IEC 60793-1-43:2015 pdf download – OPTICAL FIBRES – Part 1–43: Measurement methods and test procedures– Numerical aperture measurement.
1 Scope This part of IEC 60793 establishes uniform requirements for measuring the numerical aperture of optical fibre, thereby assisting in the inspection of fibres and cables for commercial purposes. The numerical aperture (NA) of categories A1 , A2, A3 and A4 multimode fibre is an important parameter that describes a fibre’s light-gathering ability. It is used to predict launching efficiency, joint loss at splices, and micro/macrobending performance. The numerical aperture is defined by measuring the far-field pattern (NA ff ). In some cases the theoretical numerical aperture (NA th ) is used in the literature, which can be determined from measuring the difference in refractive indexes between the core and cladding. Ideally these two methods should produce the same value. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60793-1 -1 , Optical fibres – Part 1-1: Measurement methods and test procedures – General and guidance IEC 60793-1 -21 , Optical fibres – Part 1-21: Measurement methods and test procedures – Coating geometry IEC 60793-1 -22, Optical fibres – Part 1-22: Measurement methods and test procedures – Length measurement IEC 60793-2-1 0, Optical fibres – Part 2-10: Product specifications – Sectional specification for category A1 multimode fibres
6 Sampling and specimens 6.1 Specimen length The NA ff can be impacted by the specimen length. For this reason, the specimen length is given as part of the detailed product specifications including IEC 60793-2-1 0, IEC 60793-2-20, IEC 60793-2-30 and IEC 60793-2-40. Default values are also listed in Annex B. Longer specimen lengths than what are practical to measure on a regular basis may be required for some products. In these cases a mapping function may be used as described in informative Annex A. 6.2 Specimen endface Prepare a flat endface, orthogonal to the fibre axis, at the input and output ends of each specimen. The accuracy of these measurements is affected by a non-perpendicular endface. End angles less than 2° are recommended. 7 Procedure The following procedure shall be followed: • Place the specimen ends in the support devices. The input end shall be approximately at the centre of the input place of the focused image of the constant radiance spot. • Set the optical source to the desired wavelength and spectral width. • Scan the far-field radiation pattern along a diameter and record intensity versus angular position.IEC 60793-2-20, Optical fibres – Part 2-20: Product specifications – Sectional specification for category A2 multimode fibres IEC 60793-2-30, Optical fibres – Part 2-30: Product specifications – Sectional specification for category A3 multimode fibres IEC 60793-2-40, Optical fibres – Part 2-40: Product specifications – Sectional specification for category A4 multimode fibres
8.4 Calculating far-field intensity pattern when using Technique 3 When using Technique 3 the distance, y, shall be transformed into the angle θ . This is done using the following approach: Find the central y position y 0 in the scan by typical centring techniques (the average of the 50 % points, first moments analysis, etc.). Subtract y 0 from the recorded y positions, yielding a corrected set of positions, y’. Now calculate the set of θ ’s using Equation (1 1 ): θ = arcsin(y’/f) (1 1 ) Finally, compute the far-field intensity pattern using Equation (1 0). 8.5 Calculating NA when using Technique 4 When using Technique 4, a local minimum in the far-field intensity pattern is used to determine the numerical aperture. Figure 7 shows a representative data from this measurement.