices and passive components – Basic test and measurement procedures – Part 3-43: Examinations and measurements – Mode transfer function measurement for fibre optic sources
1 Scope
This part of IEC 61 300 describes the method for measuring the mode transfer function (MTF) to be used in characterising the launch conditions for measurements of attenuation and or return loss of multimode passive components. The MTF may be measured at the operational wavelengths.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 61 300-1 , Fibre optic interconnecting devices and passive components – Basic test and measurement procedures – Part 1: General and guidance
IEC 61 300-3-4, Fibre optic interconnecting devices and passive components – Basic test and measurement procedures – Part 3-4: Examination and measurements – Attenuation
IEC 60793-1 -20, Optical fibres – Part 1-20: Measurement methods and test procedures – Fibre geometry
3 General description
The modal distribution launched into multimode fibre can vary widely with different light sources. This variation in launched modal distribution can result in significant differences in measured attenuation in the same component. The MTF test method gives information about the launched modal distribution (LMD) condition in a measured component. The MTF test method is based on a measurement of the near-field intensity distribution in the fibre [1], [2] 1 .
4 Theory
For a fibre with a power-law index profile n(r), given by,
4.1 Alternative method
If the profile factor, α , in Equation (4) is not known, then an alternative expression for MTF can be used. It is known[ 3] that in a fully-filled fibre (i.e. MTF=1 for all mode numbers) the near-field intensity profile, I o , is approximately the same shape as the square of the refractive index profile, n(r) 2 . Furthermore, the term r α -1 Equation (4) is equal (ignoring constants) to the differential of n(r) 2 and so Equation(4) can be rewritten as:
where a value of α =2 has been assumed in order to compute values for the normalised mode number.
Thus the MTF is equal to the ratio of the derivative of the intensity profile under test to the derivative of the intensity profile of the same fibre under fully-filled conditions.
4.2 Mode power distribution
For graded index multimode fibre the number of discrete modes in a particular mode group is proportional to the principal mode number. Thus higher-order mode groups contain more modes and therefore will carry more light if all the modes are equally excited. This can be represented by the mode power distribution (MPD), defined as: m m MTF m MPD × = ) ( ) ( (8)