1、 IEC 61300-3-43 Edition 1.0 2009-01 INTERNATIONAL STANDARD 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 IEC 61300-3-43:2009(E) THIS PUBLICATION IS C
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9、 11 Fax: +41 22 919 03 00 IEC 61300-3-43 Edition 1.0 2009-01 INTERNATIONAL STANDARD 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 INTERNATIONAL ELECT
10、ROTECHNICAL COMMISSION R ICS 33.180.20 PRICE CODE ISBN 2-8318-1024-2 Registered trademark of the International Electrotechnical Commission 2 61300-3-43 IEC:2009(E) CONTENTS FOREWORD.3 1 Scope.5 2 Normative references .5 3 General description 5 4 Theory5 4.1 Alternative method 7 4.2 Mode power distri
11、bution 7 4.3 Constraints8 5 Apparatus.9 5.1 General .9 5.2 Test sample 9 5.3 Sample positioning device.9 5.4 Optical system.10 5.5 Camera .10 5.6 Video digitiser .10 5.7 Calibration.10 6 Procedure 11 6.1 Mounting and aligning the sample .11 6.2 Optimisation11 6.3 Acquiring the data .11 7 Calculation
12、s .11 7.1 Background level subtraction.11 7.2 Location of centroid of intensity profile 12 7.3 Differentiating the intensity profile .12 7.4 Computing the MTF.13 8 Results.14 Annex A (informative) .16 Bibliography18 Figure 1 Example of normalised MTF.7 Figure 2 Example of normalised MPD 8 Figure 3 S
13、chematic of measurement apparatus9 Figure 4 Location of fibre centre using symmetry computation .13 Figure A.1 Sensitivity of MTF and MPD to core diameter16 Figure A.2 Sensitivity of MTF and MPD to profile factor .17 61300-3-43 IEC:2009(E) 3 INTERNATIONAL ELECTROTECHNICAL COMMISSION _ FIBRE OPTIC IN
14、TERCONNECTING DEVICES AND PASSIVE COMPONENTS BASIC TEST AND MEASUREMENT PROCEDURES Part 3-43: Examinations and measurements Mode transfer function measurement for fibre optic sources FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization compr
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23、 or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications. 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the cor
24、rect application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 61300-3-43 has been prepar
25、ed by subcommittee 86B: Fibre optic interconnecting devices and passive components, of IEC technical committee 86: Fibre optics. This standard cancels and replaces IEC/PAS 61300-3-43, published in 2006. This first edition constitutes a technical revision. The text of this standard is based on the fo
26、llowing documents: FDIS Report on voting 86B/2780/FDIS 86B/2810/RVD Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. 4 61300-3-43 IEC:2009(E) This publication has been drafted in accordance with the ISO/IEC Directives
27、, Part 2. The committee has decided that the contents of this publication will remain unchanged until the maintenance result date indicated on the IEC web site under “http:/webstore.iec.ch“ in the data related to the specific publication. At this date, the publication will be reconfirmed, withdrawn,
28、 replaced by a revised edition, or amended. A bilingual version of this standard may be issued at a later date. 61300-3-43 IEC:2009(E) 5 FIBRE OPTIC INTERCONNECTING DEVICES AND PASSIVE COMPONENTS BASIC TEST AND MEASUREMENT PROCEDURES Part 3-43: Examinations and measurements Mode transfer function me
29、asurement for fibre optic sources 1 Scope This part of IEC 61300 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 o
30、perational 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. IE
31、C 61300-1, Fibre optic interconnecting devices and passive components Basic test and measurement procedures Part 1: General and guidance IEC 61300-3-4, Fibre optic interconnecting devices and passive components Basic test and measurement procedures Part 3-4: Examination and measurements Attenuation
32、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 difference
33、s 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
34、 a power-law index profile n(r), given by, 5 0 1 2 1 , ) ( = a r n r n 1 a r(1) where a is the fibre core radius; is the profile factor ( = 2 for a parabolic profile); _ 1Figures in square brackets refer to the Bibliography. 6 61300-3-43 IEC:2009(E) is the relative index difference, given by 2 1 2 2
35、 2 1 2n n n = (2) where n 1 is the index at fibre centre; n 2is the cladding index. The near-field intensity profile in the fibre I(r) may be determined from an integration of the mode transfer function MTF() in the fibre, as follows (ignoring constants): () = a r d MTF r I ) ( ) ( (3) where is the
36、normalised propagation constant; r/a is the normalised radial position. Differentiating both sides gives the MTF as follows (ignoring constants): () a r r dr r dI MTF = = 1 1 ) ( ) ( (4) The MTF is usually plotted as in terms of the principal mode number m divided by the maximum principal mode numbe
37、r M, where 2 ) 2 ( 2 ) 2 ( + + = = a r M m(5) The term (m/M) is usually referred to as the relative mode number, or the normalised mode number. The maximum principle mode number M, is given by + = a n M 2 2 1(6) A typical normalised MTF plot is shown in Figure 1, where it can be seen, in this exampl
38、e, that normalised mode numbers up to about 0,6 are equally filled and higher order modes are progressively less well-filled. 61300-3-43 IEC:2009(E) 7 Normalised mode number 0,0 0,25 0,50 0,75 1,0 0,0 0,2 0,4 0,6 0,8 1,0 Normalised MTF IEC 2371/08 Figure 1 Example of normalised MTF 4.1 Alternative m
39、ethod If the profile factor, , in Equation (4) is not known, then an alternative expression for MTF can be used. It is known3 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 p
40、rofile, n(r) 2 . Furthermore, the term r -1Equation (4) is equal (ignoring constants) to the differential of n(r) 2and so Equation(4) can be rewritten as: () 2 1 a r o dr r dI dr r dI MTF = = ) ( ) ( ) ( (7) where a value of =2 has been assumed in order to compute values for the normalised mode numb
41、er. 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 grou
42、p 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) Because of this relationshi
43、p of modes within mode groups, the MPD transform effectively displays the relative power in the mode groups. An example of a normalised MPD is shown in Figure 2, where it can be seen, in this case, that the peak power level occurs around 0,65 normalised mode number. 8 61300-3-43 IEC:2009(E) Normalis
44、ed mode number 0,0 0,25 0,50 0,75 1,0 0,0 0,2 0,4 0,6 0,8 1,0 Normalised MPD IEC 2372/08 Figure 2 Example of normalised MPD 4.3 Constraints The MTF measurement method described herein is only valid under certain conditions, as follows: modes within a mode group carry the same power; there are random
45、 phases between the propagating modes. It has been found4 that both these conditions can be simultaneously met if the line-width of the source is sufficiently broad, leading to the so-called “mode-continuum approximation“, given by: N a 0 2 k (10) where is the optical wavelength; k 0= 2/; N is the g
46、roup index, given by d dn n N 1 1 = (11) Typically, for a 50 m core diameter fibre, with 0,21 numerical aperture, then 0,5 nm at 850 nm and 1,0 nm at 1 300 nm satisfy this condition. If the source line-width does not meet this criterion then interference between propagating modes may take place, res
47、ulting in “speckle“ in the near-field image. The method can, however, still be applied to such sources by gently shaking, or somehow agitating, the fibre under test so as to cause a temporal averaging of the speckle pattern. In this case, it is important to ensure the near-field is azimuthally symme
48、tric. This can be achieved by checking that the MTFs measured at 45 intervals around the fibre coincide with each other5. The peak of the MPD occurs at a normalised mode number of 0,8. 61300-3-43 IEC:2009(E) 9 It is known that deviation of the measured near-field intensity profile I(r) from the power law profile in Equation (1), for fibres that are well-filled, may occur towards the core/cladding boundary. It is recommended that, in this case, the alternative method for the determination of MTF described
