1、TIA/EIA TELECOMMUNICATIO SYSTEMS BULLETIN VS ITM-5 Characterization of Attenuation Uniformity of Optical Fibers TSB62-5 AUGUST 1995 (Reaffirmed September 2001) TELECOMMUNICATIONS INDUSTRY ASSOCIATION The Telmmmmicationu Indwtry Association repramis the nnimunicatiom wdor of Electronic indu6tries All
2、iance NOTICE TIA/EIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with m
3、inimum delay the proper product for his particular need. Existence of such Standards and Publications shall not in any respect preclude any member or nonmember of TIA/EIA from manufacturing or selling products not conforming to such Standards and Publications, nor shall the existence of such Standar
4、ds and Publications preclude their voluntary use by those other than TIA/EIA members, whether the standard is to be used either domestically or internationally. Standards, Publications and Bulletins are adopted by EIA in accordance with the American National Standards Institute (ANSI) patent policy.
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6、engineering data or information useful to the technical community, and represent approaches to good engineering practices that are suggested by the formulating committee. This Bulletin is not intended to preclude or discourage other approaches that similarly represent good engineering practice, or t
7、hat may be acceptable to, or have been accepted by, appropriate bodies. Parties who wish to bring other approaches to the attention of the formulating committee to be considered for inclusion in future revisions of this Bulletin are encouraged to do so. It is the intention of the formulating committ
8、ee to revise and update this Bulletin from time to time as may be occasioned by changes in technology, industry practice, or government regulations, or for other appropriate reasons. (From Project No. 3-3440-RF1, formulated under the cognizance of the TIA FO-6 Committee on Fiber Optics and the TIA F
9、O-6.6 Subcommittee on Optical Fibers.) This Document was reaffirmed by the Telecommunications Industry Association on September 14,2001. Published by TELECOMMUNICATIONS INDUSTRY ASSOCIATION 1995 Standards and Technology Department 2500 Wilson Boulevard Arlington, VA 22201 PRICE: Please refer to the
10、current Catalog of ELECTRONIC INDUSTRIES ALLIANCE STANDARDS and ENGINEERING PUBLICATIONS or call Global Engineering Documents, USA and Canada (1-800-854-7179) International (303-397-7956) All rights reserved Printed in U.S.A. ITM 5 Characterization of Attenuation Uniformity of Optical Fiber CONTENTS
11、 1 . Introduction . 1 2 . Normative references 2 3 . Apparatus 3 4 . Sampling and specimens 4 5 . Procedure 8 7 . Documentation 18 6 . Calculations and interpretation of results . 9 . Annex A Treatment of end effects . 19 Annex B GSW Algorithms 21 Annex C Filter definition and evaluation . 24 Annex
12、D Applications . 30 Annex E Comparison with IEC or ITU tests . 32 I EIA TSB62-5 95 3234600 0562806 T4 TINE IA-TSB-62-5 This page left blank. II TI NE I A-TS B-6 2- 5 ITM 5 Characterization of Attenuation Uniformity of Optical Fiber Foreword This document comes from TIA Project No. 3440, and was form
13、ulated under the cognizance of TIA FO-6.6 Subcommittee on Optical Fibers and Cables, and TIA FO-6.6.5, Working Group on Single-mode Measurements of Optical Fiber. This ITM is part of the series of informative test methods included within TINEIA TSB-62. There are five annexes, all of which are inform
14、ative. Key words: attenuation, uniformity, OTDR, . III EIA TSBb2-5 95 m 3234600 0562832 241 m TINE IA-TSB-62-5 This page left blank. iv EIA TSBb2-5 95 W 3234600 0562830 477 W ITM-5 Characterization of Attenuation Uniformity of Optical Fiber 1 Introduction 1.1 Intent This document is intended to exte
15、nd the use of OTDRs, see FOI rs 59, 60, and 61, to quantitatively characterize the uniformity of the attenuation coefficient of optical fibers. Each has particular utility under certain circumstances but none can be considered as universally optimal. The choice of a particular method will depend on
16、details of the agreement between the buyer and seller. Several methods are defined in this document. 1.2 Scope This document is restricted to the use of bi-directional OTDR traces which are required for accurate attenuation values. The document defines terminology that is used to describe several me
17、thods of characterizing attenuation uniformity. It outlines some of the details about identifying start and end locations on unidirectional traces so that the bi-directional average can be computed. The document provides guidelines on the evaluation of the quality of digital filters 1.3 Background T
18、he functional requirements on attenuation uniformity differ substantially, depending on considerations such as: - Fiber transfer to cabler Length of fiber - Cable transfer to distributor - Cable transfer to end user Length of cables and cable count - End user evaluation of installation or maintenanc
19、e records - Quality of OTDR and method of operation - Computational power and data storage A single, universally satisfactory, method is not possible. 1.4 Other This document follows a worst-case methodology. That is, a maximum value is the usual outcome of a definition. If only a worst case value i
20、s used, the user cannot derive the benefit of the portions of the fiber that are better than the worst 1 EIA TSBb2-5 95 3234b00 O562809 757 TINE IA-TSB-62-5 case. Other methodologies, such as statistical, may be more effective. These methods might incorporate some of the methods in this document, au
21、gmented with other, more complete information. 2 Normative references FOTP-59 (TINEIA-455-59A) Measurement of fiber point discontinuities using an OTDR FOTP-60 (TINEIA-455-60A) Measurement of fiber or cable length using an OTDR FOTP-61 (TINEIA-455-61 A) Measurement of fiber or cable attenuation usin
22、g an OTDR 3 Apparatus FOTP-61 contains the equipment requirements for measuring attenuation uniformity. 4 Sampling and specimens The mathematics of this section are used to provide consistent definitions for use in the other sections of the document. Many alternative and equivalent expressions might
23、 be employed by a given user. 4.1 Specimen definition A specimen is a length of optical fiber, typically unspliced fiber, but which may comprise more than one section that might be spliced or connected. Dead- zone fibers, if used, are not typically considered pari of the specimen. 4.2 Sample definit
24、ion A sample is a representative group of a given population. A sample of the fibers within a cable might be used to characterize the cable, for example. The method for characterizing the aggregate performance of a cable, based on sampled data, is beyond the scope of this document. 2 EIA TSBb2-5 75
25、3234600 0562807 984 TINEIA-TSB-62-5 4.3 Unidirectional trace A unidirectional trace is a data set that represents the OTDR back-reflected power (dB) vs. the position (km) within the fiber(s) (including an optional pigtail) into which the light is launched. Let a(x) represent a unidirectional trace,
26、with x representing position. Then, from FOTP-61: a(x) = 10 loglo P(x)/P(O) The OTDR actually samples the data at discreet locations, separated by a finite ;stance, Ax (km). The notation for the discretized array is: a i = a( i Ax) i = O to N-1, with N sampled points 4.4 Bi-directional trace A bi-di
27、rectional trace is a special average of two unidirectional traces, one taken from each end of a fiber. Let the array, a, represent the reference orientation trace and let the array, b, be the trace obtained from the other end. Let kstrta and kenda be the index value identifying the physical start an
28、d end of the specimen, from the reference direction. Let kstrtb and kendb be the index values identifying the physical start and end of the specimen, from the other direction. Let c be the array containing the bi-directional average: a i - b kendb - (i - kstrta) 2 c i - ia01 = for i=kStrta to kend,
29、Note: kenda - kstrta = kendb - kstrtb Now c is an array of N = kenda - kstrta + 1 elements numbered from O to N -1. When reflections are present at the start and end of a trace, the physical start and end locations are the positions just before the reflections, with a slight adjustment for the OTDR
30、pulse width. See Annex A for a more complete description of the end location identification. In this case, the leading reflection from the reference trace corrupts the near end of c and the leading reflection from the other trace corrupts the far end of c. The extent of these reflections shall be de
31、termined and marked with the index locations, kstrtc and kendc . The attenuation uniformity characterization is restricted to the portion of the specimen from kctrtc to kendc, inclusive. Note: The pulse width of the OTDR and the displayed reflection magnitude determine the amount of the specimen tha
32、t is obscured by end reflections. 3 EIA TSBb2-5 95 = 3234600 0562808 810 TINE IA-TSB-62-5 4.4 Inverse trace definition For some computational methods, the inverse alternate trace is useful. It is: It is just the “b“ component of equation 2. 4.5 Segment definition A segment is a contiguous length wit
33、hin the cpecimen. A segment is defined by either a start location and an end location, or by a start location and a length. If i0 and il define the start and end locations of a segment, the loss (dB) across the segment is given by: Loss(i0,il) = CiO - cil (4) The attenuation coefficient (dB/km) of t
34、he segment defined by the start and end locations is given by: Loss(i0,il) orp(i0,il) = (il -O) AX When start position and length define a segment, the notation for the attenuation coefficient is: C i - c i + n 1 n, Ax w(i, n,) = LW n, =- Ax 4.6 En d-t o-end at t en ua t i on The end-to-end attenuat
35、ion coe context of this notation it is: coefficient definition c kstrtc - c ken 29 0 28 n Reference Fiber A Specimen Fiber 27 i Fit20 B - N In b O In O W 7 W 7 (D N b N ln b O In In b O T 7 7 7 Position (rn) Figure 9 - Reflection at Dead-zone Splice Figure 10 shows the decay of the reflection. The l
36、ine, used to assess the splice loss at the reflection, also shows the extent to which the decay continues to affect the region of the OTDR trace that is associated with the specimen. 19 EIA TSB62-5 75 3234600 0562828 609 TINE IA-TS 8-62-5 28.75 28.7 28.65 28.6 28.55 28 .S 28.45 28.4 Reflection Tail
37、Closeup c Decay of Reflection I- & Linear Regression Fit Zone 8 i 1600.0 1800.0 2000.0 1200.0 1400.0 Position (m) Figure 10 - Decay of reflection If uniformity is evaluated in the region of the reflection decay, the resultant values will be inaccurate. To determine the extent of the reflection decay
38、, for a given OTDR design and pulse width, an experiment is recommended. The experiment consists of: 1. Find and measure a uniform region, away from the ends. 2. Cut the fiber so the new end begins at the start of the uniform region. 3. Measure the region again, with the end reflection extending int
39、o the known uniform region. 4. Adjust the vertical heights of the two traces, before and after cutting, so there is a substantial overlap away from the reflection decay region of the after trace. 5. Assess the difference of the overlaid traces to determine that location at which the difference becom
40、es negligible. 20 EIA TSBb2-5 75 3234bOO 0562827 545 m TINEIA-TSB-62-5 Annex B (informative) Annex B - GSW Algorithms These algorithms are set up to operate on the bidirectional loss traces. B.l Algorithm for refprence coefficient and nonuniformity parameter This computes the reference coefficient,
41、ar, (dB/krn) and the nonuniformity parameter, E, (dB). Inputs: istrt and end are the start and end positions of the trace to be characterized yi is the OTDR attenuation vs. distance curve Ax is the length increment between values (km) Lopt is the optimization length (km) Lwmin is the minimum window
42、length out puts : ay is the reference alpha (dB/km) E is the nonuniformity parameter (dB) Procedure: Full length coefficient and minimum length sliding window Lwmin 1. Lt = AX (iend - istfl), ae = (Yistfi - Yiend)/ Lt , as = O , io = - AX 2. for i=istrt to end - i0 If tmp then 0s = tmp. end 21 EIA T
43、SBh2-5 95 3234b00 0562830 267 = TINE IA-TSB-62-5 Binary search variables i Binary search 4. 5. 6. 7. 8. 9. slope of line aup - alo = x,p - XI0 anom = qo Xi0 SIP intercept of line Call Exlo(y, istrt, iend, AX, anom, Lwmin, Emax, Ls if Emax xup then go to step 12. Binary search complete, determine ref
44、erence values 6.2 Maximum excess loss algorithm This determines the maximum excess loss (MEL) and the length of the MEL segment. Usage: Call Exloss(y, istrt, iend, AX, anom, Emax, Ls) Inputs: istrt and end are start and end position of the trace to be characterized yi is the OTDR attenuation vs. distance curve Ax is the length increment between values (km) anom is the nominal coefficient (dB/km) Lwmin is the minimum length segment 22
