Microbend evaluation of selected G652D & G657 fibers and ribbons before cabling

Microbend evaluation of selected G652D & G657 fibers and ribbons before cabling 1 Dr. Bertil Arvidsson, 2 Pratik Shah, 2 Steven R. Schmid, 3 Robert Alexandersson, 3 Anders Björk 1 Fiberson AB, Hudiksvall, Sweden 2 DSM Functional Materials, 1122 St. Charles St., Elgin, IL 60120, USA 3 Ericsson AB, PDU Cables & Interconnect, Hudiksvall, Sweden Abstract We have selected several G.652.D and G.657 commercial fibers. These fibers were used to make ribbons and cable. There was sufficient length of fiber on each spool to last for various tests. Therefore each fiber was of the same quality throughout the testing. We have exposed the fibers and ribbons to microbend evaluation. The ribbons were also exposed to room & high (+60 ºC) temperature water soak for 30 days. The ribbons in the room temperature water soak were then frozen to -40 ºC and measured for attenuation of their respective fibers with an OTDR. Finally a cable was produced with fibers from the original spools. The cable design was a 24 fiber microcable with six different tubes. The cable underwent various cable tests: temperature cycling and crush. Primarily an OTDR and a power meter were used to evaluate the results. By analyzing the results we find that the fibers which handled the microbend tests best were the same that passed the ribbon and cable tests in a superior way. 1. Introduction When a new fiber is designed, microbending sensitivity is part of the evaluation as noted in recent IWCS- and OFC-publications, see [1, 2 and 3]. We discuss here to extend this technique to be part of a cable type test program. When installations are made for the last mile, concerns regarding available space are increased and therefore new cable designs are being developed with tighter dimensions. The choice of fiber is also important. The G.657 fiber category is still being discussed in standards bodies. At present we find A1, A2, B2 and B3 subcategories with different bend radius specifications. For this study we chose both G.652.D and G.657 fibers, which will be explained later. The fibers were exposed to pure fiber tests. We also made standard four fiber ribbons of the encapsulated type of all the fibers, see Figure 1. These ribbons were also exposed to testing. Finally we made a microcable, see Figs 2 and 3, with six CFU-s (compact fiber units) and four fibers in each CFU. The microbend testing was performed according to method B in IEC TR62221 expanded to include temperature cycling. Method B uses a fixed diameter drum with sandpaper. We used a quartz drum to be able to handle the temperature cycling. We show that by evaluating various fibers with microbend technique we may in the future reduce the number of tests in a type test program. Microbend tests serve as a way to filter out less interesting fibers before entering a full type test program. Figure 1. A typical four-fiber ribbon used in the study The paper also discusses important microbend parameters to improve repeatability between measurements. Keywords: Microbend; Fiber; Ribbon; Cable; Measurement; OTDR. Figure 2. The 24-fiber microcable

After winding the fiber was moved to the temperature chamber, see Figure 5. Figure 5. The fiber moved to chamber Figure 3. Microcable with 6 CFU-s The four fiber ribbon is of the encapsulated type, i.e. the outer layer in the ribbon is acrylate-coated. A CFU also has the outer layer coated with acrylate. 2. Microbend in IEC In IEC microbend test methods are only described in a technical report, see [4]. This report is now under revision. Four methods are described. We have used method B and expanded the technique to include temperature cycling. This has been proposed to be added to the revised IEC report. The fiber is wound on a quartz drum (to avoid diameter changes in the temperature cycling). The drum is covered with specified sandpaper, see Figure 4. In IEC the new draft for microbending test methods is being prepared with added information, pointing out some important parameters. Table 1 lists the parameters used in this study, which will also be considered for inclusion in the revised IEC TR 62221 microbending technical report. Table 1 Key parameters and used values 1 OTDR 2 Wavelengths: 1310, 1550 and 1625nm 3 Pulse width/lsa: 20, 50 or 100ns depending on attenuation 4 Winding tension: 1 N 5 Winding speed: 30 and 50m/min 6 Winding pitch on sandpaper spool: 0.55 7 Length on sandpaper and taped length, recommended 400m (350 was used early in the study) 8 Sandpaper P320 grit 9 Sandpaper spool size, quartz drum 280mm /280mm 10 Changing sandpaper (after each temperature cycling run; not changed after runs under ambient conditions) 11 Temperature/Humidity Figure 4. A standard prooftester was used for winding Given values in Table 1 could be different depending on fiber category or other, e.g. a multimode fiber might need a lower winding tension. We only report here what we used in our study. The technical report status in IEC means that the methods are not standardized and no specifications are given. In this paper we point out that by following the conditions in Table 1, the repeatability between measurements is quite satisfactory. Since

there are four different techniques, it is yet too premature to propose specified values. 3. Fibers, ribbons and cable 3.1 Fibers A number of fibers from different vendors were chosen for the study. The first eight were commercially available G.652.D fibers and the next two were G.657.A2 fibers. Later another fiber was added, #12, for microbend tests on the fiber only. This is an interesting fiber with only 200µm coating diameter as compared with all others of typically 242-245µm. Some fibers did not arrive in time to take part of all various tests, see Table 2. For each fiber the modefield diameter (MFD) and fiber cutoff was measured and the MAC-value calculated (MFD at 1310nm/Cutoff). A lower MAC-number for a fiber would give better macrobend performance. In the study we tried to keep track of any possible macrobend influence from the various tests. This will be further elucidated in the conclusions. Table 2 Fibers in the study Fiber Category MAC/Comment #1 G.652.D 7.16 #2 G.652.D 6.97 #3 G.652.D 6.95 #4 G.652.D 6.91 #5 G.652.D 7.17 No ribbon or cable test #6 G.652.D 7.23 #7 G.652.D 7.36 #8 G.652.D 7.47 #9 G.657.A2/B2 6.92 Bend-loss insensitive #10 G.657.A2/B2 6.87 Bend-loss insensitive #12 G.657.A2/B2 6.71 Bend-loss insensitive with coating 200µm. No ribbon or cable test. One further comment about the fibers is that fiber #4 and #5 both were manufactured in the same facility from the same glass preform type, but with different coatings. 3.2 Ribbons Each ribbon, see Figure 1, contains the same fiber from the fiber list, so Ribbon 1 is therefore a four fiber ribbon with fiber #1 and so on. The same inks and matrix material were used for all ribbons. The inline technique was used, i.e. coloring and matrix applying were performed in the same process. 3.3 Cable A 2.2 km cable was produced, see Figure 3. Each CFU contained four fibers as described in Table 3 below. Table 3 Fiber distribution in the cable CFU Four fibers 1 #3 + #3 + #6 + #6 2 #7+ #7 + #8 + #8 3 #9+ #9 + #10 + #10 4 #2 + #2 + #2 + #2 5 #1 + #1 + #1 + #1 6 #2 + #2 + #4 + #4 As was earlier explained some fibers did not arrive in time. To fill the cable in an interesting way the above combinations were chosen. CFU 3 is a bend-insensitive CFU. CFU 4 and CFU 5 contain fibers with interesting microbend results (see cable crush test results Section 8 and Figure 17). 4. Test program We started with microbend evaluation of all fibers in the study using method B in [4]. This was followed by ribbon and cable testing as described below, see [5]. The new cable test methods are a split of [5] and will be described in IEC 60794-1-2 (Reference table), -1-21(Mechanical), -1-22 (Environmental), -1-23 (Cable elements) and -1-24(Electrical). The methods we have used come from the future -21, -22 and -23. All ribbons were water-soaked at room temperature and +60 ºC (not in IEC). These tests were finished with a freezing test, which is not in IEC. The ribbons were frozen to -40 ºC. The cable was exposed to temperature cycling, crush, tensile and PMD. 5. Fiber microbend results 5.1 Temperature cycling After winding 400 m of fiber on the sandpaper drum the remaining fiber on the fiber spool and the fiber on the sandpaper drum was kept as one unit and moved to the temperature chamber, see Figure 5. The OTDR-markers were put at 350 m to avoid edge effects. We found later that we could easily put 450 m on the same sandpaper drum with OTDR-markers at 400 m. Table 4 below shows the temperature cycling valid for all microbend fiber tests in the present study: Initial value is before any winding on the sandpaper drum. After rewinding is the attenuation on the sandpaper drum right after rewinding (at +20ºC). The whole procedure took about 2 hours.

Table 4 Temperature cycling Initial +20ºC Before winding on sandpaper 6,000 Fiber 1 After rewinding +20ºC OTDR-value of sandpaper section 5,000 Fiber 2 Fiber 3 A Before the start of cycling B +20ºC -40ºC 4,000 Fiber 4 Fiber 5 Fiber 6 C after 30 min -40ºC Fiber 7 D E after 30 min -60ºC -60ºC Fiber 8 Fiber 9 Fiber 10 F back to room temperature +20ºC Steps 38 Results are given in Figs. 6 and 7 for 1310 and 1550 nm. We also measured at 1625 nm and those results were as expected, i.e. slightly higher. The fiber order (high to low attenuation), at each wavelength, was the same for all conditions. Figure 7A. Wavelength 1550 nm and markers separated by 350 m We find that fibers #4, #6, #7 and #8 have the highest attenuation and #1, #2, #5, #9 and #10 the lowest with #3 in middle. Although fibers #2, #3 and #4 have similar MAC numbers, they have significantly different microbending attenuation which points out the influence of coatings on the ultimate microbending resistance of fibers. As mentioned previously, fibers #4 and #5 come from the same manufacturer, but have different coatings. We note that the MACnumber for #5 is slightly higher than the MAC-number for #4, but fiber #5 has superior microbending performance. Therefore we draw the conclusion that #5 has a better microbending resistant coating as compared with fiber #4, see Table 2. In Figure 7B below we show how fiber #12, 200 µm coating diameter performs in comparison with fibers #1, #2 and #3. We conclude that #12 falls in the category of the best G.652.D in this study, but with nearly a 20% reduction in outer diameter compared with standard fiber. This type of performance is expected to be well suited for compact cable designs and installations where space is a premium. Figure 6. Wavelength 1310nm and markers separated by 350m 1,800 1,600 1,400 1,200 0,800 0,600 Fiber 1 Fiber 2 Fiber 3 Fiber 12 0,400 0,200 Initial Values After Rewinding A B C D E F 31 Figure 7B. Wavelength 1550 nm and markers separated by 350 m

5.2 Repeatability trials Because of the complex nature with microbend tests and a number of process parameters that could influence the result, see Table 1, we performed several trials to investigate the repeatability. Winding tension was 1 N and distance between OTDR-markers 400 m in these tests. Two fibers, one more sensitive than the other were chosen, see Figs 8 and 9. When we carefully follow the conditions as presented in Table 1, we get very good results as shown below. on the drum. The OTDR-curve did show the different behavior for each layer, see Figure 10. It is not possible to directly compare the ribbon values with the fiber results. However, we saw the same trend for the ribbons as for the fibers, i.e. the fibers with the best fiber microbend results were also the best in the ribbon testing, see Figs 11 and 12 below. Note also that fiber #5 was not in a ribbon. SETUP First Marker 2nd Marker 0,450 0,400 1310nm 1550nm First layer 2nd layer 1625nm 3rd layer 0,350 0,300 0,250 0,200 The two markers used for measuring the attenuation are separated by 235 meters so as to measure the loss of the second and third layers. This gives a sufficient length in order to get accurate and consistent measurements. 0,150 0,100 Figure 10. OTDR-curve for a ribbon under microbend 0,050 1 2 3 4 5 6 7 8 9 10 Tests igure 8. Fiber #1 in a repeatability trial 21 F Ribbon 1 Ribbon 2 2,500 Ribbon 3 Ribbon 4 1,500 Ribbon 6 3,500 1310nm 1550nm 0,500 Ribbon 7 1625nm Ribbon 8 2,500 Steps Ribbon 9 Ribbon 10 21 1,500 Figure 11. Ribbon microbend results at 1310nm 0,500 1 2 3 4 5 6 7 8 9 10 Ribbon 1 Tests igure 9. Fiber #6 in a repeatability trial 21 F 1 9,000 8,000 Ribbon 2 Ribbon 3 7,000 6,000 Ribbon 4 Therefore method B room temperature measurement has good repeatability and will be very useful for a cable manufacturer to quickly check and understand fiber to fiber variation in microbending, or they might acquire this data from their fiber manufacturer, especially when manufacturing cables having special designs and/or very tight specifications. 5,000 4,000 Ribbon 6 Ribbon 7 Ribbon 8 Ribbon 9 6. Ribbon microbend results Steps Ribbon 10 21 The ribbons were wound on the same sandpaper drum as the fibers. Since a ribbon is wider than a fiber, it was only possible to wind 130m on one layer. Therefore we put three layers of ribbons Figure 12. Ribbon microbend results at 1625nm We find that ribbons with fibers #1, #2, #9 and #10 are superior also in the ribbon testing.

7. Ribbon water-soak and ice-tests Type testing of ribbons at Ericsson has for many years consisted of several tests as described in IEC. In addition to 30 days at room-temperature water-soak also a 30 days test at +60ºC with no attenuation increase has always been included. Two examples are given below in Figs 13 and 14. In Figure 13 fiber #7 shows increased attenuation after a few days only, while fiber #2 in Figure 14 passes the test with insignificant change of attenuation after 30 days in hot water. Red fiber - 1310nm Figure 15. Bucket used for the ribbon ice-test 0,600 Blue fiber - 1310nm 0,500 White fiber - 1310nm Ribbon 1 0,400 Green fiber - 1310nm 5,000 Ribbon 2 4,500 0,300 Red fiber - 1550nm 4,000 Ribbon 3 0,200 Blue fiber - 1550nm 3,500 Ribbon 4 0,100 2,500 Ribbon 6 White fiber - 1550nm +20-40 -40-60 -60 +20 Days 0 1 2 5 6 7 8 9 12 14 Green fiber - 1550nm 1,500 Ribbon 7 Ribbon 8 18 0,500 Ribbon 9 Figure 13. Ribbon with fiber #7 in room-temperature water-soak (failure) +23 C -40 C +23 C Temperature Ribbon 10 38 Red fiber - 1310nm Figure 16. Ribbons in ice-test 0,400 0,350 0,300 0,250 0,200 0,150 0,100 0,050 Blue fiber - 1310nm White fiber - 1310nm Green fiber - 1310nm Red fiber - 1550nm Blue fiber - 1550nm White fiber - 1550nm The ribbons survived but during the ice-phase the fibers with the highest microbend sensitivity showed a large attenuation increase, see Figure 16. In Sweden you can find local areas where ice is a problem during the winter season. A fiber with higher resistance against microbending would be beneficial, say if there was a problem in a man-hole or other outdoor cable access point. Unpublished field results (B. Arvidsson). 8. Cable tests 0 1 2 5 6 7 8 9 12 14 16 21 22 23 26 27 28 29 30 +20-40 -40-60 -60 +20 Days Green fiber - 1550nm Figure 14. Ribbon with fiber #2 in +60 ºC water-soak (pass) In addition to water-soak testing we also exposed the ribbons to an ice-test from water to -40ºC and then back again to room temperature. This took almost a week, see Figs 15 and 16. 18 Four major test programs were performed on the cable: Temperature cycling between -40ºC and +70ºC, crush, tensile, see [5], and PMD, see [6 and 7]. The cable is commercially available and type tested. All fibers in the study were also commercially available at the time of testing. It was therefore expected that the cable would pass the standard IEC temperature cycling. We performed 5 cycles and the requirement of less than 0.05dB/km change was achieved. There were, however, some minor increased attenuation for fiber #4, #6, #7 and #8. The tensile testing did pass the 700N (valid for this cable type) test with no change on fiber attenuation. Regarding PMD, the low temperature measurement showed as an average slightly less than 0.1ps/ km and the high temperature showed as an average slightly above 0.1ps/ km. The fibers from the same origin were looped to get a sufficiently long measuring

length for PMD (using the interferometric test method). These different cable results were not so unexpected. Regarding the crush test we did find a different result, see Figure 17. Here we find again that fibers #1, #2, #9 and #10 also can survive the temporary load better that the other fibers in the cable. Fibres Force, N 1550nm, db Load 30s 1 1000 3.77 0 2 1.77 3 36.26 4 20.32 6 43.41 7 16.51 1550nm, db After 11. References [1] B. Overton, et al, Microbending-Resistant Fiber, Proc. International Wire&Cable Symposium, pp. 279-282 (2008) [2] S.R. Bickham, et al, Ultimate limits of Effective Area and Attenuation for High data Rate Fibers, OWA5, OFC2011 [3] Y. Yamamoto, et al, A New Class of Optical Fiber to Support Large Capacity Transmission, OWA6, OFC2011 [4] IEC TR 62221- Microbending sensitivity (presently under revision) [5] IEC 60794-1-2 (presently under revision)- Basic optical cable test procedures [6] IEC 60793-1-48 - Measurement methods and test procedures Polarization mode dispersion [7] IEC 61282-9 - Guidance on polarization mode dispersion measurements and theory 8 23.91 9 0.24 10 0.30 Figure 17. Results from crush test 9. Conclusion We have followed several fibers from fiber testing to ribbon and cable evaluation. The fiber tests were microbend testing according to TR62221, method B with a temperature cycling added. Ribbon tests also included water-soak at room-temperature and +60ºC. An ice-test was also performed. Cable tests included temperature cycling, crush, tensile and PMD. PMD is to its nature more of a random parameter and it could not be concluded that there was a correlation between PMD and microbend results. In all other results we found a correlation from fiber, ribbon and cable tests. Regarding the fiber microbend tests we could also identify the importance of coating influence. Therefore we conclude that microbend testing can be valuable for a cable factory in selecting new fibers before going into a full cable type test program. In this way costs can be reduced. 10. Acknowledgements We like to thank Sylvain Estadieu and Markus Persson from Fiberson and Angelica Äng from Ericsson. They performed all the testing in an excellent way.

12. Pictures of Authors Dr Bertil Arvidsson bertil.arvidsson@fiberson.se Bertil Arvidsson was an Ericsson expert until 2009 within the field of optical fibers and with twenty years of experience. He is chairman of the Swedish national committee of fiber optics, active in IEC, ITU and CENELEC with standardization of optical fibers and cables. Prior to joining Ericsson in 1990, he worked as a technical project manager in Sweden, the United States and Switzerland. Before that he was a university lecturer in theoretical physics. He has a doctor degree in Theoretical Physics from Uppsala, Sweden. He is presently with Fiberson AB, Hudiksvall, Sweden working as a technical expert. Steven R. Schmid Steve Schmid is currently Global Applications Development Manager for the Fiber Optic Materials Group. Previously, he held positions in product management, market development and business management. He holds a B.S. Degree in Chemistry from the University of Illinois, a M.S. Degree in Chemistry from the University of Houston and M.B.A. from IIT. He has over 30 years experience in the UV coatings industry and has authored over a dozen papers, been a named inventor on 10 patents and has made several international presentations. He was a co-recipient of an IR100 Award in 1987 and also a co-recipient of DSM s Special Inventor Award in 2001. Robert Alexandersson robert.alexandersson@ericsson.com Robert Alexandersson has a master s degree in Electrical Engineering from Chalmers, Göteborg, Sweden. He joined Ericsson 1995 and has worked with optical fibers and optical fiber cable development since 1997. He is currently an Ericsson fiber specialist. Pratik Shah Pratik Shah is an Applications Development and Technical Service (Americas) Manager in the Fiber Optic Materials Group. He has a B.S. in Polymer engineering from Pune University, MS in Plastics engineering from University of Massachusetts and an M.B.A. degree from Anderson School of Management. He is a winner of R&D 100 award in the year 2008. He is (co)author of 10 publications and a named inventor on 4 U.S. patents. Anders Björk anders.s.bjork@ericsson.com Anders Björk has a degree in Computer and Electronics from 1989. He has been working at Ericsson since then. He started with measuring techniques, type testing and development of fiber optic cables. During 1997 to 1998 he worked as Plant Manager for Opcom Cables in Kuala Lumpur, Malaysia. He is currently responsible for the project office at the Technical Department of Ericsson Cables & Interconnect.