More than 80% energy efficiency achieved in optical fiber coating applicationprocess using UV-LED lamps and novel chemistries

1Pratik Shah, 1Huimin Cao, 1Kangtai Ren 1Xiaosong Wu, 1Kate Roberts,1Todd Anderson, 2Jackie Zhao, 2Li Alex, 2Jessica Wang, 3Ad Abel

1DSM Functional Materials, 1122 St Charles St. Elgin, IL, USA2DSM Functional Materials, Zhangjiang High-Tech Park, Pudong, Shanghai,China

3DSM Functional Materials, Slachthuisweg 30, Hoek van Holland, Netherlands

Abstract

Between 2005 and 2015, total global energy use increased by 40%while the associated CO2 emissions rose by 30%. (Eia.gov) It isprojected that we will still need 40% more energy by 2040; whichis approximately 800 quadrillion. But out of that 77% will comefrom non-renewable fossil energy. As we proposed in 2014, energyrequirements are going to increase exponentially in the next 25years. Thus efficiency improvements in all sectors are needed nowto mitigate future problems.

Governments in many countries are increasingly aware of the ur-gent need to make better use of the world’s energy resources. Im-proved energy efficiency is often the most economic and readilyavailable means of improving energy security and reducing green-house gas emissions. For example, all EU countries need to estab-lish 20% energy efficiency target by 2020 and China’s latest eco-nomic development plan, provides financial incentives for localgovernments and industry to pursue a wide range of energy-savingprojects. The goal is to conserve the equivalent of some 250 millionmetric tons of coal, preventing emissions of over 600 million tonsof CO2.

With this in mind, since 2012, we have focused our studies on thedevelopment of UV-LED curable coatings which deliver high per-formance optical fiber characteristics and utilize optimum energyfor curing; expected 80% less energy with current microwavelamps used in the optical fiber industry. In this paper, we focus onUV-LED curable coatings with different lamp manufacturers andpower levels.

We have performed extensive experiments on our in-house DrawTower Simulator (DTS) and multiple draws on an actual drawtower with multiple UV-LED lamps suppliers. In continuation ofour previous study, we evaluated various fiber/coating characteris-tics such as degree of curing, adhesion, strip force (SF), mechanicalproperties, fiber fatigue (nd value), tensile strength and microbend-ing attenuation levels.

Keywords: UV-LED, energy, fiber, microbending, fiber fatigue(nd value)

1. Introduction

CRU‘s 2016 market report data indicates ~368 Million fiber km(Mfkm) were produced last year, see Fig.1 and for 2016, an opti-mistic view projects global demand of ~ 400 to 410 Mfkm, see [1].To manufacture these fibers, ample amounts of energy is required

to melt the glass preform, cool the glass strand (~125 µm) with he-lium and finally cure the coating material for protection and highspeed winding of the final fiber product. In this paper, which is acontinuation of [2], we will focus only on the energy required tocure the coating material and the future demand for enhanced fiberproperties with high operational efficiencies.

Figure 1: Historic fiber optic cable installation and global pro-jections (source: CRU 2016 market report)

Between 1990 and 2012, global energy use increased by 54% whilethe associated CO2 emissions rose by 48%, see [3] and Figure 2. Inorder to prevent future emissions, every sector should try alternateand preventative mechanisms. Our attempt here is to show an alter-nate path for the optical fiber industry, which can significantly im-pact optical fiber manufacturers both environmentally and finan-cially.

Figure 2: World energy consumption 1990-2040 [3]

Microwave powered medium pressured, mercury (Hg)-based UVlamp systems have historically been the primary resource for facil-itating the curing of optical fiber coatings. However, this systemsuffers from some fundamental limitations; such as, high electricalpower consumption, shorter life-time and use of “Hg” which is nowconsidered environmentally hazardous, see [4].

These lamps emit characteristic wavelengths of energy in the ratioof UV (25-30%), visible (5-10%) and infrared (60-65%), see Fig.3and [5]. Most of the curing energy is supplied by UVA wave-lengths. Also, these lamps require a pull exhaust system to take outall the heat generated by infrared radiation (IR), see Figs. 3, 4 and[6].

Currently, 1 to 2 KWH is required to cure the coating material forevery km of optical fiber produced. This translates to a total of 400to 800 Million-KWH required annually to cure fiber coatingsworldwide and also results in 532 to 1064 Million lbs of CO2 beinggenerated, see [7]. Financially, some 53 to 106 Million dollars (10cents = 1 KWH) will be paid to global utilities companies annually.Up to 80% of this amount can be saved if UV-LEDs are used in thissector.

Figure 3: Microwave lamp spectrum irradiance and efficiencies

Figure 4: Microwave lamp’s air cooling requirements

UV-LED technology could offer substantial benefits due to its fun-damental semiconductor characteristics and construction, such asinstant on-off, Hg-free, longer life, very low power consumptionand thus ultimate lower cost of ownership. An additional benefit ofUV-LED technology is the absence of UVC rays which typicallyproduce ozone. However, present day UV-LED curing systems en-counter a primary challenge with the lack of suitable chemistry tai-lored for the monochromatic wavelengths produced.

Over the past 40 years, most UV chemistry has been formulated toreact with broadband mercury spectrums and relies on the shorterwavelengths for surface cure and the longer wavelengths forthrough cure. We have developed specific chemistry for high power395 nm +/- 10nm UV-LED lamps.

The combination of our low volatility formulations and eliminationof undesired infrared radiation from the high speed curing processgenerates robust and consistent fiber properties.

Large preforms (8-15,000 km) are already being used in optical fi-ber production. Successful production requires coating with lowvolatility to maintain clean quartz tubes throughout the run in orderto obtain low fiber break and consistent fiber properties such ashigh nd value, low microbending and high cure conversion to takeadvantage of the high operational efficiencies.

We have already performed substantial experiments and trialswhich will be discussed in the next section.

2. Experimental

Multiple developmental coating systems were applied on a 130 µmO.D. stainless steel wire using a custom designed Draw Tower Sim-ulator (DTS), see Fig.5, at speeds ranging from 750 m/min to 2100m/min. Although the tower stands less than 6 m, the distance be-tween the coating applicators is comparable to that of a commercialfiber drawing tower.

The DTS was configured with five UV-LED systems (395 nm +/-10nm), two after the primary coating applicator and three after thesecondary coating applicator, all operating at less than 2 KWH forthe coating trials. The Wet-on-Wet (WOW) processing conditionwere performed with only 3 lamps.

Figure 5: Draw Tower Simulator (DTS)

We have performed several iterations of primary and secondarycoating systems under both WOW and Wet-on-Dry (WOD) condi-tions; however for the scope of this paper, we are concentrating onthree different coating systems with more challenging WOW con-ditions. For the purpose of nomenclature, the three clear coatingsystems will be referred to as A, B and C coating systems. All three

coating systems evaluated herein are classified as developmen-tal/non-commercial (as of this writing) optical fiber coating sys-tems.

3. Evaluations at various draw tower facilities:

We tested the coating systems with four different UV-LED lampmanufacturers (Table 1) at various draw facilities. We have per-formed 13 different experiments. The coating systems were appliedWOW to a 125 µm O.D. fiber drawn from a G652D preform atspeeds of 1500, 2000, 2500 m/min with predicted 3000 m/min in-put power and cure levels.

Table 1: Nomenclature for different lamp manufacturers

Lamp Manufacturers Nomenclature

UV-LED Lamp manufacturer 1 Lamp A

UV-LED Lamp manufacturer 2 Lamp B

UV-LED Lamp manufacturer 3 Lamp C

UV-LED Lamp manufacturer 4 Lamp D

Conventional Microwave Lamp Lamp MW

Figure 6: Total input lamp power (KWH) Vs. draw speeds withhigh curing levels

Figure 6 clearly indicates that in general UV-LED lamps can save~80+% input energy (KWH) compared to conventional microwave

lamps and provides high curing levels of both primary and second-ary coating systems. We have observed 92-100% RAU (ReactedAcrylate unsaturation) values for all thirteen combinations (Figure8).

We have also broken down different UV-LED manufacturer’s per-formance per lamp/speed/curing levels. Scattered data points aredue to some of the tower limitations on high speeds. Lamp A andB were providing better efficiency compared to Lamp C & D, seeFigure 7.

In some figures below the results are the same regardless of coatingsystem (Figs 8, 10 and 12).

Figure 7: Efficiency of each UV-LED lamp with high curinglevels (92-100% RAU)

Figure 8: Primary and Secondary coatings cure performance(%RAU) with different UV-LED lamp manufacturers.

Figure 7 and 8 indicate that Lamp A configuration can go as highas 533 m/min per lamp with Primary % RAU in upper 90s and sec-ondary %RAU nearly 100%. This observation indicates that to-day’s UV-LED technology with novel chemistry, which providesenhanced surface cure; usually a drawback of monochromaticwavelengths, are sufficient for high speed optical fiber coating ap-plications.

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4. Characterization of UV-LED cured opticalfibers

4.1 Strip force evaluations with various aging condi-tions

IEC 60793-1-32 describes measuring techniques for the strip forceparameters. We have measured fiber strip force for initial, waterimmersed, 85%RH/ 85°C, and cable gel submersion (Figure 9) con-ditions for one month. All the strip force data are well within stand-ard specifications, see Figure 10.

Figure 9: UV-LED cured fiber samples were kept under com-mercially available cable gel with both fiber ends submergedin the gel at 23°C for one month

Figure 10: Strip force aging performance (water/gel/85& 85)with different UV-LED suppliers and coating systems

The unique chemistries of the well cured primaries and secondar-ies did not show any reduction in strip force, even under the se-vere aging of 85°C for one month and with both ends of the fibersdeliberately submerged in the gel.

4.2 Reliability evaluation by two-point bending andaxial tensile tests

IEC 60793-1-33 describes measuring techniques for the n-value.We have chosen the two-point bending method, since it does notrequire very long lengths and is a fast technique to get the first es-timation of n-values for a fiber. Therefore n-value measurementswere easily obtained. We have evaluated n-value and tensilestrengths both at initial and ageing conditions (85%RH / 85°C / 30days). As Figure 11 indicates n-value is well within specification

of 20 and above. Some of the fiber samples were showing n-valuebeyond 30, which will be well suited for FTTH and other stringentapplications.

Figure 11: Initial and aging n value data by 2-point bendmethod

IEC 60793-1-31 describes measuring technique for tensile strengthby an axial tensile method, see Figure 12. We have evaluated ten-sile strengths (15% & 50%) both at initial and at 85%RH / 85°C /30 days. All the data are well within specified values.

Figure 12: T: Initial and aging ensile strength data by Axialtensile testing

4.3 Microbending Evaluations as per IEC 62221TRmethod B

The fiber is carefully wound on a quartz drum (to avoid diameterchanges in the temperature cycling), see Fig.13. The drum is cov-ered with a specified sandpaper. A standard proof-tester may be usedto prepare the sample fiber. The fiber is wound onto the surface ofthe drum in one single layer, i.e. avoiding crossovers. The windingtension has to be controlled. A winding tension between 1 N and 3 Nshould be chosen and this chosen tension should be kept the same forall tests for better repeatability. The backscattering technique may beused to measure the attenuation coefficient.

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Figure 13: Fiber wound on sandpaper wrapped quartz drumas per IEC TR62221 method B, latest edition 2012

Figure 14: Total microbending attenuations at two differentwavelengths

We have collected the results in Fig. 14 using 1 N winding tension.These values are of the same level as the best standard fibers thatwere published a few years ago, see [8]. Glass quality, fiber geom-etry, curing levels, and modulus properties are impacting on mi-crobedning attenuation levels. It is well known that microbendingsensitivity is not specifiable, but results from tests made in the sameway are comparable and very important for cable and real time at-tenuation levels.

4.4 Pull out force Evaluations

We have used FOTP 105 for the fiber coating pull out test.

Figure 15: Pull out force data with different coating systems

Adhesion levels of all fibers are significantly high, which supportsthe aging data and show minimal degradation under severe aging

conditions. Optimum adhesion levels are very important to supportcavitation strength, robustness of fibers at high proof testing andattenuation levels at various aging conditions.

5. Conclusions

Mechanical, optical and aging data supports that these fibers are notonly well-cured, but also offer fiber characteristics that demonstratethat there is a breakthrough in both UV-LED lamp technology andchemistries supporting the results for the 395 +/-10 nm wave-length. Even though extensive testing has been presented here, afull test program, including tests described in this paper, is neededto verify the repeatability of the present results.

We have observed that UV-LED lamps can deliver 80+% energyefficiency compared to conventional microwave lamps. The curingperformance and efficiency of commercially available UV-LEDlamps depends on coating chemistries, lamp power output(W/cm2), power intensity, peak wavelength (nm), optics, and lenspackage to deliver maximum output at targeted region.

The fiber optic industry needs to take advantage of these advancedtechnology chemistries and UV-LED lamps to improve their oper-ational efficiency and enhanced fiber properties package. Also, cor-porations need to be socially responsible and adapt sustainable so-lutions to reduce world’s carbon foot print.

6. References

[1] CRU 2014 market reporthttp://wireandcablenews.crugroup.com

[2] P. Shah et. al. “An innovation in optical fiber manufacturingprocess by UV-LED lamps and novel optical fiber coating designsupporting both Wet On Wet (WOW) and Wet on Dry (WOD) pro-cessing at high speeds”, Proceedings of the 63rd IWCS, 2014

[3] World energy consumption 1990-2040http://www.eia.gov/forecasts/ieo/world.cfm

[4] P. K. Swain et. al. “Advancements in UV LED technology andits impact on UV curing applications”, RadTech Europe 2011.

[5] UV/LED Curing in Graphic Arts Applications,Eileen Jaranilla-Tran,RAHN-Group

[6] The Microwaved power lamp by R.W.Stowe, Fusion UV Sys-tems Inc.

[7] Energy Carbon Footprint Calculatorhttps://carbonfund.org/calculate-your-foot-print/?gclid=Cj0KEQjw_qW9BRCcv-Xc5Jn-26gBEiQAM-iJhS36kKQ1V0P_7UwDoPx1P9rWED-Wbs88Pm6gAImUDEqcaAuzQ8P8HAQ

[8] B. Arvidsson et. al. “Microbend evaluation of selected G652D& G657 fibers and ribbons before cabling”, IWCS 2011

[9] TIA/EIA-455-72 Procedure for Assessing Temperature andHumidity Cycling Exposure Effects on Optical Characteristicsof Optical Fibers

[10] Yi Peng et. al. “Research on Improvement of Wet-freezingResistance of Optical Fiber”, Proceedings of the 59th IWCS/IICIT

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Pictures of Authors

Pratik Shah is Global Technical Marketing Manager for the Fi-ber Optic Materials Group with DSM Functional Materials. Hehas a B.S. in Polymer Engineering from Pune University, MS inPlastics engineering from the University of Massachusetts and aM.B.A. degree from Anderson School of Management. He is arecipient of R&D 100 award. He is an (co)author of numerouspublications and a named inventor on 6 U.S. patents.

Huimin Cao received a Ph.D. degree in chemistry from the Uni-versity of Missouri, Kansas City in 1998. She joined DSM in2000 and is now a R&D Manager for Analytical & ResearchTeam at DSM Functional Materials. She has 15+ yrs of experi-ence on fiber optics material research with the expertise on ma-terial science, with the focuses on material properties, structure-property relationship, and fundamentals of coating effects on op-tical fiber performance.

Kangtai Ren is currently a Senior Scientist at DSM FunctionalMaterials working on optical fiber coatings. He joined DSMSomos® in 2005, having worked on stereolithography technol-ogy for over 6 years. He received his Ph.D in Organic Chemistryfrom Nankai University, has over 30 publications and about 10issued patents or patents application.

Xiaosong Wu is the R&D Manager for Fiber Optical Materialsat DSM Functional Materials. He holds a Ph.D. degree in Pho-tochemical Sciences and has been with DSM in various posi-tions in Research and Development since 2000.

Jackie Zhao joined DSM in 2008 as the Technical Service GroupManager - Asia & Russia region in DSM Functional Materials.He has a B.S. in Applied Chemistry from Peking University anda MS in Material Sciences and Engineering from Shanghai Jiao-tong University in China. He worked for Lucent TechnologiesShanghai Optical Fiber Co between 1996 and 2002 and workedfor Jiangsu Hengtong Alpha Opto-electric Co between 2002 and2008 with total 12 years technical management experience inoptical fiber drawing technology. He is an (co)author of numer-ous publications and patents in China.

Kate Roberts is a Senior Technical Service Specialist with DSMFunctional Materials. She specializes in customer related issuesand assists with application development projects associatedwith optical fiber coatings (FTIR, Microscopy and fiber fatiguemeasurement). She received a B.S. in Zoology from Eastern Il-linois University. Kate has been with DSM since 1997.

Todd Anderson is a Senior Laboratory Specialist in the Appli-cations Development and Technical Services group at DSMFunctional Materials. He specializes in application developmentof fiber optic materials. He has a B.S. in Biology from NorthernIllinois University. Todd has been with DSM since 2000.

Jessica Wang joined DSM in 2005 as lab specialist in DSM Func-tional Materials. She has a B.S in Chemical Engineering and Tech-nology from Nanjing Tech University.

Ad Abel, Global Sales Director DSM Fiber Optic Materials,joined DSM in 1978 as R&D chemist polymer resins. Sinceearly 1986, Ad has been active in DFM’s FOM business andheld positions within R&D, product management and market-ing/sales.

Ad has contributed to various international conferences in fiberoptics and UV technology and has authored and presented anumber of technical papers. Ad has been awarded several pa-tents and is an active member of IWCS and FTTH Europe.

Ad earned a degree in organic and polymer chemistry from"Hoge School Rotterdam" and took master classes in businessand marketing.