Radio Optico

JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 26, NO. 15, AUGUST 1, 2008 2653

Simultaneous Generation of Centralized Lightwavesand Double/Single Sideband Optical Millimeter-Wave

Requiring Only Low-Frequency Local OscillatorSignals for Radio-Over-Fiber Systems

Ming-Fang Huang, Student Member, IEEE, Jianjun Yu, Senior Member, IEEE, Zhensheng Jia, Student Member, IEEE,and Gee-Kung Chang, Fellow, IEEE

Abstract—We have designed and experimentally demonstratedradio-over-fiber (ROF) systems to simultaneously generate opticalmillimeter-wave (mm-wave) and centralized lightwaves using onelow-bandwidth intensity modulator (IM) with low-frequency localoscillator (LO) signals while simplifying the transmission designand reducing the cost of the base station (BS). The techniques basedon double-sideband (DSB) and single-sideband (SSB) signals forROF systems are discussed in detail in terms of architecture ef-ficiency, bandwidth requirement, and fiber transmission perfor-mance. The repetitive frequency of the optical mm-wave carriersare four times of that of the LO in central office (CO) by usingDSB scheme. Full-duplex transmission services have been success-fully realized over 20-km single-mode fiber (SMF) based on wave-length-reuse technique. In order to mitigate chromatic dispersion,the SSB technique has also been investigated in this paper. Wehad realized an ROF system that attained dispersion-free trans-mission and a negative power penalty by using SSB generation.We also quantified the optical carrier-to-sideband ratio (CSR) ofdownstream transmission in this ROF link and established that theperformance of ROF system can be significantly improved whenthe optical signals are transmitted at a CSR value of 0 dB. Theproposed architectures require much less bandwidth of the mod-ulators, receiver sensitivity, system operation efficiency, and relia-bility.

Index Terms—Double-sideband (DSB), optical carrier reuse, op-tical millimeter-wave (mm-wave), radio-over-fiber (ROF), single-sideband (SSB).

I. INTRODUCTION

N EXT-GENERATION optical access networks will needto provide ultrahigh bandwidth for delivering HDTV and

data service to end users with flexibility at lower cost [1]–[6].Radio-over-fiber (ROF) techniques, the integrated optical andwireless access system, have become an attractive solution forincreasing the capacity, bandwidth, and mobility to serve both

Manuscript received January 30, 2008; revised April 2, 2008. Current versionpublished October 10, 2008.

M.-F. Huang is with the School of Electrical and Computer Engi-neering, Georgia Institute of Technology, Atlanta, GA 30332 USA, andalso with NEC Laboratories America, Princeton, NJ 08540 USA (e-mail:[email protected]).

Z. Jia and G.-K. Chang are with the School of Electrical and Computer En-gineering, Georgia Institute of Technology, Atlanta, GA 30332 USA (e-mail:[email protected]; [email protected]).

J. Yu is with NEC Laboratories America, Princeton, NJ 08540 USA (e-mail:[email protected]).

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

Digital Object Identifier 10.1109/JLT.2008.925653

fixed and mobile users [7], [8]. It also simplifies the configura-tion of the base station (BS) because the millimeter wave (mm-wave) signals will be generated and controlled in the centraloffice (CO). Several optical mm-wave generation approacheswere reported recently, such as direct modulation [9], opticaldouble-frequency heterodyning [10], external optical modula-tion [11], [12], etc. However, direct-modulated transmitters arelimited by the laser chirp and a lower frequency response; thedifficulty for optical heterodyning scheme is that the quality ofthe mm-wave signals depends on the coherence of two lightsources. Among them, the external intensity modulation schemegains much interest to generate optical mm-wave signals witha simplified transmitter in the CO. Different modulation for-mats, such as optical carrier suppression (OCS), double-side-band (DSB), and single-sideband (SSB) can be generated byexternal modulation schemes. In [13], we proposed and demon-strated a simplified method to provide centralized lightwavesat the CO and wavelength-reuse in the BS. Therefore, no addi-tional laser source is required in the BS. We have utilized OCSto generate optical mm-wave, and then recombined the sameoptical carrier with optical mm-wave before transmitted to BS.However, OCS needs a complex electrical driver circuit to con-trol the direct current (dc) bias and symmetrical radio frequency(RF) signals, and it also exhibits limited transmission distancedue to fiber dispersion. For example, the fiber transmission dis-tance is less than 60 km if the 2.5-Gb/s signal is carried by a40-GHz mm-wave carrier.

In 2003, Shen and Gomes [13] proposed a method to gen-erate a frequency-quadrupled electrical signal using an opticalphase modulator. In their scheme, one Fabry–Pérot filter wasused to select two second-order optical sidebands. However, thismethod relies on the optical filter to select the optical sidebandsand generate tunable mm-wave signals. It will significantly in-crease the complexity and the cost of the system while the tun-able optical filter must be used. In this paper, we proposed sev-eral new schemes to generate optical mm-wave by using DSBand SSB modulation format techniques in ROF systems. Theinput frequency of LO to generate optical mm-wave in com-monly used methods for DSB and SSB signals differ in spacingbetween optical carriers and first-order sidebands. The inputfrequency is half for DSB and the same for SSB. Meanwhile,the modulator is biased at quadrature point and a phase differ-ence of is applied [15], [16]. Case in point, for a 40-GHzoptical mm-wave generation with DSB and SSB signals, the

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2654 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 26, NO. 15, AUGUST 1, 2008

Fig. 1. Principle of frequency quadrupling scheme. Resolution of the optical spectrum is 0.01 nm. (LD: laser diode, LO: local oscillator.)

Fig. 2. Proposed DSB modulation scheme to simultaneously generate optical mm-wave and centralized lightwave in an ROF system. (IL: interleaver, IM: intensitymodulator.)

required LO frequency is 20- and 40-GHz, respectively, andthe required operation bandwidth for the modulator is also 40GHz. In [17], we proposed a scheme to generate high-frequencymm-wave using frequency quadrupling technique. However, inthis scheme, an interleaver is needed to split optical carrier andoptical mm-wave signals. In addition, one more modulator isrequired for cascaded modulation, which greatly increased thecost and complexity of the system. Reference [16] proposedan SSB modulation scheme that can be realized by the fiberBragg grating (FBG); nevertheless, the stability is an issue dueto its sensitivity to temperature variation, and also it is moredifficult to be used for WDM operation. Using the proposedscheme, we have realized DSB optical mm-wave generationfor both downstream and upstream transmission over 20-kmsingle-mode fiber (SMF). In another objective, for SSB signalgeneration, the LO frequency only needs half the frequency of

the mm-wave carrier. We also studied the impact of optical mod-ulation efficiency of the mm-wave signals on the downstreamlink performance. Optical mm-wave signals downstream trans-mission over 80-km conventional SMF-28 has been experimen-tally demonstrated and analyzed. The experimental results il-lustrate that an optimum carrier-to-sideband ratio (CSR) can beachieved for improving the performance of the ROF system.

This paper is organized into five sections. The introductionof our work is explained in Section I. Frequency quadruplingscheme for high-frequency mm-wave generation is described inSection II. The methods to realize DSB generation in our pro-posed architecture are discussed in Section III. Experimentalsetup, test results, and analysis of SSB signal generation tech-niques are presented in Section IV. Finally, the conclusions andthe list of all abbreviations are summarized in Section V andTable I, respectively.

HUANG et al.: SIMULTANEOUS GENERATION OF CENTRALIZED LIGHTWAVES AND DOUBLE/SINGLE SIDEBAND OPTICAL mm-WAVE 2655

Fig. 3. Experimental setup, measured optical spectra (0.01 nm) by frequency quadrupling scheme �RF = 10 GHz�. (IM: intensity modulator; EA: electrical am-plifier; IL: interleaver; O/E: optical–electrical converter; TOF: tunable optical filter; BERT: bit error rate taster; APD Rx: avalanche photodiode receiver.)

II. FREQUENCY QUADRUPLING TECHNIQUE

Fig. 1 shows the principle of the proposed frequency quadru-pling scheme [11]. A LiNbO intensity modulator (IM) is em-ployed to generate optical mm-wave with low-frequency RF.Downstream data and RF signal at quarter of LO frequency aremixed by using subcarrier multiplexing (SCM) technique [4]then to drive the IM. To realize an optical mm-wave carrier withfour times of LO frequency, the modulator needs to be dc-biasedat the peak output power when the LO signal is removed [11]. Ifthe repetitive frequency of the RF microwave source is , thefrequency spacing between the second-order modes is equal to

while the first-order modes are suppressed. As an example,the output optical spectrum shown in Fig. 1 is for the case of a10-GHz modulation frequency. From the figure, it can be seenthat the frequency spacing of the second-order modes is 40 GHz,and the first-order sidebands are also suppressed. Taking the ad-vantage of this property can dramatically lower the bandwidthrequirements for the optical modulator and allows the use of amuch lower frequency electrical drive signal. This can greatlyreduce the cost of the system and makes it more practical to use.

III. COST-EFFECTIVE ROF SYSTEM WITH

DOUBLE-SIDEBAND MODULATION

We had proposed a scheme to generate high-frequencymm-wave using frequency quadrupling technique in [17]. Inorder to reduce the demand of the components, we proposedand experimentally demonstrated a new and cost-effectiveROF scheme to simultaneously provide centralized lightwavesource and optical mm-wave signals using frequency quadru-pling technique. Only one single-arm intensity modulator isneeded, which simplifies the transmitter in the CO, improvestransmission power budget, and enhances system reliability.We also compared with a commonly used method in mm-wavegeneration; the LO frequency to achieve optical mm-wave ishalf of the spacing between mm-wave signals.

A. Proposed Double-Sideband Modulation Architecture

Fig. 2 shows the proposed ROF architecture compatible withbroadband access network based on SCM for generation and up-conversion of optical mm-wave signals by using one single-armintensity modulator. In the CO, downstream data and LO fre-quency are mixed by an electrical mixer and used to drive the


Fig. 4. Received eye diagrams. (a) After IM at point (a), (b) after 20-km SMF-28 at point (b), (c) reused signal for upstream at point (d), (d) downstream signalswithout fiber at point (e), and (e) downstream signals with fiber at point (e) in Fig. 3.

IM which is biased at the peak output power. At the base sta-tion, an interleaver (IL) is used to separate the incoming signalsinto two branches: the optical mm-wave signals will be broad-cast by an antenna after optical–electrical (O/E) conversion andboosted for wireless access. The remained optical carrier willbe reused and modulated by another IM and sent back to theCO for upstream transmission. Due to the lack of the electricalswitch and duplexer for circulating down- and uplink signalsat access points, we only demonstrated the baseband opticaltransmission in this proposed scheme. In addition, we can alsotransmit SCM signals for upstream data without expensive com-ponents. We calculated the power budget for both downstreamand upstream data. We assumed the output power of laser diode(LD) is 13 dBm and the insertion loss of IM, 20-km SMF-28fiber, and interleaver is 7, 5, and 2 dB, respectively. After cal-culating, we can get the power of the downstream and upstreamdata at the receivers is 15.5 and 13 dBm, respectively. Ifthere is a preamplifier within the O/E conversion at BS, the re-ceiver sensitivity can be higher than 32 dBm. Therefore, thereis about a 16.5-dB power margin in this proposed scheme fordownstream transmission. For the 2.5-Gb/s uplink data, the sen-sitivity of the avalanche photodiode (APD) can go to higher than

30 dBm. We have a power margin larger than 17 dB, which ismuch higher than the results in [17].

B. Experimental Setup and Results

The experimental setup of optical mm-wave generation,transmission, and lightwave reuse for upstream is shown inFig. 3. In CO, a continuous wave (CW) is generated by adistributed-feedback laser diode (DFB-LD) at 1538.67 nm andlaunched into a LiNbO IM. 2.5-Gb/s signals with a pseudo-random binary (PRBS) word length of are mixed witha 10-GHz microwave signal (LO signal) with a peak-to-peakvoltage of 7 V. The electrical waveform of the mixed signalsis shown in Fig. 3 as inset (i). The half-wave voltage of theIM is 3.5 V. The optical spectra with a 0.01-nm resolutionbefore and after modulation are inserted (ii), (iii) in Fig. 3,repetitively. From Fig. 3(iii), it can be seen that the first-ordermodes are almost suppressed and the power of optical carrieris 18 dB larger than second-order modes after modulation.The subcarriers are generated and separated by 40 GHz (0.32nm), four times of LO, for optical mm-wave carrier while the

Fig. 5. BER curves for both downstream and upstream data and the cor-responding eye diagrams �RF = 10 GHz�. (DS: downstream, US: upstream,B-T-B: back-to-back.)

original carrier is modulated by 2.5-Gb/s non-return-to-zero(NRZ) signals. In this experiment, we used 20-km SMF-28 fortransmission that is fit for an optical access network. After 20km of SMF-28, the optical spectrum is shown in Fig. 3, insert(iv), a 25/50-GHz interleaver is used to separate optical carrierand optical mm-wave. The optical spectra after passing throughthe interleaver from two output ports are inserted in Fig. 3(v)and (vi). Inset (v) in Fig. 3 shows that the optical mm-wavesignals are 13 dB larger than optical carrier. The experimentalresults exhibit that the residual optical carrier has negligibleeffects upon the performance of optical mm-wave signals. Inthe wireless part, one O/E converter is used, and the convertedelectrical mm-wave signal is then amplified by an electricalamplifier (EA). A 40-GHz electrical LO signal is mixed todownconvert the electrical signal to its baseband form. For theupstream part, the optical carrier is reused and modulated byan IM at 2.5 Gb/s. Due to the duplexer is not available, theupstream data is directly modulated on the IM, not via wirelessdelivery. The optical spectra before and after upstream modu-lation are shown as inset (vi) and (vii) in Fig. 3, respectively.After transmission over 20 km, the optical spectrum is shown


Fig. 6. Experimental setup and measured results by frequency doubling technique �RF = 20 GHz�. (IM: intensity modulator; EA: electrical amplifier; IL: inter-leaver; O/E: optical–electrical converter; TOF: tunable optical filter; BERT: bit error rate taster; APD Rx: avalanche photodiode receiver.)

inset (viii) in Fig. 3. One APD receiver is set to detect upstreamdata in CO. Fig. 4(a) and (b) exhibits the eye diagrams beforeand after downstream transmission at point (a) and (b) in Fig. 3.The inverse “0” and “1” bits of the eye diagrams are resultedfrom the IM which was working at the inversion logic whilewe biased at the top peak. The back-to-back eye diagram ofupstream data at point (d) in Fig. 3 and the performance fordownstream signals at point (e) in Fig. 3 with and withoutdownstream transmission fiber are shown in Fig. 4(c), (d),and (e), repetitively. The 2.5-Gb/s data carried by the 40-GHzmm-wave are explicitly observed before downconversion.Fig. 5 shows the bit-error rate (BER) measurement for bothdownstream and upstream signals and the corresponding eyediagrams. Regarding the baseband data, it is observed that thepower penalty is less than 0.8 dB at a given BER of afterover 20-km SMF-28. The penalty arises from the chromaticdispersion for the two subcarriers with 40-GHz spacing. Forupstream transmission, a negligible power penalty is observed,while the dispersion of 20-km SMF-28 has little impact on the2.5-Gb/s signals. The receiver sensitivity due to the intensitynoise of the remodulated signal is degraded a little bit andleads the differential sensitivity between downstream andupstream transmission. In order to compare with a commonlyused method in mm-wave generation, the experimental setup

Fig. 7. BER curves for both downstream and upstream data and the cor-responding eye diagrams �RF = 20 GHz�. (DS: downstream, US: upstream,B-T-B: back-to-back.)

and measured results are shown in Fig. 6 by using a doublefrequency scheme with a 20-GHz RF sinusoidal wave. The IMis biased at the linear region at 0.41 V. Fig. 6, inset (b), shows


Fig. 8. Principle of proposed ROF system. (IM: intensity modulator. RF: radio-frequency. dc : direct current. OC: optical coupler. O/E: optical–electrical converter.EA: electrical amplifier.)

the optical spectrum after IM; the spacing between subcarriersis 40 GHz. The optical eye diagrams of mm-wave signals areinserted in Fig. 6. Fig. 7 illustrates the BER performance andthe corresponding eye diagrams with the RF frequency of 20GHz. Less than 0.5-dB power penalty for both upstream anddownstream data is obtained after transmission. If we comparethe above two experiments, using 20 and 10 GHz for RFsignals, we can find that the performances after transmissionare coincident. However, the frequency quadrupling schemehas a better power sensitivity due to the different performanceof the EA in the transmitter. Furthermore, this frequency qua-drupling technology reduced the requirement of LO frequency,bandwidth of IM, and the overall cost in the system.

IV. SINGLE-SIDEBAND mm-WAVE SIGNALS GENERATION

In order to mitigate chromatic dispersion in the network,SSB modulation technique is an attractive solution to be used inROF systems. We utilized the technique in [11] for the opticalmm-wave generation to demonstrate a novel ROF architecture.The SSB signal with low-frequency LO signals and the impactof optical modulation efficiency of the mm-wave signals havebeen realized and studied in the proposed scheme. Here, wedefined the optical carrier-to-sideband ratio (CSR) of an opticalmm-wave signal as the ratio of optical power in the opticalcarrier to that of the second sideband, while the first sidebandare suppressed in this scheme.

A. Proposed Single-Sideband Modulation Architecture

Fig. 8 shows the design of ROF architecture with SSB modu-lation scheme. In the CO, downstream data and an RF signal athalf of LO frequency are mixed and used to drive the LiNbOIM. For example, if the repetitive frequency of LO is , the fre-quency spacing between optical carrier and second-order modeis while the first-order mode is suppressed. At the BS, oneoptical splitter (OS) is used to split the incoming signals fordownstream data and upstream transmission using wavelength-reuse technique. The downstream data are carried by the op-tical carrier and one of the second-order sidebands via a reg-ular optical filter. The regular optical filter can also be locatedin the CO. Optical mm-wave signals will be detected by O/E

conversion before they are boosted by an EA. Afterwards, themm-wave signals are broadcasted to the customers unit by usingan antenna. On the other hand, the remained optical carrier willbe reused for upstream transmission while the data receivedby the antenna is downconverted. The downconverted upstreamdata are modulated by an IM and sent back to CO.

B. Experimental Configuration and Results

The experimental setup for proposed scheme is shown inFig. 9. In CO, a CW is generated by a DFB-LD at 1538.75 nmand modulated by a LiNbO intensity modulator, which has a3.4-V half-voltage. 2.5-Gb/s signals with a PRBS world lengthof are mixed with a 20-GHz microwave signal (LOsignal) with a peak-to-peak voltage of 7 V. The electrical wave-form of the mixed signals is exhibited in Fig. 9 as inset (i). Theoptical spectra with a 0.01-nm resolution before and after mod-ulation are inserted (ii) and (iii) in Fig. 9. It can be seen clearlyin Fig. 8(iii), the power of optical carrier is 20 dB larger thansecond-order modes while the first-order modes are suppressedand the spacing is 40 GHz between two subcarriers. However,due to the nonlinear modulation performance and two unbal-anced arms of the IM, the first-order modes are not completelysuppressed; therefore, we use a 25/50-GHz interleaver to filterout the first-order modes. The optical spectra at the two outputports of the interleaver are shown in insert (iv) and (v) in Fig. 9.One 0.3-nm spaced tunable optical filter (TOF1) is employedto select optical carrier and single-sideband for downstreamtransmission. In the BS, an EDFA preamplifier is used. Afterone TOF2 with 3-dB bandwidth of 1 nm, one O/E converteris used, and the converted electrical mm-wave signal is thenamplified by a narrowband EA. A 40-GHz electrical LO signalis mixed to downconvert the electrical signal to its basebandform, and then a 3R receiver is used to detect the incoming datafor bit error rate (BER) tests. After downstream transmissionby SMF-28, at point (a) in Fig. 9, the optical spectra in differentCSR are inserted [see (a)–(d) in Fig. 10]. The correspondingeye diagrams after transmitted 0, 20, 40, and 82 km SMF-28before (marked as W/O in red color, , ,

, and ) and after downconversion (marked


Fig. 9. Experimental architecture of proposed new scheme and measured optical spectra (0.01 nm). (DFB-LD: distributed-feedback laser diode; IM: intensitymodulator; EA: electrical amplifier; TOF: tunable optical filter; Att.: attenuator; EA: electrical amplifier, O/E: optical–electrical converter, 3R: receiver; BERT: biterror rate tester.)

as W/ in green color, , , ,and ), measured at point (b) in Fig. 9, are alsodisplayed in Fig. 10. We change the transparent wavelength ofthe TOF1 to obtain different CSR as 0, 6, 12, and 4.6 dB (thepower of the optical carrier is lower than that of the sideband),respectively. From the eye diagrams before downconversion,inset (a-1), (b-1), and (c-1) in Fig. 10, it can be seen that the dcline is shifted when CSR is changed. The dc line is higher whenthe CSR is larger. Fig. 11 illustrates the received sensitivity atBER equals to in all cases. When CSR is higher, such as12 dB, the receiver sensitivity is lower due to the fact that largedc components exist. In the case with a CSR of 4.6 dB, thereceived sensitivity is lower than that of 6-dB CSR. The reasonis that the quality of the beating signal between the opticalcarrier and sideband is poor when the carrier is too small.The highest receiver sensitivity is appeared at CSR of 0 dB.After 20- and 40-km transmission, we obtained negative powerpenalty at 0-dB CSR, caused by the change of the pulse shape.In the case where the CSR is 6 dB, the receiving sensitivityis identical after 0-, 20-, 40-, and 82-km transmission. Thepower penalty at a CSR of 0, 6, 4.6, and 12 dB after40-kmSMF-28 is 0.8, 0, 0.2, and 0.6 dB, repetitively; on the other

hand, the power penalty after 82 km is 0.4, 0, 0.1, and 2.6 dB.It demonstrates that this proposed scheme is a dispersion-freetechnique while CSR less than 6 dB. The experimental resultsillustrate that the performance of the ROF link is dependent onthe optical CSR with optimal performance existing at a CSR of0 dB. It results from the interplay between the optical powerin the optical carrier and sideband. Due to the fact that theBER is dependent on the square root of the power, the receivedpower sensitivity is dependent on the power between opticalcarrier and sideband. For example, the power of carrierand sideband are properly proportional to the root meansquare of the total link noise . However, the receiveradmitted the largest signal , which leads to a lowerBER and improves the performance, at a CSR of 0 dB while

coincides with .

V. CONCLUSION

We have proposed and experimentally demonstrated a novelROF architecture that can simultaneously generate double-side-band and single-sideband signals and high-repetitive frequencyoptical mm-wave by using low-cost components such as a low-frequency RF signal and a low-bandwidth LiNbO intensity


Fig. 10. Experimental results of received optical spectra in different CSR and the corresponding eye diagrams (100 ps/div) in different transmission distancebefore (marked as W/O, �� , �� , �� , and �� ) and after (marked as W/, �� , �� , �� , and �� )downconversion, which measured at point (a) and (b) in Fig. 2, respectively.

modulator. The photonic frequency quadrupling for high-fre-quency mm-wave signal generation was realized by applying

proper dc bias on the intensity modulator. Compared with fre-quency doubling schemes in DSB signal generation, the results


Fig. 11. Receiving sensitivity at BER � �� in different CSR and fiberlength.

TABLE ILIST OF ABBREVIATIONS

of BER measurements showed the improved receiver sensitivityby at least 3 dB for downstream transmission in frequency qua-drupling technique and the bandwidth requirement in terms ofrepetitive frequency of the RF source is greatly reduced. Fur-thermore, the separated optical carrier in our setup is reused inthe BS; thus, the optical power can be efficiently utilized. Wealso investigated the impact of optical CSR on the performanceof mm-wave downstream link with our SSB generation tech-nique. The experimental results indicated that the receiver sensi-tivity for detecting high bit rate signals is strongly dependent onthe optical CSR with optimized performance occurring at a CSRequals to 0 dB. In addition, the receiving sensitivity was im-proved by 0.8 dB (negative power penalty) after 40-km SMF-28at a CSR of 0 dB caused by the change of the pulse shape. Be-

cause the proposed ROF systems employ a fewer number of op-tical components and only lower repetitive frequency of LO sig-nals are required in our proposed system, significant reductionon bandwidth requirements of both transmitter and receiver canbe achieved, in addition to efficient system operation and net-work reliability.

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Ming-Fang Huang (S”04) received the B.S. degreein physics from Tamkang University, Taipei, Taiwan,R.O.C., and the M.E. and Ph.D. degrees in electro-op-tical engineering from National Chiao Tung Univer-sity, Hsinchu, Taiwan, R.O.C., in 2001, 2003, and2007 respectively.

She is currently working as a Postdoctoral Fellowin the School of Electrical and Computer Engi-neering, Georgia Institute of Technology, Atlanta.Her current research interests include long-haultransmission, new modulation format technologies,

wavelength-division multiplexing passive optical network, time-division-mul-tiplexing passive optical network, and radio-over-fiber systems.

Jianjun Yu (M’03–SM’04) received the B.S. degreein optics from Xiangtan University, China, in 1990and the M.E. and Ph.D. degrees in optical commu-nications from the Beijing University of Posts andTelecommunications, Beijing, China, in 1990, 1996,and 1999, respectively.

From June 1999 to January 2001, he worked as anAssistant Research Professor at the Research CenterCOM, Technical University of Denmark, Lyngby .From February 2001 to December 2002, he was aMember of the Technical Staff at Bell Labs’ Lucent

Technologies and Agere Systems, Murray Hill, NJ. He joined the Georgia In-stitute of Technology, Atlanta, in January 2003, where he was on the researchfaculty and served as Director of the Optical Network Laboratory. He is cur-rently a Member of Technical Staff at NEC Laboratories America. He is also anAdjunct Professor at the Georgia Institute of Technology and the Beijing Uni-versity of Posts and Telecommunications. His current research interests include100-Gb/s high-speed transmission systems, new modulation-format techniques,radio-over-fiber systems and networks, wavelength-division-multiplexing pas-sive optical networks, and optical-label switching in optical networks. He hascoauthored more than 250 peer-reviewed journal and conference papers and isthe first author of more than 100 of them. He holds two U.S. patents and fivepending patents.

Dr. Yu is a Senior Member of the IEEE Lasers and Electro-Optics Society(LEOS). He served as a Guest Editor for the Special Issue on Convergence ofOptical and Wireless Networks for the JOURNAL OF LIGHTWAVE TECHNOLOGY.He is a Technical Committee Member of the IEEE LEOS annual meetings from2005 to 2007 and the Optical Fiber Communications Conference (OFC) 2009.He is an Associate Editor for the JOURNAL OF LIGHTWAVE TECHNOLOGY andOptical Society of Merica (OSA) Journal of Optical Networks.

Zhensheng Jia (S’06) was born in Tianjin, China. Hereceived the B.E. and M.S.E degree in physical elec-tronics and optoelectronics from the Electronic Engi-neering Department of Tsinghua University, BeijingChina, in 1999 in 2002, respectively. He is currentlyworking towards the Ph.D. degree in the School ofElectrical and Engineering, Georgia Institute of Tech-nology, Atlanta.

From 2002 to 2004, he worked as a Research En-gineer on transport and access networks in the Op-tical System and Network Laboratory, Technical Di-

vision, China Telecom Beijing Research Institute (CTBRI), Beijing. His re-search interests include optical millimeter-wave signal generation, transmis-sion and processing for symmetric optical-wireless access networks, high-speedTDM/WDM PON, ultrahigh-data-rate (100 Gb/s) optical transmission systems,and nonlinear optical signal processing.

Mr. Jia was one of the recipients of the 2007 IEEE/LEOS Graduate StudentsFellowship Award and 2008 PSC Bor-Uei Chen Memorial Scholarship Award.

Gee-Kung Chang (F’05) received the Bachelor’s de-gree in physics from the National Tsinghua Univer-sity, Taiwan, R.O.C., and the Master’s and Ph.D. de-grees in physics from the University of California,Riverside.

He devoted a total of 23 years of service to BellSystems—Bell Labs, Bellcore, and Telcordia Tech-nologies, where he served in various research andmanagement positions, including Director and ChiefScientist of Optical Internet Research, Director ofthe Optical Networking Systems and Testbed, and

Director of the Optical System Integration and Network Interoperability. Priorto joining Georgia Tech, he served as Vice-President and Chief TechnologyStrategist of OpNext, Inc., a spin-out of Hitachi Telecom, where he was incharge of technology planning and product strategy for advanced high-speedoptoelectronic components and systems for computing and communicationsystems. He is currently the Byers Endowed Chair Professor in Optical Net-working in the School of Electrical and Computer Engineering of the GeorgiaInstitute of Technology (Georgia Tech), Atlanta. He is an Eminent Scholar ofGeorgia Research Alliance. He serves as the leader and Associate Director ofOptoelectronics Integration and Packaging Alliance of NSF funded ERC Mi-crosystem Packaging Research Center at Georgia Tech. He is also an AssociateDirector of Georgia Tech Broadband Institute. He has been granted 40 U.S.patents in the area of optoelectronic devices, high-speed integrated circuits,optoelectronics switching components for computing and communicationsystems, WDM optical networking elements and systems, multiwavelengthoptical networks, optical network security, optical label switching routers,and optical interconnects for next-generation servers and computers. He hascoauthored over 230 peer-reviewed journal and conference papers.

Dr. Chang received Bellcore President’s Award in 1994 for his leadership rolein Optical Networking Technology Consortium. He won the R&D 100 Awardin 1996 for his contribution to the Network Access Module. He was electedas a Telcordia Fellow in 1999 for pioneering work in the optical networkingproject, MONET, and NGI. He became a Fellow of the Photonic Society ofChinese–Americans in 2000. He is a Fellow of IEEE Lasers and Electro-OpticsSociety (LEOS) and a Fellow of the Optical Society of America (OSA) for hiscontributions to DWDM optical networking and label switching technologies.He has been serving in many IEEE LEOS and OSA conferences and commit-tees. He has served three times as the lead Guest Editor for special issues ofthe JOURNAL OF LIGHTWAVE TECHNOLOGY sponsored by IEEE LEOS and theOSA. The first issue was published in December 2000 on Optical Networks,the second one in November 2004 on Metro and Access Networks, and an up-coming one in 2007 on Convergence of Optical Wireless Access Networks.

Radio Optico

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