EN 60793-1-42:2007

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Optical fibres - Part 1-42: Measurement methods and test procedures - Chromatic dispersion (IEC 60793-1-42:2007 (EQV) + corrigendum Jun. 2007)Fibres optiques - Partie 1-42: Méthodes de mesure et procédures d'essai - Dispersion chromatique (IEC 60793-1-42:2007 (EQV) + corrigendum Jun. 2007)Lichtwellenleiter - Teil 1-42: Messmethoden und Prüfverfahren - Chromatische Dispersion (IEC 60793-1-42:2007 (EQV) + corrigendum Jun. 2007)Ta slovenski standard je istoveten z:EN 60793-1-42:2007SIST EN 60793-1-42:2007en,de33.180.10Fibres and cablesICS:SIST EN 60793-1-42:20041DGRPHãþDSLOVENSKI
STANDARDSIST EN 60793-1-42:200701-november-2007

EUROPEAN STANDARD EN 60793-1-42 NORME EUROPÉENNE
EUROPÄISCHE NORM June 2007
CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2007 CENELEC -
All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60793-1-42:2007 E
ICS 33.180.10 Supersedes EN 60793-1-42:2002
English version
Optical fibres -
Part 1-42: Measurement methods and test procedures -
Chromatic dispersion (IEC 60793-1-42:2007 + corrigendum 2007)
Fibres optiques -
Partie 1-42: Méthodes de mesure
et procédures d'essai -
Dispersion chromatique (CEI 60793-1-42:2007 + corrigendum 2007)
Lichtwellenleiter -
Teil 1-42: Messmethoden
und Prüfverfahren -
Chromatische Dispersion (IEC 60793-1-42:2007 + Corrigendum 2007)
This European Standard was approved by CENELEC on 2007-05-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.

Foreword The text of document 86A/1136/FDIS, future edition 2 of IEC 60793-1-42, prepared by SC 86A, Fibres and cables, of IEC TC 86, Fibre optics, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 60793-1-42 on 2007-05-01. This European Standard supersedes EN 60793-1-42:2002. The main changes in EN 60793-1-42:2007 concern the addition of a new Annex E on chromatic dispersion fitting and the applicability to A4 fibres. This standard is to be used in conjunction with EN 60793-1-1. The following dates were fixed: – latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement
(dop)
2008-02-01 – latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow)
2010-05-01 Annex ZA has been added by CENELEC. __________ Endorsement notice The text of the International Standard IEC 60793-1-42:2007 and its corrigendum June 2007 was approved by CENELEC as a European Standard without any modification. __________

- 3 - EN 60793-1-42:2007 Annex ZA
(normative)
Normative references to international publications with their corresponding European publications
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.
NOTE
When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.
Publication Year Title EN/HD Year
IEC 60793-1-1 2002 Optical fibres -
Part 1-1: Measurement methods and test procedures - General and guidance EN 60793-1-1 2003
IEC 60793-1-41 -1) Optical fibres -
Part 1-41: Measurement methods and test procedures - Bandwidth EN 60793-1-41 20032)
1) Undated reference. 2) Valid edition at date of issue.

INTERNATIONAL STANDARD IECCEI NORME INTERNATIONALE60793-1-42Second editionDeuxième édition2007-04 Optical fibres – Part 1-42: Measurement methods and test procedures – Chromatic dispersion
Fibres optiques – Partie 1-42: Méthodes de mesure et procédures d’essai – Dispersion chromatique V Commission Electrotechnique InternationaleInternational Electrotechnical CommissionPRICE CODE CODE PRIX For price, see current cataloguePour prix, voir catalogue en vigueur

– 2 – 60793-1-42 © IEC:2007
CONTENTS FOREWORD.4
1 Scope.6 2 Normative references.7 3 Overview of methods.7 3.1 Method A, phase shift.7 3.2 Method B, spectral group delay in the time domain.7 3.3 Method C, differential phase shift.7 3.4 Method D, interferometry.8 4 Reference test methods.8 4.1 Category A1 and category A4f, A4g and A4h multimode fibres.8 4.2 Class B single-mode fibres.8 5 Apparatus.8 5.1 Launch optics.8 5.2 High-order mode filter (single-mode).8 5.3 Input positioning apparatus.9 5.4 Output positioning apparatus.9 5.5 Computation equipment.9 6 Sampling and specimens.9 6.1 Specimen length.9 6.2 Specimen end face.9 6.3 Reference fibre.9 7 Procedure.9 8 Calculations.10 8.1 Category A1 and A4f, A4g, A4h
multimode and B1.1 and B1.3 single-mode fibres.10 8.2 Category B1.2 single-mode fibres.10 8.3 Category B2 single-mode fibres.10 8.4 Category B4 and B5 single-mode fibres.11 9 Results.11 10 Specification information.11
Annex A (normative)
Requirements specific to method A, phase-shift.12 Annex B (normative)
Requirements specific to method B, spectral group delay in the time domain.17 Annex C (normative)
Requirements specific to method C, differential phase-shift.21 Annex D (normative)
Requirements specific to method D, interferometry.26 Annex E (normative)
Chromatic dispersion fitting.30
Figure A.1 – Chromatic dispersion measurement set, multiple laser system (typical).13 Figure A.2 – Typical delay and dispersion curves.13 Figure A.3 – Chromatic dispersion measurement set, LED system (typical).15 Figure B.1 – Block diagram, fibre Raman laser system.18 Figure B.2 – Block diagram, multiple laser diode system.18

60793-1-42 © IEC:2007 – 3 – Figure C.1 – Chromatic differential phase dispersion measurement set, multiple laser system.22 Figure C.2 – Chromatic differential phase dispersion measurement set, LED system.23 Figure C.3 – Chromatic dispersion measurement set, differential phase by dual wavelength method.23 Figure C.4 – Chromatic dispersion measurement set, differential phase by double demodulation.24 Figure D.1 – Fibre chromatic dispersion test set – Interferometry by fibre reference path.28 Figure D.2 – Fibre chromatic dispersion test set – Interferometry by air reference path.28 Figure D.3 – Examples of delay data.29
Table E.1 – Definition of fit types and fit coefficients; equations
for group delay and dispersion coefficient.30 Table E.2 – Slope equations.30 Table E.3 – Zero-dispersion wavelength and slope equations.31

– 4 – 60793-1-42 © IEC:2007 INTERNATIONAL ELECTROTECHNICAL COMMISSION ___________
OPTICAL FIBRES –
Part 1-42: Measurement methods and test procedures – Chromatic dispersion
FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with an IEC Publication. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, 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 correct 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 60793-1-42 has been prepared by subcommittee 86A: Fibres and cables, of IEC technical committee 86: Fibre optics. This second edition cancels and replaces the first edition published in 2001. It constitutes a technical revision. The main changes in this second edition concern the addition of a new Annex E on chromatic dispersion fitting and the applicability to A4 fibres. This bilingual version replaces the monolingual version (2007) and its corrigendum (2007). This standard is to be read in conjunction with IEC 60793-1.

60793-1-42 © IEC:2007 – 5 – The text of this standard is based on the following documents: FDIS Report on voting 86A/1136/FDIS 86A/1146/RVD
Full information on the voting for the approval of this part can be found in the report on voting indicated in the above table. The French version of this standard has not been voted upon. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. The list of all parts of the IEC 60793 series, under the general title Optical fibres, can be found on the IEC website. 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; • replaced by a revised edition, or • amended.

– 6 – 60793-1-42 © IEC:2007 OPTICAL FIBRES –
Part 1-42: Measurement methods and test procedures – Chromatic dispersion
1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the chromatic dispersion of optical fibre, thereby assisting in the inspection of fibres and cables for commercial purposes.
Chromatic dispersion varies with wavelength. Some methods and implementations measure the group delay as a function of wavelength and the chromatic dispersion and dispersion slope are deduced from the derivatives (with respect to wavelength) of this data. This differentiation is most often done after the data are fitted to a mathematical model. Other implementations can allow direct measurement (of the chromatic dispersion) at each of the required wavelengths. For some categories of fibre, the chromatic dispersion attributes are specified with the parameters of a specific model. In these cases, the relevant recommendation or standard defines the model appropriate for the definition of the specified parameters. For other fibre categories, the dispersion is specified to be within a given range for one or more specified wavelength intervals. In the latter case, either direct measurements may be made at the wavelength extremes or some fitting model may be used to allow either group delay measurement methods or implementations or storage of a reduced set of parameters that may be used to calculate the interpolated dispersion for particular wavelengths which may not have actual direct measurement values. Annex E gives a general description of chromatic dispersion fitting and outlines a number of fitting equations suitable for use with any of the measurement methods or fibre categories.
This standard gives four methods for measuring chromatic dispersion: – method A: phase shift; – method B: spectral group delay in the time domain;
– method C: differential phase shift;
– method D: interferometry.
Methods A, B, and C apply to the measurement of chromatic dispersion of the following fibres over a specified wavelength range: – class A1 graded-index multimode fibres; – category A4f, A4g and A4h multimode fibres; – class B single-mode fibres (all categories). Method D applies to the measurement of chromatic dispersion values of single-mode fibres categories B1, B2, B4 and B5 over the 1 000 nm to 1 700 nm wavelength range.
The methods can be applied to laboratory, factory and field measurements of chromatic dispersion, and the wavelength range of the measurements can be tailored as required. Measurements are made at temperature as stated in IEC 60793-1-1, Table 1 – Standard range of atmospheric conditions (Temperature
23 °C ±5 °C).
60793-1-42 © IEC:2007 – 7 – The methods are suitable for fibre or cable lengths greater than 1 km. They may also be applied to shorter lengths, but accuracy and repeatability may be compromised. Method D is the preferred method for shorter piece fibres (1 m to 10 m). Information common to all methods is contained in Clauses 1-8, and information pertaining to each individual method appears in Annexes A, B, C, and D, respectively. 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 60793-1-1:2002, Optical fibres – Part 1-1: Measurement methods and test procedures – General and guidance IEC 60793-1-41, Optical Fibres – Part 1-41: Measurement methods and test procedures – Bandwidth 3 Overview of methods 3.1 Method A, phase shift This method describes a procedure for determining the chromatic dispersion of all categories of type B single-mode fibres, category A1 graded-index multimode fibres and category A4f, A4g and A4h fibres, over a specified wavelength range using the relative phase shifts among sinusoidally modulated optical sources of different wavelengths. The sources are typically laser diodes or filtered light emitting diodes or filtered amplified spontaneous emission (ASE) sources. Relative phase shifts are converted to relative time delays, and the resultant spectral group delay data are then fitted to an equation defined for each fibre type. 3.2 Method B, spectral group delay in the time domain This method describes a procedure for determining the chromatic dispersion of all categories of type B single-mode fibres, category A1 graded-index multimode fibres and category A4f, A4g and A4h fibres with the use of a Nd:YAG/fibre Raman laser source or multiple laser diodes operating at a number of wavelengths both greater than and less than the typical zero-dispersion wavelength.
In this method, the time difference of optical pulse delay through a known length of fibre at several wavelengths is measured. A reference set of measurements shall also be taken through a short reference fibre and data are subtracted from data taken from the fibre under test to obtain relative spectral group delay. The resultant spectral group delay data are then fitted to an equation defined for each fibre type. 3.3 Method C, differential phase shift This method describes a procedure for determining the chromatic dispersion of all categories of type B single-mode fibres, category A1 graded-index multimode fibres and category A4f, A4g and A4h fibres. The dispersion coefficient at a particular wavelength is determined from the differential group delay between two closely spaced wavelengths. In this procedure, a modulated light source is coupled into the fibre under test, and the phase of the light exiting the fibre at a first wavelength is compared with the phase of the light exiting at a second wavelength. Average chromatic dispersion over the interval between the two wavelengths is determined from differential phase shift, wavelength interval and fibre length.

– 8 – 60793-1-42 © IEC:2007 The chromatic dispersion coefficient at a wavelength medial to the two test wavelengths is assumed to be equal to the average chromatic dispersion over the interval between the two wavelengths. The resultant chromatic dispersion data are then fitted to an equation defined for each fibre type. 3.4 Method D, interferometry This method describes a procedure for determining the chromatic dispersion of single-mode fibres categories B1, B2, B4 and B5 over the 1 000 nm to 1 700 nm wavelength range. By using this test method, the chromatic dispersion of a short piece of fibre can be measured. In this test method, the wavelength-dependent time delay between the test sample and the reference path is measured by Mach-Zehnder interferometer. The reference path can be an air path or a single-mode fibre with known spectral group delay. It should be noted that extrapolation of the chromatic dispersion values derived from the interferometric test in fibres of a few metres length to long fibre sections assumes longitudinal homogeneity of the fibre. This assumption may not be applicable in every case. 4 Reference test methods 4.1 Category A1 and category A4f, A4g and A4h multimode fibres For category A1 and category A4f, A4g and A4h multimode fibres, method B, spectral group delay in the time domain, is the reference test method (RTM), which shall be the one used to settle disputes. 4.2 Class B single-mode fibres For all categories of class B single-mode fibres, method A, phase shift, is the reference test method (RTM). Method C, differential phase shift, may also be used to resolve disputes. 5 Apparatus The following apparatus is common to all measurement methods. Annexes A, B, C, and D include layout drawings and other equipment requirements that individually apply for each of the methods, A, B, C, and D, respectively. 5.1 Launch optics The output from the signal sources shall be coupled to the fibre under test or the reference fibre such that the physical path length for each source is held constant during the measurement. (This requirement ensures that the relative phases of the sources do not change due to path-length changes.) Suitable devices may include multichannel single-mode optical switches or demountable optical connectors. For measurement of category A1, A4f, A4g, A4h
multimode fibre, launch conditions shall comply with method A, impulse response, of IEC 60793-1-41. 5.2 High-order mode filter (single-mode) For measurement of single-mode fibre, use a method to remove high-order propagating modes in the wavelength range of interest. An example of such a high-order mode filter is a single loop of radius sufficiently small to shift cut-off wavelength below the minimum wavelength of interest.

60793-1-42 © IEC:2007 – 9 – 5.3 Input positioning apparatus
Provide means to couple the input of the specimen to the light source. Examples include the use of x-y-z micropositioner stages, or mechanical coupling methods such as connectors, vacuum splices, three-rod splices, etc. The position of the fibre shall remain stable over the duration of the test. 5.4 Output positioning apparatus
Provide means of positioning the output end of the specimen such that the guided optical power is coupled to the system detector. Such coupling may include the use of lenses, or may be a mechanical connection to a detector pigtail. 5.5 Computation equipment
A digital computer may be used for purposes of equipment control, data acquisition, and numerical evaluation of the data. 6 Sampling and specimens 6.1 Specimen length Methods A, B, and C require the specimen to be a fibre or cable of known length sufficiently long to produce adequate phase measurement accuracy. A typical minimum length is 1 km. Because category A4f, A4g and A4h fibres have higher loss than category A1 fibres, for these A4 fibres a minimum length of 100 m is acceptable.
NOTE Reproducibility is affected when using shorter measuring length. Longer lengths generally yield better reproducibility.
Method D (interferometry) requires a typical specimen length in the range of 1 m to 10 m. 6.2 Specimen end face Prepare a flat end face, orthogonal to the fibre axis, at the input and output ends of each specimen. 6.3 Reference fibre A single mode fibre with known dispersion characteristics shall be used to compensate for chromatic delays in the optical sources and other equipment components. The length of this fibre shall be less than or equal to 0,2 % of the specimen length.
In case of A4f, A4g and A4h fibres, the length of the reference fibre shall be less than or equal to 2 m. If this length is longer than 0,2 % of the length of the specimen under test, the chromatic dispersion of the reference fibres shall be taken into account by subtracting its chromatic dispersion value from the results measured on the specimen length. NOTE The temperature of the specimen should be stable during the measurement within 0,1 °C to 1 °C, depending upon the temporal behaviour due to this change. 7 Procedure See Annexes A, B, C and D for the procedures for methods A, B, C and D, respectively. Reference fibre measurements are required for all methods. Reference fibre data can be stored for use in making measurements on the specimens. The reference fibre measurement procedure should be repeated when equipment changes on the source or receive optics or electronics occur.

– 10 – 60793-1-42 © IEC:2007 8 Calculations The calculation of relative delay appropriate for each method is given in Annexes A, B, C and D, respectively. The remainder of this clause describes the numerical fit that can be applied for all methods to the spectral group delay data normalized by length, τ(λ), see also Annex E. λ
is the wavelength
[nm] τ(λ) is the normalized spectral group delay data fit
[ps/km] D(λ)
is the chromatic dispersion coefficient, with D(λ)
= dτ(λ) /dλ
[ps/(nm.km)] λ0
is the zero-dispersion wavelength
[nm] τ(λ0) is the relative delay minimum at the zero-dispersion wavelength [ps/km] S(λ)
is the dispersion slope, with S(λ) = d D(λ) /dλ. [ps/(nm2⋅km)] S0
is the dispersion slope at the zero-dispersion wavelength
[ps/(nm2⋅km)] NOTE τ(λ) and
D(λ) may either be direct measurements or the result of fitting the direct measurements to a specified function. Where, for example, a data fitting function is specified, the parameters of the expression on the right side of the equation are determined so as to minimize the sum of squared errors with regard to the direct measurements. Once determined, this expression is used to determine the values of other various parameters.
The fit parameters are given as the variables A, B, C, D, or E, see also Annex E. 8.1 Category A1 and A4f, A4g, A4h
multimode and B1.1 and B1.3 single-mode fibres
The following applies to category A1 and A4f, A4g and A4h multimode fibres, and to category B1.1 and B1.3 single-mode fibres around 1 310 nm.
The delay or dispersion data fit shall be fitted with the 3-term Sellmeier fit type, see Annex E. Calculations for the chromatic dispersion coefficient D(λ), the zero-dispersion wavelength λ0 and the dispersion slope at the zero-dispersion wavelength S0 are shown in Annex E. In the 1 550 nm region only, the chromatic dispersion can be approximated as a linear function with wavelength (quadratic fit type to the delay data), see Annex E. 8.2 Category B1.2 single-mode fibres
The following applies to category B1.2 single-mode fibres. Depending on accuracy requirements, for wavelength intervals of up to 35 nm, the quadratic fit type is allowed in the 1 550 nm region. This fitted equation should not be used to predict chromatic dispersion at wavelengths outside the range used for the fit. For longer wavelength intervals, either the 5-term Sellmeier fit type or the 4th order polynomial fit type is recommended. It is not meant to be used in the 1 310 nm region. Calculations for the chromatic dispersion coefficient D(λ) and the dispersion slope S(λ) are shown in Annex E. 8.3 Category B2 single-mode fibres The following applies to category B2 single-mode fibres. Depending on accuracy requirements, for wavelength intervals of up to 35 nm, the quadratic fit type is allowed in the 1 550 nm region. The fitted equation should not be used to predict chromatic dispersion at wavelengths outside the range used for the fit.

60793-1-42 © IEC:2007 – 11 – For longer wavelength intervals, either the 5-term Sellmeier fit type or the 4th order polynomial fit type is recommended. It is not meant to be used in the 1 310 nm region. The corresponding chromatic dispersion coefficient D(λ), the zero-dispersion wavelength λ0 and the dispersion slope at the zero-dispersion wavelength S0 are shown in Annex E. 8.4 Category B4 and B5 single-mode fibres The following applies to category B4 and B5 single-mode fibres. For normal use over longer wavelength intervals (> 35 nm), either the 5-term Sellmeier fit type or the 4th order polynomial fit type is recommended. The fitted equation should not be used to predict chromatic dispersion at wavelength outside the range used for the fit. NOTE For B4 fibres only, the quadratic fit type may be used in case of a short wavelength interval (≤ 35 nm). The fit type should not be used to predict chromatic dispersion at wavelengths outside the range used for the fit. The corresponding chromatic dispersion coefficient D(λ) and the dispersion slope S(λ) are shown in Annex E. 9 Results 9.1 Report the following information with each measurement:
– date and title of measurement; – equation(s) used to calculate the results; – identification of specimen; – length of specimen used for length normalization; – measurement results as required by the detail specification. NOTE Examples of the information that the detail specification may require: a) Dispersion coefficient values measured at certain specified wavelengths. b) Dispersion minimum and / or maximum over a specified range of wavelengths. c) The zero-dispersion wavelength and dispersion slope at this wavelength. 9.2 The following information shall be available upon request: – method used: A, B, C or D; – description of optical source(s) and measurement wavelengths used; – modulation frequency (if applicable); – description of signal detector, signal detection electronics, and delay device; – description of computational techniques used; – date of latest calibration of measurement equipment. 10 Specification information The detail specification shall specify the following information: − type of fibre to be measured; − failure or acceptance criteria; − information to be reported; − any deviations to the procedure that apply.

– 12 – 60793-1-42 © IEC:2007 Annex A
(normative)
Requirements specific to method A, phase-shift
A.1 Apparatus A.1.1 Light source The light source shall be stable in position, intensity, and wavelength over a time period sufficiently long to complete the measurement procedure. Multiple laser diodes (for an example, see Figure A.1), wavelength-tunable laser diodes, light-emitting diodes (for example, see Figure A.3), or broadband sources (for example, a Nd:YAG laser with a Raman fibre or an ASE source) may be used, depending on the wavelength range of the measurement. The wavelength launched into the fibre under test may be selected using an optical switch, a monochromator, dispersive devices, optical filters, optical couplers, or by tuning the laser, depending on the type of light sources and measurement set-up. The wavelength selector may be used either at the input or at the output of the fibre under test. For category B1 fibres measured with a three-wavelength system in which the source wavelengths bracket the zero-dispersion wavelength, λ0 (see Figure A.2), the tolerance or instability, δλ, in center wavelength will lead to maximum errors of 3δλ in measuring λ0. Maximum errors in dispersion slope, S0, are directly proportional to δλ/Δλ (where Δλ = source wavelength spacing) and will be approximately 0,012 ps/(nm2·km) for δλ/Δλ = 1 nm/30 nm. Errors smaller than the above maximum errors can be achieved by selecting optical sources with an average wavelength close to the expected λ0 of the specimen and by using more than three wavelengths, or both. When laser sources are used, typically, a temperature-controlled, single longitudinal-mode laser diode with output power stabilization (e.g., PIN feedback) is sufficient. An additional laser may be required for the reference link for field measurement sets (see A.1.4). A.1.2 Spectral width The spectral width of the source, as measured in the specimen, shall be less than or equal to 10 nm at 50 % power points (FWHM).

60793-1-42 © IEC:2007 – 13 –
Multiple laser diodes Optical switch Spliter ConnectorTest sample or calibration fibre ConnectorVariable attenuatorDetectorAmplifier Fibre reference link (non co-located equipment) DetectorReferenceAmplifier Signal generator Phasemeter Signal Computer Electrical reference (co-locoted equipment)Fibre reference link (non co-located equipment) IEC
516/07
Figure A.1 – Chromatic dispersion measurement set, multiple laser system (typical)
Relative delay, ns/km + 6 + 4 + 2
0 – 2 0,8 1,0 1,2 1,4 1,6
0 λ × μm
τ (λ) λ0 = 1321 m
s0 = 0,0834 ps/nm2 × km
D (λ) A = – 38,360 ns/km B =
10,421 ns/km × μm2 C =
31,735 ns × μm2/km– 120 – 90 – 60 – 30 + 30 Dispersion ps/nm × km IEC
517/07
Figure A.2 – Typical delay and dispersion curves

– 14 – 60793-1-42 © IEC:2007 A.1.3 Modulator
The modulator shall amplitude modulate the light sources to produce a waveform with a single, dominant Fourier component. For example, a sinusoidal, trapezoidal or square wave modulation shall be acceptable. The frequency stability shall be a minimum of one part in 106. It is essential to prevent ambiguities of 360(n) degrees, where n is an integer, in measuring phase shift. This can be accomplished by means such as tracking 360° phase changes, or by choosing a modulator frequency sufficiently low to limit the relative phase shifts to less than 360°. Determine the maximum frequency for a 360° shift for category B1 fibres as:
fmax
= 8⋅106S0Lλi−λ02λi⎛ ⎝ ⎜ ⎞ ⎠ ⎟ 2−λj−λ02λj⎛ ⎝ ⎜ ⎞ ⎠ ⎟ 2⎡ ⎣ ⎢ ⎤ ⎦ ⎥ −1 (A.1) where fmax
is the maximum frequency for a 360° shift for category B1 fibres (MHz); L
is the maximum expected specimen length (km); S0 is the expected typical dispersion slope at λ0 (ps/nm2 × km); λ0 is the expected typical zero-dispersion wavelength (nm); λi and λj comprise the wavelength pair, used in the measurement, that minimizes fmax. The frequency of the modulator shall be sufficiently high to ensure adequate measurement precision. The following is an example of the dependence of precision on test system parameters: for category B1 fibres and a three-wavelength system, in which the source wavelengths span Δλ, maximum errors will be 0,0012 ps/nm2 · km for S0, and 0,4 nm for λ0 if the minimum modulator frequency, fmin (MHz), is:
fmin
= Δφ⋅107L(Δλ)2 (A.2) where fmin is the minimum modulator frequency (MHz); Δφ is the overall measurement equipment phase instability (degrees); L is the minimum expected specimen length (km); Δλ is the average wavelength spacing between adjacent sources (nm). Hence for Δφ = 0,1°, L = 10 km, and Δλ = 32 nm, a minimum frequency of approximately 100 MHz is required. NOTE 1 Equation (A.2) above was developed by repeatedly solving for λ0
and S0 in the three-term Sellmeier expression for group delay in Annex E with various values of wavelength spacing and phase instability.
NOTE 2 Errors smaller than the above maximum errors can be achieved by selecting sources having an average wavelength close to the expected λ0 of the specimen, and by using more than three wavelengths, or both.
The phase modulation at each light source may be adjustable to facilitate measurement-set calibration.

60793-1-42 © IEC:2007 – 15 – A.1.4 Signal detector and signal detection electronics
Use an optical detector that is sensitive over the range of wavelengths to be measured in conjunction with a phase meter. An amplifier may be used to increase the detection system sensitivity. A typical system might include a PIN photodiode, FET amplifier, and a vector voltmeter. The detector-amplifier-phase meter system shall respond only to the fundamental Fourier component of the modulating signal and shall introduce a signal phase shift that is constant over the range of received optical powers encountered. The received power range may be controlled by a variable optical attenuator. A.1.5 Reference signal
Provide a reference signal with the same dominant Fourier component as the modulating signal to the phase meter against which to measure the phases of the signal sources. The reference signal should be phase-locked to the modulating signal and is typically derived from the modulating signal. Examples of reference signal configurations (see Figures A.1 and A.3 for examples a, b,
and c): a) Where the signal sources and detector are co-located, such as in a laboratory test or during calibration, an electrical connection can be used between the signal generator and the reference port of the phase meter. b) An optical splitter, inserted before the specimen, and a detector may also be used for co-located equipment. c) For field testing of optical cables (sources and detector not co-located), an optical link can be used, typically comprising a modulated light source, fibre, and detector similar to those used for the specimen. d) A reference signal for field testing can also be transmitted on the fibre under test using wavelength division multiplexing.
Light emittingdiode Connector Test sample or calibration fibre ConnectorVariable attenuatorDetector Amplifier Fibre reference link (non co-located equipment) DetectorReferenceAmplifier Signal generatorPhasemeter Signal Computer Electrical reference (co-locoted equipment)Connector MonochromatorIEC
518/07
Figure A.3 – Chromatic dispersion measurement set, LED system (typical)

– 16 – 60793-1-42 © IEC:2007 A.2 Procedure A.2.1 Calibration Insert the reference fibre (6.3) into the measurement apparatus, and establish a reference signal (A.1.5). Measure and record the phase, φin(λi), for each signal source. Alternatively, if the signal sources are phase adjustable, then with the reference fibre in place, the phases of all signal sources shall be equalized. Then perform specimen measurements as described in A.2.2. In this case φin(λi) = 0 for the calculations of A.3.1. A.2.2 Specimen measurements
Insert the specimen into the measurement apparatus, and establish a reference signal (see A.1.5). Measure and record the phase, φout (λi), of each signal source. NOTE Perform all specimen and calibration or equalization measurements with the input optical power level at the detector adjusted to a range that minimizes level-dependent phase shifts in the detector and detector electronics. A.3 Calculations A.3.1 Subtract the measured input phase at each wavelength from the output phase at that wavelength. The relative group delay is:
τ(λi) =
()()[]Lf⋅⋅−360106iinioutλφλφ
for all λi (A.3) where τ(λi)
is the relative group delay (ps/km); φout (λi) were measured in A.2.2 (degrees); φin (λi)
were measured in A.2.1 (degrees); f (MHz)
is the frequency of the modulation waveform; L (km)
is the specimen length minus the calibration specimen length. A.3.2 Using the delay data of A.3.1, calculate the best fit to one of the delay equations in Annex E. A.3.3 Using these best-fit values of the appropriate coefficients from Clause 8, calculate the dispersion, D(λ), or other parameters as required by the detail specification. Refer to Figure A.2 as an example of the delay data, τ(λ), and the calculated dispersion, D(λ). A.3.4 Dispersion can be specified through the zero-dispersion wavelength, λ0, and slope, S0, or by specifying the chromatic dispersion coefficient at one or more wavelengths, or both. In some cases, the zero-dispersion wavelength and slope parameters are only used to calculate the dispersion coefficient at wavelengths well away from the zero-dispersion wavelength.
When the zero-dispersion wavelength is specified, the measurement wavelengths should bracket the zero-dispersion wavelength or include data at a wavelength within 100 nm. When the zero-dispersion wavelength and slope are used only for the calculation of dispersion coefficients at wavelengths far away from the zero-dispersion wavelength, the measurements shall span the wavelengths with which the calculation is used. When the dispersion coefficient is specified, the measurements shall span the wavelengths at which the dispersion coefficient is specified. See Annex E for information on the wavelength ranges measured and the suitable fitting technique.

60793-1-42 © IEC:2007 – 17 – Annex B
(normative)
Requirements specific to method B, spectral group delay in the time domain
B.1 Apparatus B.1.1 Light source B.1.1.1 Fibre Raman laser A fibre Raman laser system, consisting of a synchronously mode locked and Q-switched Nd:YAG laser pumping an appropriate length (approximately 200 m) of single-mode fibre, spectrally filtered by a device such as a grating monochromator, shall be capable of producing optical pulses of short duration (< 400 ps full-width half max (FWHM)) and of sufficient intensity and spatial and temporal stability to perform the measurements described (see Figure B.1). B.1.1.2 Multiple laser diodes Multiple (three or more) injection laser diodes at several wavelengths shall be considered sufficient for purposes of these measurements if they are of short duration (less than 400 ps FWHM), are stable in intensity, and can be stably triggered over the duration of the measurement (see Figure B.2). B.1.1.3 Wavelength-tunable laser diodes
One or more wavelength-tunable laser diodes (for example, an external-cavity laser) may be used if they produce pulses of short duration (less than 400 ps FWHM), are stable in intensity, and can maintain a stable wavelength and be stably triggered over the duration of the measurement. B.1.1.4 Spectral width The spectral width of the source, as measured in the specimen, shall be less than or equal to 10 nm at 50 % power points (FWHM).

– 18 – 60793-1-42 © IEC:2007
DetectorAmplifier Signal ComputerMonochromatorFibre Raman laser NL. YAG Laser
(1,06 μm) mode-locked
Q-switched SMWG Test or
reference sample Sampling CROTime delay generator Trigger Attenuator IEC
519/07
Figure B.1 – Block diagram, fibre Raman laser system B.1.2 Signal detector Use a high-speed optical detector, such as a germanium avalanche photodiode, that is sensitive over the range of wavelengths used. It shall be linear within 10 % over the range of intensities encountered. Note that the main constraint on linearity is simply that the pulse peak is not compresse
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