An OCDMA Scheme to Reduce Multiple Access Interference and Enhance Performance for Optical Subscriber Access Networks

Transcription

1 An OCDMA Scheme to Reduce Multple Access Interference and Enhance Performance for Optcal Subscrber Access etworks Sango Park, Bong Kyu Km, and Byoung Wh Km We propose a new optcal code dvson multple access (OCDMA) scheme for reducng multple access nterference (MAI) and enhancng performance for optcal subscrber access networks usng modfed pseudorandom nose (P)-coded fber Bragg gratngs wth bpolar OCDMA decoders. Through the bpolar OCDMA decoder and the modfed P codes, MAI among users s effectvely depressed. As the data are encoded ether by a unpolar sgnature sequence of the modfed P code or ts complement accordng to whether the data bt s or 0, the bt error rato (BER) can be more mproved wth the same sgnal to nterference plus nose rato over the conventonal on-off shft keyng-based OCDMA system. We prove by numercal analyss that the BER of the proposed bpolar OCDMA system s better than the conventonal unpolar OCDMA system. We also analyze the spectral power dstorton effects of the broadband lght source. Keywords: Optcal CDMA, modfed P codes, bpolar, fber Bragg gratng (FBG), multple access nterference (MAI). Manuscrpt receved Jan. 8, 003; revsed July, 003. Ths work was partally supported by the KOSEF (grant no. R ). Sango Park (phone: , emal: ps63863@etr.re.kr), Bong Kyu Km (emal: bongkm@etr.re.kr), and Byoung Wh Km (emal: kbw@etr.re.kr) are wth Broadband Convergence etwork Research Dvson, ETRI, Daeeon, Korea. Sango Park s also wth School of Computer, Informaton & Communcaton, Seowon Unversty, Cheongu, Korea. I. Introducton A future subscrber access system needs a broadband transmsson lnk that offers nteractve multmeda servces, such as voce, hgh qualty vdeo-on-demand, and hgh speed data. Fber-optc transmsson systems, such as the fber-to-thehome and the fber-to-the-curb, have been ntroduced nto subscrber access networks to provde hgh transmsson qualty. Fgure shows an ATM-based passve optcal network (PO) n whch several optcal network unts (OUs) are connected to an ATM-based optcal lne termnaton (OLT) by an optcal fber []. In ths ATM-based PO system, the ATM cells supply resdental customers wth servces such as hgh qualty TV, Internet protocol and dgtal vdeo-on-demand. Moreover, non-atm servces, such as publc swtched telephone networks (PSTs), narrowband ntegrated servce dgtal networks (ISDs), and power dgtal subscrber lnes (DSLs) can be provded []. ATM-based PO technology usng optcal spltters s preferable for optcal subscrber access networks because t provdes low cost and flexble sharng of the resource bandwdth. Therefore, we consder the PO structure as an effectve multple access method for the optcal subscrber access network. We nvestgated the multple access method for the up-lnk of the ATM-based PO because conventonal multplexng methods, such as tme dvson multple access (TDMA), are appled to the down-lnk and for the sake of a smple analyss. TDMA s one of the solutons that are sutable for the up-lnk of the ATM-based PO for sharng the bandwdth of optcal channels. However, the TDMA-based ETRI Journal, Volume 6, umber, February 004 Sango Park et al. 3

2 Outdoor type sngle user OU Central offce Twsted par POTS/ISD PC RG ATM Outdoor type mult user Optcal spltter OLT IP Vdeo-ondemand Twsted par OU PC RG Indoor type PC OU Optcal fber Fber to the curb (~0 km) OLT: optcal lne termnaton OU: optcal network unt RG: resdental gateway Fber to the home Fg.. ATM-based PO system. PO has to solve many problems, such as medum access control (MAC) for precse packet nterleavng, access delay, and clock phase algnment. Thus, code dvson multple access (CDMA) s a strong canddate for creatng effectve multple methods [3] for the optcal subscrber access network because of ts asynchronous access and code multplexng [4], [5]. Moreover, the optcal CDMA method s preferable for multplexng n the optcal doman because t uses broad bandwdths n optcal devces for the electrcal CDMA method [6] and the E/O converson. Thus, we propose a fber-optc asynchronous subscrber access system for optcal subscrber access networks wth a new optcal CDMA (OCDMA) method. Up to ths tme, OCDMA methods have been studed and developed for optcal systems, such as local area networks (LAs), because of ther asynchronous access propertes. The man OCDMA methods use the followng: optcal delay lnes [7], [8] or optcal swtches [9]-[] wth optcal orthogonal code (OOC) for the tme doman; fber Bragg gratng (FBG) or arrayed wavegude gratngs (AWGs) and OOCs for the optcal frequency doman []; and FBGs or AWGs for optcal wavelength-hoppng/tme spreadng [3], [4]. OCDMA usng OOCs has many problems, such as a lmtaton on the number of dstnct code sequences and low optcal power because there are fewer s than 0s. One of the key ssues for OCDMA s to reduce the multple access nterference (MAI) among channels (or users). One study proposed an FBG-based OCDMA wth maxmal length codes to reduce MAI, where only data s encoded as n the conventonal OCDMA on-off shft keyng; t has a unpolar capacty [5]. Furthermore, the spectral power dstorton effects of the broadband lght source were not consdered. In ths paper, we propose a new method for optcal subscrber access to reduce multple access nterference and enhance performance n optcal frequency doman OCDMA systems. Because all data are encoded durng half of the modfed P sequences, the bt error rates (BERs) wth a bpolar OCDMA decoder [6] are better than when there s a unpolar decoder. We also propose modfed P codes to reduce the MAI wth a bpolar OCDMA decoder. Through the bpolar OCDMA decoder and modfed P codes, dgtal data can be regenerated wthout MAI among users. We also dscuss 4 Sango Park et al. ETRI Journal, Volume 6, umber, February 004

3 OU 0 data 0 FBG_E FBG_D data 0 OC OA OC data M- FBG_E OU M- OLT FBG_D data M- FBG_E: FBG encoder FBG_D: FBG decoder OC: optcal coupler OA: optcal amplfer Fg.. Optcal subscrber access system usng OCDMA wth modfed P codes and FBGs. the effect of the spectral power dstorton of the broadband lght source and the nose components. OU no. 0 Code sequence II. Optcal Subscrber Access System Usng OCDMA wth Modfed P Codes and FBGs The optcal subscrber access system usng OCDMA wth modfed P codes and FBGs s shown n Fg.. M OUs are connected to a fber-optc lnk by usng an n: optcal coupler, where data are multplexed by the CDMA scheme at the FBG encoder. M optcal coded sgnals are transmtted to an OLT. At the OLT, an optcal amplfer s equpped to compensate for the optcal loss of one optcal coupler and M optcal coded sgnals from M OUs are power splt nto each of n FBG decoders and then correlated wth one of the same code patterns at the FBG encoder. In the conventonal OCDMA wth a bpolar capacty usng P codes, such as gold codes and maxmal length codes, MAI takes place because the number of 0s s not equal to the number of s. The modfed P codes have the same number of s and 0s to elmnate the MAI. Table llustrates the modfed P code sequences for a code length (n) of 8 as an example. User # s assgned by modfed P code sequences, C = ( C ( 0), C (), K, C ( n ) ). The stuff bt of 0 s nserted at the end of each code n order to equalze the numbers of s and 0s. Thus, modfed P code sequences have an even code length and equal number of s and 0s. Fgure 3 depcts the FBG encoder and decoder for an optcal subscrber access system. We used a broadband optcal source P code Stuff bt Table.. Modfed P code sequences for the code length of 8. such as a super lumnescence dode and nserted a bandpass flter at ts output port to splt the lght source wth a spectrally unform shape. Unformly splt lght source streams are drected to the FBG encoder for the spectral encodng. The transmtted lght feld and the reflected lght feld from the FBGs are nversely encoded n the wavelength doman due to the transmsson and the reflecton characterstcs of the FBG as C and C, respectvely, at the OU #. A optcal swtch, such as a Mach-Zehnder ntensty modulator, selects the reflected lght feld f the data bt s or the transmtted lght feld f the data bt s 0. At the FBG encoder, the data are encoded ether by a unpolar sgnature sequence of the modfed P code f the data bt s or ts complement f the ETRI Journal, Volume 6, umber, February 004 Sango Park et al. 5

4 data bt s 0. When the OU #0 s assgned to modfy the P code sequences, C 0 = (,,,0,0,, 0, 0), the FBGs are placed wth central wavelengths of λ 0, λ, λ, and λ 5. When the OU #0 transmts the data bt, the encoded optcal sgnals are generated wth the reflected optcal sgnals λ 0, λ, λ, and λ 5 at the FBG encoder #0 by usng an optcal swtch. Whle the OU #0 transmts the data bt 0, the encoded optcal sgnals are generated wth the transmtted optcal sgnals λ 3, λ 4, λ 6, and λ 7 at the FBG encoder #0 by usng an optcal swtch. As an n optcal coupler connects an OLT wth n FBG encoders, each FBG encoder at the OU transmts ts spectral encoded sgnal to all FBG decoders at the OLT. The FBG decoder uses two photo dodes to elmnate MAI and mprove the bt error rate (BER) compared to the conventonal decoder wth a unpolar capacty at the same sgnal to nterference plus nose rato (SIR). The transmtted lght feld and the reflected lght feld complement each other at the FBGs. Out of the receved sgnal spectra, the transmtted lght feld s detected by the upper photo dode PD and the reflected lght feld s drected to the lower photo dode PD by a crculator and detected. The two output current sgnals are subtracted and ntegrated at the low pass flter (LPF), and the desred data are regenerated by a dscrmnator. III. Theoretcal Analyss of SIR and BER Whle the CDMA decodng pattern at the FBG decoder matches the receved sgnal spectrum from the same pattern of the FBG encoder, the upper photo dode PD detects the sgnal when the data bt s 0 and the lower photo dode PD detects the sgnal when the data bt s, and the complement photo dode does not detect any sgnal. The subtracted current of the two photo dodes for the desred sgnal of OU # s gven by n = = α L C (, for a data bt of, () s k = 0 n = = α L C (, for a data bt of 0, () s k = 0 0 L are the output powers of the broadband lght source for all users, and α, L, M, and n are the responsvty of the photo dode, the optcal attenuaton rato between the lght source and the photo dode, the number of connected OUs, and the code length, respectvely. In addton, p ( reflects the spectral shape of the broadband source, and we assume t follows a Gaussan dstrbuton. The transmtter optcal power P s s defned as the summaton of 0), ), K, n ). As an where p = p = = pm = ( 0), ), K, n ) ) data λ λ Lght source 0 BPF p 0 λ 0 λ λ λ 3 C 0 Optcal swtch data 0 C 0 FBG_E0 (a) FBG encoder at the OU #0 λ 5 λ λ λ 0 PD (t) PD LPF Dscrmnator data 0 FBG-D0 (t) (b) FBG decoder for OU #0 at the OLT Fg. 3. The schematc dagram of the FBG encoder and FBG decoder. 6 Sango Park et al. ETRI Journal, Volume 6, umber, February 004

5 deal case, we assume the optcal loss s / n where we consder the splttng losses of two optcal couplers but not the nserton losses of the optcal couplers, FBGs, optcal swtch, and crculators. Whle the CDMA codng pattern at the FBG decoder msmatches the sgnal spectrum receved from a dfferent pattern of the FBG encoder, the upper photo dode PD and the lower photo dode PD detect the sgnals smultaneously. The total current s obtaned by summng all the nterference components (from OU #) contrbuted to the OU # wth respect to ( ), each of whch s calculated by the dfference between the detected currents at the PD and PD. The current subtracted from the two photo dodes for the nterference at the decoder # s gven by I I C ( [ C ( C ( )], n = α L k k 0 = = for a data bt of, and (3) C ( [ C ( C ( )], n = α L k k 0 = = for a data bt of 0. (4) When there are spectrally flat lght sources, the nterference n k = 0 = currents are zero because C ( [ C ( C ( ] 0. However, because the general lght sources have nonflat spectrum dstrbuton, the nterference current wll be detected. In ths case, the desred sgnal power S and the nterference power I at the output of the LPF are gven by and S = s (5) M = I 0, I =, (6) respectvely. The addtve nose power s composed of the relatve ntensty nose power, shot nose power, recever thermal nose power, and optcal amplfer nose powers. Here we gnore the optcal sgnal beat nose power because t can be suppressed by the subtracton process after detecton at the two photo dodes [3]. The nose power s gven by = (7) RI SHOT Each nose power s gven by TH SSP SPSP. SHOT = s D r, (8) RI ξ RI ( P W ) D, = + (9) eα r sp r 8kBT TH = Dr, (0) R ssp spsp L P 4 r = α sp Dr, () M n sp = α W, () P = L C ( C (, (3) r = 0 k = 0 where e, ξ RI, kb, T, RL, Dr, W, and P r are the electrc charge, power spectral densty (PSD) of the relatve ntensty nose, Boltzmann constant, nose temperature, load resstance, data bt rate, optcal flterng bandwdth, and recevng optcal power n one PD of the -th decoder, respectvely. The PSDs of the amplfed spontaneous emsson s gven by sp sp ηsp G = h υ, (4) η G a where ηsp, ηa, hυ and G are the spontaneous emsson factor, quantum effcency, photon energy, and gan of the optcal amplfer, respectvely. Thus, the sgnal to nterference rato (SIR), the sgnal to nose rato (SR) and the SIR are gven by SIR = S, I (5) SR = S, (6) SIR = S, ( + I) (7) respectvely. The power component at the output of the LPF s the sum of the desred sgnal power, nterference power, and nose power. We consdered a system n whch the nterference from one OU s not sgnfcantly stronger than that from any other OU because optcal fber has a small transmsson loss. The nterference s a random varable and ndependent n each OU for the large smultaneous OU number and code length. Hence, we can consder that the MAI and nose at the output of LPF s a zero-mean Gaussan dstrbuted functon [0], [7]. Assumng that the data bts and 0 are transmtted wth a probablty of 0.5, the BER s gven by ETRI Journal, Volume 6, umber, February 004 Sango Park et al. 7

6 I BER = erfc 4 I D I 0 D I +, erfc σ 4 (8) σ 0 where I and I 0 are the mean currents for the data bt and 0, respectvely, and I D s the threshold current. Addtonally, σ 0 and σ are the current standard devaton of the nterference and the nose current for the data bts and 0, respectvely [4]. As I 0 and σ 0 are equal to I and σ, respectvely, n the proposed system wth a bpolar capacty, and I s 0, the BER s expressed as D I BER = erfc =. erfc SIR σ (9) By contrast, the BER of the conventonal on-off shft keyng wth only a unpolar capacty [5] can be wrtten as [8] BER = erfc SIR. 8 (0) Thus, the proposed system can easly acheve the same performance at a lower SIR by 6 db than that of the conventonal system wth a unpolar capacty. IV. umercal Results and Dscussons In ths secton, we dscuss some numercal results for the proposed OCDMA system. Table shows the parameters used for the numercal calculatons. Here, the spectral power dstorton rato of the broadband lght source wth Gaussan dstrbuton s defned as the rato of the dfference between the maxmum and mnmum output power to the maxmum output power of the broadband lght source as follows: n / ) 0) Power dstorton rato 00(%). n / ) () Fgure 4 shows the SIR and SIR curves as a functon of the spectral power dstorton rato of the broadband lght source for code lengths of 3 and 8 and 0 dbm total optcal power of the broadband lght source. The number of connected OUs s fewer than the code length by one. The SIR s the same regardless of the number of connected OUs. In the case of a spectral power dstorton rato of 0, the SIR s nfnte, namely the MAI s free for the spectrally flat broadband lght source. When the spectral power dstorton s lmted to wthn 0%, an SIR of 0 db can be guaranteed. Consderng the nose power, the SIR s more domnated by the SR than the SIR when the spectral power dstorton rato s small. The SIR s domnated by the thermal nose when the number of connected OUs SIR (db) Table. Parameters used for the numercal calculatons. Parameters Values Responsvty of PD, α 0.8 A/W PSD of relatve ntensty nose, ξ RI -5 db/hz Load resstance, R L 50 Ω Data bt rate, D r 55.5 Mb/s ose temperature, T 300 K Optcal flterng bandwdth, W THz Spontaneous emsson factor of OA, η sp.0 Quantum effcency of OA, η a 0.5 Optcal path loss /n Optcal amplfer gan, G n Optcal attenuaton rato, L n /n SIR for M=3, n=3 SIR for M=3, n=3 SIR for M=7, n=8 SIR for M=7, n=8 Ps = 0 dbm Spectral power dstorton raton (%) Fg. 4. SIR and SIR curves as a functon of spectral power dstorton rato. ncreases, because the attenuaton rato ncreases n proporton to the OU number. Thus, the SIR s not affected by the spectral power dstorton when the number of connected OUs s 7 wth a code length of 8. Fgure 5 shows the BER of the recovered sgnal as a functon of the spectral power dstorton rato. The thermal nose deterorates the BER when the number of connected OUs s large. The allowed tolerances of the spectral power dstorton rato are 34% and 8% wth a BER of 0-9 when the numbers of connected OUs are 3 and 7 wth code lengths of 3 and 8, respectvely. The BERs wth the proposed bpolar OCDMA are dramatcally mproved over the conventonal unpolar OCDMA systems []. Fgure 6 shows the relatonshp among the SIR, SIR, and the OU number for spectral power dstorton ratos of 0% 8 Sango Park et al. ETRI Journal, Volume 6, umber, February 004

7 Bt error rato E-3 E-6 E-9 E- E-5 E-8 Conventonal Scheme [] E- M=7, n=8 M=3, n=3 E-4 Proposed Scheme M=7, n=8 E-7 M=3, n=3 Ps=0 dbm E Spectral power dstorton (%) Fg. 5. BER curves as a functon of spectral power dstorton rato. SIR (db) Fg. 6. Relatonshp among the SIR, SIR, and the OU number for spectral power dstorton ratos of 0 and 0%. Acceptable dstorton rato (%) BER 0-9 Ps =-3dBm Ps = 0dBm Ps = 6dBm umber of OUs SIR for 0 dstorton SIR for 0% dstorton SIR for 0% dstorton Ps= 0 dbm umber of OUs Fg. 7. Interrelatonshp between the smultaneous OU number and the spectral power dstorton rato at a BER of 0-9. and 0%. Here, the code lengths are the same as the OU numbers plus. The SIR s constant regardless of the OU number and s nfnte for spectral power dstorton ratos of 0 %. Fgure 7 shows the nterrelatonshp between a smultaneous OU number and the spectral power dstorton rato of the broadband lght source wth varous transmtted optcal peak powers at a BER of 0-9. Here, the code lengths are the same as the OU numbers plus. The spectral power dstorton should be lmted to wthn 33% to keep the smultaneous user number constant at a BER of 0-9 when the transmtted optcal peak power s 6 dbm. When the transmtted optcal peak power s smaller than 6 dbm, the spectral power dstorton should be strctly depressed because of the thermal nose as the smultaneous OU number connected to the proposed system ncreases wth a BER of 0-9. V. Concluson We have proposed an OCDMA scheme to reduce multple access nterference (MAI) and enhance performance for optcal subscrber access networks usng modfed P coded FBGs wth a bpolar OCDMA decoder. Through the bpolar OCDMA decoder and modfed P codes, MAI among OUs can be elmnated when there s no spectral power dstorton. As the data are encoded by ether a unpolar sgnature sequence of the modfed P code or ts complement accordng to whether the data bt s or 0, the BER can be mproved under the same SIR compared wth the on-off shft keyng-based OCDMA system. We have also taken account of the spectral power dstorton effects of the broadband lght source. We showed that the spectral power dstorton should be lmted to wthn 33 % to keep the smultaneous user number constant at a BER of 0-9 when the total transmtted optcal power s 6 dbm. When the transmtted optcal power s small, the spectral power dstorton rato should be strctly depressed because of the thermal nose. References [] ITU-T Recommendaton G.983., Broadband Optcal Access Systems Based on PO, Oct [] M. D. Prycker, W. Verbest, and D. Mestdagh, ATM Passve Optcal etworks: Preparng the Access etwork for BISD, Proc. of ISS, 99, pp [3] K. Lee, K.C. Kang, T. Lee, and S. Park, An Optmzaton Approach to Routng and wavelength Assgnment n WDM All- Optcal Mesh etworks wthout Wavelength Converson, ETRI J., vol. 4, no., Apr. 00, pp [4] T. Pfeffer, B. Deppsch, M. Kaser, and R. Hedemann, Hgh Speed Optcal etwork for Asynchronous Multuser Access Applyng Perodc Spectral Codng of Broadband Sources, Electroncs Lett., vol. 33, no. 5, 997, pp.4-4. ETRI Journal, Volume 6, umber, February 004 Sango Park et al. 9

8 [5] G. Elenberger, T. Pfeffer, I. Voorde and P. Vetter, Optcal Solutons for the Access etwork, Alcatel Telecom. Revew, 3rd quarter, 998, pp [6] J.-H. Oh, K.-D. Km, and L.B. Mlsten, Convolutonally-Coded and Spectrum-Overlapped Multcarrer DS-CDMA Systems n a Multpath Fadng Channel, ETRI J., vol. 3, no. 4, Dec. 00, pp [7] K. Ktayama, H. Satobayash and. Wada, Optcal Code Dvson Multplexng (OCDM) and Its Applcaton to Photoncs etworks, IEICE Trans. Fundam., vol. 8-A, no., 999, pp [8] J.A. Saleh, Code Dvson Multple-Access Technques n Optcal Fber etworks-part I: Fundamental Prncples, IEEE Trans. Comm., vol. 37, Aug. 989, pp [9] S. Park, K. Tsukamoto, and S. Komak, Proposal of Drect Optcal Swtchng CDMA for Cable-To-The-Ar System and Its Performance Analyss, IEICE Trans. Comm., vol. 8-B, no. 6, 998, pp [0] F. Khalegh and M. Kavehrad, A ew Correlator Recever Archtecture for oncoherent Optcal CDMA etworks wth Bpolar Capacty, IEEE Trans. Comm., vol. 44, no. 0, Oct. 996, pp [] B.S. Ham, A ovel Method of All-Optcal Swtchng: Quantum Router, ETRI J., vol. 3, no. 3, Sept. 00, pp [] J. Huang, D. Hsu, and Y. Wang, Photonc CDMA etworkng wth Spectrally Pseudo-Orthogonal Coded Fber Bragg Gratngs, IEICE Trans. Comm., vol. 83-B, no. 0, 000, pp [3] K. Yu, J. Shn, and. Park, Wavelength-Tme Spreadng Optcal CDMA System Usng Wavelength Multplexers and Mrrored Fber Delay Lnes, IEEE Photoncs Tech. Lett., vol., no. 9, 000, pp [4] H. Fathallah, A. Rusch, and S. LaRochalle, Passve Optcal Fast Frequency-Hop CDMA Communcaton System, J. Lghtwave Tech., vol. 7, no. 3, Mar. 999, pp [5] J. Huang and D. Hsu, Fber-Gratng Based Optcal Spectral Codng wth early Orthogonal M-Sequence Codes, IEEE Photoncs Tech. Lett., vol., no. 9, 000, pp [6] S. Park, K. Tsukamoto, and S. Komak, Proposal of ovel Optcal Polarty-Reversng Correlator for Optcal CDMA Rado Hghway etwork, Wreless Personal Comm., vol. 4, ssue, Aug. 000, pp [7] P.A. Humblet and M. Azzoglu, On the Bt Error Rate of Lghtwave Systems wth Optcal Amplfers, IEEE Lghtwave Tech., vol. 9, no., ov. 99, pp [8] G.P. Agrawal, Fber-Optc Comm. Systems, nd ed., John Wley & Sons Inc., 997, pp Sango Park receved hs BS and MS degrees n control and nstrumentaton engneerng from Seoul atonal Unversty n Korea n 983 and 985. He receved hs PhD degree n communcaton engneerng from Osaka Unversty n Japan n 999. From 984 to 99 he was wth Samsung Electroncs Ltd. n Korea. From 99 to 000 he was wth ETRI n Korea. He s currently a Professor n the School of Computer, Informaton & Communcaton at Seowon Unversty n Korea. He has also been a Vstng Researcher n ETRI snce 00. He s engaged n research on rado, optcal, and mcrowave-photoncs communcaton systems. He s a member of the Insttute of Electroncs and Informaton Communcaton Engneers of Japan (IEICE). Bong Kyu Km receved hs BS degree n physcs from Hanyang Unversty n Korea n 989 and MS and PhD degrees n physcs from KAIST n Korea n 99 and 996. From 996 to 999 he was wth Photoncs Research Center of KIST n Korea. He s currently a Senor Researcher n the WPO Technology Team, Broadband Convergence etwork Research Dvson, ETRI n Korea. Hs research nterests nclude optcal access networks, optcal communcaton systems, and optcal measurng systems. Byoung Wh Km receved a PhD degree n electrcal and computer engneerng from Unversty of Colorado, Boulder, Colorado n 993. From 983 to 988, he was nvolved n the development of a dgtal swtchng system n ETRI. Snce he oned ETRI agan n 994, he has been workng on III-V compoundsemconductor optcal swtches based on the stran-nduced pezoelectrc effects, network archtectures and systems for Internet protocol over WDM, optcal cross connect systems, actve optcal access networks based on WDM, and WDM-PO archtectures and systems. Currently he serves as the Team Leader for the WDM-PO Technology Team. Hs research nterests nclude theoretcal physcs of compound semconductor materals and optoelectronc devces as well as optcal networks and systems. 0 Sango Park et al. ETRI Journal, Volume 6, umber, February 004