JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 19, OCTOBER 1, 2009 4311

A Seamless Evolution Method With ProtectionCapability for Next-Generation Access Networks

Jong Hoon Lee, Member, IEEE, Ki-Man Choi, Jung-Hyung Moon, Sil-Gu Mun, Hoon-Keun Lee,Jun-Young Kim, and Chang-Hee Lee, Senior Member, IEEE, Member, OSA

Abstract—We propose and demonstrate a seamless evolutionmethod with protection capability for next-generation (NG) ac-cess networks. Both a time-division-multiplexing passive opticalnetwork (TDM-PON) and a wavelength-division-multiplexing(WDM-PON) can be accommodated in the same fiber infra-structure and failures of feeder fibers and distribution fibers areprotected for each service. Remote reconfigurations of the remotenode (RN) for protection and/or evolution can be achieved within48 ms by instantaneous optical powering at the central office (CO)while maintaining the RN in a passive state.

Index Terms—Evolution method, next-generation access,passive optical network (PON), protection, wavelength bandcombiner/splitter, wavelength division multiplexing (WDM-PON),wavelength locked Fabry–Perot laser diode (F-P LD).

I. INTRODUCTION

A S service providers begun to deploy time-division-mul-tiplexing passive optical networks (TDM-PONs),

next-generation (NG)-PON has been actively discussed forfuture access services [1]–[3]. The NG-PON can be either aTDM-PON supporting higher bandwidth than the current PONor a wavelength-division-multiplexing (WDM)-PON. CurrentTDM-PON will be upgraded to NG-PON in the near futureto accommodate bandwidth growth and new applications [4].Considering the fact that optical outside plant (OSP) lifetime ismore than 25 years, smooth evolution to NG-PON in the samefiber infrastructure is needed.

A few evolution methods maintaining both the wavelengthband and fiber infrastructure of the legacy PON have been pro-posed and experimentally demonstrated [5]–[8]. These can beachieved by allocating specific wavelength band to specific ser-vice by using passive WDM devices which can combine andsplit the different wavelength bands to single strand fiber and

Manuscript received January 30, 2009; revised April 24, 2009. First publishedMay 26, 2009; current version published August 26, 2009. This work was sup-ported in part by the Brain Korea 21 Project, School of Information Technology,Korea Advanced Institute of Science and Technology (KAIST).

J. H. Lee was with the Korea Advanced Institute of Science and Technology(KAIST), Daejeon 305-701, Korea. He is now with the Ubiquitous AccessTechnology Research Team, Electronics and Telecommunications ResearchInstitute (ETRI), Daejeon 305-700, Korea (e-mail: alfred07@kaist.ac.kr;alfred07@etri.re.kr).

K.-M. Choi is with the Network Infra Research Department, Korea TelecomNetwork R&D Laboratory, Daejeon, 305-811, Korea (e-mail: kiman@kt.com).

J.-H. Moon, S.-G. Mun, H.-K. Lee, J.-Y. Kim, and C.-H. Lee are withthe Korea Advanced Institute of Science and Technology (KAIST), Dae-jeon 305–701, Korea (e-mail: jhmoon99@kaist.ac.kr; exatto@kaist.ac.kr;alltoone@kaist.ac.kr; domipopo@ee.kaist.ac.kr; chl@ee.kaist.ac.kr).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JLT.2009.2023608

installed at the central office (CO) and the remote node (RN).A remotely reconfigurable RN for evolution to NG-PON is alsoproposed and demonstrated without field reconfiguration of theRN by craft-man, while maintaining the RN in a passive state[8], [9]. Then, each optical latching switch (OLS) at the RN canbe remotely reconfigured according to the control informationimposed on instantaneous optical powering at the CO [9]. It maybe noted that reconfigurable remote nodes in the PON were alsoproposed and demonstrated with optical fuse, variable opticalsplitter [10]–[13], which can increase the reliability of the PONwithout sending truck roll to the RN.

The evolution to NG-PON became more realistic [14],[15]. Especially, WDM-PON based on the wavelength lockedFabry–Perot laser diode (F-P LD) has been already commer-cialized [16]–[18] and color-free operation of a WDM-PONwith 40 Gb/s (32 1.25 Gb/s) capacity is also demonstratedfor future NG-PON [19]. With increasing demand of higherbandwidth, reliable service in the PON becomes more andmore important. Many schemes for protection capabilitywere proposed either in the TDM-PONs [20]–[23] or in theWDM-PONs [24]–[28]. However, self-restorable or serviceprotection became complicated and difficult, when we considerarchitecture that supports evolution of legacy PON to NG-PON.

In this paper, an evolution of legacy PON to NG-PON withprotection capability is proposed and demonstrated. A legacyPON can be evolved to a NG-PON with the same PON in-frastructure. The failures of the feeder fiber and/or distributionfibers can be protected with remote reconfigurations of the RN,while maintaining the passive nature of the outside plant.

The rest of this paper is organized as follows. In Section II,operating principles of proposed evolution method with protec-tion capability are described. Agnostics of proposed evolutionmethod and control function for less than 50-ms restoration timeare also discussed. Section III provides experimental results fordemonstrating the feasibility of proposed evolution method. Fi-nally, Section IV concludes the paper with discussions.

II. PROPOSED EVOLUTION METHOD

WITH PROTECTION CAPABILITY

A. Operation Principle

The proposed evolution architecture with protection ca-pability is shown in Fig. 1. A TDM-PON is considered as alegacy PON and a WDM-PON is assumed for a NG-PON.They are accommodated in the same PON infrastructure witha pair of fibers, which is essential to provide protection pathand be deployed in physical diverse paths for fiber dig-ups[29]. The TDM-PON signal and the WDM-PON signal are

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4312 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 19, OCTOBER 1, 2009

Fig. 1. Proposed evolution architecture with protection capability for next-generation access networks.

combined to one of feeder fiber (FF-1 or FF-2) by using 3-portwavelength band combiner/splitter 1 (WC1) [6]–[8] and 1 2switch (SW1) at the CO. They are transmitted to the RN andcoupled to WC2 through the 1 2 switch (SW2). Then, theoptical switches (SW1 and SW2) have the same state to provideboth working and protection paths. The separated signals bythe WC2 are connected to optical power splitter (OPS) forlegacy services and to an arrayed waveguide grating (AWG) forNG services. Each output of the OPS and AWG are combinedwith corresponding pairs of distribution fibers through a 2 2optical switch to provide upgrade path and protection capabilityfor each service.

TDM-PON services are provided to legacy subscribersthrough each upper distribution fiber and corresponding to thebar state of optical switches both at the RN and subscribersides. When legacy subscribers want to have NG services,the WDM signals are transmitted to NG optical network ter-minals (ONTs) through each lower distribution fiber. Then,TDM-PON services and WDM-PON services can be providedto each subscriber independently. New NG services can also beprovided to new subscribers with WDM-PON and be protectedby 1 2 switches and a pair of distribution fibers.

In normal operation, TDM-PON signal and WDM-PONsignal are transmitted through feeder fiber 1(FF-1). The opticalswitches at the CO and the RN (SW1, SW2) are in bar state.When the feeder fiber 1(FF-1) is failed, the optical switch SW1is changed to cross-state. Then, optical power with controlinformation for reconfiguring the state of SW2 can be providedat the CO [8], [9] to the RN through feeder fiber 2 (FF-2).Finally, a protection path is formed by changing the opticalswitch SW2 to the cross state. It may be noted that opticalswitches at the RN has the latching variant.

For protection of distribution fibers, fiber fault is detectedboth at the CO and subscriber sides (or ONTs) and the stateof corresponding optical switch at the RN will be reconfiguredremotely. Simultaneously, the state of optical switch at the sub-scriber sides also changed. We have a several different sce-narios for the protection of the distribution fiber dependent onservice provision scenarios. As legacy subscribers are evolved,they can have the TDM-PON service and/or WDM-PON ser-vice. When there is only one type of service either TDM-PONservice or WDM-PON service, a specific subscriber can be pro-tected for the distribution fiber failure. For a new WDM-PONsubscribers (NG-ONT NG-ONT n) can be considered asa subscriber with only a single service. Then new protectableNG services can be provided to new subscribers through 1 2switches and a pair of distribution fibers. When both TDM-PONand WDM-PON service are provided simultaneously, a specificservice that has higher priority can be protected for a subscriberwhile lower priority service can not be maintained. It may benoted that both services can be protected by adding WCs bothat the RN and the ONT, such as the feeder fiber protection.

B. Agnostics

The proposed network architecture in Fig. 1 is agnosticabout both TDM-PON and WDM-PON technologies. It can beapplicable for ethernet PON (E-PON), gigabit PON (G-PON),and WDM-PON with various types of optical sources. It maybe noted that the architecture can be modified as shown inFig. 2, when we use a colorless or color-free optical sourcesfor WDM-PON [16], [27], [30]. The 2 AWG can provide aworking path or a protection path by utilizing its routing char-acteristics. Each port of 2 AWGs is coupled to workingand protection fiber with different wavelength assignments.

LEE et al.: SEAMLESS EVOLUTION METHOD WITH PROTECTION CAPABILITY 4313

Fig. 2. Evolution architecture with different feeder fiber configuration for colorless or color-free WDM-PON and protected TDM-PON with 2�� splitter.

Then failures of the feeder fiber can be protected by changingthe status of two optical switches (SW1 and SW2) at the CO,which is used to couple two broadband light sources (BLS)to each port of 2 AWGs orderly. For TDM-PON, 1 2optical switch for feeder fiber protection at the RN can also beeliminated by using a 2 OPS, which can provide dedicatedworking and protection path. Then, failures of the feeder fibercan be protected by changing the status of optical switch (SW3)at the CO.

For the protection of distribution fiber failures, different con-figuration of switching block (SB) can be constituted with theconsiderations of the loss margin, flexibility and blocking char-acteristics. Minimum loss can be achieved for usage of a 2 2switch. For the configuration of switching blocks 3 (SB-3), bothservices can be transmitted through a distribution fiber and bothservice can be protected when one fiber is failed. In this case,only one service is switched to the un-failed fiber and the otherservice can be maintained. If we use an 1 2 switch and a WC asshown in switching block 4 (SB-4), we can protect only one ser-vice. Selective disconnection of erratic or invalid ONTs, whichcause the denial of service in the TDM-PON, can be achievedwith SB-5 [10], [11].

C. Control Function

The timing plan and waveform for powering and control isshown in Fig. 3(a). The selection information of a specific OLSis encoded with sync signal (start bit) just after the first opticalpowering pulse. The received optical power is converted to elec-trical power through photovoltaic converter at the RN and storedin a storage capacitor for the operation of control unit only. Thecontrol unit decodes the encoded control information and selectsthe specific OLS. Then the second optical powering pulse is sup-plied for the selected OLS switching, maintaining the decodedoutput of the control unit. Since typical power consumption ofthe control unit is very low compared to the switching power of

the OLS, relatively long powering time in the previous schemeto store the energy for an OLS switching [9] can be reducedeffectively.

Fig. 3(b) shows the functional block diagram of control unit.The optical power from the CO was converted into electricalpower through photovoltaic converter at the RN. It was storedat a storage capacitor and used for operation of the control unitonly. Then, electrical power level can be maintained for properoperation of control unit during decoding process. After de-coding, a specific OLS is activated by the second optical power.In this way, each OLS can be switched for each restorationprocess with reduced switching time.

III. EXPERIMENTAL RESULTS

The experimental setup to demonstrate the feasibility ofproposed evolution method with protection capability is shownin Fig. 4. A TDM-PON with a split ratio of 32 is assumed asa legacy PON. A WDM-PON based on the wavelength-lockedF-P LDs is used as a NG-PON [16], [19]. For demonstratingagnostics about both TDM-PON and WDM-PON, we used a2 32 splitter for TDM-PON [20] and two 2 40 AWGs with100-GHz channel spacing and flat-top passband for WDM-PON[27]. For upstream and downstream of TDM-PON signals, di-rectly modulated distributed-feedback (DFB) lasers at 1310 nmand 1490 nm were used, respectively. For WDM-PON, we used2 40 AWGs with 100-GHz channel spacing and flat-top pass-band. The center wavelength difference from each two inputport to an output port was 1.6 nm. The free spectral range (FSR)of the AWG was about 54 nm. We assigned the C-band forthe upstream signals and L-band for downstream signals. Thebroadband light source (BLS) was an erbium-doped-fiber-am-plifier (EDFA) based amplified spontaneous emission (ASE).The F-P LDs with 0.1% reflectivity was directly modulated at1.25 Gb/s. Then 30-channel of upstream signals and 1-channelof downstream signal was constituted due to availability of the

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Fig. 3. Control functions for reconfiguring a specific OLS with less than 50-ms restoration time. (a) Timing plan and waveform for powering and control.(b) Functional block diagram of control unit at the RN.

Fig. 4. Experimental setup to demonstrate the feasibility of proposed evolution method with protection capability.

F-P LDs. The length of feeder fibers and distribution fiberswere 10 km, 10 km, respectively. The injection powers of theC/L-band BLS were dBm/0.2 nm and dBm/0.2 nm,respectively.

To demonstrate the protection of feeder fiber failure, self-re-storable PON with 2 32 power splitter and 2 40 AWGs wereconstituted as shown in Fig. 4. For WDM-PON, the first inputport and second input port of 2 40 AWG were connected tothe feeder fiber 1 (FF-1) and the feeder fiber 2 (FF-2) throughthe optical switches (SW2, SW3) and the WCs (WC1, WC2) atthe CO. Similarly, the first input port and the second input portof 2 40 AWG at the RN were connected to the feeder fiber 1

(FF-1) and the feeder fiber 2 (FF-2) through WC3 and WC4, re-spectively. The TDM-PON signal was selectively combined toone of feeder fiber (FF-1 or FF-2) by using WCs (WC1, WC2)and switch (SW1) at the CO and two input port of 2 32 powersplitter was also connected to the each feeder fiber through WCs(WC3, WC4) at the RN. For the protection of distribution fiber,2 2 optical switch was located at the RN and the subscribersides. Each service can be protected by remote reconfigurationof the RN through an optical powering at the CO.

Protection capability was demonstrated both for the failuresof feeder fiber and distribution fibers. For simulation of a fibercut at the feeder fiber, an optical switch was inserted between

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Fig. 5. Measured protection characteristics of feeder fiber failure. (i) Monitored upstream signal at the feeder fiber 1 (FF-1). (ii) L.O.S. output of CO receiver toactivate the optical switch (SW1) at the CO. (iii) The measured upstream at the OLT. (iv) Downstream signals at the ONT.

the feeder fiber 1(FF-1) and WC3. Fig. 5 shows the measuredrestoration characteristics of TDM-PON for the feeder fiberfailure. The fiber fault was detected at the CO and the state ofoptical switch (SW1) was changed by the loss-of-signal (LOS)output of optical receiver at the CO. The trace (i) representsthe monitored upstream signal at the feeder fiber 1 (FF-1). Thetrace (ii) is the LOS output of the OLT receiver, which was usedto activate the corresponding optical switch (SW1) at the CO.The traces (iii) and (iv) are measured upstream and downstreamsignals at the CO and the ONT. The total restoration timeof feeder fiber was less than 1 ms. It may be noted that thepropagation delay of 20 km fiber from the CO to the ONT isalso indicated.

For the distribution fiber failure, the fault was detected bothat the CO and the ONTs. Then, optical power with control in-formation was supplied at the CO and the corresponding switchat the RN was reconfigured remotely. Insertion loss of the op-tical powering path was less than 8 dB. A photovoltaic converter(PPC-9LW, JDSU) with 25% conversion efficiency at 1480 nmwas used to convert optical power to the electrical power. A con-trol unit implemented with discrete CMOS logic gates decodesselection information and change the state of a specific switchcorresponding to the protection path for distribution fiber fail-ures. Fig. 6 shows measured protection characteristics with theimplemented control unit. The optical power for this experimentwas 25 dBm at the CO, which was limited by nonlinearity in-duced penalty [8]. A pulse code for reconfiguring a specific OLS(SW2) was followed by the first optical powering pulse that con-verted through photovoltaic converter and was stored at 30 Fcapacitor for the operation of a control unit only. The first 25 mspowering pulse, 7 bits code of 1.4-ms bit time including a syncbit and the second 25-ms powering pulse were encoded at theCO by using an optical switch with less than 0.5 ms switchingtime as shown in trace (i). The detected powering pulses andcontrol information for reconfiguring a specific optical switchand the generated clock for decoding the control informationare shown in traces (ii) and (iii), respectively. A specific OLSaccording to decoded control information was selected at the8th bit time of generated clock. The second powering pulse

was supplied just after finishing decoding process (at the 9thbit time). Then, a specific OLS corresponding to the protectionpath was switched within 12 ms, which was well matched to theswitching time without control unit at the same RN power [8].Monitored outputs of upstream and downstream TDM-PON sig-nals through the 2 2 coupler are shown in traces (iv) and (v),respectively. Upstream signal was blocked just after fiber cut,while downstream signal was maintained until the reconfigura-tion of the RN. The upstream and downstream TDM-PON sig-nals at the OLT and ONTs are shown in curves (vi) and (vii),respectively. The measured total restoration time with the re-mote reconfiguration of the RN was less than 48 ms. It may benoted that this restoration time can be reduced further by usingOLSs with low power consumption [31] and/or a photovoltaicdevice with high conversion efficiency [32].

We also conducted experiments for protections of the WDM-PON. The LOS output at each receiver was detected both atthe CO and at the subscriber side to change the state of corre-sponding switches. The measured results were almost the sameas in Figs. 5 and 6.

Transmission performances were measured with bit-error-rates (BERs) of the upstream and downstream signals for eachservice and each protection scenarios. In normal operation,the BERs of the upstream and the downstream of TDM-PONsignals were measured with and without WDM-PON signalsas shown in Fig. 7. We also measured the BERs of TDM-PONwith WDM-PON in different protection paths. There werenegligible BER differences among TDM-PON signal only andTDM-PON signals with WDM-PON in different optical paths.

The BERs of WDM-PON were measured both in the normaland protection states with and without TDM-PON signals. AnL-band F-P LD and C-Band F-P LDs are directly modulated at1.25-Gb/s for downstream and upstream signals, respectively.We used optical receivers whose decision threshold level wasadjusted automatically according to the detected average op-tical power [33], [34]. The upstream and downstream BERs ofWDM-PON were almost the same regardless for the existenceof TDM-PON as shown in Fig. 8. When the feeder fiber wasin fault, all wavelengths for the upstream and downstream sig-

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Fig. 6. Measured protection characteristics by an optical powering at the CO. (i) Optical powering with control information at the CO. (ii) Detected poweringpulse and control information by photovoltaic converter at the RN. (iii) Generated clock for decoding control information. (iv) Monitored outputs at the 2� 2coupler for upstream signal. (v) For downstream signal. (vi) Upstream signal at the OLT. (vii) Downstream signal at the ONT.

Fig. 7. The measured BERs of (a) 1310-nm TDM upstream and (b) 1490-nmTDM downstream in different optical paths with and without WDM-PONsignal.

nals in restoration state were shifted to 200 GHz longer wave-length due to the routing property of the AWGs. There were neg-ligible BER differences both in the normal and protection states.It is notable that color-free operation for upstream signals anda downstream signal can be achieved with dBm/0.2 nminjection powers of BLS for all WDM-channels.

TABLE IRELIABILITY PERFORMANCE

Insertion loss of optical switches was less than 0.6 dB bothfor the cross state and the bar state. Insertion loss of each 3-portTF filters including edge filter and CWDM filters was less than0.2 dB and 0.4 dB for the reflection port and the pass port, re-spectively. The measured insertion loss of implemented WCswas nearly 1 dB for 1410-nm downstream signal, 0.8 dB for1310-nm upstream signal and 0.8 dB for WDM signals, whichinclude the connector losses [6]. The total insertion loss of ourexperimental setup due to additional components for evolutionwith protection capability (two 1450-nm CWDM filters for op-tical powering, two WCs and three/four switches for TDM-PON/WDM-PON) was 4.4 dB for TDM downstream signal,3.8 dB for TDM upstream signal and 4.4 dB for WDM sig-nals. Thus, system reach compromised by additional insertionlosses is about 16 km, 13.8 km, and 16 km for TDM down-stream signal, TDM upstream signal and WDM signals, respec-tively (fiber loss: 0.275 dB/km). It is expected that the insertionloss can be reduced by integrating WC in a single device [6],[7].

IV. DISCUSSION AND CONCLUSION

To understand effectiveness of the protection with remote re-configuration of the RN, we calculate connection availability

LEE et al.: SEAMLESS EVOLUTION METHOD WITH PROTECTION CAPABILITY 4317

Fig. 8. Measured BERs of (a) WDM upstream and (b) WDM downstream indifferent restorable optical paths with and without TDM-PON signal.

of a channel [35]. As shown in Table I, significant decrease(about 14 times) of mean downtime can be achieved both inTDM-PON and WDM-PON. For the calculation of improve-ment in availability, we assumed that both feeder and distribu-tion fibers have a working path and a protection path. Then 6hours of mean time to repair (MTTR) and 570 FIT/km ( FIT

failure per hours) for fiber cables were used, which corre-sponds to five cable breaks per year in a 1000-km network [35].Here, almost 60% of fiber cable failures were caused by fibercable dig-ups, which can be defined as damage to fiber cableduring an activity to penetrate the ground [29].

Compared to conventional protection schemes in the PONwithout remote reconfigurations of the RN [20]–[28], proposedmethod does not require additional redundant devices except theswitches at the RN. Efficient wavelength band usage without re-dundant wavelength band allocation can also be achieved, whichis suitable for future WDM-PON with high split ratio.

In conclusion, we proposed and demonstrated a seamless evo-lution method with protection capability. Protections for feederfiber and distribution fibers were achieved both for TDM-PONand WDM-PON. Measured restoration time with remote recon-figuration of the RN was less than 48 ms, which is satisfied forthe requirement of SONET and Metro Ethernet Forum (MEF2).The proposed method can be useful for evolution of legacy PONto NG-PON with high reliability. It is also applicable for anykinds of PON architecture, while maintaining the merits of thePON infrastructure.

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Jong Hoon Lee (M’08) was born in 1975. He received the M.S. and Ph.D.degrees from the Graduate School of Electrical Engineering and Computer Sci-ence, Kyungpook National University (KNU), Daegu, Korea, in 2000 and 2007,respectively.

He was with the Photonic Network Research Lab, Korea Advanced Insti-tute of Science and Technology (KAIST), Daejeon, Korea, as a PostdoctoralResearcher from 2007 to 2009. He is now with the Ubiquitous Access Tech-nology Research Team, Electronics and Telecommunications Research Institute(ETRI), Daejeon, Korea. His current research interests include optical commu-nications devices and networks.

Ki-Man Choi was born in 1978. She received the M.S. and Ph.D. degrees fromthe Department of Electrical Engineering and Computer Science, Korea Ad-vanced Institute of Science and Technology (KAIST), Daejeon, Korea, in 2004and 2008, respectively.

She spent six months at KAIST as a Postdoc. She has been working as aResearcher at the Network Infra Research Department, Korea Telecom NetworkTechnology Laboratory, Daejeon, Korea. Her research interests include opticalcommunication and network. Her current research interests are WDM-PON andnetwork management.

Jung-Hyung Moon was born in 1980. He received the M.S. degree in elec-trical engineering from Korea Advanced Institute of Science and Technology(KAIST), Daejeon, Korea, in 2005. He is currently working toward the Ph.D.degree in optical communication systems at KAIST.

His research interests include lightwave systems and optical access networkbased on WDM-PON.

Sil-Gu Mun received the B.S. degree in electronics from Kyungpook NationalUniversity, Daegu, Korea, in 2003 and the M.S. degree in electrical engineeringfrom Korea Advanced Institute of Science and Technology (KAIST), Daejeon,Korea, in 2005. She is currently working toward the Ph.D. degree in opticalcommunication systems at KAIST.

Her research interest includes lightwave systems and high-speed optical ac-cess network.

Hoon-Keun Lee received the B.S. degree in electronics from Kyungpook Na-tional University, Daegu, Korea, in 2006. He is currently in a M.S.-Ph.D. jointprogram at the Korea Advanced Institute of Science and Technology (KAIST),Daejeon, Korea.

His research interest includes lightwave systems and optical access networksbased on WDM-PON.

Jun-Young Kim received the B.S. degree in electronics from Inha University,Incheon, Korea, in 2007. He is currently in a M.S.-Ph.D. joint program at theKorea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea.

His research interest includes lightwave systems and optical access networksbased on WDM-PON.

Chang-Hee Lee (S’82–M’90–SM’08) was born in1961. He received the M.S. and Ph.D. degrees fromthe Department of Electrical Engineering, KoreaAdvanced Institute of Science and Technology(KAIST), Daejon, Korea, in 1983 and 1989, respec-tively.

He spent a year at Bellcore (Bell CommunicationsResearch) as a Postdoc. He worked with the Elec-tronics and Telecommunications Research Institutefrom 1989 to 1997 as a Senior Researcher. Since1997, he has been a Professor with KAIST. His

major interest is optical communications and networks. He has spent over20 years as an Engineer in the area of optical communications, includingsemiconductor lasers. He was Technical Leader for the 2.5- and 10-Gb/soptical-transmission-system development, including optical amplifiers at theElectronics and Telecommunications Research Institute. He is an author of 170journal and conference papers. He is the holder of 23 U.S. patents and morethan 50 additional patents are pending in the U.S.

Dr. Lee is a member of Optical Society of America (OSA).