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Masataka Nakazawa 　（中澤　正隆） Research Institute of Electrical Communication （電気通信研究所）

台湾中山大學　 Seminar 高雄 , Dec., 6th, 2007. Advanced optical fiber technology for high-speed optical communication. Masataka Nakazawa 　（中澤　正隆） Research Institute of Electrical Communication （電気通信研究所） Tohoku University （東北大學） 2-1-1 Katahira, Aoba-ku, Sendai-shi, 980-8577 Japan.

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Masataka Nakazawa 　（中澤　正隆） Research Institute of Electrical Communication （電気通信研究所）

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  1. 台湾中山大學　Seminar 高雄, Dec., 6th, 2007 Advanced optical fiber technology for high-speed optical communication Masataka Nakazawa　（中澤　正隆） Research Institute of Electrical Communication（電気通信研究所） Tohoku University（東北大學） 2-1-1 Katahira, Aoba-ku, Sendai-shi, 980-8577 Japan

  2. Advanced photonic network ・OTDM / ETDM ・High capacity WDM ・Multi-wavelength processing Recently 100 Gbit/s ETDM is feasible ■ High speed/high capacity transport system ○Mode-locked lasers ○Pulse compression/reshaping devices ○Dispersion/PMD compensation devices ○Ultrafast demultiplexing (NOLM, SMZ) ○Optical 3R regenerator/Adaptive optical equalizer ■ Ultrafast photonic devices Core node ■ Networking devices ・ Wavelength routing ・ Optical packet routing ・ Optical switching (OXC, Burst, Packet) ○OADM(FBG, AWG, Tunable filters) ・ Optical header recognition ・ Optical buffer memory ○Wavelength conversion/Tunable optical source IDC, ISP Edge node ISP

  3. Fiber key technologies for ultrafast optical transmission • Ultrashort optical pulse generation in the pico-femtosecond region • Pulse generation using mode-locked lasers/high-speed modulation • Pulse compression using DF-DDF • Pedestal reduction of compressed pulses using DI-NOLM • Compensation of the total dispersion of a transmission line • Third- and fourth-order dispersion compensation • (3) Ultrafast demultiplexing • Ultrafast NOLM with 1 ps switching window In ultrahigh-speed systems at > 160 Gbit/s, fiber devices are widely used. • Advantages of fiber devices are • Ultrafast response speed of 10 fs • Low loss  Excellent figure of merit • Ultra wide band (800-1600 nm) • Low noise • High reliability

  4. Outline • (1) Optical sources • (2) Pulse compression and reshaping • (3) Transmission line • Dispersion management • Nonlinear fiber effects • PCF and PBF and their applications • (4) Demultiplexing • (5) A new transmission scheme using optical Fourier transformation / • Parabolic pulse generation • (6) Summary

  5. 1.28 Tbit/s OTDM transmission using advanced fiber technologies M. Nakazawa et al., Electron. Lett., vol. 24, 2027 (2000).

  6. Single-channel 1.28 Tbit/s and 2.56 Tbit/s DQPSK transmission H. G. Weber et al., Electron. Lett., vol. 42, 178 (2006).

  7. 1.48 mm LD WDM Coupler PM-EDF PM-DSF Optical filter (Soliton Effect) Intensity Modulator PZT Coupler Phase-locked-loop (PLL) Stabilization 40 GHz 90 mA Isolator Regeneratively Mode-locked Loop Coupler Electro-Absorption Modulator DBR Gain Amp 40 GHz, ps Optical Output 40 GHz Clock Extraction Circuit Phase Controller 0.7 mW 40 GHz Microwave Output InGaAsP R = 10 % R = 30 % High Voltage Controller Synthesizer DBM Cavity length = 3.8 mm Feedback Circuit 10~40 GHz MLFL and MLLD

  8. Regeneratively and harmonically mode-locked fiber laser f f A B 1.48mmLD Intensity |E|2 PM-EDF (15 m) Filter PZT Timet Optical filter B A Intensity modulator Isolator PM-DSF (70 m) f f Clock extraction circuit SPM Phase controller Optical output pulses frep= 40 GHz Frequency t t fFSR= 2 MHz (2x104 harmonics) M. Nakazawa et al., Electron. Lett., vol. 32, pp. 461-462, Feb. (1996). M. Nakazawa et al., Electron. Lett., 30, 1603 (1994)

  9. 2.2 nm (273 GHz) 1.4 ps Resolution: 1 kHz Linear scale [a.u.] 1 kHz 10 kHz/div Output pulse characteristics at 40 GHz Autocorrelation waveform Optical spectrum 40 GHz clock spectrum Time-bandwidth product = 0.36 (Nearly transform-limited sech pulse) Features: (1) Transform-limited picosecond pulse (2) Symmetric comb profile (3) Ultranarrow linewidth (4) Ultrastable repetition rate (5) 1~3 mW Output (easy amp. with EDFA)

  10. Outline • (1) Optical sources • (2) Pulse compression and reshaping • (3) Transmission line • Dispersion management • Nonlinear fiber effects • PCF and PBF and their applications • (4) Demultiplexing • (5) A new transmission scheme using optical Fourier transformation / • Parabolic pulse generation • (6) Summary

  11. Pulse compression using a dispersion decreasing fiber (DDF) Adiabatic soliton compression GVD t = 3 ps 10 ps/nm/km t < 100 fs 0.1 ps/nm/km z D : GVD t : pulse width D Soliton energy E  t • Pulse width t can be compressed when D is adiabatically decreased as a function of distance z. • 3 ps pulses can be compressed to < 100 fs at 10 GHz.

  12. Wavelength tunable femtosecond pulse compression using a dispersion-flattened DDF K. Tamura and M. Nakazawa, PTL, 11, 319 (1999).

  13. Pedestal elimination using a dispersion-imbalanced nonlinear optical loop mirror (DI-NOLM) K. Tamura and M. Nakazawa, PTL, 11, 230 (1999).

  14. 54 fs pulse generation in a polarization-maintaining dispersion-flattened dispersion decreasing fiber

  15. 0.09 nm (11 GHz) SBS Source spectrum leaked through the circulator Problem in ultrahigh-speed pulse compression EDFA DDF 40 GHz, 1.7 ps Mode-locked Fiber Laser (MLFL) Optical Spectrum Analyzer Linewidth ~1 kHz (a) Compressed (b) Uncompressed Output waveforms • In ultrahigh-speed pulse compression that exceeds 40 GHz, the optical power of each longitudinal mode increases, and stimulated Brillouin scattering (SBS) occurs. • Output power from DDF varied randomly due to SBS, resulting in unstable compression. Optical spectrum of backscattered light from DDF

  16. Outline • (1) Optical sources • (2) Pulse compression and reshaping • (3) Transmission line • Dispersion management • Nonlinear fiber effects • PCF and PBF and their applications • (4) Demultiplexing • (5) A new transmission scheme using optical Fourier transformation / • Parabolic pulse generation • (6) Summary

  17. SMF DSCF 25 km 5 km Femtosecond pulse propagation in a dispersion-managed fiber 30 km 30 km 29.99 km 0.1 km 0 km 0 km Time GVD

  18. Dispersion-managed transmission line Dispersion management Line (DML) Each portion; Non-zero dispersion (For FWM suppression) Total; Zero and flat dispersion (For wide-band transmission) D+ D- L D+ Positive Disp. Positive Slope D- Negative Disp. Negative Slope + Power Nonlinearity D [ps/nm/km] D+ Total Trade-off between D. slope and Aeff in SLA+IDF 0 Wavelength D- K.Mukasa et al., ECOC97 Proceeding, Mo3C-127 (1997)

  19. Intensity Intensity 1.6 ps/div 1.6 ps/div Time Time Intensity Intensity 1.6 ps/div 1.6 ps/div Time Time Pulse waveforms 1.28 Tbit/s – 0 km (Pre-Chirped) 1.28 Tbit/s – 70 km (a) (b) After Polarization Demultiplexing (c) (d)

  20. Nonlinear effects in fibers and their applications SPM • pulse compression • supercontinuum generation • intensity filter • soliton effect XPM • all-optical switch (demultiplexer, regenerator) • wavelength converter FWM • parametric amplifier • optical limiter • wavelength converter • demultiplexer • phase conjugator SRS • amplifier • modulator SBS slow light • amplifier • narrowband filter •

  21. Stimulated Raman Scattering (SRS) Gain coefficient Frequency (cm-1) F. Forghieri et al., Optical Fiber Telecommunications IIIA , I. P. Kaminow and T. L. Koch Eds., Academic Press (1997). M. Nakazawa, Appl. Phys. Lett., 46, 628 (1985).

  22. Gain-flattened 10.2-THz continuous bandwidth inline optical repeater 10.2 THz, 84 nm (1536-1620nm) 15 Total 10 Gain (dB) 5 P-EDFA Raman 0 1540 1560 1580 1600 1620 Wavelength (nm) The largest bandwidth of 10.2 THz was achieved using P-EDFA gain-blocks and a two-l pumped Raman amplifier gain-block By courtesy of NTT Masuda et al., OFC2007

  23. Parametric amplifiers based on FWM • Two-pump amplifier • broadband • polarization-independent operation is obtained with orthogonal polarization pumps HNLF (1 km) g = 17 W-1km-1 K. K. Y. Wong et al., PTL 14,911 (2002).

  24. Spectral broadening of an optical comb using PCF J. K. Ranka et al., Opt. Lett., vol. 25, pp. 25-27 (2000). Broadened comb with PCF Ti:Sapphire laser Comb based on a mode-locked laser Photonic crystal fiber (PCF) By courtesy of AIST

  25. Octave-spanning comb using femtosecond fiber laser and HNLF Pump Isolator WDM coupler Coupler Oscillator Polarizer +controller Er:fiber Drum PZT OSA Oscillator Amplifier • HNLF • Length: 20 cm • Zero dispersion wavelength: 1447 nm • nonlinear coefficient g: 21 /W/km • frep: 54 MHz • Pulse width: 90 fs • Center wavelength: 1560 nm • Average power: 40-50 mW M. Nakazawa, et al. Electron. Lett. 29, 1327, 1993 Octave-spanning comb 0 -10 -20 Norm.spectral power (dB) -30 -40 1020 2040 -50 Wavelength (nm) H. Inaba et al., Opt. Express, 14, 5223 (2006).

  26. n f(n) frep fCEO Carrier envelope offset (fCEO) Carrier envelope phase frep fCEO frep - fCEO 45dB at 100 kHz RBW The Fourier transformation between time and frequency axes Carrier envelope offset beat f(n) = nfrep + fCEO fCEO = (Df/2p)frep : fCEO is obtained by one octave method. Ref.: Th. Udem et al., Phy. Rev. Lett., 82, 3568 (1999).

  27. Long-term frequency measurement of iodine stabilized Nd:YAG laser Continuous measurement over 1 week! H. Inaba et al., Opt. Exp. 14, 5223 (2006). By courtesy of AIST

  28. Nonlinear optical properties of SWCNT • SWCNT (Single-Wall Carbon Nano Tube) • Saturable absorption effects in infrared wavelengths • Recovery time < 1 ps • Possibility of simple, low cost, ultrahigh-speed nonlinear optical material in the 1.5 mm band • Applications: • Pulse shaping • ASE noise reduction • Passively mode-locked laser [1] Y. –C. Chen, et al., Appl. Phys. Lett., vol. 81, 975 (2002). [2] Y. Sakakibara et al., Japan patent 2001-320383. SWCNT

  29. Passively mode-locked fiber laser with SWNT/PMMA as a saturable absorber Polarization controller PMMA/SWNT Cavity length: 10.3 m Lens Lens Collimator Collimator PM optical isolator Z-axis movable stage Focal Point Diameter: 10 mm EDFA PM optical isolator 120 SWNT/PMMA Optical output 100 1550 nm PM coupler 80 Absorbance [%] 60 SWNT 40 SWNT (S1 absorption) 20 0 1000 1500 2000 2500 Wavelength [nm] PMMA with SWNT SWNT: produced by HiPCO method SWNT concentration: 500 ppm Linear absorption spectra M. Nakazawa et al., Opt. Lett., 31, 915 (2006).

  30. Laser output characteristics Pump power: 60.3 mW Optical spectrum Autocorrelation waveform FWHM= 317 fs (sech) Time-bandwidth product = 0.26 Output power = 5.2 mW Repetition rate = 19.4 MHz

  31. Classification of photonic crystal fibers

  32. Dispersion characteristics of PCF GVD GVD + + Strongly guiding Air-silica (structural dispersion) PCF 0 Bulk Silica (material dispersion) − − 0.6 0.8 1 1.2 1.4 1.6 0.6 0.8 1 1.2 1.4 1.6 Wavelength (mm) Wavelength (mm) (a) (b) d L ・Conventional fiber (doped core fiber) structural dispersion < 0 ・Zero dispersion wavelength > 1.28 mm

  33. 10 Gb/s x 4ch WDM transmission at 850 nm using PCF Channel 1 Channel 2 Channel 3 Channel 4 21 dB 10 dB/div 20 ps/div Received optical power (dBm) Wavelength (nm) Photonic crystal fiber 5 km VCSEL1 VCSEL2 Si-APD BERT LN modulator 10 Gb/s, NRZ AWG AWG VCSEL3 Air hole pitch: 3.4 mm Air hole diameter: 1.2 mm Mode field diameter: 5.3 mm Transmission loss: 5.2 dB/km Dispersion: -62.8 ps/nm/km Optical amplifier (EDFFA) Optical amplifier (EDFFA) VCSEL4 Light source in the 800 nm region WDM MUX WDM DEMUX Eye diagram and optical spectrum (Ch.1) Bit error rate • 10 Gbit/s-2 km transmission was also achieved without EDFFA. • 40 Gbit/s-2 km transmission was also demonstrated. VCSEL: Vertical Cavity Surface Emitting Laser AWG: Arrayed Waveguide Grating EDFFA: Erbium-Doped Fluoride Fiber Amplifier Si-APD: Silicon Avalanche Photo Diode BERT: Bit Error Rate Tester [1] Y. Oikawa et al., Photon. Technol Lett, 19, 613 (2007). [2] H. Hasegawa et al., Electron. Lett., 43, 117 (2007). [3] H. Hasegawa et al., Electron. Lett., 43, 642 (2007).

  34. All-fiber acetylene (C2H2) gas cell using PBF Splice with SMF Transmission spectrum Application ・Frequency standard ・Compact frequency-stabilized laser ・Interaction between light and atom End view cleaved from a few mm from the splice F. Benabid et al., Nature, vol.434, 488 (2005).

  35. 1 Gsymbol/s, 64 coherent QAM optical transmission[1] FBG OFS： Optical frequency shifter EDFA: Erbium-doped fiber amplifier DSF: Dispersion-shifted fiber PC: Polarization controller Pol: Polarizer PD: Photo-detector DBM: Double balanced mixer Synthesizer (fOFS =2.5 GHz) PC1 Pilot signal OFS ⊥ Optical Filter (～5nm) PC3 Q EDFA EDFA C2H2 Frequency- Stabilized Fiber Laser[2] PC2 QAM Modulator // EDFA Attenuator EDFA I DSF 75 km DSF 75 km Arbitrary Waveform Generator IF signal fIF=fsyn+fOFS=4 GHz ⊥, // PC4 Pol Digital Signal Processor A/D PD // // EDF 1.48 mm LD High voltage controller Feedback circuit ｜fOFS- fLO｜=fsyn PZT Feedback Circuit PC5 PD ⊥ DBM PC6 WDM coupler Lock-in amplifier Cavity length ~ 4 m (FSR= 49.0 MHz) FBG Synthesizer (fsyn= 1.5 GHz) Circulator // MLP EDFA 90/10 coupler Local Oscillator C2H2 cell Coupler (Tunable Fiber Laser) PD Feedback circuit LN modulator Laser output [1] J. Hongo et al., Photon. Technol. Lett., 19, 638 (2007). [2] K. Kasai et al., OFC2006, OWM4

  36. Reflection spectrum of PM FBG filter Maximum reflectance 65 % Side lobe suppression 13 dB Linewidth 1.3 GHz Center wavelength 1538.21 nm Measured reflection spectrum A. Suzuki et al., IEICE ELEX, vol. 3, 469 (2006).

  37. Experimental results for 1 Gsymbol/s, 64 QAM transmission over 150 km Q Q I I Transmission power: - 5 dBm Back-to-back Constellation map After 150 km transmission 10-3 Bit Error Rate Eye pattern (I) 10-4 3 dB 10-5 -28 -26 -34 -32 -30 Received Power [dBm] Eye pattern (Q) Bit Error Rate characteristics (a)Back-to-back (Received power: -27 dBm) (b)After 150 km transmission (Received power: -24 dBm)

  38. Experimental result for polarization-multiplexed 1 Gsymbol/s, 128 QAM (14 Gbit/s) transmission over 160 km -1 -1 -1 0 0 0 +1 +1 +1 I symbol I symbol I symbol -1 -1 -1 0 0 0 +1 +1 +1 Q symbol Q symbol Q symbol Q Q Q Constellation diagram I I I Eye pattern (I) Eye pattern (Q) (a) Back-to-back (Received power: -29.5 dBm) (b) 160 km transmission for orthogonal data (Received power: -26.5 dBm) (c) 160 km transmission for parallel data (Received power: -26.5 dBm)

  39. Outline • (1) Optical sources • (2) Pulse compression and reshaping • (3) Transmission line • Dispersion management • Nonlinear fiber effects • PCF and PBF and their applications • (4) Demultiplexing • (5) A new transmission scheme using optical Fourier transformation / • Parabolic pulse generation • (6) Summary

  40. 1.28 Tbit/s OTDM transmission using advanced fiber technologies M. Nakazawa et al., Electron. Lett., vol. 24, 2027 (2000).

  41. Reduction of walk-off in NOLM for demultiplexing Group delay characteristics of walk-off free NOLM M. Nakazawa et al., Electron. Lett., 34, 907 (1998).

  42. Error-free 320 Gb/s simultaneous add-drop multiplexing using NOLM Add port Drop port H. C. Hansen Mulvad et al., OFC2007, OTuI5.

  43. Outline • (1) Optical sources • (2) Pulse compression and reshaping • (3) Transmission line • Dispersion management • Nonlinear fiber effects • PCF and PBF and their applications • (4) Demultiplexing • (5) A new transmission scheme using optical Fourier transformation / • Parabolic pulse generation • (6) Summary

  44. f Distortion-free transmission using time-domain optical Fourier transformation (OFT) Conventional optical transmission Jitter, Higher- order dispersion, PMD, Adaptive equalization, … Waveform disturbed. Transmitted spectrum may vary. t t t Compensation of individual waveform distortion in time domain No rigid restrictions on input spectrum f Distortion-free transmission with optical Fourier transformation (OFT) Transform spectrum into waveform in time domain Spectral shape must be maintained. Dt PM GVD t t f OFT CLK Transform-limited pulse DtDn=0.44 (Gaussian) DtDn=0.32 (Sech) Simultaneous elimination of all linear distortions (including time-varying perturbations) Dn

  45. Distortion-free transmission using time-domain optical Fourier transformation (OFT) PM CLK ３ １ ２ Advantage: Any linear distortions (even when they vary with time) can be eliminated simultaneously with only one circuit. v(t) u(z, t) uchirp(t) D = k”L V(w) U(z, w) GVD １ The transmitted pulse is linearly chirped in the form (K is the chirp rate) Time OFT ２ When uchirp(t)is passed through a GVD medium, the outputv(t) is expressed as ３ WhenD =1/K, the output v(t) is written in the following form Time The output waveform is proportional to the input spectrumU(z,w), w = t/D. M. Nakazawa et al, PTL, vol. 16, 1059 (2004).

  46. 40 GHz Phase Modulator 160  40 Gbit/s DEMUX PC EDFA EDFA CLK SMF Phase Shifter Phase Shifter f f 1:4 MUX 10 GHz OFTC 160 Gbit/s-1,000 km OTDM DPSK transmission using time-domain OFT DPSK Modulator 40 GHz MLFL (1550 nm) 40  160 Gbit/s MUX PC SMF 50 km IDF 25 km EDFA PLL Q Q PC 40 Gbit/s 215-1 PRBS PPG x13 40 GHz 975 km transmission line 160 Gbit/s transmitter Back-to-back 975 km (without OFTC) 975 km (with OFTC) OOK 1 1 0 1 EDFA DI ATT Error Detector Balanced PD Data  Optical intensity Receiver (Demux, OFT, and demodulation) DPSK 1 1 0 1 Data  Optical phase change

  47. All-optical time-domain OFT by XPM in fiber with a parabolic pulse uchirp(t) v(t) us(t) Chirp rate K GVD uc(t) D = 1/K Nonlinear coefficient g, Length l Apply linear chirp to a signal us(t) by cross-phase modulation with a control pulse (parabolic pulse) uc(t). Phase modulation df and chirp dw applied to signal us(t) P0 t t i.e., chirp rate [1] T. Hirooka et al., CLEO-PR2005, CFJ3-4INV. [2] T. T. Ng et al., OFC2007, JWA58.

  48. 40 GHz bright and dark parabolic pulse generation using AWG Parabola fitting Parabola fitting 64 ch AWG pulse shaper VOA PS Parabola-shaping optical filter (pre-shaping) 40 GHz mode-locked fiber laser 128 ch current source Bright parabolic pulse Dark parabolic pulse

  49. Elimination of third-order dispersion by all-optical FT at 40 GHz 3 ps 10 ps 3 ps 3 ps Optical Sampling Scope Transmission Fiber (Dl) 40 GHz Mode-locked Fiber Laser Optical Delay Line Polarization Controller 5 nm 1550 nm, 1.7 ps Clock Recovery GVD HNLF 1 km g = 17 W-1km-1 lzero disp= 1543 nm 40 GHz Mode-locked Fiber Laser AWG Pulse Shaper Optical Spectrum Analyzer Pctrl = 28.5 dBm 1st Parabolic Filtering Line by Line Shaping 1537 nm, 1.7 ps Distorted Signal Pulse OFT Output Dark Parabolic Pulse OFT Output (Sinusoidal PM)

  50. Summary We have reviewed advanced fiber technologies and their applications to high-speed optical communication, in which we showed that such fiber device technologies are indispensable to realize ultrahigh-speed communication. Key fiber technologies cover various fields such as (1) Optical source (2) Pulse compression and reshaping (3) Transmission line (4) Nonlinear effects (5) Demultiplexing Advanced fiber device technology will largely accelerate ultrahigh-speed optical communication as the fibers have an excellent figure of merit due to low loss and long-length characteristics.

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