Clausen, Anders

Jeppesen, Palle

Le, Nghi Trong Quang

Oxenløwe, Leif Katsuo

Seoane, Jorge

Siahlo, Andrei

Zhenbo, Xu

A novel method of tuneable dispersion compensation at which phase modulation is applied in the receiver part is proposed for OTDM systems. Compensation of dispersion of 3.2 ps/nm at 160 Gb/s OTDM transmission is demonstrated

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Downloaded from orbit.dtu.dk on: Dec 17, 2017Tunable dispersion compensation using phase modulation in receiver partSiahlo, Andrei; Clausen, Anders; Oxenløwe, Leif Katsuo; Seoane, Jorge; Xu, Zhenbo; Jeppesen, Palle;Le, Nghi Trong QuangPublished in:Technical Digest Optical Fiber Communication Conference 2004Publication date:2004Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Siahlo, A., Clausen, A., Oxenløwe, L. K., Seoane, J., Zhenbo, X., Jeppesen, P., & Le, N. T. Q. (2004). Tunabledispersion compensation using phase modulation in receiver part. In Technical Digest Optical FiberCommunication Conference 2004 (pp. ThU4). USA: IEEE.I Tunable dispersion compensation using phase modulation in receiver part A.I. SiaNo, A.T. Clauseu, L.K. OxenlBwe, J. Seoaue, Z. Xuand P. Jeppeseu Q. N.T. Le COM Center, Teclmicd Univsr.siry r,lDmmark, DTU-Building 345V, DK-ZXW Lynghy. Dramurk PLone: t45  452537M. F u : + 4 5  45MliSXI. E-mrril:unrBc~,rn.~,”.~k O F C  Fit<,l Dmrwrk k P ~ i o y o r k m  680, DK-ZOOS Bnnrlhy. Uenmrrrir Abstract: A novel method o f  tuneable dispersion compensation at which phase modulation i s  applied in the receiver pan is  proposed for OTDM systems. Compensation o f  dispersion of 3.2 oslnm at I60 Gbls OTDM transmission i s  demonstrated. 02003 Optical Society of America OClS codes: (060.4510) Optical coininmications (060.2360) Fiber oplics links and subsystems 1. Introduction As the channel rate in communication systems increases, the tolerances for dispersion are strongly reduced. Some transmission experiments at bit rates o f  I 60  Gbls have been demonstrated using carefully designed transmission lines with accumulated dispersion less than I .2 pdnm [I]. The maximum demo,nstrated tolerable accumulated dispersion for successful demultiplexing from 160 Gbls of 2 pslnm was demonstrated 121. Since the dispersion of transmission system can bc changed due to temperature changes [3,4], network reconliguration, wavelength changes and other factors, tunable dispersion compensating i s  required. Detection of dispersion in transmission system i s  possible by monitoring, for example, intensity of timing frequency components 151. Chirped fiber grating can be used for tunable compensation of dispersion and slope at 160 Gbls [6]. but i t  requires complex fabrication method and i t  has limitcd bandwidth. Dispersion and slope can bc compcnsatcd by tunablc prc-chirping using cosinusoidal phase modulation o f  the input pulses [2,7]; an increase i n  tolerance of accumulated dispersion to 4 pslnm i n  system using pre-chirping was demonstrated [ 2 ] .  Compensation by pre-chirping is  convenient. because i t  i s  simple, does not depend on wavelength, and does not need an advanced fabrication method. Ideally, however, pre-chirping subsystem should be placed at the beginning o f  a transmission span to apply the right chirp to pulses before transmission. As the tunable pre-chirping i s  situated in the transmitter, dynamic control o f  i t  would require control signal transmitted from the system receiver to the system transmitter, intraucing a substantial complexity to lhe setup. In the present work we show that cosinusoidal phase modulation used for dispersion compensation can be placed after transmission, i.e., in the receiver part. First we explain the possibility of using phase modulation for post compensation. Then we demonstrate successful demultiplexing from 160 to I O  Gbls of a system with a dispersion of 3.2 pslnm using the mentioned post-compensation. 2. Principle of post-compensation by phase modulation The purpose o f  dynamic dispersion compensation i n  O T D M  system i s  to maintain thc pulse width after transmission if dispersion of the system i s  changed in order to avoid overlapping of pulses of neighboring channels. A dispersion compensating subsystem (DCS) used for pre-chirping in [2,7] consists o l t w o  dispersive fibers with opposite sign of dispersion and a phase modulator (PM) in between; adjusting the amplitude of the phme modulation in the DCS changes the pulse width after transmission [Z]. Similarly adjusting the amplitude o f  the P M  can change the pulsewidth if the DCS is placed after transmission. Since the bit-rate o f  the OTDM signal (160 Gbls) exceeds the repetitjon rate of the control signal applied to P M  (I0 GHz), the cosinusoidal phase modulation used to compensate for pulse broadening i s  optimized only for one OTDM channel. However, the difference between the phase of the control signal to the P M  for nearest channels i s  small (2rd16). therefore a number of channels wil l be compensated. Thus, post-compensation by phase modulation can eliminate overlapping between the pulses o f  the target channel and the nearest neighboring channels. Figure I shows results o f  simple modeling of using o f  DCS after transmission for dispcrsion compensation at 160 Gbls. We used the same dispersions o f  the fibers i n  DCS, the same amplitude of phase modulation and the same width of the pulses of OTDM signal as in subscquent experiment. Tne eye-diagram shows number o f  not-overlapped channels. (a) (b) Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 17,2010 at 08:41:27 EST from IEEE Xplore.  Restrictions apply. ThU4 L 1 m 6 0  M RJ 100 Time [PSI Figure 1 .  (a) Principle of opentian of post-compensation using phase modulation and (b) eye-diagram of I60 G h k  signal after DCS obtained by simulations 3. Experimental results Experimental setup used to confirm the possibility of dispersion post-compensation using a PCU is shown i n  figure 2. " "- Figure 2. Experimental setup (left); eye-diagram of the 160 Gbls signal at the input to the without (right, top) and with (right, bottom) extra SMF (PM in DCS is ~ den Off) .. iultiplexing NOLM In the transmitter pan (TX) the mode-locked fibre-ring laser (FRL) operating at a wavelength of 1558 nm generates short pulses with FWHM of 3.0 ps a1 10 GHz. The pulse train is data modulated with a 2'-l tu 2 " - I  PRBS sequence in a LiNbO, MZ modulator. The 10 Gbls signal is multiplexed tu 160Gbls by a fiber-delay multiplexer maintaining the properties of the 2'-1 PRBS (kindly provided by HHI Institute, Berlin). The receiver pan (RX) includes the DCS, the nonlincar optical loop mirror (NOLM) as a demultiplexer [XI, and a preamplified 10 Gbls receiver with BER analyzer. The DCS includes a DCF with accumulated dispersion OS - 17.6 pslnm, a PM and a SMF with accumulated dispersion of + 17.6 pslnm. Wavelength-converted to 1540 nm by another NOLM, pulses from the FRL are applied as the control signal to the demultiplexing NOLM. The control signal is also ole converted and amplified by a narrow-band electrical amplifier to obtain cosinusoidal RF signal. This cosinusoidal RF signal is applied tu the PM in the DCS and as a clock to BER analyzer. Both NOLMs contain HNLFs with very low dispersion (less than 0.2 pslnm at operating wavelengths) and dispersion slope. Lengths of the HNLFs are 400 m and 500 ni. Due to the low dispersion of the HNLF in the demultiplexing NOLM walk-off between control and data signals and pulse broadening of the two are negligible. The two time delays in the RX part sewe tu synchronize control signals to the PM and tu NOLM and data signal. These time delays were optimized when only one OTDM channel is injected into the NOLM. The system was evaluated withou1,and with an extra SMF fibcr having accumulated dispersion of 1.7 pslnm. Autocorrelation traces of the 160 Gbls signal injected into the NOLM are shown i n  figure 3. Without extra SMF the pulses of the data signal are broadened to 3.5 ps before injecting in the demultiplexing NOLM. This broadening occurs due tu the internal dispersion of the setup of 1.5 pslnm. The eye diagram of the 160 Gbls signal based on 3.5 ps pulses is shown in figure 2, top-right. The structure of the OTDM signal on eye-diagram and pulses of different channels on autocorrelation traces can be seen. With the extra SMF fiber dispersion of the system becomes 3.2 pslnm and the pulses'are broaden to 4.75 ps at the input to the NOLM. The eye-diagram of OTDM signal is more diffused (figure 2,  right-bottom) and OTDM structure cannot be seen on autocorrclation trace. When the phase modulation with amplitude of 0.811 is applied in the setup with an additional fiber, the width of the pulses of one OTDM channel, demultiplexing by the NOLM, becomes 3.5 ps again; however, the structure of OTDM signal on autocorrelator cannot he seen because only one of 16 channels has narrow pulsewidth. Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 17,2010 at 08:41:27 EST from IEEE Xplore.  Restrictions apply. ThU4 3 (b) Figure 3. Autocorrelation traces of the signal at the input to the demultiplexing NOLM. Black lines: only one channel is transmitted through the system: grey lines: multiplexed signal. (a) Setup without an extra fiber; (b) setup with the extra SMF fiber; total accumulated dispersion of the setup is 3.2 pslnm; (cj total accumulated dispersion of the setup is 3.2 pdnm and post-compensation is used. Figure 4 shows results for demultiplexing of the signal sent to the RX without extia SMF fiber (DL= 1.5 pslnm) and with extra SMF (DL= 3.2 pslnm). Error-free (IE-9) operalion can be reached when DL= 1.5 pslnm. The minimum value of the BER of IE-7 can be reached with the extra SMF. Applying phase modulation improves the performance and an error-free operation can be reached with penalty of 2 dB. The BER- curves in figure 4 are given for the same OTDM channel with and without an extra SMF; however, all OTDM channels gave error-free demultiplexing without an extra SMF and with an extra SMF and post-compensation. 9 10 . . -35 -30 -25 Rx power [dBrnl Figure 4. BER curves for demultiplexing of the signal sent to RX without an extra fiber (DL = I .5 pslnm) and with the extra SMF ( D k 3 . 2  pslnm) with and without post-compensation by the PCU. 4. Conclusion In this paper we have for the first time proposed and demonstrated tunable dispersion post-compensation for 160 Gbls by phase modulation. The performance of the transmission and demultiplexing was found to be error free for the dispersion of the system of 3.2 pslnm. 5. References 1. R. Ludvig el a 1  "Enabling lrmaiiiasion a 160 Gbirls". OFC"02 (2002). paper TuAl 2. A. Siahlo el  al. "Using a phase nidulutor for islpmveniee of the ~olcrmcr 10 second-order dispersion in a I60 Gbh transnirrion sysleni'. 3. T.Kuto el at, 'Tenlpcrarure dependence of chrormtic dispersion in vacious types of optical fibers". 01:C'OO (2000). I. pp. 104-10(, 4. I. Ralhje and M. Andersen,, "Tenipelarure Induced Change in Ihc Dispersion Spectrum of Dispersion Compensuling F ikn" .  OFC'03 (2003). 5. G .  Ishikawa and H. Ooi. ''Dcnmssarion of auioimlic dirpcmion equalization in 40 Gbitls OTDM rransnission", ECOC'98 (19!!8), 1. pp.519- 6. S. Wrkrbryashi er al, 'Tunable Dirpcrsion Slopc Compensator Bared on Chirped FBGr with Tenlpcrriure Distibuiion for 160 Gbirls". 7. E. Hellsirijni el ut. " Evaluaiion of third order dispersion conlpensation by phase aiodukiion for 160 Gbls RZ dara using an all-oplicd 8. L.K. Oxenbwe el al., " A pholonic crystal fibre used as a 160 10 IO  Gbls denuliipleier". OECC'OZ (2003. p p e r  PD-1-4 ECOC'O1 (2003). paperTu 4.7.2 pvperFKl 520 OFC'03 (20031. paper M R 7  sampling sysleni', ECOC'OZ (2002). pspet 6.1.5 Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 17,2010 at 08:41:27 EST from IEEE Xplore.  Restrictions apply. 

Tunable dispersion compensation using phase modulation in receiver part

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Tunable dispersion compensation using phase modulation in receiver part

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