We report, for the first time to our knowledge, an optically powered wavelength-division-multiplexing (WDM) communication system with distributed parametric amplification in the dispersion-shifted fiber. The parametric pump for the amplification of WDM signals also acts as the power supply for the receiver component. The proposed scheme is also a potential candidate for the last mile transmission. Successful musical signal transmission has been demonstrated. Additionally, four channels of 10-Gb/s WDM signals are used to get more precise performance evaluation of the system. The power penalties of less than or equal to 1.35 dB at a bit-error rate of 10-9 are achieved for all WDM channels in the presence of 10-dB parametric gain. © 2006 IEEE.published_or_final_versio

Cheung, KKY

Liang, Y

Wong, KKY

Xu, X

Yang, S

Yuk, TI

IEEE Photonics Technology Letters

HKU Scholars Hub

Title Optically powered WDM signal transmission system withdistributed parametric amplificationAuthor(s) Xu, X; Cheung, KKY; Yang, S; Liang, Y; Yuk, TI; Wong, KKYCitation Ieee Photonics Technology Letters, 2010, v. 22 n. 16, p. 1232-1234Issued Date 2010URL http://hdl.handle.net/10722/135103Rights Creative Commons: Attribution 3.0 Hong Kong License1232 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 22, NO. 16, AUGUST 15, 2010Optically Powered WDM Signal TransmissionSystem With Distributed Parametric AmplificationXing Xu, Student Member, IEEE, Kim K. Y. Cheung, Sigang Yang, Yu Liang, T. I. Yuk, andKenneth K. Y. Wong, Member, IEEEAbstract—We report, for the first time to our knowledge, an op-tically powered wavelength-division-multiplexing (WDM) commu-nication system with distributed parametric amplification in thedispersion-shifted fiber. The parametric pump for the amplifica-tion of WDM signals also acts as the power supply for the receivercomponent. The proposed scheme is also a potential candidate forthe “last mile” transmission. Successful musical signal transmis-sion has been demonstrated. Additionally, four channels of 10-Gb/sWDM signals are used to get more precise performance evaluationof the system. The power penalties of less than or equal to 1.35 dBat a bit-error rate of     are achieved for all WDM channels inthe presence of 10-dB parametric gain.Index Terms—Distributed amplification, fiber-optics communi-cations, optical parametric amplifier (OPA), photovoltaic, powerover fiber.I. INTRODUCTIOND ISTRIBUTED parametric amplification (DPA), one ofthe candidates for the distributed amplification of opticalsignal, has been studied in recent research [1]. Different fromthe discrete optical parametric amplifier (OPA) in the speciallyfabricated highly nonlinear dispersion-shifted fiber (HNL-DSF)[2], [3], DPA adopts the widely available DSF in which thetransmission and amplification of the optical signal can befulfilled simultaneously. The most favorable merit of DPA liesin its capability of minimizing the signal power variation alongthe transmission span which provides the best tradeoff betweenthe noise figure and fiber nonlinearities [4], [5]. Furthermore,facing the increasing worldwide energy-awareness, in order toenhance the energy-efficiency of the communication system,the residual power of the optical parametric pump can beutilized as the power supply for the receiving component.Actually, optically supplied energy has been well known fora long time, from using solar radiation as a power source forsatellites to the more down to earth application example ofsolar battery for household equipment. In an optically poweredcommunication system, both the optical signal and the powerfor remote equipment are distributed in the optical fiber.Manuscript received February 12, 2010; revised April 20, 2010; acceptedJune 05, 2010. Date of current version July 23, 2010. This work was supportedin part by a grant from the Research Grants Council of the Hong Kong Spe-cial Administrative Region, China (Project HKU 7179/08E and Project HKU7183/09E).The authors are with the Massachusetts Institute of Technology, Cambridge,MA 02139 USA, on leave from the Department of Electrical and ElectronicEngineering, The University of Hong Kong, Hong Kong, S.A.R. China(e-mail: xuxing@eee.hku.hk; cheungky@eee.hku.hk; sgyang@eee.hku.hk;yliang@eee.hku.hk; tiyuk@eee.hku.hk; kywong@eee.hku.hk).Color versions of one or more of the figures in this letter are available onlineat http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/LPT.2010.2052796When we take the “last mile” transmission into account, opti-cally powered fiber link could easily find its position. Unlike thetraditional “last mile” transmission, i.e., twisted pairs or elec-trical cable connections, optical fiber has the advantages of lowattenuation, large transmission bandwidth, and high signal-to-noise ratio (SNR), not to mention the economical factor in thelong-run of maintenance and repair [6], [7]. Another possiblechoice for the “last mile” transmission is free space optics (FSO)or optical wireless links [8], [9]. However, in most realistic “lastmile” transmission environments, reflection, refraction, or evenabsorption due to obstacles or unfavorable air conditions likerain and fog, particularly over longer transmission spans, can se-riously influence the connections. Recently, with the advancesof low-cost high-power lasers, low-power-consumption elec-tronic circuits and highly efficient photodiodes, optically pow-ered communication systems have attracted wide-spread atten-tion. Optically powered radio-over-fiber remote units [10], opti-cally powered LAN systems [11], and optically powered videolink [12] have all been demonstrated. The above experimentstruly provide potential possibility for the “last mile” transmis-sion, however, these former experiments were multimode-fiber(MMF)-based [10]–[12]. Although MMF could tolerate higheroptical power due to larger core dimension, in practice, single-mode fiber (SMF) and DSF could afford much higher data rateand have lower attenuation. More importantly, with the assis-tance of DPA, the SNR of the transmitted data will be securedfor the “last mile” transmission.While in this letter, together with the demonstration of an op-tically powered musical signal transmission link, a four-channeloptically powered wavelength-division-multiplexing (WDM)signal transmission system with DPA has been achieved withina 10-km DSF. In the mean time, the energy-efficiency of theproposed communication system is guaranteed by a commer-cially available InP-based concentrated photovoltaic (CPV)cell, which can provide up to 26% power conversion ratio atthe input optical illumination ranged from 1300 to 1550 nm.II. PRINCIPLE AND EXPERIMENTAL SETUPA simple graph in Fig. 1 shows the scheme of musical signaltransmission. The analog musical signal from the MP3 playerwas first converted to a digital signal string by a digital signalgenerator (HP 8648C), after which the generated electricalsignal was then modulated through a Mach–Zehnder modulator(MZM) onto the optical carrier channel for transmission. Thelarge optical power from the pump branch acted as both thepower supply for the remote signal receiver unit and the para-metric pump for the signal propagating along a spool of 10-kmDSF. The fiber has the loss of 0.20 dB/km for both the signalwavelength at around 1543 nm and the pump wavelength at1041-1135/$26.00 © 2010 IEEEXU et al.: OPTICALLY POWERED WDM SIGNAL TRANSMISSION SYSTEM WITH DPA 1233Fig. 1. Optically powered musical signal transmission with DPA (N.B. Somedevices used during the experiment have been omitted in the diagram forbrevity). CW: continuous wave; TLS: tunable laser source; PD: photodiode;CPV: concentrated photovoltaic cell.Fig. 2. Experimental setup. WDMC: WDM coupler; AWG: arrayed-wave-guide grating.1548.8 nm. A 23-dBm pump power at fiber input was adoptedto generate a 10-dB gain at the signal wavelength. At thereceiver, after convertion by an photodiode (PD) powered bythe CPV cell, the signal was then converted back into a digitalsignal and the clear music was broadcast out by a sound speakerinside the RF communication test set (HP 8920A) used duringour experiment at the receiving end.In order to make practical performance evaluation, a four-channel WDM signal scheme was introduced. Fig. 2 shows theexperimental setup of the transmission system with DPA. Theinput signals, located at the wavelength of 1542.9, 1543.76,1544.65, and 1545.45 nm, respectively, were generated by com-bining the output of four continuous-wave (CW) tunable lasersources (TLS2-5) with three 50/50 couplers and then intensity-modulating them together by an MZM which was driven by a10-Gb/s pseudorandom binary sequence (PRBS) fromthe bit pattern generator (BPG). The polarization controllers(PC3-6) after each laser source were used to minimize the in-sertion loss of each channel by aligning its state of polariza-tion (SOP) with the transmission axis of the MZM. A spool of8-km SMF was deployed to decorrelate different channels in thetime domain. On the other branch, the parametric pump, sourcedfrom TLS1 wavelength at 1548.8 nm, was first phase-ditheredwith a phase modulator (PM) which was driven by a 10-Gb/sPRBS, to suppress the stimulated Brillouin scattering(SBS). A double-stage erbium-doped fiber amplifier (EDFA)scheme was applied to amplify the pump power upto 23 dBmFig. 3. Optical spectra at the output of DSF with (blue solid line) and without(black dotted line) pump. (OSA resolution bandwidth: 0.02 nm).before the fiber input. The optical bandpass filter (OBPF1) be-tween two EDFAs was used to reduce the amplified spontaneousemission (ASE) noise level from EDFA1. A circulator (CIR)was inserted after EDFA2 to avoid the reflection and monitorthe SBS level. One WDM coupler (WDMC1) with the passingband of 3 nm around 1549 nm was applied to trim down the ASEnoise from EDFA2. After combining with WDMC2, the pumpand the signals were then launched together into the 10-km DSFwhich has the nonlinear coefficient of 2 W km and thezero-dispersion wavelength (ZDW) of 1548 nm. By control-ling the variable optical attenuator (VOA), the signal powers atthe input of DSF were maintained at less than 19 dBm, whilethe pump power at the same point was 19.5 dBm. This ensuredthat the pump was not depleted and the generation of signal-re-lated nonlinear effects, such as four-wave-mixing (FWM) andcross-gain modulation (XGM), would be insignificant. The SOPof the pump and signals were aligned by PC2 and PC7 to attainthe maximum optical parametric gain.The optical spectra at the output of DSF with and withoutpump are shown in Fig. 3. The power of four channels at theinput of DSF was 19.3, 18.92, 19.16, and 19.07 dBm,respectively. The corresponding ON–OFF gains were 10.06,10.57, 10.83, and 10.33 dB. At the receiving end, afterWDMC3, the residual pump power of 15.2 dBm (33.1 mW)was sent to the CPV cell to generate the electrical power for thesignal receiving component. Finally, four channels of 10-Gb/sWDM nonreturn-to-zero (NRZ) signals were demultiplexedby an arrayed-waveguide grating (AWG) and the performanceof each channel was then quantified by the bit-error-rate tester(BERT).III. EXPERIMENTAL RESULTS AND DISCUSSIONFig. 4 lists the measured eye-diagrams of the received10-Gb/s NRZ signals. Clear and widely open eye-diagrams areobserved for all channels, which indicate the high quality of thereceiving WDM signals. The noise observed on the mark levelis mainly due to the conversion of pump phase modulation tosignal intensity modulation along the DSF with the process ofparametric amplification.Each channel was turned OFF sequentially to quantify thesignal crosstalk amongst channels as shown in Fig. 5. It can beobserved that there is no observable spurious FWM components1234 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 22, NO. 16, AUGUST 15, 2010Fig. 4. Received eye-diagrams of four individual WDM channels.Fig. 5. Spectra with one channel OFF after DPA. (OSA resolution bandwidth:0.02 nm).Fig. 6. BER plots for the back-to-back signals and the signals after DPA: onlyone channel ON (1 ch: circle); 4 channels ON (4 chs: triangle).(more than 28 dB lower than the signals) generated. The cor-responding BER of each channel was measured and comparedagainst the back-to-back (B2B) signals (Fig. 6). Two differentconfigurations were considered during the BER measurementprocess: 1) only one channel was turned ON; 2) all four channelswere turned ON. Error-free operations are attained for all chan-nels and the power penalties ranged from 1.08 to 1.33 dB at aBER of for the single-channel case; additional penaltiesfrom 0.02 to 0.15 dB were measured in the four-channel casewhich indicate nearly negligible impact on these WDM chan-nels.Fig. 7 shows the output curve of the CPV cell with differentinput optical power at the pump wavelength. According to thecurve, the corresponding output voltage could reach 4.53 V,which was enough for the bias voltage of the 5-V photodiode(PD) as the optical signal to electrical signal converter. Consid-ering the relatively small amount of power at the far-end sub-scriber (6.6 mW in our experiment, according to the 20% typ-Fig. 7. Response curve of the CPV cell with the input pump light at 1548.8 nm.ical energy conversion ratio of the CPV cell), in addition to thepossible deployment in the “last mile” transmission, potentialapplication lies in the optically powered sensor network locatedin a relatively inaccessible environment. Our scheme of com-bining DPA and optical power transmission provides a potentialmethod for the recycle of optical pump in distributed amplifica-tion.IV. CONCLUSIONWe have demonstrated an optically powered WDM signaltransmission system with DPA in the DSF. Less than or equalto 1.35-dB power penalties at the BER of are obtained forall channels at the presence of 10-dB parametric gain. The in-corporation of DPA and optical power transmission during theexperiment provides a new solution for the “last mile” transmis-sion.REFERENCES[1] G. Kalogerakis, M. E. Marhic, K. K. Y. Wong, and L. G. Kazovsky,“Transmission of optical communication signals by distributedparametric amplification,” J. 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Optically powered WDM signal transmission system with distributed parametric amplification

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Optically powered WDM signal transmission system with distributed parametric amplification

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