1、INTERNATIONAL TELECOMMUNICATION UNION lTU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.651 (02198) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Transmission media characteristics - Optical fibre cables Characteristics of a 501125 pm multimode graded index optical fib
2、re cable ITU-T Recommendation G.651 (Previously CClTT Recommendation) ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G. 1 OO-G. 199 INTERNATIONAL ANALOGUE CARRIER SYSTEM TRANSMISSION SYSTEMS INDIVIDUAL CHAR
3、ACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE G.300-G.399 SYSTEMS ON METALLIC LINES GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER- G.200-G.299 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE G.400-G.449 WITH METALLIC LINES SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNE
4、CTION COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY TESTING EQUIPMENTS TRANSMISSION MEDIA CHARACTERISTICS General Symmetric cable pairs Land coaxial cable pairs Submarine cables G.450-G.499 G.600-G.609 G.610-G.619 G.620-G.629 G.630-G.649 Characteristics of optical components and sub-systems DIGI
5、TAL TRANSMISSION SYSTEMS TERMINAL EQUIPMENTS DIGITAL NETWORKS DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.660-G.699 G.700-G.799 G.800-G.899 . G.900-G.999 For further details, please refer to ITU-T List of Recommendations. ITU-T RECOMMENDATION G.651 CHARACTERISTICS OF A 50/125 pm MULTIMODE GRADED INDE
6、X OPTICAL FIBRE CABLE Summary This Recommendation covers the geometrical and transmissive properties of multimode fibres having a 50 pm nominal core diameter and a 125 pm nominal cladding diameter. Test methods and the meanings of the terms used are in clauses 6 and 2 respectively. Source ITU-T Reco
7、mmendation G.651 was revised by ITU-T Study Group 15 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 10* of February 1998. FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommu
8、nication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardizati
9、on Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. l. In
10、 some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recog
11、nized operating agency. INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of cla
12、imed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property, protected by patents, which may be required to implement this R
13、ecommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O ITU 1998 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic
14、 or mechanical, including photocopying and microfilm, without permission in writing from the ITU. 11 Recommendation 6.651 (02/98) STD-ITU-T RECMN G.65L-ENGL L998 4862593 0649256 T70 1 2 3 3.1 3.2 3.3 4 4.1 4.2 5 5.1 5.2 6 6.1 6.2 CONTENTS Page Scope Definitions Fibre characteristics Geometrical char
15、acteristics of the fibre 3 . 1 . 1 Core diameter 3.1.2 Cladding diameter . 3.1.3 Concentricity error 3.1.4 Non-circularity Optical properties of the fibre . 3.2.1 Refractwe index profile 3.2.2 Numerical aperture Material properties of the fibre . 3.3.1 Fibre materials . 3.3.2 Protective materials .
16、3.3.3 Prooftest level . Factory length specifications Attenuation coefficient . Baseband response 4.2.1 Modal distortion bandwidth: amplitude response . 4.2.2 Modal distortion bandwidth: phase response 4.2.3 Chromatic dispersion . Elementary cable sections Attenuation . Baseband response (overall -3
17、 dB optical bandwidth) 5.2.1 Modal distortion bandwidth Test methods . Reference test method and alternative test method for geometrical and optical parameters measurements : 6.1.1 General 6.1.2 Intrinsic quality factor . . 6.1.3 Geometrical characteristics . The reference test methods for geometric
18、al parameters and the alternative test method for numerical aperture: the refracted near-field technique 6.2.1 General 6.2.2 Maximum theoretical numerical aperture and refractive index difference . Recommendation G.651 (02/98) 1 3 3 3 3 4 4 4 4 4 4 4 4 5 5 5 5 5 6 6 6 6 7 7 9 9 10 . 111 6.2.3 Test a
19、pparatus 6.2.4 Preparation of fibre under test . 6.2.5 Procedure . 6.2.6 Presentation of results . 6.3 Alternative test method for geometrical parameters: the near-field technique . 6.3.1 General 6.3.2 Test apparatus 6.3.3 Procedure . 6.3.4 Presentation of the results . 6.4 Reference test method for
20、 the numerical aperture: far-field light distribution . 6.4.1 Object 6.4.2 Specimen preparation 6.4.3 Apparatus 6.4.4 Procedure . 6.4.5 Results . 6.4.6 Presentation of results . 6.5 Reference test method and alternative test methods for attenuation measurements 6.5.1 Objectives 6.5.2 Definition 6.5.
21、3 Description 6.5.4 Field of application 6.6 The reference test method: the cutback technique 6.6.1 Launching conditions 6.6.2 Apparatus and procedure . 6.6:3 Presentation of results . 6.7 First alternative test method: the insertion loss technique 6.7.1 Launching conditions 6.7.2 Apparatus and proc
22、edure . 6.7.3 Presentation of results . 6.8 Second alternative test method: the backscattering technique 6.8.1 Launching conditions . 6.8.2 Apparatus and procedure . 6.8.3 Presentation of results . 6.9 Reference test method for baseband response measurements 6.9.1 Object 6.1 O Reference test method
23、6.1 O . 1 Test apparatus 6.10.2 Procedure . Page 11 11 11 12 13 13 13 15 15 16 16 16 16 16 17 17 18 1.8 18 18 18 19 19 21 22 22 22 22 24 24 24 24 25 26 26 27 27 28 iv Recommendation G.651 (02/98) 6.1 0.3 Presentation of results . Appendix I . Algorithm for geometrical parameters . I . 1 Core centre
24、and diameter 1.2 Cladding centre and diameter . Page 29 30 30 30 Recommendation G.651 (02/98) V Recommendation G.651 CHARACTERISTICS OF A 50/125 pm MULTIMODE GRADED INDEX OPTICAL FIBRE CABLE (Malaga-Torremolinos, 1984; amended at Melbourne, 1988, Helsinki, 1993 and Geneva, 1998) 1 Scope This Recomme
25、ndation covers a graded index, multimode fibre, which may be used in the region of 850 nm or in the region of 1300 nm or alternatively may be used in both wavelength regions simultaneously. This fibre can be used for analogue and for digital transmission. Its geometrical, optical, transmission and m
26、echanical characteristics are described below. 2 Definitions 2.1 alternative test method: A test method in which a given characteristic of a specified class of optical fibres or optical fibre cables is measured in a manner consistent with the definition of this characteristic and gives results which
27、 are reproducible and relatable to the reference test method and to practical use. 2.2 attenuation coefficient: In an optical fibre it is the attenuation per unit length. NOTE - The attenuation is the rate of decrease of average optical power with respect to distance along. the fibre and is defined
28、by the equation: i -a- P(z) = P(0)lO lo where: P(z) is the power at distance z along the fibre; P(0) is the power at z = O; a is the attenuation coefficient in dBh if z is in km. From this equation the attenuation coefficient is: This assumes that a is independent of z. 2.3 bandwidth (of an optical
29、fibre): That value numericaly equal to the lowest frequency at which the magnitude of the baseband .transfer function of an optical fibre decreases to a specified fraction, generally to -3 dB optical (-6 dB electrical), of the zero frequency value. NOTE - The bandwidth is limited by several mechanis
30、ms: mainly modal distortion and chromatic dispersion in multimode fibres. 2.4 chromatic dispersion: The spreading of a light pulse per unit source spectrum width in an optical fibre caused by the different group velocities of the different wavelengths composing the source spectrum. Recommendation G.
31、651 (02/98) 1 STD-ITU-T RECPlN G.651-ENGL L998 m 4862593 06492b0 IT1 m NOTE - The chromatic dispersion may be due to one or more of the following: material dispersion, waveguide dispersion, profile dispersion. Polarization dispersion does not give appreciable effects in circularly-symmetric fibres.
32、2.5 chromatic dispersion coefficient: The chromatic dispersion per unit source spectrum width and unit length of fibre. It is usually expressed in ps/(nm . km). 2.6 cladding: The outermost region of constant refractive index in the fibre cross-section. 2.7 cladding mode stripper: A device or materia
33、l that encourages the conversion of cladding modes to radiation modes. 2.8 core: The central region of an optical fibre through which most of the optical power is transmitted. 2.9 core area: The core diameter of a multimode optical fibre is defined from the refractive index profile as that diameter
34、passing through the core centre and intersecting the index profile at the points n3 such that: n3 = n2 + k(n, - It2) where: n2 is the refractive index of the homogeneous cladding; n, is the maximum refractive index; and k is a constant commonly called the “k factor”. The refractive index profile can
35、 be measured by profiling techniques such as the Refracted Near- Field measurement (RNF) or Transverse Interferometry (TI), and by measurement of the near field-of a fully-illuminated core such as the Transmitted Near-Field measurement (TNF). It is recommended that curve fitting be used with both th
36、e index profiling and the TNF techniques to improve the measurement precision of the core diameter. NOTE 1 - Typically, k = 0.025 for either the fitted profiling methods or the unfitted TNF method is equivalent to k = O for the fitted TNF method. NOTE 2 - For fibres with refractive index profiles th
37、at have gradual transition region at their core/cladding boundary, a value of k = 0.05 for the unfitted TNF method is equivalent to k = O for the fitted TNF method. 2.10 core (cladding) centre: For a cross-section of an optical fibre, it is the centre of that circle which best fits the outer limit o
38、f the core area (cladding). NOTE 1 - These centres may not be the same. NOTE 2 - The method of best fitting has to be specified. 2.11 core (cladding) diameter: The diameter of the circle defining the core (cladding) centre. 2.12 core (cladding) diameter deviation: The difference between the actual a
39、nd the nominal values of the core (cladding) diameter. 2.13 corekladding concentricity error: The distance between the core centre and the cladding centre divided by the core diameter. 2.14 cqre (cladding) tolerance field: For a cross-section of an optical fibre, it is the region between the circle
40、circumscribing the core (cladding) area and the largest circle, concentric with the first one, that fits into the core (cladding) area. Both circles shall have the same centre as the core (cladding). 2.15 maximum theoretical numerical aperture: A theoretical value of numerical aperture calculated us
41、ing the values of refractive index of the core and cladding given by: 2 Recommendation G.651 (02/98) where: y11 is the maximum refractive index of the core; y12 is the refractive index of the innermost homogeneous cladding. NOTE - The relationship between NA (2.19) and NA, is given in 6.2.2. 2.16 mo
42、de filter: A device designed to accept or reject a certain mode or modes. 2.17 mode scrambler; mode mixer: A device for inducing transfer of power between modes in an optical fibre, effectively scrambling the modes. NOTE - Frequently used to provide a mode distribution that is independent of source
43、characteristics. 2.18 core (cladding) non-circularity: The difference between the diameters of the two circles defined by the core (cladding) tolerance field divided by the core (cladding) diameter. 2.19 numerical aperture: The numerical aperture NA is the sine of the vertex half-angle of the larges
44、t cone of rays that can enter or leave the core of an optical fibre, multiplied by the refractive index of the medium in which the vertex of the cone is located. 2.20 reference surface: The cylindrical surface of an optical fibre to which reference is made for jointing purposes. NOTE - The reference
45、 surface is typically the cladding or primary coating surface. In rare circumstances it could be the core surface. 2.21 reference test method: A test method in which a given characteristic of a specified class of optical fibres or optical fibre cables is measured strictly according to the definition
46、 of this characteristic and which gives results which are accurate, reproducible and relatable to practical use. 2.22 (refractive) index profile: The distribution of the refractive index along a diameter of an optical fibre. 3 Fibre characteristics The fibre characteristics dealt with in this clause
47、 are those which ensure the interconnection of fibres with acceptable low losses. Only the intrinsic fibre characteristics (not depending on the cable manufacture) are recommended in this clause. They will apply equally to individual fibres, fibres incorporated into a cable wound on a drum, and fibr
48、es in installed cables. 3.1 Geometrical characteristics of the fibre 3.1.1 Core diameter The recommended nominal value of the core diameter is 50 Pm. The core diameter deviation should not exceed the limits of k 3 Pm. 3.1.2 Cladding diameter The recommended nominal value of the cladding diameter is
49、125 Pm. The cladding diameter deviation should not exceed the limits of k 3 Pm. Recommendation G.651 (02/98) 3 3.1.3 Concentricity error The recommended concentricity error should be less than 6%. 3.1.4 Non-circularity 3.1.4.1 Core non-circularity The recommended core non-circularity should be less than 6%. 3.1.4.2 Cladding non-circularity The recommended cladding non-circularity should be less than 2%. 3.2 Optical properties of the fibre 3.2.1 Refractive index profile For fibres dealt with in this Recommendation, the normalized index profile is expressed as: d(x) =
