1、TIA/EIA TELECOMMUNICATIONS SYSTEMS BULLETIN ITM-12 Microbend Sensitivity Test Methods TSB62-12 OCTOBER 2001 TELECOMMUNICATIONS INDUSTRY ASSOCIATION NOTICE TIA/EIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufactur
2、ers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such Standards and Publications shall not in any respect preclude any member or nonmembe
3、r of TIA/EIA from manufacturing or selling products not conforming to such Standards and Publications, nor shall the existence of such Standards and Publications preclude their voluntary use by those other than TIA/EIA members, whether the standard is to be used either domestically or internationall
4、y. Standards, Publications and Bulletins are adopted by EIA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, TIA/EIA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard, Publi
5、cation, or Bulletin. Technical Bulletins are distinguished from TIA/EIA Standards or Interim Standards, in that they contain a compilation of engineering data or information useful to the technical community, and represent approaches to good engineering practices that are suggested by the formulatin
6、g committee. This Bulletin is not intended to preclude or discourage other approaches that similarly represent good engineering practice, or that may be acceptable to, or have been accepted by, appropriate bodies. Parties who wish to bring other approaches to the attention of the formulating committ
7、ee to be considered for inclusion in future revisions of this Bulletin are encouraged to do so. It is the intention of the formulating committee 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 ot
8、her appropriate reasons. (From Project No. 3-4731, formulated under the cognizance of the TIA FO-6.6 Subcommittee on Optical Fibers .) Published by TELECOMMUNICATIONS INDUSTRY ASSOCIATION 2001 Standards and Technology Department 2500 Wilson Boulevard Arlington, VA 22201 U.S.A. PRICE: Please refer to
9、 the 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. TSB-62-12 TSB-62-12 Microbend Sensitivity Test Methods Contents . For
10、eword .I i i 1 Introduction . 1 2 Normative references 3 3 Test Procedures 4 3.1 3.2 3.3 3.4 Method A . Expandable Drum 4 Method Method Method B . Fixed C . Wire Diameter Drum 6 mesh . 7 D . Basketweave 10 4 Results common to all methods 13 Annex A (informative) . 15 i TSB-62-12 This page left blank
11、. ii TSB-62-12 TSB-62-12 Microbend Sensitivity Test Methods Foreword From TIA Project No. 4731, formulated under the cognizance of TIA FO-6.6 Subcommittee on Optical Fibers. This ITM is part of the series of test methods included within TIAEIA TSB-62. There is one annex, which is informative. Key wo
12、rds: microbend sensitivity, cabling effects, expandable drum, fixed drum, wire mesh, basketweave, attenuation, attenuation coefficient, transmission, fiber length, elongation, linear pressure, OTDR, iii TSB-62-12 This page left blank. iv TSB-62-12 1 Introduction 1 .I Scope This technical report is i
13、ntended to characterize the microbend sensitivity of optical fibers, thereby guiding fiber and cable manufacturers regarding the design of various coatings and basic fibers as they apply to the design and performance of cable. For the purposes of this technical report, the term microbending should b
14、e properly distinguished from macrobending. The spirit of these two terms is to identify whether the bending is small or large. Through many years, experiments with small and large bends provided a link between bend size and specific qualities of the resulting loss spectra of the optical fiber under
15、 test, thereby producing new, functional definitions for micro- and macrobending. The following definitions will attempt to capture some of the art and intuition behind these historic terms, while maintaining the integrity of their original intent. Moreover, since bend loss is a function of waveleng
16、th, these terms should be defined in the context of a given wavelength range. This report will use the typical wavelength region of interest for telecommunication fibers: 1200 to 1700 nm. Macrobending is usually characterized by a constant, moderately large bend radius leading to an exponential incr
17、ease in the loss as a function of wavelength. This loss in known to be physically induced by an optical tunneling phenomena, where the light from a propagating mode leaks out toward the outside of the bend. In the event that the bend radius is not constant, the type of bending could still be conside
18、red macrobending provided the different bend radii are all generally large, and the loss is still dominated by the optical tunneling phenomena with exponential wavelength dependence. Microbending, on the other hand, is random microscopic fiber axis perturbations along the length of the fiber. Such r
19、andom microbending is typically indicated by a uniform loss across the te leco m mu n ica t io ns wave length band . Of cou rse , ce rtai n m icro be nd scenarios can be created (small, periodic bending) where the loss response is not uniform, but these cases are typically not accidental and may in
20、fact be engineered into the fiber for a specific purpose. Regardless of the statistics of the microbends however, they can generally be described by some form of coupled-mode theory, treating the bends as small perturbations to the otherwise straight fiber. Thus, micro- and macrobends can be disting
21、uished both by the underlying physics and the appearance of the resulting loss spectra, provided the spirit of these terms is maintained. The transition from microbending to macrobending as bend radius is increased is a continuous process, meaning that the boundary typically contains features of bot
22、h types of loss. Moreover, such a boundary would be more 1 TSB-62-12 appropriately described in terms of the bend statistics (random versus constant, for example) than the absolute bend radius. Therefore this report will not attempt to limit its scope with absolute specifications of bend radii, but
23、will rather leave this discrimination to those reviewing the above qualities of the fiber under test. For the purposes of this technical report, microbend and macrobend will be defined in terms of bend loss in optical fiber. The spirit of these two terms is to identify whether the bending is small o
24、r large. Through many years, several different regions of bend quality emerged. Since bend loss is a specified function of wavelength, the typical region of interest for telecommunication fibers is 1200 to 1700 nm. Macrobending is usually characterized by a constant moderately large bend radius lead
25、ing to an exponential increase in the loss as a function of wavelength physically induced by an optical tunneling phenomena, where the light from a propagating mode leaks out toward the outside of the bend. Spectrally uniform microbending is microscopic in nature, usually characterized as a collecti
26、on of random small bends, rapidly varying in both radius and orientation induced by factors that are usually described by coupled-mode theory. Microbend is dependent on the type of bend - usually random, periodic. The boundary between microbend / macrobend (combination region) is continuous and depe
27、ndent on the wavelength properties usually in the mm range. Although they can be very useful tools for evaluating fiber and cable designs, the current state-of-the-art of these test procedures are such that test results may prove to be misleading. These tests are not recommended for use in comparing
28、 different types of optical fibers, nor should test results be compared from one facility to another nor from one technique to another. The ability of a coating to prevent microbend loss can be dependent upon temperature. The temperature(s) at which this test is to be performed for expandable drum,
29、fixed drum and wiremesh shall be specified in the Detail Specification. The basketweave technique is a temperature dependent, microbend sensitivity test with the recommended temperatures defined within the text. 1.2 Description This technical report describes four techniques for the measurement of m
30、icrobend sensitivity of optical fiber: - method A using an expandable drum for category B fibers. 2 TSB-62-12 - method B using a fixed diameter drum for category AI and B fibers. - method C using a wire mesh and applied loads for category AI and B fibers. - method D using a “basketweave“ wrap on a f
31、ixed diameter drum for category B fibers. Methods A and C offer the capability to measure the microbend sensitivity over a wide range of applied linear pressure or loads. Method B may be used to determine the microbend sensitivity for a fixed linear pressure. Method D may be used to determine the mi
32、crobend sensitivity at low temperatures. The results from the four methods can only be compared qualitatively. This is a non-routine test used in the general evaluation of optical fiber. This parameter is not generally specified within a detail specification. 2 Normative references Test or inspectio
33、n requirements may include, but are not limited to, the following refe re nces: FOTP-60 Measurement of Fiber or Cable Length using an OTDR TINEI IA-455-60). FOTP-61 Measurement of Fiber or Cable Attenuation using an OTDR TINEI IA-455-61 ). IEC 60793-1 -4: Optical fibers - Generic specification - sec
34、tion 4: Measuring methods for transmission and optical characteristics (1 995). ITM-62 Microbend Sensitivity Test Methods (TIA/E IA-455-62). TIA/EIA -455-A Standard Test Procedure for Fiber Optic Fibers, Cables, Transducers, Sensors, Connecting and Transmitting Devices, and Other Fiber Optic Compone
35、nts. 3 TSB-62-12 3 Test Procedures 3.1 Method A - Expandable Drum This section describes a technique for the measurement of the loss increase due to microbend effects induced by the application of linear pressure to a single- mode optical fiber. 3.1 .I Apparatus. The apparatus is an expandable drum,
36、 the diameter of which can be changed continuously. In order to avoid any loss contribution due to macrobend effects a minimum drum diameter of 200mm is recommended. The curvature at any edges of the expanded segments of the drum shall also exceed 200mm diameter. The drum surface shall be coated wit
37、h a material of fixed roughness, for example: a sandpaper/lapping film PSA - grade 40pm - mineral A1203. It shall be possible to wind at least 400m of the fiber to be tested onto the rough surface. The winding pitch shall be controlled to prevent the fiber turns from overlapping. While expanding the
38、 drum, the fiber elongation shall be measured using the method described in IEC 60793-1-22 Method E - Phase Shift. The attenuation measurement shall be conducted using either the cut back technique (method IEC 60793-1 -40 Method A), the backscatter technique (method IEC 60793-1 -40 Method C) or by t
39、he direct transmitted power measurement technique (method IEC 60793-1 -46 Method A). 3.1.2 Procedure The fiber to be tested shall be carefully wound onto the coated drum with no tension in one single layer avoiding any crossing or overlapping. The fiber shall be fixed to avoid any relative slipping.
40、 While expanding the drum, the changes in attenuation coefficient and phase shall be recorded. 3.1.3 Calculations. The fiber elongation (E ) can be found from: f is the modulation frequency (Hz); 4 TSB-62-12 L is the length of the sample (km); V is the constant depending on the photo-elastic coeffic
41、ient (k), of the speed of light in a vacuum (c) and the effective group index of refraction (Nef): For BI fibers, V is typically 726 km/s/degree. From this the linear pressure P can be calculated: Where T is the tension applied to the fiber (N); R E is the radius of the expandable drum in rest condi
42、tion (mm); is the Youngs modulus of the fiber (GPa) typically 70.3 GPa for silica; A is the cross-sectional area of the fiber (glass part) (mm2). The changes in attenuation coefficient (dB/km) are plotted as a function of the linear pressure P (N/mm) or the elongation E (%). The points obtained are
43、interpolated by a straight line passing through the origin, the slope of which gives the microbend sensitivity (dB/km)/(N/mm) or (dB/km/%) of the tested fiber. 3.1.4 Results. The following details shall be presented: - test apparatus arrangement; - minimum diameter of the expandable drum; - roughnes
44、s and type of material used to cover the drum; - length of fiber wound onto the expandable drum; 5 TSB-62-12 - plot of measured change in attenuation coefficient as a function of the calculated linear pressure or of the elongation; - relative humidity and ambient temperature during the test. 3.2 Met
45、hod B - Fixed Diameter Drum This section describes a procedure to measure the microbend sensitivity of category AI and B fibers. This technique gives the loss increase due to microbend effects for a fixed linear pressure applied to the fiber. 3.2.1 Apparatus. The apparatus consists of a fixed diamet
46、er drum. In order to avoid macrobend effects the minimum drum diameter shall be 200mm. The surface of the drum shall be coated with a material of fixed roughness (for example: sandpaper - lapping film PSA - grade 40p m - mineral Al2O3). It shall be possible to wind at least 400m of the fiber to be t
47、ested onto the coated surface of the drum. The attenuation measurement shall be performed using the cutback technique (method IEC 60793-1-40 Method A) or by the backscatter technique (method IEC 60793-1-40 Method C). 3.2.2. Procedure The fiber to be tested shall be wound onto the coated surface of t
48、he drum in one single layer, i.e. avoiding cross-overs. The winding tension shall be 3 N. Measure the attenuation coefficient of the fiber under test. Calculate the attenuation increase due to microbend by subtracting the intrinsic attenuation coefficient of the fiber. 3.2.3. Calculations. The micro
49、bend sensitivity is found from the following relationship: (dB/km)/(N/mm) QR- a Microbend sensitivity = - - - T P Where (4) a is the attenuation increase due to the microbend sensitivity (dB/km); 6 TSB-62-12 P R T The complete procedure may be repeated using different winding forces. is the linear pressure (N/mm), see equation (3); is the radius of the fixed drum (mm); is the winding tension applied to the fiber (N); 3.2.4. Results specific to method B - Fixed Diameter Drum. The following details shall be presented: - test apparatus arrangement; - diameter of drum; - roughness and ty
