1、EIA TSBb2-b 7.5 k. 3234600 0.562843 042 TELECOMMUNICATIONS SYSTEMS BULLETIN I ITM-6 I I Characterization of Mode Field Diameter and Cutoff Wavelength of Single-Mode Optical Fiber by OTDR TSB62-6 AUGUST 1995 TELECOMMUNICATIONS INDUSTRY ASSOCIATION nqnrraytkcHaiirh(*uSlq i,nrcYiwlahtkUrmil.lA.iiBI*i M
2、DSIRYASSMWN Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,- EIA TSBb2-6 95 3234600 0562842 T7 NOTICE TINEIA Engineering Standards and Publications are designed to serve the pub
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9、 as may be occasioned by changes in technology, industry practice, or government regulations, or for other appropriate reasons. Published by OTELECOMMUNICATIONS INDUSTRY ASSOCIATION 1995 Standards and Technology Department 2500 Wilson Boulevard Arlington, VA 22201 PRICE: Please refer to the current
10、or call Global Engineering Documents, USA and Canada (1-800-854-7179) Catalog of EM, JEDEC and TIA STANDARDS and ENGINEERING PUBLICATIONS International (303-397-7956) All rights reserved Printed in U.S.A. Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for
11、 ResaleNo reproduction or networking permitted without license from IHS-,-,-ITM-6 Characterization of mode field diameter and cutoff wavelength of single-mode optical fiber by OTDR Contents 1 . Introduction . 1 2 . Normative references 3 3 . Apparatus . 3 4 . Sampling and specimens 4 5 . Procedure .
12、 7 6 . Calculations and interpretation of results . 11 7 . Documentation . 12 . . Annex A Splice loss guideline . 13 Annex C Comparison of this method to IEC or ITU standards 16 AnnexB References . 16 i Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for R
13、esaleNo reproduction or networking permitted without license from IHS-,-,- EIA TSB62-b 95 m 3234600 0562845 798 TINE IA-TS 8-62-6 This page left blank. II Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted wit
14、hout license from IHS-,-,- EIA TSB62-6 95 H 3234600 0562846 624 = TINE IA-TSB-62-6 ITM-6 Characterization of mode field diameter and cutoff wavelength of single-mode optical fiber by OTDR Foreword (This foreword is informative and is not part of this standard.) This document comes from TIA Project N
15、o. 3465, and was formulated 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 TIAEIA TSB-62. There are three annexes, a
16、ll of them informative. Key words: attenuation, loss, mode field diameter (MFD), cutoff wavelength, OTDR. . III Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-EIA TSB62-6 95 32
17、34600 O562847 5b0 TINE IA-TSB-62-6 This page left blank. iv Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,- EIA TSB62-6 95 m 3234600 0562848 4T7 ITM-6 Characterization of mode
18、field diameter and cutoff Wavelength of single-mode optical fiber by OTDR 1 Introduction 1.1 Intent This method describes the calculation of single-mode optical fiber mode field diameter (MFD) and cutoff wavelength at the fiber ends using backscatter measurements from an optical time domain reflecto
19、meter (OTDR). 1.2 Scope The method is limited in three ways: - Reference fiber - Empirical cutoff wavelength equations - OTDR nonlinearity The measurement is made by comparison to a reference pigtail fiber with known values of MFD and cutoff wavelength. This reference fiber should be of a similar si
20、ngle-mode design as the fiber that is being characterized. An example of a fiber design difference is that of matched clad fiber vs. depressed clad fiber. Note: An empirical mapping can sometimes be used for characterization of a fiber of one design with a reference fiber of another design. This map
21、ping is specific to the design pair. The equations for cutoff wavelength are derived from considering ideal fiber designs and the theoretical cutoff wavelength definition. Measured cutoff wavelength is not a theoretical value, and varies with the definition, i.e., fiber cutoff (FOTP-80) or cable cut
22、off (FOTP-170). Empirical relationships that follow the theoretical forms are evaluated for each fiber design and cutoff wavelength definition. The measurement is limited to MFD and cutoff wavelength at the reference- sample joint because OTDRs are nonlinear. This attribute is often specified by ins
23、trument manufacturers. Although typical specification values are sufficient for attenuation coefficient measurements, they are not sufficiently stringent to 1 Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted
24、 without license from IHS-,-,-EIA TSBb2-6 95 H 3234600 0562849 333 TINE IA-TSB-62-6 allow accurate characterization of MFD and cutoff wavelength over the entire fi ber length. 1.3 Background OTDRs are used to measure the attenuation coefficient of optical fiber with bi- directional measurements. The
25、y are also used to measure point discontinuities and fiber length, determine splice and fiber break location, and to characterize attenuation uniformity. This method extends the use of OTDRs to the characterization of two additional optical fiber properties: mode field diameter and cutoff wavelength
26、. The extension is based on sound optical fiber theory and has been reported in the literature 1,2,3,4,5,6. Bi-directional backscatter traces are required to characterize MFD. Bi- directional traces at two wavelengths are required to characterize cutoff wave length. The backscatter loss over a segme
27、nt of fiber can be measured from each direction. The average of the two values yields the attenuation loss over the segment. The difference of the two backscatter loss values can be used to compute the relative change in mode field diameter over the segment. This method measures the backscatter loss
28、 across a segment containing a splice between the fiber under test and a reference fiber. The reference fiber has a known MFD value so a value for the fiber under test can be estimated. When the method is completed at two substantially separate wavelengths, e.g., 131 O nm and 1550 nm, the MFD at eac
29、h wavelength can be determined. Cutoff wavelength is related to the ratio of MFD values at the two wavelengths. This relationship follows a theoretical form that contains parameters which can be refined for each combination of fiber design and cutoff wavelength definition. 1.4 Other This method is m
30、ost often used in manufacturing, where the fiber design is well known. The method is a surrogate for the primary methods of measuring MFD and cutoff. The latter methods shall be used to resolve disputes in value. Periodic validation of the results of this method, using a primary method, is recommend
31、ed. 1.5 Safety Use the safety procedures found in FOTP-61. 2 Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-EIA TSBb2-6 95 m 3234600 0562850 055 m TINE IA-TSB-62-6 - 2 Normativ
32、e references FOTP-59 (TINEIA-455-59A), Measurement of Fiber Point Discontinuities using an OTDR FOTP-61 (TINEIA-455-61 A), Measurement of Fiber or Cable Attenuation using an OTDR FOTP-80 (TINElA-455-80), Measurement of Cutoff Wavelength of ncabled Single-Mode Fiber by Transmitted Power FOTP-164 (TIN
33、EIA-455-164), Field Diameter by Far-Field Scanning Single-Mode Fiber, Measurement of Mode FOTP-165 (TINEIA-455-1 65), Field Diameter by Near-Field Scanning Single-Mode Fiber, Measurement of Mode FOTP-167 (TINEIA-455-1 67, Aperture Method in the Farfieid Mode Field Diameter Measurement - Variable FOT
34、P-170 (TINEIA-455-1 70), Fiber by Transmitted Power Cable Cutoff Wavelength of Single-Mode FOTP-174 (TINEIA-455-174), Fiber by Knife-Edge Scanning in the Far Field Mode Field Diameter of Single-Mode Optical 3 Apparatus 3.1 OTDR Use the equipment described in FOTP-61 for doing OTDR backscatter measur
35、ements. The actual center wavlengths of the OTDR should be known to within 2 nm for best results. An error of 2.5 nm will shift the MFD value by about 0.025 pm. A similar error in wavelength will shift the cutoff value by about 7 nm when wavelengths in the 1310 and 1550 region are used. For cutoff w
36、avelength, use wavelengths from the 1310 nm window (1310 f 25 nm) and the from 1550 nm window (1 550 k 25 nm). 3 Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,- EIA TSB62-6 75
37、3234600 0562853 T93 TINE IA-TSB-62-6 3.2 Optional auxiliary switches Various optical switching schemes can be used to make this method more efficient. Figure 1 illustrates an example in which an OTDR with lasers at two wavelengths is employed to do bi-directional backscattering measurements. The two
38、 reference fibers allow characterization of both ends of the fiber under test. 31 0/1550 nm Reference Fiber A A OTDR A Fiber Under Test V I. Reference Fiber i3 Splice B Figure 1 - Optical Switch Arrangement Note: The splices indicated on figure 1 can be butt joints. 3.2 Optional computer A computer,
39、 used for evaluating the loss across the splices, is recommended. 4 Sampling, specimens, and definitions 4.1 Specimen A specimen is a single-mode optical fiber. The specimen can be characterized for MFD and cutoff at one or both ends. 4.2 Sampling A sample is a representative selection from a popula
40、tion of fibers. This method describes the characterization of individual specimens. Some sampling is needed for validation of the result or for refining the equations that are used. 4.3 Primary methods These are the methods used for MFD and cutoff wavelength given in 2.0. 4 Copyright Telecommunicati
41、ons Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,- _ EIA TSBb2-6 95 = 3234600 0562852 928 TINE IA-TSB-62-6 4.4 Reference fiber Use two single-mode optical fibers that have been measured for MFD at one or
42、more wavelengths. If the method is to be used for cutoff wavelength, the reference fibers are also measured for cutoff wavelength. A reference fiber is typically of the same design as the fiber under test and is of a length sufficient to avoid the OTDR dead-zone. If the reference fiber is not of the
43、 same design as the fiber under test, a mapping of the values generated by this method and the values generated by a primary method shall be completed. 4.5 Orientation and notation This method will describe the characterization of position A of Figure 1. The notation of this section can be inverted
44、for characterization of position B. The backscatter loss across position A is measured by launching light of one or more wavelengths into both reference fiber A and reference fiber B. hj is a particular wavelength. RFA is Reference Fiber A. RFB is Reference Fiber B. LA ( hi) is the loss across splic
45、e A when launching hi through RFA. LB ( hi) is the loss across splice A when launching hi through RFB. b is the measured cutoff wavelength at the end of RFA. h,s is the cutoff wavelength derived from this method for the specimen. WA(hj) is the measured MFD at hj at the end of RFA. Ws(hj) is the MFD
46、at hj derived from this method for the specimen. Figures 2 and 3 shows these loss values on two backscatter traces. 5 Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-EIA TSBb2-6
47、 95 = 3234600 0562853 864 TINE IA-TSB-62-6 h m E. s a L a, O L c al s m (B Y U m Ref e re nce .I. Position B Reference Fiber B Position (km) Figure 2 - View from Reference A h m 0 L $ 2 m O Q a, L c v) Y o CCI Reference Fiber B gosition Splice B Reference Fiber A Position (km) Figure 3 - View from R
48、eference B 6 Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,- EIA TSBb2-6 95 W 3234600 0562854 7T0 TINE IA-TSB-62-6 4.6 Relationship of MFD to cutoff wavelength For characterizi
49、ng cutoff wavelength, a function relating the value of cutoff wavelength to the ratio of values of the MFD at two wavelengths shall be used. For step-index fibers, the following function, from Marcuse l, can be used. 0.65 + 0.434 + 0.0149 W(hl) - Vi2) 0.65 + 0.434 tcp“ - + 0.0149 er Alternatively, the foll
