Research Article Remotely Powered and Reconfigured Quasi-Passive Reconfigurable Nodes for Optical Access Networks

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1 Journal of Electrical and Computer Engineering Volume 6, Article I 98, pages Research Article Remotely Powered and Reconfigured uasi-passive Reconfigurable Nodes for Optical Access Networks Yingying Bi, Shunrong Shen, Jing Jin, Ke Wang,,, and Leonid G. Kazovsky epartment of Electrical Engineering, Stanford University, Stanford, CA 9, USA Centre for Neural Engineering (CfNE), University of Melbourne, Melbourne, VIC, Australia epartment of Electrical and Electronic Engineering, University of Melbourne, Melbourne, VIC, Australia Correspondence should be addressed to Yingying Bi; yybi@stanford.edu Received November ; Accepted January 6 Academic Editor: Iraj Sadegh Amiri Copyright 6 Yingying Bi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. uasi-passive Reconfigurable (PAR) nodes have been proposed to provide flexible power/wavelength allocation in optical access networks. PAR only consumes power during reconfiguration, which is remotely transmitted from the central office, thus maintaining the passive nature of the network. In this paper, a PAR control circuit is designed, and a remotely powered and reconfigured PAR (i.e., one wavelength, two power levels, and two output ports) with a. F/ V supercapacitor (SC) remotely charged by a 8photodiode array is experimentally demonstrated. The charged SC can power the PAR for at least 6 s with consecutive reconfigurations ( ms each) or two reconfigurations within a maximum period of hours, before the SC needs to be recharged. In addition, the demonstrated PAR remote power scheme is compared with the previously proposed irect Photovoltaic Power option both theoretically and experimentally. Results show that the SC based remote power mechanism is capable of driving a large number of reconfigurations simultaneously and it is better for large dimension PARs.. Introduction Passive Optical Networks (PONs) have been widely deployed in optical access networks. However, current PONs have the limitations of inflexible power/wavelength allocation due to the use of static passive components such as fixed power splitters and wavelength division multiplexing (WM) couplers. Next-generation optical access networks should have sufficient intelligence and reconfigurability to manage different power and bandwidth requirements without sacrificing energy efficiency. Therefore, the uasi-passive and Reconfigurable (PAR) node has been proposed in our previous studies[].theparnodecancombinethefollowingfunctions simultaneously in a quasi-passive manner in future PONs: () splitting the input power into adjustable levels and assigning them to different optical network units (ONUs) according to the ONUs distances from the central office (CO); () dynamically allocating wavelengths to different groups of outputs based on user-specific bandwidth requirements. Another important advantage of PAR is that it is quasi-passive; that is, it only requires power during reconfiguration with no steady-state power consumption. The PAR has been experimentally demonstrated using discrete components including optical latching switches (OLSs),dBcouplers,andWMcouplers[].OLSsarethe key components to realize the quasi-passive feature since it only consumes power during reconfiguration, and Microelectromechanical Systems- (MEMS-) based OLSs have been utilized [, ]. The MEMS-OLS can be driven by a. V V electrical signal, and a control logic is also needed to select between the bar/cross states. As a branching device in the remote node (RN), the PAR can be remotely powered by transmitting optical power from the CO through the feeder fiber []. This avoids on-site maintenance and configuration atthern.moreover,withouthavinganylocalpowersupply, the passive nature of the RN is maintained. One straightforward way of PAR remote power is transmitting high power light to the RN during reconfigurations. At the RN, the power light is converted into electrical power by a photovoltaic power converter (PPC), which is used

2 Journal of Electrical and Computer Engineering to power the PAR and its control circuit directly. This irect Photovoltaic Power scheme has been proposed and demonstrated in our previous studies []. An eight-in-series InGaAs P array was used to convert the optical power at 8nmintotheelectricalpowerforPARreconfiguration. In this design, every time PAR needs to be reconfigured, it is directly powered with the P array. The reconfiguration of PAR is initiated and ended by turning on and off the high power laser in the CO. Experimental results have shown that a minimum dbm optical feed into each P is required to power one OLS, while 9 dbm is required to power two OLSs in parallel. irect Photovoltaic Power option is a promising solution topowerasmalldimensionpar.however,forlargedimension PARs, this option requires a high instantaneous power from the PPC [] or multiple PPCs with multiple wavelengths [], thus lacking scalability. To overcome these limitations, there is another option, storing the energy in a supercapacitor, which has been proposed to power switching units in metro or access networks, for example, an electrooptic switch []. However, a systematic comparison between the two options, that is, the irect Photovoltaic Power option and Charged Supercapacitor Power option, is still missing. In this paper, a PAR remote power mechanism using energy stored in an optically charged supercapacitor, that is, the Charged Supercapacitor Power option, is proposed, investigated, and experimentally demonstrated. Furthermore, the irect Photovoltaic Power and Charged Supercapacitor schemes for PAR remote power are compared both theoretically and experimentally. In addition, a control circuit thatcanbeusedtoreconfigureparstatesisdesignedand demonstrated with remote power. The rest of paper is organized as follows. Section presents the principle of Charged Supercapacitor Power scheme for PAR remote power. In Section, two PAR remote power mechanisms are analyzed and compared. Section shows the designed control circuit for PAR remote reconfiguration, and the experimental demonstration of a PAR node using the designed remote power system and control circuit. Conclusions of this paper are given in Section.. Charged Supercapacitor Power of PAR The PARs can be remotely powered using the supercapacitor (SC), which is also known as ultracapacitor. ifferent fromaregularcapacitor,theschasamuchlargercapacitance, which is often rated in farads [6]. Therefore, SCs typically store to times more energy per unit volume than electrolytic capacitors. Compared with rechargeable batteries, SCs can accept and deliver charges more rapidly, tolerate more charging and discharging cycles, and have fewer safety issues. Therefore, using charged SC is an attractive choice for PAR remote power. The proposed general architecture of the PAR remote power system using a SC is shown in Figure. In this design, when reconfigured, PAR is powered by the SC in the RN, which is charged by the remote power system optically. Unlike the irect Photovoltaic Power option, the power and control signals of the PAR node are not transmitted simultaneously. The high power laser is turned on only during the SC charging process, while the control signal is generated and transmitted during the discharging process for PAR reconfiguration. To avoid current leakage that decelerates charging, an analog switch is used to isolate the load from the SC during the charging process. Therefore, the reconfigurationprocessisinitiatedandendedbyswitching on and off the analog switch... Charging of the Supercapacitor. In our proposed PAR remote power system, the SC was charged with a PPC (PPC asshowninfigure).theppcwasa 8 InGaAs P array, and its IV curves under different optical power conditions are plotted in Figure. A. F/ V SC was used and the charging curve was measured as shown in Figure. According to Figure,thechargingprocessoftheSCwiththeParraycan be divided into two stages. The first stage is constant current charging, where the voltage on the SC increases linearly with time. The second stage is saturation charging, where the voltage slowly approaches the open circuit voltage of the P array as the photocurrent drops sharply. To save the charging time, the charging should be stopped before the second stage. According to Figure, the charging stopping voltage (V )is about.6 V. The charging time T charge is then approximately T charge = (C V ) I charge, I charge =P in R P, () where C, V, I charge, P in,andr P are the SC capacitance, charging stopping voltage, charging current, input optical power of each P, and responsivity of the P. The charging time, which is the time it takes for the SC tobechargedfromvto.6v,wasmeasuredandshownin Figure.Itisclearthatahigherfeedpowerisdesiredforfaster charging; however, the responsivity of the Ps decreases as the input light intensity increases due to the photocurrent saturation, as shown in Figure. Therefore, the optical feed power of the P array should be selected to achieve both reasonably high conversion efficiency and acceptable charging time. dbm optical feed per P (i.e., dbm into the whole P array), where the P array has a high responsivity of.97 A/W, was chosen in our demonstration of the PAR remote power (Section.). It takes s to charge the SC from V to.6 V. Using the equivalent circuit model of the PPC with a capacitor load, the capacitor charging voltage as a function of time can be calculated theoretically through transient analysis [7]. Table lists the theoretical charging time of the.fscwithaneight-in-seriesidealingaasparray, together with the corresponding experimental results. It can be seen that the experimental values are higher and the difference becomes more significant as the optical feed increases due to the deteriorating photocurrent saturation... ischarging of the Supercapacitor. When the fully charged SC is used to power the PAR, a discharging stopping voltage, denoted as V,andtheSCcapacitance should be selected appropriately so that the reconfiguration of

3 Journal of Electrical and Computer Engineering Center office Feeder fiber Remote node Power laser laser λ C λ P λ P λ C PPC PPC SC OLSs circuit. ONU ONU N OLT λ S λ S PAR PPC: photovoltaic power converter OLS: optical latching switch SC: supercapacitor OLT: optical line terminal ONU: optical network unit Optical path Electrical path Figure : General architecture of the PAR remote power system. 6 Current (ma) dbm per P 8 dbm per P 6 dbm per P dbm per P dbm per P Figure : Experimental IV curves of the 8Parray. dbm per P 8 dbm per P 6 dbm per P 6 Time (s) dbm per P dbm per P Figure : Experimental charging curves of a. F SC. Table : Charging time of. F SC (from V to.6 V). Optical feed per P Theoretical charging time Experimental charging time dbm s s 8 dbm 87 s 79 s 6dBm s s dbm s s PAR can be stably completed before the SC voltage reaches V.TheSCcapacitancecanbedecidedusing Charging time (s) Responsivity (A/W) P PAR T rec = C(V V ), () where P PAR, T rec, C, V,andV are the average power consumption of the PAR node, reconfiguration time, the SC Input optical power (dbm) Figure : Trade-off between the charging time and responsivity.

4 Journal of Electrical and Computer Engineering capacitance, and charging and discharging stopping voltages. The reconfiguration time (T rec ) may vary in applications but should be longer than the minimum driven pulse width of the OLSs. For the OLS used in experiments, the minimum pulse width is ms according to the data sheets [8] and. ms in the measurements []. Theconsumedcurrentaswellasthepowerconsumption of the OLS we used rises to a peak value when the voltage supplyiscloseto.8v[].asaresult,althoughtheolscan work at a lower voltage of. V, the SC discharging stopping voltage was selected at. V to avoid the current peak. This voltage can be further reduced if a C-C converter is used to boost the SC voltage to a constant value. However, this expedites the discharging of the SC due to the additional C- C converter power consumption. In our analysis and demonstration, a large SC (. F) is chosen which is envisioned to power PAR nodes with multiple OLSs and the control circuitry. The discharging time of the SC, which is defined as the time it takes for the voltage to drop from.6 V to. V, was measured when the SC was used to drive one or two OLSs, and the results are shown in Figure. With one OLS as the load, the discharging time is 7 s (the OLS was continuously reconfigured). In addition, the discharging time is lowered to s when the number of OLSs increases to two.. Comparison of ifferent Remote Power Options.. Theoretical Analysis. As mentioned in Section, the PAR node can be remotely powered using two schemes, namely, irect Photovoltaic Power (Option ) and Charged Supercapacitor Power (Option ). To compare these two options, the following assumptions are made: (i) Both options have the same optical link including km long feeder fiber, band coupler/splitters, and power splitters. Thus both options have the same optical link loss, which can be calculated as listed in Table. (ii) Both options have the same PPC, which has eight Ps in series and the responsivity of each P is.9 A/W. (iii) Both options have the same control circuit. Wedefinethefollowingmetricstocomparethetwooptions.... System Energy Efficiency (SEE). The System Energy Efficiency of PAR remote power is defined as follows: SEE = = Energy provided to PAR Energy output by the power laser Energy fed into the PPC Energy output by the power laser Energy provided to PAR Energy fed into the PPC. () Fiber attenuation (. db/km at 8 nm) Band coupler/splitter insertion loss (. db/each) Connector loss (. db/each) Power splitter excess loss Total loss Table : Optical link loss.. db.8 db. db.db. db E %... One-OLS load Two-OLSs load Time (s) Figure : ischarging curves of a. F, V SC with one-ols and two-ols load. Let E = E = Energy fed into the PPC Energy output by the power laser, Energy provided to PAR Energy ed into the PPC. Both options have the same E =.(see Table ), which is determined by the optical link loss. E can be calculated using E Option = P PAR T rec N P in T rec =V PAR R p N, E Option = P PAR T rec = V N P in T charge V V R p N, where V PAR, V, V, N, andr P are the average voltage of PAR, charging and discharging stopping voltages, number of Ps, and the responsivity of Ps. For Option, E is proportional to the PAR operation voltage, thus having a minimum value when V PAR =.V. For Option, E depends on the charging and discharging stopping voltages, which have theoretical maximum value () ()

5 Journal of Electrical and Computer Engineering. System energy efficiency... Option : V PAR =V Option : V PAR =. V Option : V =V Option : V =V Maximum number of OLSs 8 6 V (V) Figure 6: System Energy Efficiency (SEE). when V = VandV = V. As illustrated in Figure 6, the minimum SEE of Option equals the maximum SEE of Option, where both are 8.%. Therefore, to power the same PAR, Option is more energy efficient, thus requiring less total energy.... Maximum Number of Simultaneously Powered OLSs (N OLS ). The OLSs in PAR can be powered either simultaneously or sequentially, or by using a combination of both. Simultaneous powering takes less time but requires higher instantaneous power. Here the two remote power mechanisms of PAR are compared in terms of the maximum possiblenumberofolssthatcanbedrivensimultaneously when the available power from the high power laser is the same. N OLS can be calculated using (6) and (7), respectively. For Option, N OLS depends on the current generated by the PPC. To power a large number of OLSs in parallel, high opticalpowerisrequiredtobefedintoeachpintheppc (P in ). For Option, N OLS depends on the energy stored in SC as well as the percentage of energy used for discharging. As discussed in previous sections, V =.6 VandV =.V were selected. N OLS of Option is also proportional to the ratio T charge /T rec, which is denoted by T. For a longer charging time, more energy can be stored in the SC to power more OLSs. Similarly, a shorter reconfiguration time results in less energy being distributed to each OLS. Based on (6) and (7), the maximum number of OLSs that can be powered simultaneously (N OLS ) for both options is shown in Figure 7: N OLS Option = P in R P I OLS, (6) N OLS Option = T charge T rec V V V V OLS P in R P I OLS. (7) It can be concluded from Figure 7 that as long as T is larger than, that is, the charging time is at least four times as long as the reconfiguration time, Option can power more 6 8 Laser output power (mw) Option Option : T= Option : T= Figure 7: Maximum number of OLSs powered simultaneously (N OLS ). OLSs simultaneously with the same total power provided by the high power laser. T is typically larger than ; therefore, Option is more suitable for a high dimension PAR which has a larger number of OLSs, especially when the optical power that can be transmitted to the RN is limited. If a high dimension PAR needs to be powered using Option, the OLSs should be powered sequentially at the cost of a longer PAR reconfiguration time.... Total Time to Complete the Reconfiguration (T total ). To compare T total of Option and Option, we made two more assumptions as follows: (i)bothoptionsareusedtopowerthesameparwith NUM OLSs. (ii) Both options have the same total available power, which is only enough to power NUM OLSs simultaneously using Option ; that is, NUM = N OLS (Option ). Therefore, to power NUM OLSs using Option, they should be divided into subgroups and the subgroups are powered in sequence. Assume that each subgroup contains N OLS (Option ) OLSs.Thenumberofsubgroups(M) isthe ratio between N OLS (Option ) and N OLS (Option ), which can be obtained by using (6) and (7): M= N OLS (Option ) N OLS (Option ) = T charge V V. (8) T rec V V OLS We can prove that the second term in (8) is smaller than ; therefore, M is smaller than T charge /T rec. For Option, the time it takes to complete the reconfiguration is the sum of the reconfiguration time of M subgroups, which is less than T charge (see (9)). For Option, all the NUM

6 6 Journal of Electrical and Computer Engineering Table : System Energy Efficiency comparison. Option : irect Photovoltaic Power Option : Charged Supercapacitor Power Theoretical Experimental Theoretical Experimental E % % % % E 7.% % 7.% 7% SEE 8.% %.%.% OLSscanbepoweredsimultaneouslyinT rec.however,the total time to complete the reconfiguration is the sum of T charge and T rec (see ()), which is longer than using Option : T total (Option )=M T rec < T charge T T rec =T charge, rec (9) T total (Option ) = T charge +T rec. ().. Experimental Results. Experiments were carried out to investigate both PAR remote power options. The results on SEE are listed in Table. In both options, the output power of the pump laser was mw ( dbm), and the insertion loss of the optical path (including the band coupler/splitter, fiber, connectors, and power splitters) was about 6 db. Therefore, dbmopticalpowerwasfedintoeachp(p in )ofthe 8 P array. Using Option, a minimum dbm P in was required to power one OLS, which worked at the minimum power consumption point (. V/ ma/ mw). The overall system conversion efficiency is % []. Using Option, the same dbm optical feed charged a.f/vscfromvto.6vins.thechargedscwas capable of powering the same OLS for 7 s before the SC voltage dropped below. V. The overall system conversion efficiency is.%. Although Option has a higher SEE, the same optical powerisonlyenoughtopowerone OLS.Topower two OLSssimultaneously,atleast9dBmfedinto each P is required []. On the other hand, the number of simultaneously powered OLSs using Option is not limited by the optical power fed into each P. As long as the extra charging time is acceptable, Option is capable of powering alargenumberofolss. In summary, both options have pros and cons in different applications. With a higher SEE and shorter T total,option ismoreadvantageouswhentheremotepowerapplication is energy constraint or time constraint, while Option wins when the available optical power is the bottleneck. Therefore, these two schemes should be selected according to application requirements: Option should be used in small dimension PARs or sequential reconfiguration of OLSs in PARs, while Option, with the potential of powering more OLSs simultaneously, is a better solution for high dimension APRs.. Remote of PAR The control signal of the PAR, which decides the states of OLSs, can be also remotely and optically transmitted, converted by another PPC and further decoded by the control circuit. In this section, the general architecture of PAR control circuit is proposed and the implementation of a controlcircuitthatiscapableofcontrollingaparwitheight OLSs is demonstrated...architectureofparcircuit. Figure 8 shows the general architecture of PAR control circuit, which has four function units. () Analog Switch Unit. Thisunitcontainstwostagesof cascaded analog switches. The first switch (SW) is kept off during the SC charging process. uring reconfiguration, SW is turned on so that the SC is connected as the power supply for the control circuit. Though designed for Option, the same control circuit can be used in Option, with SW being removed since the power supply is controlled by the power laser in the CO directly. The second stage switch (SW) connects the power supply to the subgroup of OLSs in PAR that needs to be powered. This not only avoids providing power to the OLSs whose states are unchanged to reduce the total energy required in the SC, but also simplifies the control circuit since different subgroups share the same electrical devices. Both switches SW and SW should have small resistance and fast switching properties. () SW Unit. The function of this unit includes detectingthearrivalofcontrolsignalssoastoturnonsw and detecting the completion of the reconfiguration so as to turn off SW. This unit is always powered on; thereby it must have very small current and power consumption. () Clock Generator Unit. When powered on, this unit generates the clock at a certain frequency, which is used for synchronization. Requirements for this unit are low power consumption, reliability, and high-quality synchronization. () Signal ecoding Unit. This unit is a serial in parallel out system that can extract the status information of PAR from the control signal and map it onto the designated subgroup of OLSs. Besides low power consumption, this unit should also be reliable and scalable especially for high dimension PARs... Circuit emonstration. Based on the four function units, a control circuit as shown in Figure 9 was designed anddemonstratedwhichhadfoursubgroupsandwascapable ofpoweringtwoolsssimultaneouslyineachsubgroup.

7 Journal of Electrical and Computer Engineering 7 Supercapacitor Analog switches SW SW signal SW Unit Clock generator signal decoding unit Optical latching switches (PAR) Power signal Clock Figure 8: General architecture of PAR control circuit. Supercapacitor Analog switches SW SW signal clk FF clr clk FF clr Clock generator signal decoding unit clk 8-bit shift register clk FF clk FF clk FF A B PAR OLS SW Unit MR Binary counter clk clk 8-bit shift register clk FF OLS Figure 9: circuit example. An example of the control signal, which is the input of designed control circuit, is shown in Figure 9. The control signal consists of starting bits, synchronization bits, and PAR state bits. The first up-edge of the starting bits is detected by the SW Unit to turn on SW so that the control circuit is powered on. The synchronization bits are detected by the control signal decoding unit to map the PAR state to the outputs of the four -type flipflops, which will remain there unless the SW is turned off and the power supply of the control circuit is cut off. There are four PAR state bits, in the example, where the first two digits are to select the subgroup of OLSs and the last two digits correspond to the bar/cross states of the two OLSs in each subgroup. The timing diagram is plotted in Figure. In practice, the control signal may be repeated several times to guarantee the correct reconfiguration of the PAR state. In the current design, one straightforward way to scale up thecontrolcircuitistoenlargethenumberofolssineach subgroup. However, the size of shift register, the number of -type flip-flops, and the length of control signal all scale up quickly. The use of SW can help mitigate this problem, since the control circuit can be scaled up by simply adding more branches in SW, thus increasing the number of subgroups. It should be noted that current design of the control circuit has not been optimized in terms of power consumption. Lower power digital chips can be used for more versatile operations, and more robust control coding is also subject to future research... Remote Reconfiguration of a PAR. The remote power and control of a PAR using a SC was experimentally demonstrated using the setup as shown in

8 8 Journal of Electrical and Computer Engineering Starting bits Synchronization bits PAR state bits signal Clock Shift register Shift register Shift register Shift register Shift register Shift register Shift register 6 Shift register 7 Internal trigger FF output FF output FF output FF output Figure : Timing diagram of the control signal decoding unit. 6 Supercapacitor circuit supply logic on OLSs Time (s) Supercapacitor circuit supply logic on OLSs signal Time (ms) Figure : ischarging of the SC with the control circuit and OLS load. Figure. The power laser was operated at the 8 nm wavelength, while the control light and payload signal was transmitted at nm and 9 nm, respectively. The 6 6 nm/ 7 nm/8 97 nm band coupler/splitter was used to couple/decouple the power, control, and signal lights into/out of a km single mode feeder fiber. Once decoupled from fiber, the power light was split by a 8 power splitter, and each output port was connected to a P. The 8Parraywasusedtochargea.F/VSC.The control light was split by a power splitter, converted by

9 Journal of Electrical and Computer Engineering 9... Time (h). F SC leakage. F SC self-discharge Figure:Leakageandself-dischargeofa.FSC. the P array, and then injected into the control circuit, whosedetailedstructureisshowninfigure7.inthe PAR, two OLSs combined with one db coupler can achieve three states at the two output ports (P output, P output ): (P, ), (, P) and(/p, /P), where P is the total input power of PAR. uring the charging process, the SC is charged to.6 V in s with dbm output power from the power laser. No power penalty of the payload signal was observed when the power light was transmitted together with the payload signal inthesamefiber[]. uring the discharging process, an arbitrary function generator was programmed to generate the control signal, whichwasmodulatedontothenmopticalchannel.after being converted to the electrical domain by a InGaAs P array in PAR, the encoded switching instructions were extracted by the control circuit to toggle the states of the OLSs.Toensurethecorrectnessofcontrolprocess,thesame control signal was repeated for three cycles. In each cycle, the control circuit and power supply to the OLSs remained on for ms and off for ms. In such configuration, there were consecutive cycles before the SC voltage dropped below. V, as illustrated in Figure. The energy consumption of each reconfiguration cycle can be calculated to be 8.6 mj. As illustrated in Figure, the leakage of SC was characterized when it was connected with the control circuit without any reconfiguration operation. When there is no reconfiguration request, it takes hours for the SC voltage to drop below. V. Therefore, within approximately hours, another reconfiguration can be operated without charging the SC again. This leakage rate is slow enough compared to the charging time, which is in the order of several minutes. We also characterized the self-discharge of the SC as shown in Figure. It takes 7 hours for the SC to self-discharge to. V when no load is connected. This places an upper limit of the leakage time with different control circuit design. In Figure, we capture the change of the optical signal at output of the PAR node under two reconfigurations: from (, P) to(/p, /P) and from(/p, /P) to(p, ). It is clear that the PAR can be reliably reconfigured using the proposed remote power and control system. Though equipped with a PAR, our testbed can support the reconfiguration of a higher dimension PAR with eight OLSs since a analogswitchisusedasswinthecontrol circuit.. Conclusion A PAR remote power mechanism using the energy stored in a supercapacitor at the RN has been proposed and demonstrated. The supercapacitor has been charged by remotely transmitted optical power from the CO. This Charged Supercapacitor Power scheme (Option ) has been compared with the previously demonstrated irect Photovoltaic Power solution (Option ). It has been shown that Option can guarantee that the RN is fully passive and has no energy leakage when there is no reconfiguration, while it is only suitable for small dimension PARs due to the limited power provided. On the other hand, Option has been shown to be capable of powering a larger number of OLSs simultaneously, thus making the remote power of high dimension PARs possible. With the proposed remote power schemes, the flexible power/wavelength management and graceful system upgrade enabled by PARs can be realized without having local power supplies and on-site reconfiguration at the RN. However, there is additional cost due to the additional components for remote power, such as high power lasers. Since the additional components are only added in either thecoorrn,thecostissharedbymultipleendusers. In addition, with the quasi-passive characteristics, remote powering of PARs is only needed during reconfigurations. Given the low network reconfiguration frequency, remotely powered PARs preserve the passive nature and maintain high energy efficiency of the network. A control circuit has also been designed to remotely reconfigure PARs by transmitting control signals from the CO. Based on Option, a remote power and control system has been demonstrated which can reconfigure a PAR node with eight OLSs divided into four subgroups, without having any local power supply. It has been shown that a. F/ V SC, which is charged to.6 V, can power a PAR for 6 s. With ms of each reconfiguration, the implemented remote power system has been able to support at least consecutive reconfigurations before the SC needs to be recharged. It has also been shown that the charging cycle takes s with dbm optical feed into the 8Parray,which is negligible compared to the leakage time of the system (in the order of tens of hours). Conflict of Interests The authors declare that there is no conflict of interests regarding the publication of this paper.

10 JournalofElectricalandComputerEngineering Power laser 8 nm laser nm Signal laser 9 nm λ P Band coupler λ C Feeder λ fiber S km Band splitter λ P λ C 8 splitter splitter λ S 8 P array P array Supercapacitor. F/ V SW Unit signal Analog switches SW Input Clock generator AWG OLS signal decoding unit db PAR SW Power supply Output Output Figure : Testbed of the PAR remote power and reconfiguration. voltage on OLS Power supply on OLS Zero power level signal signal Half power level Half power level Full power level Time (ms) Optical signal Time (ms) Figure : Experimental results of the PAR remote reconfiguration. Acknowledgments This work has been partially funded by the Center for Integrated Systems, Stanford University. The authors would like to thank Sercalo for providing OLSs for their experiments. References [] Y. Bi, J. Jin, A. R. haini, and L. G. Kazovsky, PAR: a quasi-passive reconfigurable green node for dynamic resource management in optical access networks, Journal of Lightwave Technology, vol., no. 6, Article I 6699, pp.,. [] Y. Bi, J. Jin, A. haini, and L. G. Kazovsky, Experimental demonstration of a high-dimension quasi-passive reconfigurable (PAR) node, in Proceedings of the Conference on Lasers and Electro-Optics (CLEO ), paper STuJ.7, Optical Society of America, San Jose, Calif, USA, June. [] Y. Bi, J. Jin, and L. G. Kazovsky, First experimental demonstration of a remotely powered quasi-passive reconfigurable node, IEEE Photonics Technology Letters, vol.7,no.9,pp.99 99,. [] H. Ramanitra, P. Chanclou, Z. Belfqih, M. Moignard, H. Le Bras, and. Schumacher, Scalable and multi-service passive optical access infrastructure using variable optical splitters, in Proceedings of the Optical Fiber Communication Conference, and the National Fiber Optic Engineers Conference (OFC 6), IEEE, Anaheim, Calif, USA, March 6. [] B.Schrenk,A.Poppe,M.Stierle,andH.Leopold, Passiveoptical switching engine for flexible metro-access, in Proceedings of the European Conference on Optical Communication (ECOC ), pp., Cannes, France, September. [6] Supercapacitor, the role of the supercapacitor. [7] M. M. Mahmoud, Transient analysis of a PV power generator charging a capacitor for measurement of the I V characteristics, Renewable Energy, vol., no., pp. 98 6, 6. [8] MEMS OLS ata Sheet, pdfs/slx.pdf.

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