Key Technologies of WDM-PON for Future Converged Optical Broadband Access Networks [Invited]

Chang et al. VOL. 1, NO. 4 /SEPTEMBER 2009/J. OPT. COMMUN. NETW. C35

Key Technologies of WDM-PON forFuture Converged Optical Broadband

Access Networks [Invited]Gee-Kung Chang, Arshad Chowdhury, Zhensheng Jia, Hung-Chang Chien, Ming-Fang Huang,

Jianjun Yu, and Georgios Ellinas

ttogmvttt(bemaassptEsobFcus(tnmcobtoWtatm

Abstract—The wavelength-division-multiplexedpassive optical network (WDM-PON) is considered tobe the next evolutionary solution for a simplified andfuture-proofed access system that can accommodateexponential traffic growth and bandwidth-hungrynew applications. WDM-PON mitigates the compli-cated time-sharing and power budget issues in time-division-multiplexed PON (TDM-PON) by providingvirtual point-to-point optical connectivity to multipleend users through a dedicated pair of wavelengths.There are a few hurdles to overcome before WDM-PON sees widespread deployment. Several key en-abling technologies for converged WDM-PON systemsare demonstrated, including the techniques forlonger reach, higher data rate, and higher spectral ef-ficiency. The cost-efficient architectures are designedfor single-source systems and resilient protection fortraffic restoration. We also develop the integratedschemes with radio-over-fiber (RoF)-based optical-wireless access systems to serve both fixed and mo-bile users in the converged optical platform.

Index Terms—Wavelength-division-multiplexedpassive optical network (WDM-PON); Broadband ac-cess.

I. INTRODUCTION

T HE rapidly growing number of broadband sub-scribers and the increased use of video-based ser-

vices with high-definition quality are forcing carriers

Manuscript received March 31, 2009; revised May 18, 2009; ac-cepted May 28, 2009; published August 25, 2009 �Doc. ID 109513�.

G.-K. Chang (e-mail: [email protected]), A. Chowdhury (e-mail: [email protected]), H.-C. Chien (e-mail: [email protected]), and M.-F. Huang (e-mail: [email protected]) arewith the School of Electrical and Computer Engineering, GeorgiaInstitute of Technology, Atlanta, GA 30332, USA.

J. Yu (e-mail: [email protected]) is with NEC LaboratoriesAmerica, Princeton, NJ 0854, USA.

Z. Jia (e-mail: [email protected]) is with TelcordiaTechnology, Red Bank, NJ.

G. Ellinas (e-mail: [email protected]) is with the Department ofElectrical and Computer Engineering, University of Cyprus, Nicosia,Cyprus.

Digital Object Identifier 10.1364/JOCN.1.000C35

1943-0620/09/040C35-16/$15.00 ©

o look for bandwidth solutions. It is commonly agreedhat passive optical networks (PONs) are highly rec-gnized as the most promising candidates for next-eneration access systems because of low cost, simpleaintenance and operation, and high-bandwidth pro-

ision [1]. Because of its point-to-multipoint architec-ure, multiplexing techniques are required in a PONo offer multiple access capability. Time-division mul-iple access (TDMA) PONs, like today’s Ethernet PONEPON) and gigabit PON (GPON), are being deployedy many carriers to provide triple-play services. How-ver, TDMA PON cannot keep up with the require-ents of future access network evolution regarding

ggregated bandwidth, attainable reach, and allow-ble power budget. WDM-PONs can mitigate these is-ues for guaranteeing high bandwidth and quality ofervice to each subscriber. WDM-PONs offer higherer optical network unit (ONU) bandwidth, low split-ing loss, and maximum link reach as opposed toPON and GPON systems [1–3]. WDM-PONs canerve distances up to 80–100 km without the need forptical amplification, which blurs the traditionaloundary of metro and access networks as shown inig. 1. The metro core or wide-area access networkonnecting the optical backbone consists of reconfig-rable optical add–drop multiplexers (ROADM) toupport flexible configuration. An optical line terminalOLT), as the aggregating–deaggregating interface tohe ROADM, transmits and receives the optical sig-als to and from the remote node (RN). Typically, theain services include direct residential access, dedi-

ated access for business, and backhauling of copperr radio access networks. To make full use of the hugeandwidth offered by optical fiber and flexibility fea-ures presented via wireless, the convergence of radio-ver-fiber (RoF)-based optical-wireless networks andDM-PON are regarded as the most promising solu-

ion to increase the capacity, coverage, bandwidth,nd mobility in environments such as conference cen-ers, airports, hotels, and shopping malls and ulti-ately to homes and small offices [4,5].

In this paper, we review recent research efforts on

2009 Optical Society of America

scssRs2osldab

PflldrmpFdAt(sdfoDica(t1t2tuscwm2tSPlmtmdt

C36 J. OPT. COMMUN. NETW./VOL. 1, NO. 4 /SEPTEMBER 2009 Chang et al.

advancing WDM-PON technologies for future opticalaccess networks. In Section II, we experimentallydemonstrate the architecture design based on differ-ent modulation formats for bidirectional connectionsusing a single light source at the central office (CO). Aself-survivable WDM-PON architecture with central-ized wavelength monitoring, protection, and restora-tion capability is demonstrated in Section III. InSection IV, an impairment mitigation technique toeliminate the Rayleigh backscattering (RB) andFresnel backreflection effects in long-reach, bidirec-tional single-fiber WDM-PON systems is demon-strated based on carrier-suppressed subcarrier modu-lation. In the same section, we introduce a remotesignal regeneration and upconversion method to sig-nificantly increase the dispersion tolerance for upcon-verted optical millimeter-wave signals in the extendedRoF WDM-PON systems. Finally, the flexibility andtransport feasibility in metro and wide-area accessDWDM networks with multiple ROADM nodes for60 GHz optical millimeter-wave signals are presentedin Section V.

II. ARCHITECTURE DESIGN FOR BIDIRECTIONALCONNECTIONS USING A CENTRALIZED LIGHT SOURCE

A. Spectrally Efficient Scheme Based on DPSK andDuobinary

To support ever-increasing bandwidth demand foruser-specific applications such as video-on-demand,HDTV, etc. in a cost-effective manner, the number ofwavelengths in the future WDM-PON system must beincreased. Shrinking the DWDM channel spacing be-tween the adjacent channels from currently available100 or 50 GHz to the future 25 GHz is thus highly de-

Fig. 1. (Color online) Metro and wide-area WDM-PON architec-ture and future network requirements.

irable. Also, to make the WDM-PON system moreost effective and easily manageable, the future ONUhould have the capability to reuse the downstreamignal by remodulating it with upstream data [6–8].ecently, we proposed and experimentally demon-trated a spectrally efficient, dispersion-tolerant5 GHz spaced DWDM-PON system using a 25 GHzptical interleaver (IL), 10 Gbit/s differential phasehift keying (DPSK) downstream signal, and remodu-ated 10 Gbit/s duobinary upstream signal [9]. Usinguobinary for the upstream signal does not requireny additional demodulator at the CO and exhibitsetter dispersion tolerance for the remodulated signal.

The experimental setup of the proposed DWDM-ON is shown in Fig. 2. The CW carrier generated

rom a distributed feedback (DFB) laser at wave-ength 1546 nm is injected to an optical phase modu-ator (PM) with a bandwidth of 10 GHz. The PM isriven by 10 Gbit/s downstream data with a pseudo-andom bit sequence (PRBS) length of 231−1. Theodulated DPSK signal is passing through the odd

ort of a 50/25 GHz optical IL. Insets (i) and (ii) ofig. 2 show the optical spectra of the 10 Gbit/s DPSKownstream signals before and after the 25 GHz IL.fter the IL, the DPSK DS signal is amplified and

ransmitted over 25 km of standard single-mode fiberSMF-28) to the ONU. At the ONU, a 3 dB opticalplitter is used to tap half of the optical power for theownstream receiver. A Mach–Zehnder delay inter-erometric demodulator (DI) with a free spectral rangef 12.5 GHz is used to convert the phase-modulatedPSK signal to an intensity-modulated signal before

t is received by a regular direct detection PIN re-eiver. The other 50% of the DPSK signal is amplifiednd injected into a 10 GHz optical intensity modulatorIM). Inset (iii) of Fig. 2 shows the optical spectra ofhe remodulated signal. The IM is driven by the0 Gbit/s upstream (US) data for duobinary modula-ion. The PRBS length of the upstream data is set to31−1. A fourth-order Bessel–Thomson low-pass elec-rical filter (LPF) with 3 dB bandwidth of 2.8 GHz issed as a duobinary encoder for the 10 Gbit/s up-tream data. A tunable electric delay is used to syn-hronize the bit position of the downstream signalith the upstream data. The IM is biased at the trans-ission null point, and the driving voltage is set to

V�. The remodulated duobinary upstream signal isransmitted back to the CO through another 25 km ofMF-28 before being received by a direct directionIN receiver. In order to eliminate the unwanted Ray-

eigh backscattering noise in the bidirectional trans-ission, we used a dual-fiber transmission architec-

ure. Figure 3 shows the bit-error-rate (BER)easurements of both the DPSK downstream and the

uobinary upstream before and after their respectiveransmission. The insets of Fig. 3 show the corre-

Tluc5t

B

(rmccwlpttafmibbqs


sponding optical eye diagrams. The eyes are clear andopen with a good extinction ratio. For DPSK down-stream, we used only one single direct direction opti-cal receiver after demodulation at the DI. At a 10−10

BER, the power penalty of the 10 Gbit/s DPSK down-stream signal is about 0.6 dB after 25 km of single-mode fiber without any dispersion compensation. Onthe other hand, at a 10−10 BER, the power penalty fora 1 Gbit/s duobinary upstream is less than 0.5 dB af-ter the corresponding upstream transmission over25 km of SMF without dispersion compensation.

Fig. 2. Experimental setup and optical spectra for downstream an

Fig. 3. (Color online) BER measurements and optical eyediagrams.

hus, the end-to-end power penalty of the remodu-ated signal after 50 km (25 km downstream+25 kmpstream) is about 1.1 dB. The power penalty isaused mainly by the accumulated dispersion at the0 km SMF and the signal remodulation process athe ONU.

. WDM-OFDM-PON

Orthogonal frequency-division multiplexingOFDM) is an effective modulation format, which hasecently received much attention in fiber-optic trans-ission systems because of its high spectrum effi-

iency and resistance to a variety of dispersions, in-luding chromatic dispersion [10–13]. In this section,e built up a WDM-OFDM-PON with a centralized

ight wave and direct detection. The principle of theroposed architecture is illustrated in Fig. 4. The op-ical line terminal (OLT) designed consists of N dis-ributed laser sources. One IM is employed to gener-te upconverted OFDM intensity-modulated signalsor WDM-OFDM downstream transmission. Theodulated data streams are orthogonal to each other

n the frequency domain, meaning that the cross talketween the subchannels is eliminated. OFDM base-and signals are upconverted to a high radio fre-uency (RF) carrier by an electrical mixer with an RFource. Since the spectrum bandwidth of the OFDM is

pstream signals. The resolution of the optical spectra is 0.01 nm.
d u

tlg7fabTwTftitptir2isdraTTn5c2cplHdr


small, a low RF source can be used to carry high-speedOFDM signals. For example, 10 GHz RF signals caneasily carry 10 Gbit/s 16-QAM OFDM signals. In theRN, one DEMUX is used to separate channels and de-liver to each ONU. The downstream signals are sentto two paths after passing through a 3 dB coupler.One part is fed to an OFDM receiver after passingthrough one narrowband optical filter (OF). This opti-cal filter is used to reduce the fading effects after itconverts double-sideband signals to single sideband.Without this filter, the power penalty will be large at acertain transmission distance due to a fading effect.For the upstream link, the downstream OFDM signalis remodulated by another IM. Consequently, the cen-tralized light wave is realized because there is no ad-ditional light source in the ONU.

The experimental setup is presented in Fig. 5. In

Fig. 4. (Color online) Principle of proposed WDM-OFDM-PON ar-chitecture. LO, local oscillator; OF, optical filter; IM, intensitymodulator; DS/US Rx, downstream/upstream receiver.)

Fig. 5. (Color online) Experimental setup of proposed new scheme.spectra and the electrical eye diagrams, which are at the correspon

he CO, one CW light wave was generated by a DFBaser at 1541.74 nm. An OFDM baseband signal wasenerated offline and uploaded into a Tektronix AWG102 arbitrary waveform generator (AWG). The wave-orms produced by the AWG were continuously outputt 10 Gsamples/s and 10 bits DAC, and the outputandwidth was 2.5 GHz based on the Nyquist law.he 16 QAM OFDM signals at 10 Gbits/s are mixedith a 10 GHz sinusoidal wave by an electrical mixer.he mixed RF signal is first electrically amplified be-

ore using it to drive an optical IM. The optical spec-rum with 0.01 nm resolution after the IM is shown innset (i) of Fig. 5. After 25 km SMF-28 transmission,he separated downstream traffic was divided into twoarts by a 3 dB optical coupler. One part is deliveredo the downstream OFDM receiver, and the other parts prepared for upstream signals. At the downstreameceiver, the WDM-OFDM signal was filtered by a5/50 GHz spaced optical interleaver (IL) with a pass-ng bandwidth of 0.2 nm, the spectrum is shown in in-et (ii) in Fig. 5. The received RF OFDM signal wasownconverted first and then sampled by a Tektronixeal-time oscilloscope (TDS6154C) at 10 Gsamples/sfter direct detection by a 45 GHz photodetector (PD).he digital signal processing work was done offline.he electrical spectra of the OFDM signal, the LO sig-al, and the mixed signals are exhibited in Figs.(a)–5(c), respectively. The mixed OFDM and local os-illator (LO) signals after intensity modulation and5 km SMF-28 are shown in Figs. 5(d) and 5(e). It islearly seen that the waveform of 16-quadrature am-litude modulation (QAM) OFDM optical signalooked like a return-to-zero-shaped CW optical signal.ence, it can be remodulated to carry the upstreamata. For the upstream link, the RF OFDM signal wasemodulated by an optical IM at a 1.75 Gbit/s data

(iii) Measured optical spectra �0.01 nm�. (a)–(e) Measured electricalg points (a)–(e) in the setup. IL, interleaver.

(i)–din

stDapvdsdstObfib(W

psC

Fts


rate with a PRBS length of 231−1. Figure 5(iii) showsthe optical spectrum for upstream signals before re-modulation. The BER curves and the correspondingconstellations of downstream 16-QAM intensity-modulated OFDM signals with and without an inter-leaver are exhibited in Fig. 6(a). Without an IL at thereceiver side, there is an obvious power penalty ofabout 2.5 dB after 25 km of SMF transmission. OneIL is used to filter out one sideband in order to studythe fading effects. After employing a 25/50 GHzspaced IL, there is no obvious power penalty aftertransmission. Therefore, the fading effect due todouble-sideband modulation leads to a 2.5 dB powerpenalty in this proposed architecture. However, usingIL to filter out one of the sidebands degrades receiversensitivity even in back-to-back transmission. TheBER of the back-to-back without IL has higher re-ceiver sensitivity, as more information from triplepeaks (baseband and the two first-order sidebands) isreceived by the receiver. Figure 6(b) illustrates themeasured BER curves and the corresponding eye dia-gram for upstream signals after transmission. It canbe clearly seen that the eye diagram is widely openedafter transmission. The power penalty is less than0.2 dB after transmission over 25 km of SMF-28 at aBER equal to 10−9.

C. Triple-Play Services Over DWDM-PON

In this subsection, a novel bidirectional DWDM-PON system using a single carrier-suppressed lightsource to provide download (DL), upload (UL), andvideo selectcast (VS) services simultaneously is pre-sented. The architecture for the novel bidirectionalDWDM-PON, which provides DL, UL, and VS ser-vices simultaneously with a single light source, is

Fig. 6. (Color online) Measured BER curves. (a) B–T–B and afteintensity-modulated OFDM signals at 10 Gbits/s with and without

hown in Fig. 7. In the CO, CWs are separated intowo parts by a power splitter. One part provides bothL and VS services based on pairs of carriers gener-ted by optical carrier suppression (OCS). The otherart of the CWs provides ONU carriers for UL ser-ices. Therefore, each CW can be used to carry threeifferent services to one ONU. For different ONUs,pecific VS signals are modulated onto correspondingifferent carriers. In the RN, a WDM demultiplexereparates the light waves for different ONUs and dis-ributes them to their destinations via SMFs. In theNUs, DL and VS signals are received after opticalandpass filters; carriers for UL are reflected, ampli-ed, and at the same time modulated with UL signalsy reflective semiconductor optical amplifiersRSOAs). UL signals are received in the CO after a

DM demultiplexer.

Figure 8 shows the experimental setup for the pro-osed novel bidirectional DWDM-PON system using aingle light source for DL, UL, and VS services. In theO, eight CWs are generated by eight DFB lasers at

km of SMF-28 and the corresponding constellations for 16-QAMIL. (b) After 25 km of SMF for a 1.75 Gbit/s upstream signal.

ig. 7. Schematic diagram for the bidirectional DWDM-PON sys-em using a single light source to provide DL, UL, and VS servicesimultaneously.

r 25an

52tOtsDcr10ttafB

Fcbt

FD


wavelengths 1555.1, 1555.9, 1556.7, 1557.5, 1558.3,1559.1, 1559.9, and 1560.7 nm. They are multiplexedby an AWG with 100 GHz spacing. The output of theAWG is split into two parts by a 50:50 optical powersplitter. The upper part goes through an OCS module.OCS is realized by a dual-arm LiNbO3 Mach–Zehndermodulator (MZM) driven by two complementaryclocks at the frequency of 25 GHz. Two subcarriers geta total power of 9 dBm and then are separated by a50/100 GHz interleaver into two groups; one group ismodulated by an external IM with 231−1 PRBS DLsignals at 10 Gbit/s. The other group of subcarriers ismodulated by another IM with 231−1 PRBS signals at2.5 Gbits/s to provide VS signals. All modulated lightwaves are combined by an optical coupler. On theother hand, the lower part of the CWs passes a vari-able optical attenuator (VOA) to match the powerlevel of the first part. There are 24 channels with a to-tal power of 12 dBm for transmission. Having trans-mitted over a 20 km SMF span, the 24 channels arefed into a 25/50 GHz interleaver. The 16 subcarriersgenerated after OCS with 50 GHz separation gothrough the same port of the interleaver and are thensplit by a 50:50 power splitter for receiving. Tunableoptical filter (TOFs) with a 3 dB bandwidth of 0.2 nmare used in the experiment to simulate an AWG andfixed bandpass filters for multi-ONUs in the architec-ture. For UL service, one of the eight CW light wavesis selected by a TOF and then reflected and modulatedby an RSOA. As UL signals, 1.25 Gbit/s PRBS signalswith a word length of 231−1 are directly modulatedonto the CW by the RSOA, which also amplifies theoptical power up to 2 dBm. The received optical spec-tra are illustrated in Fig. 9. Figure 9(a) shows theoriginal 8 CW channels multiplexed by the AWG, andFig. 9(b) shows 16 subcarriers generated by OCS. Thespacing between each two neighboring subcarriers is

Fig. 8. (Color online) The experimental setup for a novel bidirec-tional DWDM-PON system using a single light source for simulta-neous DL, UL, and VS services. LD, laser diode; PC, polarizationcontroller; DAM, dual-arm modulator; VOA, variable optical at-tenuator; IM, intensity modulator; CIR, circulator; IL, interleaver.

0 GHz with a carrier suppression ratio higher than5 dB. Figure 9(c) shows the complete spectrum of aotal of 24 channels for DL, UL, and VS. For eachNU, the spacing between VS and UL, as well as be-

ween UL and DL, is 25 GHz. A detailed spectrum ishown in Fig. 9(d); from left to right are VS, UL, andL light waves. Figure 10 shows the measured BER

urves. For DL service, after 20 km transmission, theandomly selected channels 1555.3, 1557.7, and560.9 nm suffer power penalties of approximately.5 dB, while for UL and VS services, after the sameransmission distance, the power penalties are lesshan 0.5 dB. Such results reside in the differencemong the bit rates. VS service has the best BER per-ormance, since a 2.5 Gbit/s 3R receiver is employed.ER performance shows negligible differences among

ig. 9. (Color online) Received optical spectra for (a) 8 original CWhannels, (b) 16 subcarrier channels generated by OCS, (c) the com-ination of 8 CWs and 16 modulated subcarrier channels, and (d)he detailed spectrum of the fourth group in (c).

ig. 10. (Color online) BER curves and eye diagrams for 10 Gbit/sL, 2.5 Gbit/s VS, and 1.25 Gbit/s UL transmission.

wPatnse�otutsimau�mflptpOtmtfia

pstOmLdsmnc(acsitnsdRut21


randomly selected channels, which means the archi-tecture is scalable over a wide band range.

III. SELF-PROTECTION IN WDM-PON

As data rates in the future WDM-PON access net-works are envisioned to reach 10 Gbits/s for both up-stream and downstream links, network reliability andsurvivability of such networks need to be addressedcarefully. Several schemes have been reported to real-ize protection and restoration functions for WDM-PONs [14–19]. We proposed and demonstrated a cen-trally managed self-survivable, bidirectional WDM-PON architecture [20] using the OCS [21] techniqueand a systematic, cyclic wavelength assignmentscheme to protect the upstream and downstream ser-vices for N ONUs, using only N units of laser diodes atthe CO in both working and protection modes. Thisself-survivable protection scheme detects and restoresall types of network failures at feeder/distribution fi-bers, AWG in RNs, and transmitters at the CO andONUs.

Figure 11 shows the proposed architecture and

Fig. 11. (Color online) (a) System architecture of the proposed self-survivable WDM-PON and (b) wavelength assignment for upstreamand downstream signals in the working and protection mode.

avelength assignment of the self-survivable WDM-ON network providing centralized light sources andprotection scheme for N ONUs in a bidirectional

ransmission system. At the CO, N wavelength chan-els ��1 . . .�N� are used to provide both the down-tream and upstream light sources for N ONUs. Forach �I �I=1. . .N�, two subcarrier channels (�ID andIU) are generated by the OCS technique. However,nly one OCS unit is used for N wavelength channelso generate their respective subcarrier channels. Wesed a clockwise wavelength sharing scheme amonghe ONUs to provide centralized light sources for up-tream and downstream directions in both the work-ng and the protecting modes. In the normal working

ode, the subcarrier channels �ID and �IU generatedt wavelength �I are used to provide downstream andpstream channels, respectively, for the Ith ONUONUI�, for I=1. . .N. However, in the protectionode, ONUI is served by the wavelength channel �I−1

or I=2. . .N, and for I=1, ONU1 is served by the wave-ength channel �N. After the OCS, the working androtection carriers designated to ONUI are fed intohe network unit controller �NUC-I�. NUC-I performsrotection switching and transceiver operation forNUI. At NUC-I, an optical switch is used to select

he appropriate wavelength channel based on theode of operation (working or protection) of ONUI, de-

ermined by the optical power monitor. An interleaverlter (IL) is used to separate the downstream (DS)nd upstream (US) carriers.

Figure 12 shows the experimental setup of the pro-osed WDM-PON system. At the CO, two CW DFB la-ers at 1541.45 nm ��1� and 1542.24 nm ��2� providehe upstream and downstream carrier signals forNU1 and ONU2 in both working and protectionodes. The CW signals are injected into a dual-driveiNbO3 MZM with V� of 3.0 V. The modulator isriven by a pair of 12.5 GHz complementary RF sinu-oidal signals. Once the MZM is biased at the trans-ission null, the optical carrier of the injected CW sig-

als are suppressed, and two pairs of subwavelengthhannels ��1d ,�1u� and ��2d ,�2u� are generated. Insetsa) and (b) of Fig. 12 show the optical spectra beforend after the OCS. The separation between two sub-hannels at each wavelength is 25 GHz, and a carrieruppression ratio of over 30 dB is achieved. An opticalnterleaver �ILa� with 25 GHz channel spacing is usedo separate the upstream and downstream subchan-els before modulation at the CO, and 100 GHzpaced interleavers (IL1, IL2, IL3) are used to separateistinct wavelength channels �1 and �2 at the CO andN. A 2�1 electromechanical optical switch (SW) issed as a protection switch. The transmission dis-ance between the CO and the ONU is 20 km (SMF-8). Each downstream and upstream channel carries0 Gbit/s data with a PRBS word length of 231−1. In-

dtrttad

A

fFaRtRbuss1ipellawid


set (c) of Fig. 12 shows the optical spectra of the10 Gbit/s DS signals and the unmodulated upstreamcarrier signals, and inset (d) of Fig. 12 shows the sepa-rated upstream and downstream channels at theONU. The insertion loss at the CO is compensated byplacing an additional optical amplifier after IL2. Thelaunching power per wavelength channel is set to3 dBm in the downstream direction. The channelspacing of IL3 at the ONU is 50 GHz, and the 3 dBbandwidth of the TOF is 0.21 nm. Figure 13 shows theBER and the eye diagrams of the downstream and up-stream signals. At a 10−10 BER, the power penalties ofthe 10 Gbit/s downstream and upstream channel areless than 0.7 and 1.2 dB, respectively, after 20 km bi-

Fig. 12. (Color online) Experimental setup of WDM-PON test

Fig. 13. (Color online) BER measurements and optical eye dia-grams at various points in the WDM-PON testbed: (a) 10 Gbit/sdownstream, (b) 10 Gbit/s upstream.

irectional transmission both in working and protec-ion modes. The power penalties are due mainly to theesidual fiber chromatic dispersion and cascaded fil-ering effects at the CO, RN, and ONU. The upstreamransmission suffers an additional 1.5 dB power pen-lty compared with the downstream. This could beue to the unwanted reflections at the circulators.

IV. LONG-REACH TRANSMISSION FOR WDM-PON

. Impairment Mitigation for Rayleigh Backscattering

WDM-PON using single-fiber architecture may suf-er from impairments due to unavoidable RB andresnel backreflections, which could be even worse inlong-reach scenario. Several methods to mitigate theB effects have been proposed [22–25]. However,

hese schemes either cannot completely eliminate theayleigh carrier backscattering and Rayleigh signalackscattering or require additional light sources forpstream carriers or separate fiber links for down-tream and upstream signals. Therefore, we propose aimple architecture to realize an RB-noise-eliminated,15 km long-reach, single-fiber, full-duplex, central-zed WDM-PON system [26]. Figure 14 shows the ex-erimental setup of the proposed long-reach, RB-liminated WDM-PON system. At the CO, a DFBaser is used to generate the CW light wave at a wave-ength of 1546.172 nm. The optical signal is fed inton optical PM, driven by 10 Gbit/s downstream dataith a PRBS length of 231−1. The downstream signal

s then transmitted to the ONU over 115 km of stan-ard SMF (SMF-28) via the local exchange (LE) and

using a centralized light source and protection for two ONUs.
bed

tO1c2Totrtsabdlat12aSmsaaf


the RN. The LE is situated 100 km from the CO andconsists of two erbium-doped fiber amplifiers (EDFAs)in a bidirectional fashion. An AWG is used as the RN,which is placed right after the LE. A dispersion com-pensation fiber (DCF) module with total dispersion of1760 nm/ps is used at the CO to compensate for thedispersion generated by the long-reach distribution fi-ber between the CO and the LE. The injection powerof the DS signal at the dispersion compensation fiberand after the LE is set to 3 dBm in both positions. Atthe ONU, the odd port of a 25 GHz optical IL with afree spectral range of 100 GHz is used to pass theDPSK downstream traffic. The IL is realized by cas-cading one 25/50 GHz and another 50/100 GHz opti-cal interleaver. A 3 dB optical coupler (OC) is used totap 50% of the DPSK DS signal, which is later re-ceived by using a differential interferometer delay de-modulator and a PIN receiver. The remaining 50% ofthe DS signal is remodulated by a 10 GHz lithium nio-bate IM with V� of 3.4 V in order to carry the up-stream data. The optical carrier-suppressed subcar-rier modulation (OCS-SCM) of 2.5 Gbit/s upstreamdata with a PRBS length of 231−1 is realized at the15 GHz subcarrier frequency. Figure 15(a) shows theoptical spectra before and after the remodulation atthe IM and the upstream signal after passing through

Fig. 14. (Color online) Experimental setup of the proposed lon2.5 Gbit/s upstream signals.

Fig. 15. Optical spectra at ONUI and the CO, depicting the remodlution of 0.01 nm).

he even port of the IL. It is shown that, after theCS-SCM, the original carrier at wavelength546.172 nm is suppressed over 15 dB, and two sub-arriers with a separation of 30 GHz and carrying.5 Gbit/s upstream data are generated. At the CO, aOF with 3 dB bandwidth of 0.21 nm is used insteadf another IL to separate the upstream signal fromhe accumulated RB and reflection noise before it iseceived by a regular PIN receiver. Figure 15(b) showshe optical spectra before and after the TOF. It is ob-erved that the RB and backreflections accumulatedt the original carrier �1546.172 nm� are filtered outy the TOF. We measured the BER and optical eyeiagrams of both the downstream and the remodu-ated upstream signal before and after transmission,s shown in Fig. 16. The eyes are open with a good ex-inction ratio. At a 10−10 BER, the power penalty of0 Gbit/s DPSK downstream and remodulated.5 Gbit/s OCS-SCM upstream signal is less than 0.5nd 1.9 dB, respectively, after 115 km of bidirectionalMF-28 transmission. The power penalties are causedainly by the filtering effects at the ONU and CO, re-

idual dispersion of the remodulated signal, and theccumulated amplified spontaneous emission noise atmplifiers. When the upstream signal is separatedrom the reflected phase-modulated signal using the

ach WDM-PON with 10 Gbit/s downstream and RB-eliminated

tion of the DPSK downstream signal to carry upstream data (reso-

g-re

ula

mwmNRfctwvcwcd(debla1sewbtat


optical filter, part of the phase signal is converted toan intensity signal, thus contributing to the addi-tional cross talk as seen from some fluctuation in “1s”in the back-to-back (b2b) eye diagram of the US sig-nals.

B. Extended Reach for 60 GHZ RoF

RoF technology operating on an unlicensed 60 GHzband can be easily integrated with WDM-PON to si-

Fig. 16. (Color online) Measured BER and optical eye diagrams ofthe 10 Gbit/s downstream signal and remodulated 2.5 Gbit/s up-stream signal.

Fig. 17. (Color online) Scheme for generation

ultaneously transport multichannel, multigigabitireless and wired signals as last miles and lasteters solutions for in-building applications [27].onetheless, the transmission distance for a 60 GHzoF system is only a few tens of kilometers, resulting

rom the time shifting of the codes caused by fiberhromatic dispersion. Such a short propagation dis-ance will limit the applications of an RoF system asell as increase the deployment cost. Recently, we de-eloped and experimentally demonstrated a novel ar-hitecture of a long-reach WDM 60 GHz millimeter-ave (mm-wave) RoF system, which can transmit 8

hannels with 2.5 Gbit/s hybrid wired and wirelessata over 125 km of standard single-mode fiberSSMF) by using a remote OCS technique without anyispersion compensation [28]. Figure 17 shows thexperimental setup for a long-reach WDM 60 GHzand RoF access network. At the CO, eight narrowinewidth optical carriers from eight tunable laserst wavelengths from 1554.908 to1560.508 nm with00 GHz spacing were used as the optical sources, ashown in inset (a) of Fig. 17. The eight optical carri-rs, followed by separate polarization controllers,ere coupled together by an AWG and then modulatedy a 2.5 Gbit/s PRBS with a word length of 231−1. Af-er being transmitted over 100 km of SMF, the gener-ted 8�2.5 Gbit/s signals were fed into an LE andhen amplified by an EDFA. In order to upconvert

60 GHz millimeter wave by using PM and IL.
of

bpg1isFcdtwrc

wiflUoamscas

DwucpbnreFtswpaat(s6c

osw


baseband data to 60 GHz millimeter-wave, a OCS for-mat was achieved by a dual-arm MZM biased at V� of2.1 V and driven by two complementary 30 GHzclocks, which were generated by a 1:4 frequency mul-tiplier and 7.5 GHz clock source. The optical spectrumof eight channels after upconversion is shown in Fig.17 as inset (b). The separation between two subcarri-ers at each channel is 60 GHz �0.48 nm�, and a carriersuppression ratio of about 20 dB was achieved. Asshown in Fig. 17, we also demonstrated another wayto generate a 60 GHz millimeter-wave: downstreamdata was injected into a PM, which was driven by a30 GHz RF clock and formed a carrier suppression of20 dB by adjusting the amplitude of the clock, andthen a 50/200 IL was utilized to filter out the un-wanted sidebands. The optical spectra before and af-ter the IL are shown in Fig. 17 as insets (i) and (ii),respectively. After upconversion, one of eight channelsat 1557.508 nm was filtered with an AWG before beingtransmitted over 25 km of SMF to the base station(BS). Inset (c) of Fig. 17 clearly shows the relationshipbetween modulated signals and the passband of oneport of the AWG. The optical spectrum after the AWGis shown in Fig. 17 as inset (d). At the BS, the wiredsignals are directly detected by a compact 2.5 Gbit/sreceiver with 3R function, which can filter out thehigh-frequency millimeter-wave part. On the otherhand, for wireless transmission, optical-to-electricalconversion was completed by a 60 GHz bandwidthPIN photodiode. After photodetection, the downlinksignal was amplified by an electrical amplifier (EA)and then downconverted to baseband form. Basebanddata was retrieved by mixing the converted electricalsignal with a 60 GHz LO signal, which was generated

Fig. 18. (Color online) BER curves of wired and wirelesstransmission.

y a 15 GHz clock signal and a 1:4 frequency multi-lier. For wireless transmission, the optical eye dia-rams of millimeter-wave signals after 100 and25 km of SMF transmission are shown in Fig. 18. Its seen that the eye diagram after 125 km transmis-ion has more distortion but is still clear and open.igure 18 also shows the measured BER curves andorresponding eye diagrams for wired and wirelessata. The power penalties at the given BER of 10−9 af-er 125 km transmission are about 0.5 and 1.4 dB forired and wireless data, respectively. The penalties

esult from the chromatic dispersion for the two sub-arriers with 60 GHz spacing.

V. CONVERGENCE BETWEEN ROF AND WDM-PON INLOCAL AND METRO ACCESS

Wavelength-selective switch (WSS)-based ROADMith a low-cost configuration is expected to be compat-

ble with DWDM optical-wireless networks to supportexible optical routing in optical-wireless networks.sing the flexibility offered by ROADMs, the number

f BSs sharing a wavelength channel can be adapted,nd thus the available capacity per BS can be tuned toatch its traffic demands. For example, when a hot

pot with high traffic load emerges, the respective BSan provide an extra millimeter-wave carrier as soons another wavelength channel is directed to this hotpot via remote software control in ROADMs [29–31].

Figure 19 depicts the experimental setup forWDM optical-wireless signals over an optical linkith 12 cascaded WSSs. At the CO, one laser array issed to generate eight wavelength signals with adja-ent 100 GHz spacing. We employ an AWG to multi-lex the eight light waves before they are modulatedy a LiNbO3 MZM. We mix 2.5 Gbit/s electrical sig-als with a 20 GHz sinusoidal wave to realize subcar-ier miltiplexing (SCM) for the wireless signals. Theye diagram of mixed electrical signals is shown inig. 19, inset (i). The transmission is performed

hrough six ROADM (two WSSs in one ROADM ashown in Fig. 19) nodes and four 40 km LEAF fibersith a dispersion coefficient of 4.5 ps nm/km. The out-ut power of each EDFA in the transmission link isround 8 dBm. The insertion loss of each WSS isround 4.5 dB for all the wavelengths. The cumula-ive filtering shape of WSSs is shown in Fig. 19, insetii). After transmission over 160 km LEAF, the disper-ion compensation fiber with a total dispersion of94 ps and 10 dB loss is used to compensate for fiberhromatic dispersion.

At the BS, a 50/25 GHz optical interleaver with twoutputs is used to separate the optical carrier and theubcarriers. Compared with the optical millimeter-ave signals without cascaded WSSs, high-order side-


Fig. 19. (Color online) Experimental setup for 8�2.5 Gbit/s WDM optical-wireless signals in 12 cascaded WSSs links.

Fig. 20. (Color online) Optical spectra evolution to generate RoF-WDM-PON channels.

saoswtvtauaonm


bands are filtered out while first-order sidebands arekept intact after passing through 12 WSSs. The un-even spectrum arises from the smaller gain accumu-lation at long wavelengths in multiple EDFAs. Theevolution of optical spectra for all the channels alongthe optical links is shown in Fig. 20. It is noted thatthe carrier is suppressed more than 20 dB.

VI. CONCLUSION

We have demonstrated several key technologies in-cluding the techniques for longer reach, higher datarate, and higher spectral efficiency in advancingWDM-PON systems for future broadband optical ac-cess to the end users. In new modulation formats, anovel WDM-OFDM-PON transmission system withcentralized light wave and direct detection for down-stream 16-QAM intensity-modulated OFDM at10 Gbits/s and uplink 1.75 Gbit/s remodulated on–offkeying (OOK) signals is demonstrated. The fading ef-fects from double-sideband signals lead to a 2.5 dBpower penalty in this architecture. However, the fad-ing effect is removed when the double-sidebandOFDM downstream signals are converted to singlesideband after shape filtering. The power penalty isnegligible for both single-sideband OFDM down-stream and the remodulated OOK upstream signalsafter more than 25 km of standard SMF transmission.Because OFDM is an effective modulation format fora next-generation optical network, this proposedscheme can provide significant improvement in bothsystem reliability and flexibility. Again a spectrally ef-ficient 25 GHz spaced DWDM-PON system is demon-strated for 10 Gbit/s DPSK downstream and remodu-lated 10 Gbit/s duobinary upstream signals based onan optical IL and wavelength-reusable technique. Theproposed scheme can support more wavelength-specific application to more users in a cost-effectivemanner. In addition, we demonstrated a bidirection-al DWDM-PON system using a single carrier-suppressed light source to provide triple-play servicesof downlink, uplink, and video services simulta-neously. The cost-efficient architectures are designedfor single-source systems and resilient protectionfor traffic restoration. We proposed and experimen-tally demonstrated a centrally protected, bidirec-tional, WDM-PON system that detects and restoresgeneric failures of feeder and distribution fibers, fail-ure of RN components, and failure of transmitters atthe central office. Reduction of Rayleigh backscatter-ing noise is critical in bidirectional single-fiber WDM-PON systems. We proposed a long-reach, bidirec-tional, centralized WDM-PON, where, elimination ofRB noise and Fresnel reflection noise is performed byusing an OCS-SCM technique of upstream signal atthe ONU and an optical IL at the ONU and CO. This

imple RB noise-reduction technique can facilitatechieving a longer optical transmission distance ofver 125 km in the full-duplex single-fiber WDM-PONystem. Finally, we developed the integrated schemesith an RoF-based optical-wireless WDM-PON sys-

em to serve both fixed and mobile users in the con-erged optical platform. The longer transmission dis-ance in such an RoF-based WDM-PON system ischieved by using simultaneous multichannel remotepconversion of 60 GHz millimeter-wave radio signalst the LE station. In addition, the transport feasibilityf superbroadband optical wireless WDM-PON sig-als over flexible WSS-based ROADM nodes is experi-entally demonstrated.

REFERENCES

[1] L. G. Kazovsky, W.-T. Shaw, D. Gutierrez, N. Cheng, and S.-W.Wong, “Next-generation optical access networks,” J. LightwaveTechnol., vol. 25, no. 11, pp. 3428–3442, Nov. 2007.

[2] R. Bavey, J. Kani, F. Bourgart, and K. McCammon, “Optionsfor future optical access networks,” IEEE Commun. Mag., vol.44, no. 10, pp. 50–56, Oct. 2006.

[3] C. Bock, J. Prat, and S. D. Walker, “Hybrid WDM/TDM PONusing the AWG FSR and featuring centralized light generationand dynamic bandwidth allocation,” J. Lightwave Technol., vol.23, no. 12, pp. 3981–3988, Dec. 2005.

[4] T. Koonen, “Fiber to the home/fiber to the premise: what,where, and when?,” Proc. IEEE, vol. 94, no. 5, pp. 911–934,May 2006.

[5] G.-K. Chang, Z. Jia, J. Yu, and A. Chowdhury, “Super broad-band optical wireless access technologies,” in Optical FiberCommunication Conf. and Expo. and The Nat. Fiber Optic En-gineers Conf., San Diego, CA, OSA Technical Digest (CD),Washington, DC: Optical Society of America, Feb. 24, 2008, pa-per OThD1.

[6] W. Hung, C.-K. Chan, and F. Tong, “An optical network unit forWDM access networks with downstream DPSK and upstreamremodulated OOK data using injection locked FP laser,” IEEEPhoton. Technol. Lett., vol. 15, no. 10, pp. 1476–1478, 2003.

[7] L. Xu and H. K. Tsang, “Differential phase shift keying forasynchronous upstream remodulation of dark return-to-zerodownstream channel,” in Optical Fiber Communication Conf.and Expo. and The Nat. Fiber Optic Engineers Conf., San Di-ego, CA, OSA Technical Digest (CD), Washington, DC: OpticalSociety of America, Feb. 24, 2008, paper OWH6.

[8] C. W. Chow, Y. Liu, and C. H. Kwok, “Signal remodulation withhigh extinction ratio 10-Gbps DPSK signal for DWDM-PONs,”in Optical Fiber Communication Conf. and Expo. and The Nat.Fiber Optic Engineers Conf., San Diego, CA, OSA Technical Di-gest (CD), Washington, DC: Optical Society of America, Feb.24, 2008, paper OThT2.

[9] A. Chowdhury, H. C. Chien, and G. K. Chang, “Centralized,colorless, wavelength reusable 25 GHz spaced DWDM-PONwith 10 Gbps DPSK downstream and re-modulated 10 Gbpsduobinary upstream for next-generation local access system,”in 34th European Conference on Optical Communication, 2008.ECOC 2008, Brussels, Belgium, Sept. 21–25, 2008, paperWe.3.F.4.

[10] D. Qian, J. Yu, J. Hu, L. Zong, L. Xu, and T. Wang, “8�11.5-Gbps OFDM transmission over 1000 km SSMF usingconversional DFB lasers and direct-detection,” in Optical FiberCommunication Conf. and Expo. and The Nat. Fiber Optic En-gineers Conf., San Diego, CA, OSA Technical Digest (CD),

NtGSwvpdETGDoGBaetmlgp


Washington, DC: Optical Society of America, Feb. 24, 2008, pa-per OMM3.

[11] J. Yu, M. F. Huang, D. Qian, L. Chen, and G. K. Chang, “Cen-tralized lightwave WDM-PON employing 16-QAM intensitymodulated OFDM downstream and OOK modulated upstreamsignals,” IEEE Photon. Technol. Lett., vol. 20, no. 18, pp. 1545–1547, 2008.

[12] B. J. Schmidt, A. J. Lowery, and J. Armstrong, “Experimentaldemonstration of 20 Gbps direct-detection optical OFDM and12 Gbps with a colorless transmitter,” in Optical Fiber Com-munication Conf. and Expo. and The Nat. Fiber Optic Engi-neers Conf., Anaheim, CA, OSA Technical Digest Series (CD),Washington, DC: Optical Society of America, March 25, 2007,paper PDP18.

[13] D. Qian, J. Hu, P. N. Ji, and T. Wang, “10 Gbps OFDMA-PONfor delivery of heterogeneous services,” in Optical Fiber Com-munication Conf. and Expo. and The Nat. Fiber Optic Engi-neers Conf., San Diego, CA, OSA Technical Digest (CD), Wash-ington, DC: Optical Society of America, Feb. 24, 2008, paperOWH4.

[14] X. Sun, C. Chan, and L. Chen, “Survivable WDM-PON archi-tecture with centralized alternate-path protection switchingfor traffic restoration,” IEEE Photon. Technol. Lett., vol. 18, no.4, pp. 631–633, Feb. 2006.

[15] Z. Wang, X. Sun, C. Lin, C. Chan, and L. Chen, “A novel cen-trally controlled protection scheme for traffic restoration inWDM passive optical networks,” IEEE Photon. Technol. Lett.,vol. 17, no. 3, pp. 717–719, March 2005.

[16] C. Sue, “A novel 1:N protection scheme for WDM passive opti-cal networks,” IEEE Photon. Technol. Lett., vol. 18, no. 13, pp.1472–1774, July 2006.

[17] T. Chan, C. Chan, L. Chen, and F. Tong, “A self-protected ar-chitecture for wavelength-division-multiplexed passive opticalnetworks,” IEEE Photon. Technol. Lett., vol. 15, no. 11, pp.1660–1662, Nov. 2003.

[18] B. Zhang, C. Chan, and C. Lin, “A survivable WDM passive op-tical network with colorless optical network units,” in 11th Op-toelectronics and Communications Conf. (OECC), Kaohsiung,Taiwan, July 3–7, 2006, paper 5E2-2-1.

[19] S. Park, D. K. Jung, D. J. Shin, H. S. Shin, S. Hwang, Y. J. Oh,and C. S. Shim, “Bidirectional wavelength-division-multiplexing self-healing passive optical network,” in OpticalFiber Communication Conf. and Expo. and The Nat. Fiber Op-tic Engineers Conf., Anaheim, CA, Technical Digest (CD), Op-tical Society of America, March 6, 2005, paper JWA57.

[20] A. Chowdhury, M. F. Huang, H. C. Chien, G. Ellinas, and G. K.Chang, “A self-survivable WDM-PON architecture with cen-tralized wavelength monitoring, protection and restoration forboth upstream and downstream links,” in Optical Fiber Com-munication Conf. and Expo. and The Nat. Fiber Optic Engi-neers Conf., San Diego, CA, OSA Technical Digest (CD), Wash-ington, DC: Optical Society of America, Feb. 24, 2008, paperJThA95.

[21] O. Akanbi, J. Yu, and G. K. Chang, “A new scheme for bidirec-tional WDM-PON using upstream and downstream channelsgenerated by optical carrier suppression and separation tech-nique,” IEEE Photon. Technol. Lett., vol. 8, no. 2, pp. 340–342,2006.

[22] T. Yoshida, S. Kimura, H. Kimura, K. Kumozaki, and T. Imai,“A new single-fiber 10-Gbps optical loopback method usingphase modulation for WDM optical access networks,” J. Light-wave Technol., vol. 24, no. 2, pp. 786–796, 2006.

[23] C. W. Chow, G. Talli, and P. D. Townsend, “Rayleigh noise re-duction in 10-Gbps DWDM-PONs by wavelength detuning andphase-modulation-induced spectral broadening,” IEEE Photon.Technol. Lett., vol. 19, no. 6, pp. 423–425, 2007.

[24] J. A. Lazaro, C. Arellano, V. Polo, and J. Prat, “Rayleigh scat-tering reduction by means of optical frequency dithering in

passive optical networks with remotely seeded ONUs,” IEEEPhoton. Technol. Lett., vol. 19, no. 2, pp. 64–66, 2007.

[25] H. H. Lin, C. Y. Lee, S. C. Lin, S. L. Lee, and G. Keuser,“WDM-PON systems using cross-remodulation to double net-work capacity with reduced Rayleigh scattering effects,” in Op-tical Fiber Communication Conf. and Expo. and The Nat. FiberOptic Engineers Conf., San Diego, CA, OSA Technical Digest(CD), Washington, DC: Optical Society of America, Feb. 24,2008, paper OTuH6.

[26] A. Chowdhury, H. C. Chien, M. F. Huang, J. Yu, and G. K.Chang, “Rayleigh backscattering noise-eliminated 115-kmlong-reach bidirectional centralized WDM-PON with 10-GbpsDPSK downstream and remodulated 2.5-Gbps OCS-SCM up-stream signal,” IEEE Photon. Technol. Lett., vol. 20, no. 24, pp.2081–1083, Dec. 2008.

[27] J. J. V. Olmos, T. Kuri, and K. Kitayama, “Dynamic reconfig-urable WDM 60-GHz millimeter-waveband radio-over-fiber ac-cess network: architectural considerations and experiment,” J.Lightwave Technol., vol. 25, no. 11, pp. 3374–3380, Nov. 2007.

[28] Y.-T. Hsueh, H.-C. Chien, Z. Jia, A. Chowdhury, J. Yu, andG.-K. Chang, “8�2.5-Gbps, 60-GHz radio-over-fiber accessnetwork with 125-km extended reach using remote optical car-rier suppression,” in 21st Annu. Meeting of the IEEE Lasersand Electro-Optics Society, 2008. LEOS 2008, Acapulco,Mexico, Nov. 9–13, 2008, paper ThN3.

[29] C. Lim, A. Nirmalathas, D. Novak, and R. Waterhouse, “Capac-ity analysis for WDM fiber-radio backbones with star-tree andring architecture incorporating wavelength interleaving,” J.Lightwave Technol., vol. 21, no. 12, pp. 3308–3314, Dec. 2003.

[30] J. C. Attard and J. E. Mitchell, “Optical network architecturesfor dynamic reconfiguration of full-duplex, multi-wavelength,radio over fiber,” J. Opt. Netw., vol. 5, no. 6, pp. 435–444, June2006.

[31] Z. Jia, J. Yu, and G.-K. Chang, “A full-duplex radio-over-fibersystem based on optical carrier suppressing and reuse,” IEEEPhoton. Technol. Lett., vol. 18, no. 16, pp. 1726–1728, Aug.2006.

Gee-Kung Chang (F’05) received his Bach-elor’s degree in physics from the NationalTsinghua University, Taiwan, and his Mas-ter’s and Ph.D. degrees in physics from theUniversity of California, Riverside. He de-voted a total of 23 years of service to BellSystems—Bell Labs, Bellcore, and TelcordiaTechnologies, where he served in various re-search and management positions, includ-ing Director and Chief Scientist of OpticalInternet Research, Director of the Optical

etworking Systems and Testbed, and Director of the Optical Sys-em Integration and Network Interoperability. Prior to joiningeorgia Tech, he served as Vice President and Chief Technologytrategist of OpNext, Inc., a spinoff of Hitachi Telecom, where heas in charge of technology planning and product strategy for ad-anced high-speed optoelectronic components and systems for com-uting and communication systems. He is currently the Byers En-owed Chair Professor in Optical Networking in the School oflectrical and Computer Engineering of the Georgia Institute ofechnology (Georgia Tech), Atlanta. He is an Eminent Scholar of theeorgia Research Alliance. He serves as the leader and Associateirector of the Optoelectronics Integration and Packaging Alliance

f the NSF-funded ERC Microsystem Packaging Research Center ateorgia Tech. He is also an Associate Director of the Georgia Techroadband Institute. He has been granted 40 U.S. patents in thereas of optoelectronic devices, high-speed integrated circuits, opto-lectronics switching components for computing and communica-ion systems, WDM optical networking elements and systems,ulti-wavelength optical networks, optical network security, optical

abel switching routers, and optical interconnects for next-eneration servers and computers. He has coauthored over 230eer-reviewed journal and conference papers. Dr. Chang received

borlthap

mtpt

FntlmtNATcpeLtwaJMitt


the Bellcore President’s Award in 1994 for his leadership role in theOptical Networking Technology Consortium. He won the R&D 100Award in 1996 for his contribution to the Network Access Module.He was elected as a Telcordia Fellow in 1999 for pioneering work inthe optical networking project, MONET, and NGI. He became a Fel-low of the Photonic Society of Chinese–Americans in 2000. He is aFellow of the IEEE Lasers and Electro-Optics Society (LEOS) and aFellow of the Optical Society of America (OSA) for his contributionsto DWDM optical networking and label switching technologies. Hehas been serving on many IEEE LEOS and OSA conferences andcommittees. He has served three times as the lead Guest Editor forspecial issues of the Journal of Lightwave Technology sponsored byIEEE LEOS and the OSA. The first issue was published in Decem-ber 2000 on Optical Networks, the second one in November 2004 onMetro and Access Networks, and a third one in 2007 on Conver-gence of Optical Wireless Access Networks.

Arshad Chowdhury (M’07) received hisB.S in computer science and engineeringfrom Bangladesh University of Engineeringand Technology, Dhaka, Bangladesh in 1995and his M.S in computer engineering fromWright State University, Dayton, OH, USA,in 1999. He received his Ph.D. degree inelectrical and computer engineering fromthe Georgia Institute of Technology, At-lanta, Georgia, USA, in 2006. From 1999 to2002, he worked as a Research Scientist in

the Optical Internetworking Research division at Telcordia Tech-nologies, Red Bank, New Jersey, where he was actively involvedwith DARPA-initiated Next-Generation Internet (NGI) optical labelswitching (OLS) and ATD/MONET. He is currently working as a Re-search Engineer and managing the Optical Network ResearchLaboratory in the School of Electrical and Computer Engineering atthe Georgia Institute of Technology. His research interests includeoptical wireless radio-over-fiber convergence, optical packetswitched (OPS) networks using optical label switching technology,next-generation TDM/WDM access systems, spectral efficientmodulation formats and ultrahigh data rate �10 Gbit/s� opticaltransmission systems, and optical-wireless interconnections forhigh-speed computing and server systems. He has been granted 15U.S. patents on optical layer survivability, optical multicasting, andswitching as coinventor and three other pending patents on radio-over-fiber and PON systems.

Zhensheng Jia (S’06) received his B.E.and M.S.E degrees in physical electronicsand optoelectronics from Tsinghua Univer-sity, Beijing, China, in 1999 and 2002, re-spectively, and his Ph.D. degree in the fieldof superbroadband optical-wireless accessnetworks from the Georgia Institute ofTechnology, Atlanta, Georgia, in 2008. From2002 to 2004, he worked as a Research En-gineer on transport and access networks inthe Optical System and Network Lab,

China Telecom Beijing Research Institute (CTBRI), where he wasresponsible for DWDM systems over ultralong-haul optical links inChina Telecom’s optical backbone networks. Currently, Dr. Jia isworking on architecture design of core optical networks, RF/wireless photonic signal processing, and component design andsimulation as a Senior Research Scientist in Telcordia Technologies.Dr. Jia has been author or coauthor of over 70 peer-reviewed journalarticles and conference papers. He also serves as an active reviewerfor many technical publications. Dr. Jia was one of the recipients ofthe 2007 IEEE/LEOS Graduate Students Fellowship Award and2008 PSC Bor-Uei Chen Memorial Scholarship Award.

Hung-Chang Chien (M’06) received hisB.S and M.S in electrical engineering fromNational Chung Cheng University, Taiwan,in 1999 and 2001, respectively, and hisPh.D. in electro-optical engineering fromNational Chiao Tung University, Taiwan, in2006. He is currently working as a ResearchEngineer in the School of Electrical andComputer Engineering, Georgia Institute ofTechnology, Atlanta, Georgia, USA. His re-search interests include millimeter-wave-

and radio-over-fiber system, next-generation TDM/WDM passiveptical networks, in-building distributed antenna systems, fibering lasers, and all-optical signal regeneration using injection-ocked laser diodes. Dr. Chien has authored and coauthored morehan 60 peer-reviewed journal articles and conference papers. Heas been granted one U.S. patent on all-optical signal regenerationnd has two other pending patents on radio-over-fiber systems andassive optical networks.

Ming-Fang Huang (S’04) received her B.S.degree in physics from Tamkang University,Taipei, Taiwan, in 2001 and her M.S. andPh.D degrees in electro-optical engineeringfrom National Chiao Tung University, Hsin-chu, Taiwan, in 2003 and 2007, respectively.She is currently working as a Research En-gineer at the School of Electrical and Com-puter Engineering, Georgia Institute ofTechnology, Atlanta, Georgia. Her currentresearch interests include long-haul trans-

ission, enabling technologies for 100 Gb/s WDM transmission, op-ical packet-switched techniques, wavelength-division multiplexingassive optical networks (WDM-PONs), and radio-over-fiber sys-ems.

Jianjun Yu (M’03–SM’04) received his B.Sdegree in optics from Xiangtan University,Hunan, China, in June 1990, and his M.E.and Ph.D. degrees in electrical engineeringfrom the Beijing University of Posts andTelecommunications, Beijing, China, inApril 1996 and January 1999, respectively.From June 1999 to January 2001, heworked at the Research Center COM, Tech-nical University of Denmark, Lyngby, Den-mark, as an Assistant Research Professor.

rom February 2001 to December 2002, he worked for Lucent Tech-ologies and Agere Systems, New Jersey, USA, as a member of theechnical staff. He joined the Georgia Institute of Technology, At-anta, Georgia, in January 2003, where he was a research faculty

ember and served as the Director of the Optical Network Labora-ory. He is currently a Senior Member of the Technical Staff withEC Laboratories America, Princeton, New Jersey. He is also andjunct Professor and Ph.D. supervisor at the Georgia Institute ofechnology and the Beijing University of Posts and Telecommuni-ations. As the first author, he has more than 100 publications inrestigious journals and conferences. He is the holder of 3 U.S. pat-nts with 20 others pending. Dr. Yu is a Senior Member of the IEEEasers and Electro-Optics Society (LEOS). He served as a guest edi-or for a special issue, “Convergence of optical and wireless net-orks,” for the IEEE and OSA Journal of Lightwave Technology andspecial issue “Radio-over-fiber-optical networking” for the OSA

ournal of Optical Networking. He was a Technical Committeeember (TPC) of the IEEE LEOS 2005–2007 annual meeting and

s now serving as a TPC of OFC 2009–2010. He is an Associate Edi-or for the Journal of Lightwave Technology and the Journal of Op-ical Communications and Networking.

nwwNpniilnh


Georgios Ellinas (M’89-SM’07) holds B.S.,M.S., M.Phil., and Ph.D. degrees in electri-cal engineering from Columbia University.He is currently an Assistant Professor ofElectrical and Computer Engineering at theUniversity of Cyprus. Prior to joining theUniversity of Cyprus, he was an AssociateProfessor of Electrical Engineering at theCity College of the City University of NewYork (2002–2005). Before joining academia,he was a Senior Network Architect at Tel-

lium (2000–2002) and a Senior Research Scientist in Telcordia Tech-

ologies’ (formerly Bellcore) Optical Networking Research Group,here he performed research for the DARPA-funded Optical Net-orks Technology Consortium (ONTC), Multiwavelength Opticaletworking (MONET), and Next Generation Internet (NGI)rojects from 1993 to 2000. He has coauthored two books on opticaletworking and more than 100 journal and conference papers and

s also the holder of 29 patents on optical networking. His researchnterests are in the areas of optical architectures, routing and wave-ength assignment algorithms, fault protection–restoration tech-iques in arbitrary mesh optical networks, optical access networks,ybrid optical-wireless access networks, and complex networks.

Key Technologies of WDM-PON for Future Converged Optical Broadband Access Networks [Invited]

Documents