2044 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 30, NO. 23, DECEMBER 1, 2018

Field Trial of Real-Time 400GbE SuperchannelUsing Configurable Modulation Formats

Kevin Smith, Yu Rong Zhou , Mike Gilson, Weiwei Pan, Wei Huang, Lihong Shen,Wei Peng, Kunxu Peng, Paul Brooks, Chris Cole, and Chengpin Yu

Abstract— We report a successful field trial of real-time opticalsuperchannel transport of 400Gb/s Ethernet client traffic over a216-km flexible grid G.652 fiber link using 64GBaud flexiblerate optical transponders. We demonstrated, for the first time,error free transport of 400 GbE client traffic over an ultra-efficient optical superchannel of 2 × 200G using modulationformats DP–16QAM, DP–8QAM, and DP–QPSK. Error freeperformance of 400GbE ultra-efficient optical superchannel wasachieved at different channel separations as narrow as 37.5 GHzfor DP–16QAM, 39 GHz for DP–8QAM, and 50 GHz forDP–QPSK. We also successfully demonstrated non-contiguous400GbE optical superchannel, where the optical sub-channelsare in non-adjacent spectral slots across the whole C-band(3.85 THz apart). Stable long term (overnight) error free opticalperformance and end-to-end 400 GbE full throughput weremeasured.

Index Terms— Optical fiber communication, network, coherentcommunication, optical superchannel, 400GbE.

I. INTRODUCTION

TRAFFIC continues to grow at a fast pace owing tohigh speed broadband, video, cloud and data center

services. On the line side, coherent 100Gb/s has been widelydeployed to meet the increasing bandwidth demand. Highspeed technologies beyond 100Gb/s, exploring advanced mod-ulation formats, higher baud rate and superchannels, havebeen in extensive research and development over recentyears [1]–[3]. On the client side, deployed Ethernet speedshave increased from 10Gb/s to 40Gb/s and 100Gb/s, and inthe future towards Terabit per second as signposted in theEthernet Alliance roadmap [4], [5]. In December 2017, IEEEapproved 802.3bs Ethernet standard for 200Gb/s and 400Gb/s[6], in which different 400GbE client interfaces are defined,such as 400GBASE-LR8 for 10km reach using single modefiber and 400GBASE-SR16 for 100m reach using multi-modefiber. Different pluggable optical transceiver technologies for400GbE interfaces are also under research and development.MSA-compatible CFP8 [7] is the first form factor avail-able with early interoperability demonstrated [8]. Other new

Manuscript received August 10, 2018; revised September 21, 2018; acceptedOctober 3, 2018. Date of publication October 16, 2018; date of current versionNovember 20, 2018. (Corresponding author: Yu Rong Zhou.)

K. Smith, Y. R. Zhou, and M. Gilson are with British Telecommunications,Ipswich IP5 3RE, U.K. (e-mail: yu.zhou@bt.com).

W. Pan, W. Huang, L. Shen, W. Peng, and K. Peng are with HuaweiTechnologies, Ipswich IP5 3RE, U.K.

P. Brooks is with Viavi Solutions, 72800 Eningen, Germany.C. Cole and C. Yu are with Finisar, Sunnyvale, CA 94089 USA.Color versions of one or more of the figures in this letter are available

online at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/LPT.2018.2875657

form factors, such as QSFP-DD and OSFP, are in advanceddevelopment [9]. It is therefore very important for networkoperators to demonstrate the ability of their networks totransport this new high speed Ethernet client traffic. An earlyfield trial for 400GbE transport was reported using 2×200GDP–16QAM with CFP8 400GBASE-SR16 client optics [10].Although 400GbE client signal can be transported over a400G single carrier, it has limited optical reach, suitable forshorter, metro distances [11]. Therefore, for longer reaches(>∼1000km) optical superchannels based on 200G singlecarrier are extremely attractive for 400GbE transport.

In this letter, we report a successful field trial of real-timesuperchannel transport of 400GbE client traffic over a flexiblegrid field installed G.652 fiber link of 216km using 64GBaudflexible rate optical transponders. The 400GbE client signal(400GBASE-LR8) is mapped into 2×OTUC2 (200G) datastreams [12] in the 400G (2×200G) superchannel. We demon-strated, for the first time, error free transport of 400GbEover ultra-efficient optical superchannels of 2×200G usingconfigurable modulation formats including DP – 16QAM,DP – 8QAM and DP – QPSK. Error free performance ofultra-efficient 400GbE optical superchannels was achieved atchannel separations as narrow as 37.5GHz for DP – 16QAM,39GHz for DP – 8QAM and 50GHz for DP – QPSK.We also successfully demonstrated non-contiguous 400GbEoptical superchannel where the sub-channels are in non-adjacent spectral slots across the whole C band (e.g. 3.85THz).Stable long term (overnight) error free optical and end-to-endperformance was measured with 400GbE full throughput.

II. FIELD TRIAL CONFIGURATION

The real-time 400GbE superchannel field trial was con-ducted over a 216km flexible grid G.652 fiber link between BTlabs at Adastral Park and BT exchange in Bishops Stortfordvia the Colchester exchange as shown in Fig. 1. The net-work element equipment, using Huawei OSN9800/8800 WDMequipment, is located at Adastral Park, which includesflexible grid ROADM, EDFA amplifiers, 64GBaud flexiblerate optical transponders, OTN cross-connects and an early400GbE client interface. EDFA amplifiers are used in theBT exchanges without in-line dispersion compensation. The64GBaud optical transponders are software configurable into100G DP – QPSK, 200G DP – 16QAM, 200G DP – 8QAMand 200G DP – QPSK, which enables transmission distancesfrom metro to long haul distances. DSP (Digital SignalProcessing) is applied in the 64GBaud optical transponderat both the transmitter for optimised spectral shaping, and

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SMITH et al.: FIELD TRIAL OF REAL-TIME 400GbE SUPERCHANNEL 2045

Fig. 1. 400GbE superchannel field trial configuration over a 216km flexiblegrid optical link.

the receiver for compensating system impairments such aschromatic dispersion and PMD. In the transponder, soft-decision FEC based on advanced LDPC encoding/decodingtechnique is used with FEC overhead ratio of 25% for 200GDP – 16QAM/DP – 8QAM, and 11% for 200G DP – QPSK.The headend equipment and in-line amplifiers are configuredand managed using Huawei’s iManager Unified Network Man-agement System (U2000). A Viavi ONT 400Gb/s Ethernettester generates the 400GbE traffic, which is connected tothe 400GbE client interface with CFP8 400GBASE-LR8 clientoptics from Finisar [8]. The 400GbE client signal is mappedinto 4×ODUFlex 100G and subsequently into 2×OTUC2(200G) data streams in the 400G superchannel [12], whichcomprised two 200G optical sub-channels combined togethervia an optical coupler, configured to the 3 modulation for-mats (DP – 16QAM, DP – 8QAM and DP – QPSK). Thesuperchannel is added to the optical link via the flexible gridROADM. A number of other optical channels at 40G, 100Gand 200G are combined with the 400GbE superchannel viathe flexible grid ROADM. On the receive side, the 400GbEsuperchannel signal is split and connected to individual portsvia an optical splitter, and the coherent receivers are tuned toselect the relevant sub-channels. The Ethernet tester is usedto verify the end-to-end 400GbE performance using differentframe sizes, e.g. fixed 64 bytes frame and random frame sizesbetween 64 and 1518 bytes.

III. FIELD TRIAL RESULTS

In this section, we present key results and findings fromthe 400GbE superchannel field trial. In section III A – C,we demonstrate 400GbE superchannel transport using the3 software configurable modulation formats DP – 16QAM, DP– 8QAM and DP – QPSK. Section III D describes results fromour demonstration of non-contiguous 400GbE superchannel.In section III E, we show long term error free performanceof ultra-efficient 400GbE optical superchannel co-propagatingalongside optical channels at 40G, 100G and 200G.

A. 400GbE Optical Superchannel Using DP – 16QAM

We first demonstrated 400GbE transport over a superchan-nel of 2×200G DP – 16QAM with a baud rate of 32GBaud.Fig. 2 shows the optical spectra (0.02nm resolution) and per-formance of the 400GbE optical superchannel as a function ofOSNR for channel separations at 37.5GHz and 50GHz. Errorfree performance was achieved with 400GbE full throughput,

Fig. 2. Spectra and performance of 400GbE superchannel using DP –16QAM.

Fig. 3. Spectra and performance of 400GbE superchannel using DP – 8QAM.

where the minimum required OSNR is 18.2dB and 19.8dB for50GHz and 37.5GHz respectively, corresponding to the pre-FEC BER threshold of ∼3.2×10−2. It is clear that the higherspectral efficiency achieved at 37.5GHz (∼33% improvement)results in a penalty of ∼1.6dB. Both 200G sub-channels showconsistent and similar optical performance as shown in thefigure.

B. 400GbE Optical Superchannel Using DP – 8QAM

DP – 8QAM is a long haul 200G technology with ahigher baud rate (45GBaud), which can operate in standard50GHz grid as well as flexible grid. We investigated theperformance of 400GbE optical superchannel using 2×200GDP – 8QAM at different channel spacings. Fig. 3 shows theoptical spectra (0.02nm resolution) and performance with2×200G DP – 8QAM at 50GHz and 43.75GHz channelseparations. Error free 400GbE full throughput was achievedat minimum OSNR of 17.1dB for 50GHz and 17.9dB for43.75GHz with pre-FEC BER threshold of ∼3.1×10−2.Compared to 50GHz spacing, there is a small penalty of<1dB at 43.75GHz spacing.

We further investigated the 400GbE superchannel perfor-mance at varying channel spacing with finer granularity.We measured the minimum OSNR required for error freeperformance of 400GbE at different spacings, verified by the400GbE Ethernet tester. Fig. 4 shows the optical penalty asa function of channel spacing compared with the minimumrequired OSNR at 75GHz separation. We see only a smallpenalty (<1dB) for channel spacings ≥ 43.75GHz, for channelspacings less than 43.75GHz the penalty increases steeply.

2046 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 30, NO. 23, DECEMBER 1, 2018

Fig. 4. Penalty of 400GbE superchannel (DP – 8QAM) vs channel spacing.

Fig. 5. Spectra and performance of 400GbE superchannel using DP – QPSK.

Error free performance was achieved for channel separationsas narrow as 39GHz with an optical penalty of ∼8dB.This clearly demonstrates the feasibility of an ultra-efficient400GbE DP – 8QAM superchannel up to a spectral efficiencyof 5.13 bit/s/Hz. (∼28 % improvement over 50GHz spacing).Similar characteristics for OSNR penalty vs channel spacingcurves for DP – 16QAM and DP – QPSK have been reportedpreviously [1], [2]. We note, in all cases the sub-channels arecombined with a passive coupler, and the dominant source forthe OSNR penalty is the crosstalk between the sub-channels.

C. 400GbE Optical Superchannel Using DP – QPSK

DP – QPSK enables longer 200G reach using high baud rate(64GBaud). We demonstrated 400GbE superchannel trans-port using 2×200G DP – QPSK over the field trial link.Fig. 5 shows the optical spectra (0.02nm resolution) and pre-FEC BER performance of the DP – QPSK 400GbE super-channel as a function of OSNR for different channel spacings.At 75GHz spacing, error free performance of 400GbE isachieved for a minimum OSNR of 15.4dB. For higher spectralefficiency at 56.25GHz spacing, we see only a small penaltyof <0.5dB. The highest efficiency was achieved at 50GHzseparation. Despite the overlap of the two sub-channels asshown in the Fig. 5, error free 400GbE with full throughputwas achieved for OSNR as low as 17.8dB.

Table 1 summaries the key parameters (modulation format,baud rate, channel spacing, spectral efficiency and mini-mum required OSNR for error free performance) of all the400GbE superchannels described in section III A – C. Clearly,DP – QPSK has the lowest OSNR required for error free per-formance (e.g. at 75GHz spacing, it is 1.7dB lower comparedto the DP – 8QAM 400GbE superchannel at 50GHz spacing),

TABLE I

SUMMARY OF DIFFERENT 400GbE SUPERCHANNELS AND THE PERFOR-MANCE

Fig. 6. Demonstration of (a) standard 400GbE superchannel and (b) NCsuperchannel (2×200G DP – 8QAM) in C band, x-axis: wavelength (1528 –1563nm, 3.5nm/division, 0.02nm resolution), y axis: amplitude (5dB/division).

and hence is suitable for longest 200G reach. However, usinghigh baud rate (64GBaud) the wider spectrum (∼60GHz)associated with DP – QPSK requires flexible grid support. DP– 16QAM has the highest spectral efficiency (5.33bit/s/Hz),however the higher OSNR requirement limits its applicationto metro distances. DP – 8QAM is a particularly usefulformat, providing long haul reach together with higher spectralefficiency, and able to operate in both standard 50GHz andflexible grid environments.

D. 400GbE Non-Contiguous Optical Superchannel

Optical superchannels are generally envisaged as using sub-channels located in adjacent spectral slots. In some cases, theremight be insufficient contiguous spectral slots to accommo-date the whole superchannel spectrum. Non-contiguous (NC)optical superchannels allow the exploitation of non- adjacentspectral slots for the sub-channels.

Fig. 6a shows a standard 400GbE superchannel using2×200G DP – 8QAM at a channel separation of 43.75GHz,together with a number of other optical channels across the Cband including 40G, 100G and 200G of different modulationformats. In Fig. 6b, we demonstrate a NC DP – 8QAM400GbE superchannel with the 2 sub-channels in slotsseparated by as much as 3.85THz (∼30.8nm) across the full

SMITH et al.: FIELD TRIAL OF REAL-TIME 400GbE SUPERCHANNEL 2047

Fig. 7. Optical performance of 400GbE superchannel (2×200G DP –8QAM).

Fig. 8. Long term performance of ultra-efficient 400GbE superchannel(a) 2×200G DP – 16QAM at 37.5GHz spacing; (b) 2×200G DP – 8QAM at39GHz spacing and (c) 2×200G DP – QPSK at 50GHz spacing.

C band. Error free performance was achieved with 400GbEfull throughput. Fig.7 shows the long term pre-FEC BERperformance measured for the standard and non-contiguous400GbE superchannels shown in Fig. 6. For standard 400GbEsuperchannel at 43.75GHz spacing, the 2 sub-channels havethe pre-FEC BER values at ∼1.1×10−3 and ∼7.2×10−4

during a measurement period of 19 hours. For the non-contiguous 400GbE superchannel in Fig. 6b, the pre-FECBER is ∼4.5×10−5 and ∼4.2×10−5 for the 2 sub-channels.This improved performance over the standard superchannelconfiguration is due to the larger spacing and reduced inter-action with adjacent optical channels. Although not shownhere, we also successfully demonstrated error free NC 400GbEsuperchannels using DP – 16QAM and DP – QPSK.

E. Long Term Error Free End-to-End Performance ofUltra-Efficient 400GbE Optical Superchannels

Fig. 8 shows the long term (overnight) pre-FEC BER of themost spectrally efficient 400GbE superchannels demonstratedfor all 3 modulation formats. For DP – 16QAM 400GbEsuperchannel at 37.5GHz spacing, the pre-FEC BER measuredwas ∼5.8×10−3 and ∼6.7×10−3 for the 2 sub-channels fora measurement period of ∼14.5 hours. For DP – 8QAM400GbE superchannel at 39GHz spacing, stable long termerror free performance was measured with pre-FEC BERof 2.1×10−2 and 2.4×10−2 for the 2 sub-channels. For DP– QPSK 400GbE superchannel at 50GHz spacing, pre-FEC

BER of 3.9×10−3 and 2.5×10−3 was measured for the 2 sub-channels. Stable long term pre-FEC BER performance wasachieved for all the 400GbE superchannels. In all cases, wemeasured end-to-end error free 400GbE full throughout duringthe long term measurement period shown in Fig. 8.

IV. CONCLUSIONS

In this letter, we report a successful field trial of real-time optical superchannel transport of 400Gb/s Ethernet clienttraffic over a flexible grid G.652 fiber link of 216km using64GBaud flexible rate optical transponders. The 400GbEclient signal (400GBASE-LR8) is mapped into 2×OTUC2(200G) data streams in the 400G (2×200G) superchannel.We demonstrated, for the first time, error free transportof 400GbE over ultra-efficient superchannels of 2×200G usingDP – 16QAM, DP – 8QAM and DP – QPSK. Error freeperformance was achieved for 400GbE ultra-efficient opticalsuperchannel at different channel separations as narrow as37.5GHz for DP – 16QAM, 39GHz for DP – 8QAM and50GHz for DP – QPSK. We also successfully demonstrated400GbE non-contiguous optical superchannels with the sub-channels separated as much as 3.85THz across the full C band.Stable long term error free optical performance and end-to-end 400GbE full throughput were measured, demonstrating thepractical viability of the 400GbE superchannel transmission.

ACKNOWLEDGMENT

The authors would like to acknowledge the help and supportfrom colleagues, Qianhui Ning, Steve Bowers, Mulin Lu,Shipeng Wu (Huawei), J. Casey (Viavi) and M. Fletcher(Laser 2000).

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