Opt Quant ElectronDOI 10.1007/s11082-014-9928-9

56 Gb/s OOK transmission in robust and bend-insensitiveGGP 80-µm ultra-large-core (ULC) MMF for lightpeak

Chi-Wai Chow · Ling-Gang Yang · Jiun-Yu Sung ·Hong-Quan Su · Chien-Hung Yeh · Ci-Ling Pan ·Gary Chou

Received: 15 December 2013 / Accepted: 8 April 2014© Springer Science+Business Media New York 2014

Abstract We demonstrate for the first time a recorded 56-Gb/s transmission in a new typerobust and bend-insensitive glass-glass-polymer structured 80-µm ultra-large-core multi-mode fiber (ULCMMF) using simple and single-polarization on-off-keying for Lightpeak.The LCMMF design is presented. Experimental results show that the ULCMMF could be agood choice for consumer applications in the near future.

Keywords Ultra-large-core · Multi-mode fiber · Lightpeak · OOK

1 Introduction

Recently different designs of optical fibers have been used in optical communications (Chowet al. 2007; Lee 2008; Yan et al. 2005). And optical communications using multimode fiber(MMF) are well established in data centers with a significant turnover yearly. It is expected

C.-W. Chow · L.-G. Yang · J.-Y. Sung · H.-Q. SuDepartment of Photonics, Institute of Electro-Optical Engineering,National Chiao Tung University, Hsinchu 30010, Taiwan

C.-H. Yeh (B)Information and Communications Research Laboratories,Industrial Technology Research Institute (ITRI), Hsinchu 31040, Taiwane-mail: yeh1974@gmail.com

C.-H. YehGraduate Institute of Applied Science and Engineering, Fu Jen Catholic University,New Taipei 24205, Taiwan

C.-L. PanDepartment of Physics and Institute of Photonics Technologies,National Tsing-Hua University, Hsinchu 30013, Taiwan

G. ChouPrime Optical Fiber Corporation, Chu-Nan, Miao-Li County, Taiwan

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to keep growing due to the heavy use of cloud computing. There is also a trend that the useof MMF will replace copper cable in consumer electronics, and MMF based optical inter-connects may move from specialized applications in data centers to the ubiquitous use inconsumer computers in the future. In 2010, Intel introduced the Lightpeak technology (Adda-gatla et al. 2010) to provide high speed video and data communications using optical fiber incomputer. In 2011, Thunderbolt (codenamed Lightpeak) was released as a hardware interface(Hakes and Smith 2011) allowing high speed connections of external peripherals to comput-ers. The early version of Thunderbolt cable has the maximum length of 3 m using copper-based cable. Starting from 2013, Corning produced optical fiber-based Thunderbolt cablehaving a maximum length of 100 m (www.corning.com/opcomm/opticalCablesbyCorning/products/thunderbolt.aspx). It can support 10 Gb/s bi-directional using Thunderbolt v1; and20 Gb/s bi-directional when using Thunderbolt v2 host and Thunderbolt v2 devices. Thesewere enabled by the Corning ClearCurve® VSDN® optical fiber and operated using 850 nmlaser source. Hence we can see that the manufacturing of robust, bend-insensitive and longlifetime MMF is crucial. In consumer electronics, the frequent wear-and-tear of MMF isunavoidable, and this could produce high optical coupling misalignment. Larger fiber corediameter will result in larger optical connectivity tolerances.

In this work, we present the design of a new type of robust and bend-insensitive glass-glass-polymer (GGP) structured 80 µm ultra-large-core multimode fiber (ULCMMF). TheGGP structure can significantly improve the fiber lifetime while not affecting the optical char-acteristics of the fiber. Besides, instead of using complicated hole-assisted (Yan et al. 2005) ornano-engineered ring-assisted (Li et al. 2009) structures, a solid single-trench-assisted struc-ture is used in the ULCMMF. Furthermore, a recorded 56 Gb/s transmission is demonstratedusing single-polarization on-off-keying (OOK) modulation in 100 m ULCMMF supportingthe length requirement of Lightpeak (Addagatla et al. 2010). The design parameters for theLCMMF are also presented.

2 Design, fabrication and parameters of the GGP 80-µm ULCMMF

Modified chemical vapor deposition (MCVD) is used to deposit a relatively thick layer of SiF4

(silicon tetrafluoride, refractive index = 1.4162) for producing the low refractive index trenchbetween the fiber core and cladding. As the developed core/cladding ratio in the ULCMMFis ∼ 0.8, which is much larger than that in traditional MMF (core/cladding ∼0.6), a thinnersilica tube for the preform fabrication is used. By optimizing the MCVD process as willas using a thinner silica tube, the 80-µm ULCMMF has been successfully fabrication. Thecross-section schematics of the conventional single-mode fiber and our designed ULCMMFare shown in Fig. 1. The refractive index profile and the photo of the ULCMMF preformare shown in Fig. 1a and b respectively. The low refractive index trench is 2-µm thick andthe refractive index can be decreased by −0.3 % when compared with the cladding layer.Later bending evaluation shows that this layer is good enough for making the ULCMMFbend-insensitive.

To protect the SiF4 layer from water erosion and increase the lifetime of the fiber, apolymer coating is applied at the outside cladding layer. This is also known as the GGP(Glass-Glass-Polymer) design developed by the 3M Corporation (US Patent No US PatentNo). Prime Optical Fiber Corporation has been manufacturing GGP fiber (licensed by 3M)since 1999. In the hot-water bending fatigue test, our fabricated fiber with and without GGPwere inset into 90 ◦C hot water with bend diameter of 3.5 mm. An acoustic sensor is usedto detect the fiber breaking time. At 50 % failure probability, the average fiber breaking

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Fig. 1 Cross-section schematics of the conventional single-mode-fiber (SMF) and our designed ULCMMF.a ULCMMF refractive index profile, b Photo of the fabricated ULCMMF preform

time can be greatly extended from 90.5 s (without GGP) to 124,000 s (with GGP) (1,370times longer lifetime). Other parameters of the 1-km ULCMMF sample: the numerical aper-ture (NA) is 0.28, the measured core, cladding, polymer and acrylate coating diameters are81.3-, 114.6-, 124.1- and 243.8-µm respectively. The core, cladding and polymer and acry-late coating non-circularity are 2.43, 0.21, 0.28 and 0.6 % respectively. The attenuations are4.64 dB/km@850 nm, 2.21 dB/km @1,300 nm and 0.57 dB/km@1,550 nm.

3 Experiment, results and discussion

Figure 2a shows the experimental setup. A distributed feedback laser diode (LD) at wave-length 1,550 nm was encoded by an electro-absorption modulator (EAM), which was electri-cally driven by a 56 Gb/s non-return-to-zero (NRZ), pseudorandom binary sequence (PRBS)215 − 1 data produced by a bit-error-rate tester (BERT). The modulated optical signalwas then center launched into 100 m ULCMMF. A variable optical attenuator (VOA) wasused to vary the received power before the PIN photodiode (PD) for bit-error-rate (BER)measurement.

Figure 3a shows the measured BER at back-to-back (B2B) and after the ULCMMF. Thepower penalties at forward error correction (FEC) limit (BER of 3.8×10−3) and BER = 10−5

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100 m ULCMMF56Gb/s

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Fig. 2 Experimental setup of the 56 Gb/s OOK transmission in the ULCMMF

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Fig. 3 a Measured BER, b 56Gb/s eye-diagram at back-to-back (B2B), c 56Gb/s eye-diagram after trans-mission, and d Measured bending loss of the ULCMMF and conventional 50µm core-diameter MMF

are < 0.5 dB and < 2 dB respectively. The power penalty is due to the modal dispersion ofthe MMF. The B2B and transmitted eye-diagrams are shown in Fig. 3b, c, which are clearlyopen. Bend losses were measured using mandrels with different diameters. Figure 3d showsthe measured bend loss for a bend-insensitive ULCMMF compared to a standard 50µmdiameter MMF. Each fiber was wrapped 10 turns in each mandrel. At the bend-diameter of5 mm, the bend loss decreased from 2.5 dB of standard MMF to 0.5 dB in the ULCMMF.

4 Conclusion

We demonstrated for the first time a recorded 56-Gb/s transmission in a new type robust andbend-insensitive GGP 80-µm ULCMMF using simple and single-polarization OOK. Thepower penalties at FEC limit (BER of 3.8 × 10−3) and BER = 10−5 were < 0.5 dB and < 2dB respectively. Experimental results showed the fiber could be a good choice for consumerapplications.

Acknowledgments This work was supported by the Science and Industrial Park (SIPA) project.

References

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