Excursion-Free Dynamic WavelengthSwitching in Amplified Optical Networks

Atiyah S. Ahsan, Colm Browning, Michael S. Wang, Keren Bergman,Daniel C. Kilper, and Liam P. Barry

Abstract—Dynamic optical networking with rapid wave-length reconfiguration is a promising capability to supportthe heterogeneous, bursty traffic rapidly growing inmetro-area networks. A major obstacle to realizing dynamicity inthe optical layer is the channel power excursions that occurdue to continuously changing input conditions into gaincontrolled optical amplifiers. Here we present a techniqueof distributing an optical signal across multiple wave-lengths chosen to reduce or cancel the power dynamicsso that excursion-free switching can be achieved in anoptically amplified transparent network. The use of varia-ble wavelength dwell times for excursion-free switchingusing arbitrary wavelength pairs is presented. Spectralefficiency lost in utilizing multiple wavelengths isrecovered through time-division multiplexing two signalsdistributed over the same wavelengths.

Index Terms—Erbium-doped fiber amplifiers; Opticalpower excursion; Wavelength division multiplexing;Wavelength switching.

I. INTRODUCTION

G rowing demand for speed and bandwidth, along withincreasing energy consumption in today’s networks,

are driving the need for intelligent next-generation net-working architectures that can efficiently scale whilefulfilling tightening energy and optical spectrum con-straints. Current quasi-static optical networks, with peaktraffic capacity provisioning of large static “big pipes,”make poor use of available resources and are ill-equippedto support emerging traffic trends [1]. Network traffic isincreasing at near-exponential rates, and new sources ofdemand are continuously emerging [2]. With the adventof the Internet of Things, the number of data-intensive de-vices connected to the Internet is projected to reach 50 bil-lion by 2020. Bulk data transfer between geographicallydistributed data centers over commodity Internet is onthe rise due to growing big data and cloud computingapplications. This inter-data-center traffic is bursty, with

the amount of data transferred ranging from several tera-bytes to petabytes [3,4]. The rapid growth in metro-onlytraffic, which is expected to surpass long-haul traffic by40% in 2017, is further contributing to the high volumeof less aggregated, bursty network traffic. Dynamic opticalnetworking capabilities, in which bandwidth is allocated inreal time in the physical (optical) layer in response tochanging traffic demands, become increasingly desirableto enable next-generation networks to support such unpre-dictable, high-bandwidth but short-lived traffic flows [5].

Fast wavelength reconfiguration is key to achieving adynamic optical network. While there has been significantwork on protocols to enable dynamic wavelength reconfig-uration and studies have shown light-path setup timesbelow 3 s [6–8], fast wavelength reconfiguration has yetto be implemented at scale in commercial networks. Akey unresolved obstacle to implementation is the channelpower excursions that arise and propagate throughout anetwork due to changing channel wavelength configura-tions in an automatic gain controlled (AGC) opticallyamplified system [9]. Recent studies on dynamic opticalnetworks either use prereserved wavelengths or assumethat the power dynamics problem will be solved—but todate, no comprehensive solution exists [5]. To realize atruly dynamic optical network, it is necessary to developtechniques that allow reconfiguration on the order of sec-onds or faster while maintaining stable network operation.Previous work has demonstrated that power excursionscan be reduced by using a center-of-mass-based wavelengthassignment approach [10]. However, this was only shown toprovide a 15% improvement, while limiting the availableconfiguration.

In this work, we propose a new approach of distributingthe optical power of a single signal over multiple wave-lengths such that the sum of the individual gain excursionscancels, thus mitigating the power dynamics of wavelengthreconfiguration. The networking problem being addressedby this technique is discussed in detail in Section II. Theproposed technique and the experimental setup are de-scribed in Sections III and IV, respectively. The use of thistechnique to null power excursions of 2 dB is experimen-tally demonstrated using 1) wavelengths that cause equaland opposite power excursions and 2) wavelengths thatcause opposite excursions of different magnitudes byvarying the wavelength dwell time. Time-division multi-plexing (TDM) of two signals distributed over the samewavelengths is successfully implemented to avoid loss ofhttp://dx.doi.org/10.1364/JOCN.7.000898

Manuscript received March 12, 2015; revised July 14, 2015; acceptedJuly 23, 2015; published August 21, 2015 (Doc. ID 234945).

A. S. Ahsan (e-mail: asa2157@columbia.edu), M. S. Wang, and K.Bergman are with the Department of Electrical Engineering, ColumbiaUniversity, New York 10027, USA.

C. Browning and L. P. Barry are with the Department of Electronic andElectrical Engineering, Dublin City University, Dublin 9, Ireland.

D. C. Kilper is with the College of Optical Sciences, University of Arizona,Tucson, Arizona 85721, USA.

898 J. OPT. COMMUN. NETW./VOL. 7, NO. 9/SEPTEMBER 2015 Ahsan et al.

1943-0620/15/090898-08$15.00/0 © 2015 Optical Society of America

spectral efficiency. These results are presented inSection V.

II. PROBLEM BACKGROUND

Channel powers in networks have to be maintainedwithin a certain range to meet the optical signal-to-noiseratio requirements and avoid cross-talk from high-powerneighboring channels (lower bound) and to avoid nonlineartransmission impairments (upper bound). Channel powerexcursions can be highly detrimental when they causedeviation from this required power range. These power ex-cursions occur because AGC algorithms maintain constantgain by monitoring the total input and output opticalpowers, and do not take into account the wavelength-dependent gain arising from the gain tilt and ripple ofthe amplifier and fiber plant. Consequently, a change ininput wavelength configuration into an amplifier, evenfor constant input power on each channel, can affect thegain of individual channels, as depicted in Fig. 1.Consider initially λC as the only input channel. If λ1, whichhas higher gain than λC, is added at the same input power,the total input power doubles, but the total monitored out-put power increases by more than a factor of 2. In order tomaintain constant gain, the AGC decreases the gain and λCundergoes a negative power excursion. The reverse processhappens if λ2 is added instead, and λC undergoes a positivepower excursion. The size of the excursions depends on avariety of factors such as the number of channels, the chan-nel distribution, and the number of links. These excursionscan further be impacted by spectral hole burning and meangain-dependent gain tilt in erbium-doped fiber amplifiers(EDFAs) and stimulated Raman scattering (SRS) in thetransmission fiber [11]. Excursion values as high as7.5 dB for a 20 channel add/drop have been reported [12].

The channel power coupling effect described above growswith a cascade of amplifiers [13], and power divergences of15 dB were observed in recirculating loop experimentswith AGC EDFAs [9]. As a result, the effect of a singlereconfiguration event can propagate through the networkand cause persistent power excursions and network insta-bility, and even oscillations in the worst case [14,15]. Thisissue is particularly acute in mesh metro-area networks,which is characterized by a large number of shortamplified ROADM links with many amplifiers. In currentgeneration quasi-static optical transmission systems,

power excursions are avoided by using offline planningtools and long reconfiguration times encompassing manyadjustments along an optical path [9,16]. This reconfigura-tion time has to be decreased to the order of secondsin order to enable promising technologies for emerging traf-fic patterns such as real-time wavelength switched opticalbypass, physical layer protection/restoration, and energy-efficient transceiver sleep modes. Thus it is imperativeto develop techniques that enable excursion-free, rapidwavelength reconfiguration.

III. PROPOSED TECHNIQUE

A. Principle of Operation

The proposed technique distributes the optical power ofa single signal over multiple wavelengths such that theindividual gain excursions cancel one another, so thatthe power dynamics of wavelength reconfiguration are re-duced or eliminated. Fast-tunable lasers that can switchbetween wavelengths on nanosecond time scales are usedto distribute the optical power. EDFAs have gain responsetime constants on the order of hundreds of microseconds oreven milliseconds and therefore do not respond to anypower fluctuations occurring at a faster time scale. For ex-ample, if the tunable laser switches over N wavelengthswith equal dwell times summing to less than a microsec-ond, the EDFA perceives it as N static channels, each at(1/N) the total laser power. By using balanced wavelengths,which cause equal and opposite power excursions, thepower fluctuations that arise when switching these signalscan be negated.

Due to network constraints it may not always be possibleto choose a balanced pair/set of wavelengths that causeequal and opposite excursions. However, by varying thedwell time ratio (DTR) between a pair of unbalancedswitching wavelengths, their relative contributions tothe resultant excursions can be skewed so that excur-sion-free operation is achieved. For example, two unbal-anced wavelengths, λ1 and λ2, added at equal power,cause excursions of �x and −y dB, respectively, wherejxj > jyj. Since the amount of excursion caused by a wave-length depends on its power, zero net excursion can beachieved by decreasing the power on λ1 and increasingthe power on λ2. For the fast-switching scenario, the effec-tive power on a wavelength, as perceived by the EDFA, isproportional to the dwell time on that wavelength, and ex-cursion-free switching using λ1 and λ2 can be achieved byincreasing the dwell time on λ2.

B. Time-Division Multiplexing for SpectralEfficiency

Since the signal is switching over multiple wavelengths,it occupies only a single wavelength at any given instant intime. Thus there are times when a wavelength is not beingutilized but is still reserved for the signal, resulting in spec-tral inefficiency. While this is not a problem in lightly

Fig. 1. Automatic gain control (AGC) amplifier output spectrumfor three channels, λ1, λ2, and λc. Solid curve shows the gainspectrum (dB), and dashed curve shows the mean gain acrossall channels, Gm. Arrows indicate channel output powers for equalinput power on each.

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loaded networks, it is not scalable for networks that havehigher traffic demands. For example, if signals are distrib-uted over two wavelength positions, then the total spectralefficiency of the systemwould be reduced by 1/2. In order toovercome this issue, TDM can be used. For example, ini-tially signal 1 is distributed over λ1 and λ2 but occupies ei-ther the λ1 or the λ2 time slot at any given instant in time.When a new demand for capacity is initiated, and signal 2is provisioned, it can be distributed over λ1 and λ2 as well byensuring that it occupies the λ1 slot when signal 1 is at λ2and vice versa. The effective power on each wavelength, asperceived by the EDFA, doubles in this case. This concept isillustrated in Fig. 2.

C. Network Considerations

New wavelength assignment and network control tech-niques have to be developed in order to deploy this para-digm in the network. The response of an AGC amplifiedsystem can be modeled using the dynamic power controlequations outlined in [17]. The model predicts the outputpowers of WDM channels from an amplified system for dif-ferent input conditions so that wavelength sets can bechosen intelligently for zero excursion. The model requiresinformation about the accumulated gain ripple in theamplified link, and this can be measured using probe wave-length signals [18,19]. Fast-tunable lasers can also be usedas short duration probes for gain spectrum measurements.In systems that use a wide variety of makes and models ofamplifiers, the variation in gain ripple will limit how wellthe power excursions are reduced. The extent of benefit willdepend on how many wavelengths the signals are distrib-uted over and how well they sample the range of gain spec-tra. Synchronization techniques for the TDM operation

have to be explored. Signals from the same source locationmay use a common low-frequency clock for synchroniza-tion. Additional TDM synchronization will be requiredwhen sources from different locations are multiplexed.

Since a signal is distributed over multiple wavelengths,the amount of dispersion will be different for the differentwavelengths across the band. Electronic dispersion com-pensation needs to rapidly compensate for the differentamount of dispersion, and this can be achieved by usingpreset values given that the switching is between knownwavelength sets. For metro-area networks, where dynam-icity will be most beneficial, differences in dispersion arenot going to be considerable as the distances traversedare relatively short.

Data on the switching wavelengths can be receivederror-free within nanoseconds of the switching event.Previously, it was demonstrated that for mth power doubledifferential QPSK signals, data transmission is error free30 ns after switching [20]. For direct detection burst modeorthogonal frequency division multiplexing (OFDM) sig-nals, error-free transmission is achieved after 8 ns [21].Note that additional delaysmay be introduced due to groupdelay differences between channels at different wave-lengths. For dispersion shifted fibers and dispersion com-pensated systems, this effect is likely to be negligible.For uncompensated standard single-mode fiber (SSMF) de-lays on the order of 1 ns/km are possible leading to 100 nsscale delays in large metro networks. This introduces someamount of overhead in the system. For example, for 200 nsdwell time on each wavelength, which is the configurationfor this experiment, the overhead (neglecting fiber groupdelay variations) is 15% for DD-QPSK and 4% for DD-OFDM signals. The overhead can be decreased by increas-ing the dwell time on each wavelength. For dwell times of10 μs (which is still significantly lower than the EDFA re-sponse time), the overhead is less than 1%. The capacityloss due to this amount of overhead is acceptable since thistechnique allows wavelength reprovisioning on the order ofseconds and faster, limited by the switching speeds and notby the optical power tuning. Wavelength reprovisioningusing current techniques can take up to days and resultsin significantly greater capacity loss. The world recordfor the fastest wavelength provisioning was recently re-ported as 19 min and 1 s [16].

D. Scope of Current Work

Themain focus of this work is to investigate the ability ofthe proposed technique to achieve excursion-free fast wave-length reconfiguration. Power fluctuations of the channelsin the system are studied as the introduction of switchingchannels in the network will affect existing channelsthrough power coupling effects; consequently, power excur-sions on these other channels are the best indicators of boththe transmission quality of the channels and the networkstability. We establish the parameters (wavelength andwavelength dwell time) that can be adjusted so that anyavailable wavelength sets can be used for excursion-free wavelength reconfiguration. We ensure that spectral

Fig. 2. (a) Single signal, S1, distributed over two wavelengths (λ1and λ2) as perceived by the EDFA. (b) Additional signal S2 alsodistributed over the same wavelengths. (c) Power at the two wave-lengths at nanosecond time scale, illustrating how TDM isachieved.

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efficiency can be maintained by successfully implementingexcursion-free TDM fast wavelength switching. Futurework will investigate 1) the transmission performance ofdifferent modulation formats for TDM fast wavelengthswitching, 2) network control techniques for TDMsynchronization of sources from different locations, and3) wavelength assignment using offline models and gainspectrum probing.

IV. EXPERIMENT

The experimental setup is shown in Fig. 3. A softwarecontrolled sampled grating–distributed Bragg reflector(SG-DBR) fast-tunable laser is used to perform wavelengthswitching. The laser can operate in both static and fast-switchingmodes and can access 83 wavelengths (numbered11–94) across the 50 GHz ITU grid in the C-band. In fast-switching mode, each wavelength can be assigned a dwelltime of between 200 ns and 10 μs. Since the power couplingeffect due to the wavelength switching is agnostic to thepresence of data and depends solely on the wavelength con-figuration and power values, a comb source in conjunctionwith a wavelength selective switch (WSS) is used to intro-duce additional wavelengths across the band. This pro-vides the flexibility to study a wide range of channelconfigurations, and the results for a worst-case scenarioare presented in the following section. The input powerof all wavelengths is maintained at −23 dBm per wave-length into the first EDFA. All EDFAs operate in constantgain mode at �18 dB. Two spans of SSMF (25 and 20 km)are used, and VOAs after each span adjust the opticalpower to an average of −23 dBm per wavelength. A WSSis used to drop one of the static wavelengths that aredetected with a 250 MHz PIN detector, followed by a2 MSa/s data acquisition (ADC) board to measure powerdynamics.

In order to study TDM operation, the transmitter blockof the setup diagram in Fig. 3 is replaced with the trans-mitter block shown in Fig. 4. As only one SG-DBR wasavailable, the TDM operation was synthesized by timemultiplexing a pair of CW signals from the comb sourceusing electro-optic switches. In this case the switchingwavelengths are always on as the fast electro-opticswitches are used to switch, alternately, between the two

wavelengths. The two pairs of signals are synchronizedwith a common clock and combined in a 50/50 optical com-biner. Note that this is also an alternative implementationto using a fast-tunable laser source: using multiple singlewavelength signals and selectively activating or modulat-ing them with a fast switch or modulator. The switch dwelltime in this experiment for the TDM case was varied frommicroseconds to seconds, with no additional excursions onother wavelengths.

V. RESULTS AND DISCUSSION

A. Balanced Wavelength Switching: BasicOperation

Figure 5(a) shows the experimental and modeled powerexcursion amplitudes, caused by transmission through oneEDFA, on wavelength 1547.72 nm (No. 45) when an addi-tional wavelength is added at a wavelength correspondingto the “Channel Index” on the horizontal axis. The figureshows that the observed wavelength experiences both pos-itive and negative excursions as channels are added at dif-ferent wavelengths across the spectrum. These excursionsare not symmetric as the tilt and ripple functions of theEDFA are not symmetric and the tilt varies with the gain.The figure shows that the addition of wavelength No. 11(1561.44 nm) causes an opposite excursion to that causedby wavelength No. 73 (1536.61 nm): �0.4 dB (referred tohere as a “balanced” pair). These excursions are shownin the time domain in Fig. 5(b). This figure also shows thatno excursion is caused when the laser switches quickly(dwell time = 200 ns) between these two balanced wave-lengths. Since the dwell time of the two fast-switchingchannels is below the gain response time of the EDFA(microseconds), they have the same effect as two staticchannels that cause opposite excursions. Thus, by distrib-uting the channel power over two ormore wavelengths thatare balanced in this way, the system no longer exhibitschannel power excursions when the new signal is addedor removed. Thus, persistent power excursions, whichare a key limitation preventing dynamic wavelength oper-ation, are removed.

Fig. 3. Experimental setup to study the power excursions causedby wavelength switching in a three EDFA metro-scale network.

Fig. 4. Experimental implementation of a fast-switching TDMtransmitter using a comb source and electro-optic switches.WSS, wavelength selective switch.

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B. Balanced Wavelength Switching: NetworkScenario

It is important to show how excursion-free fast wave-length switching can work in a metro network scenarioas excursions grow larger with each additional amplifieralong the path [13]. To study this we examine wavelengthswitching of such wavelength distributed signals in aWDMsystem (the setup in Fig. 3) with multiple wavelengths.Figure 6 shows the output spectra of theWDM signals used

to test the technique. The accumulated wavelength-dependent gain ripple through the system is 7.5 dB.Here the tilt is adjusted to be high to emulate the effectof a much larger amplified system. A single amplifier withlarge ripple or tilt has been shown to be equivalent to a cas-cade of identical amplifiers with a combined ripple and tiltof the same form, neglecting gain-dependent tilt [13].Excursions on four wavelengths provided by the combsource (pink) are measured as the SG-DBR is repeatedlymoved (on a millisecond time scale) from one balanced pair(switching on a nanosecond time scale) of wavelengths(light blue, 1538.98 and 1539.77 nm) to an unbalanced pair(black, 1529.95 and 1530.33 nm); i.e., the SG–DBR initiallyswitches on a nanosecond time scale between two balancedwavelengths (light blue), and is quickly reconfigured toswitch between two unbalanced wavelengths (black).This reconfiguration, between the balanced pair and theunbalanced pair, is continuously repeated on millisecondtime scales. The samemeasurements are made as the laserrepeatedly tunes from one balanced pair (light blue) to an-other balanced pair (orange, 1535.45 and 1554.95 nm).

The resultant excursions on the four static wavelengthsin the system (pink channels in Fig. 6) are shown in Fig. 7,which exhibits excursions of around 2 dB on each channel,as the laser repeatedly tunes between a balanced pair andan unbalanced pair. In contrast, excursion-free operation isobtained on all wavelengths when the laser repeatedlytunes between two balanced pairs of wavelengths. We ob-serve similar behavior in simulation. Note that the tuningback and forth between different wavelength pairs, shownin these figures, is on the scale of hundreds of microsec-onds, which is the typical response time of AGC EDFAs.These results show how choosing the nanosecond switchingwavelength locations intelligently can provide excursion-free addition, and rerouting, of packet/burst/circuitswitched data channels in a network.

C. Variable Dwell Time Ratio

The results in the previous section show the mitigationof power excursions using balanced wavelengths with

Fig. 5. (a) Excursions on wavelength 1547.72 nm due to additionof wavelengths across the C-band. (b) Excursions on wavelength1547.72 nm in the time domain due to addition of individual wave-lengths and a balanced pair.

Fig. 6. Output spectra of static WDM wavelengths and groups ofbalanced and unbalanced switching wavelengths.

Fig. 7. Excursions on all static wavelengths, including predic-tions from the simulation model.

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equal dwell times. As dwell times are well below the EDFAresponse time, the addition of this pair of switching wave-lengths is the equivalent, to the amplifier, of adding twostatic wavelengths at 3 dB below their actual input power;i.e., the equal allocation of sub-EDFA response dwell timestranslates (from the point of view of the EDFA) to distrib-uting the instantaneous optical power equally over twowavelengths. This effect can be observed in Fig. 6 becausethe sweep time of the optical spectrum analyzer used isalso significantly longer than the dwell time. In the figure,switching wavelength pairs are both shown to have a powerof 3 dB below neighboring static wavelengths, even thoughall launch powers are maintained instantaneously at−23 dBm. As the AGC EDFA algorithm works by monitor-ing the total input optical power, power excursions arisingfrom the addition of new wavelengths depend on the inputpower of those wavelengths (as they appear to the EDFA)and, by extension, the ratio of the switching wavelengthdwell times.

Figure 8 shows unbalanced switching wavelengths withvariable DTRs used for excursion-free operation. The samestatic wavelengths (pink) and initial balanced switchingwavelengths (blue), as outlined in Subsection V.B, are used.This time, however, the laser is reconfigured to switch be-tween the unbalanced pair 1561.42 and 1530.33 nm [solidblack, Fig. 8(a)]. A second unbalanced pair, 1549.75 and1530.33 nm [dashed black, Fig. 8(b)], is also demonstrated.Figure 9(a) shows excursions on all static channels whenthe laser is reconfigured from the balanced pair (blue) tothe unbalanced pair [solid black, Fig. 8(a)], for DTRs of1:1 and 4:1. When equal dwell times are employed thereis a residual excursion of about 1 dB on all wavelengths.However, with a DTR of 4:1, excursion-free operation isachieved as the effective contributions to excursion, fromeither wavelength, are equalized. Figure 9(b) shows thesame results for the second wavelength pair used [dashedblack, Fig. 8(b)]. In this case, a wavelength closer to the mean gain of the channel, 1549.75 nm, is used in

conjunction with 1530.33 nm to balance the excursions.As the new wavelength causes smaller excursion thanthe previous one, an increased DTR of 6:1 is required toachieve excursion-free operation.

Fig. 8. Spectra of the network configuration with a balancedwavelength pair (blue) and balanced wavelength pairs with differ-ent dwell time ratios (black).

Fig. 9. Excursions on all static wavelengths for (a) wavelengthswitching with DTRs of 1:1 and 4:1 (solid black, Fig. 8) and(b) wavelength switching with DTRs of 1:1 and 6:1 (dashed black,Fig. 8).

Fig. 10. Power excursion from balanced TDM wavelengthswitching.

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D. Time-Division Multiplexing

The effect of TDM switching signals on channel power isalso studied. Figure 10 shows the excursions on the wave-lengths in the system (pink in Fig. 6) when the two timemultiplexed CW signals are changed, between the two bal-anced wavelength pairs (light blue and orange in Fig. 6) asoutlined in Subsection V.B. Excursions of <0.1 dB areachieved on all measured wavelengths. In the TDM con-figuration, for dwell times ranging from seconds down to125 μs, negligible excursions are observed as the multi-plexed wavelengths smoothly alternate within the timeslots and are well synchronized.

VI. CONCLUSION

Excursion-free wavelength switching and reconfigura-tion has been shown in the transmission of WDM wave-lengths through multiple transient controlled EDFAsand fiber spans by using a novel technique of distributingthe signals over multiple channels using a fast-tunable la-ser. Results presented show how varying the ratio of dwelltimes, between distributed signal wavelengths, can offer anadditional degree of freedom when choosing wavelengthsthat can provide excursion-free operation. Furthermore,this excursion balancing technique has been applied tothe case in which full TDM switching is employed, to pre-serve the spectral efficiency of the system, again exhibitingnegligible power excursions. While many implementationissues remain to be studied for commercial viability, thiswork has investigated the basic operating principles andfirst (to the best of our knowledge) demonstration of thetechnique, which opens up an entirely new form ofwavelength-division multiplexing. This technique has thepotential to enable the rapid growth, or rerouting, of wave-lengths in a network without causing excursions on otherwavelengths, which is highly desirable in next-generationreconfigurable networks.

ACKNOWLEDGMENT

The authors acknowledge the Fulbright Commission ofIreland, the Centre for Telecommunications Value-ChainResearch (CTVR), the IPIC research center, and the NSFERC on Integrated Access Networks (Grant EEC-0812072) for supporting this work.

REFERENCES

[1] D. C. Kilper, G. Atkinson, S. K. Korotky, S. Goyal, P. Vetter, D.Suvakovic, and O. Blume, “Power trends in communicationnetworks,” IEEE J. Sel. Top. Quantum Electron, vol. 17,no. 2, pp. 275–284, 2011.

[2] “Cisco Virtual Network Index” [Online]. Available: http://www.cisco.com/c/en/us/solutions/collateral/service‑provider/visual‑networking‑index‑vni/VNI_Hyperconnectivity_WP.html.

[3] “Cisco Global Cloud Index: Forecast and Methodology 2013–2018,” Cisco White Paper [Online]. Available: http://www.cisco.com/c/en/us/solutions/collateral/service‑provider/global‑cloud‑index‑gci/Cloud_Index_White_Paper.html#_ftnref1.

[4] M. Ajay, A. Chiu, R. Doverspike, M. D. Feuer, P. Magill, E.Mavrogiorgis, J. Pastor, S. L. Woodward, and J. Yates,“Bandwidth on demand for inter-data center communication,”in Proc. of the 10th ACMWorkshop on Hot Topics in Networks,Cambridge, MA, 2011, p. 24.

[5] A. L. Chiu, G. Choudhury, G. Clapp, R. Doverspike, M. Feuer,J. Gannett, J. Jackel, G. Kim, J. Klincewicz, T. Kwon, G. Li, P.Magill, J. M. Simmons, R. A. Skoog, J. Strand, A. Lehmen, B.Wilson, S. Woodward, and D. Xu, “Architectures and protocolsfor capacity efficient, highly dynamic and highly resilient corenetworks [Invited],” J. Opt. Commun. Netw., vol. 4, pp. 1–14,2012.

[6] R. Skoog, G. Clapp, J. Garnnett, A. Neidhardt, A. VonLehman, and B. Wilson, “Architectures, protocols and designfor highly dynamic optical networks,” Opt. Switching Netw.,vol. 9, pp. 240–251, 2012.

[7] X. J. Zhang, S. S. Lumetta, A. L. Chiu, and R. Doverspike,“Heuristic resource optimization for dynamic wavelength ser-vices on optically reconfigurable networks [Invited Paper],” inProc. of the 19th Int. Conf. on Computer Communications andNetworks, Zurich, Aug. 2, 2010.

[8] S. Spadaro, J. Perello, F. Agraz, S. Azodolmolky, M. Angelou,Y. Qin, R. Nejabati, D. Simeonidou, P. Kokkinos, E.Varvarigos, Y. Ye, and I. Tomkos, “Experimental demonstra-tion of an enhanced impairment-aware path computationelement,” in Optical Fiber Communication Conf. (OFC), LosAngeles, CA, 2011, paper OMW5.

[9] F. Smyth, D. Kilper, S. Chandrasekhar, and L. Barry,“Applied constant gain amplification in circulating loop ex-periments,” J. Lightwave Technol., vol. 27, pp. 4686–4696,2009.

[10] K. Ishii, J. Kurumida, and S. Namiki, “Wavelength assign-ment dependency of AGC EDFA gain offset under dynamicoptical circuit switching,” in Optical Fiber CommunicationConf. (OFC), San Francisco, CA, 2014, paper W3E.4.

[11] C. Fürst, R. Hartung, J. P. Elbers, and C. Glingener, “Impactof spectral hole burning and Raman effect on transparent op-tical networks,” in European Conf. and Exhibition on OpticalCommunication (ECOC), Rimini, Italy, Sept. 21, 2003,paper Tu4.2.5.

[12] A. Lieu, C. Tian, and T. Naito, “Transmission and interactionsof WDM burst signals in cascaded EDFAs,” in OpticalFiber Communication Conf. (OFC), Anaheim, CA, 2006,paper OTuD5.

[13] D. C. Kilper, C. A. White, and S. Chandrasekhar, “Controlof channel power instabilities in constant-gain amplifiedtransparent networks using scalable mesh scheduling,”J. Lightwave Technol., vol. 26, no. 1, pp. 108–113, 2008.

[14] Y. Pan, D. C. Kilper, and G. Atkinson, “Persistent channelpower deviations in constant gain amplified long-chainROADM networks,” in Optical Fiber Communication Conf.(OFC), Los Angeles, CA, Mar. 6, 2011, paper JWA10.

[15] Y. Pan, D. Kilper, A. Morea, J. Junio, and V. Chan, “Channelpower excursions in GMPLS end-to-end optical restorationwith single-step wavelength tuning,” in Optical FiberCommunication Conf. (OFC), Los Angeles, CA, Mar. 4,2012, paper JTh2A.

[16] “Infinera and DANTE Set GuinnessWorld Record on GÉANTNetwork” [Online]. Available: http://www.infinera.com/j7/servlet/NewsItem?newsItemID=371.

[17] J. Junio, D. C. Kilper, and V. W. S. Chan, “Channel powerexcursions from single step channel provisioning,” J. Opt.Commun. Netw., vol. 4, pp. A1–A7, 2012.

904 J. OPT. COMMUN. NETW./VOL. 7, NO. 9/SEPTEMBER 2015 Ahsan et al.

[18] Y. Pointurier, M. Coates, and M. Rabbat, “Cross-layer moni-toring in transparent optical networks,” J. Opt. Commun.Netw., vol. 3, pp. 189–198, 2011.

[19] N. Sambo, F. Cugini, I. Cerutti, L. Valcarenghi, P. Castoldi, J.Poirrier, E. Le Rouzic, and C. Pinart, “Probe-based schemes toguarantee lightpath quality of transmission (QoT) in trans-parent optical networks,” in European Conf. and Exhibitionon Optical Communication (ECOC), Brussels, Sept. 21,2008, paper P.5.11.

[20] A. J. Walsh, J. Mountjoy, A. Fagan, C. Browning, A. D. Ellis,and L. P. Barry, “Reduced OSNR penalty for frequency drifttolerant coherent packet switched systems using doubly dif-ferential decoding,” in Optical Fiber Communication Conf.(OFC), San Francisco, CA, Mar. 9, 2014, paper Th4D.8.

[21] C. Browning, K. Shi, A. D. Ellis, and L. P. Barry, “Opticalburst-switched SSB-OFDM using a fast switching SG-DBRlaser,” J. Opt. Commun. Netw., vol. 5, pp. 994–1000, 2013.

Atiyah Ahsan received the B.Sc. degree in electrical engineering(summa cum laude, thesis with highest honors) from TuftsUniversity, Boston, and the M.Sc. degree from ColumbiaUniversity, New York, in 2010 and 2012, respectively. From May2012 to January 2013, she worked as a student collaborator ona project led by Dr. Daniel Kilper at Bell Labs Alcatel Lucent.She is currently a Ph.D. candidate at the Columbia UniversityLightwave Research Laboratory under the advisement ofDr. Keren Bergman. Her research is focused on advanced opticalperformance monitoring techniques and cross-layer architecturesfor next-generation dynamic access and metro networks.

Colm Browning graduated from Trinity College Dublin (DublinUniversity), Ireland, in 2009 with an honors degree in electronicengineering (B.A.I.) and an ordinary degree in mathematics(B.A.). He then received his Ph.D. from Dublin City University,Dublin, Ireland, in 2013 for his study on the use of orthogonal fre-quency division multiplexing in optical communications systems.In 2014 Dr. Browning was awarded a Fulbright Fellowship in orderto undertake visiting research at Columbia University, New York,USA. Dr. Browning is currently working as a post-doctoral re-searcher in the Radio and Optical Communications Laboratoryat Dublin City University.

Michael S. Wang received the B.S.E. degree from PrincetonUniversity, Princeton, New Jersey, in 2008, and the M.S. andPh.D. degrees from Columbia University, New York, in 2010and 2014, respectively, all in electrical engineering. His doctoralthesis focused on energy efficient, cross-layer enabled, dynamicaggregation networks for next-generation Internet.

Keren Bergman (S’87–M’93–SM’07–F’09) received her B.S.degree from Bucknell University, Lewisburg, Pennsylvania, in

1988 and her M.S. and Ph.D. degrees from the MassachusettsInstitute of Technology, Cambridge, Massachusetts, in 1991 and1994, respectively, all in electrical engineering. She is currentlythe Charles Batchelor Professor and Chair of ElectricalEngineering, Columbia University, New York, where she also di-rects the Lightwave Research Laboratory. Her research programsinvolve optical interconnection networks for advanced computingsystems, photonic packet switching, and nanophotonicnetworks on-chip. She is a Fellow of The Optical Society (OSA)and a Fellow of the Institute of Electrical and ElectronicEngineers (IEEE).

Daniel C. Kilper (SM’07) is a research professor in the College ofOptical Sciences, University of Arizona, and the administrative di-rector of the Center for Integrated Access Networks (http://www.cian‑erc.org/), an NSF engineering research center. He receivedhis Ph.D. in physics from the University of Michigan. From2000 to 2013, he was a member of the technical staff at BellLabs, Alcatel-Lucent. He served as the founding technicalcommittee chair of the GreenTouch Consortium and was theBell Labs Liaison Executive for the Center for Energy-EfficientTelecommunications at the University of Melbourne, Australia.While at Bell Labs, he received the President’s Gold MedalAward and was a member of the President’s Advisory Councilon Research. He is an adjunct professor at Columbia Universityand a senior member of the IEEE. He serves as an editor onthe green communications and computing series for IEEECommunications Magazine. Dr. Kilper has conducted researchon optical performance monitoring and on architectures and con-trol systems for energy-efficient optical networks. He has coau-thored four book chapters and more than 100 peer-reviewedpublications.

Liam P. Barry (SM’10) received the B.E. degree in electronic en-gineering and the M.Eng.Sc. degree in optical communicationsfrom University College Dublin, Ireland, in 1991 and 1993, respec-tively, and the Ph.D. degree from the University of Rennes, France,in 1996. From February 1993 until January 1996, he was aResearch Engineer in the Optical Systems Department ofFrance Telecoms Research Laboratories (CNET) in Lannion,France. In February 1996, he joined the Applied Optics Centre,Auckland University, Auckland, New Zealand, as a ResearchFellow, and in March 1998 he took up a lecturing position inthe School of Electronic Engineering, Dublin City University. In1999, he established the Radio and Optical CommunicationsLaboratory, which is part of the Rince Institute. He is currentlya Professor in the School of Electronic Engineering and aPrincipal Investigator for Science Foundation Ireland, Dublin,Ireland. His research interests include all-optical signal process-ing, hybrid radio/fiber communication systems, and wavelengthtunable lasers for reconfigurable optical networks. Dr. Barry hasserved as a TPC member for the Optical Fiber CommunicationConference (OFC), the European Conference on OpticalCommunication, and the Conference on Lasers and Electro-Optics Europe, serving as a Chair of the opto-electronic devicestrand for OFC 2010.

Ahsan et al. VOL. 7, NO. 9/SEPTEMBER 2015/J. OPT. COMMUN. NETW. 905