2003 6 20 Research on mode-locked optical fiber laser 1 36303 Abstract- For future ultrahigh-speed optical communications, an ultrashort optical pulse train at a high repetitionrate will be indispensable. Among many pulse generation techniques, mode-locked fiber lasers can generate high-quality short pulses at such a repetition rate and a harmonic modelocking technique must be employed. But a fiber laser is harmonically mode-locked, many supermodes appear and the amplitude of the output pulse fluctuates with time. In this letter, I report the stabilization scheme of mode-locked fiber laser. GHz TDM GHz [1]-[4] m m (Fig.1) ( m λ / 2n) = L (1) Fig.1 view showing a frame format of resonator 1
Fig.2(a) pulse line 1 / δν [5] δν ν Fig.2(b) Spectral profile of (a) ν = ( c / 2nL) m (2) ν λ ν n LiNbO 3 L m 1.48µm Fig.2(a) Fig.2(b) 1 ν 1 t p δν δν = c / 2nL 1.55mm GHz LiNbO 3 Fig.3 PM-DSF 200m 3ps/km/nm µ Fig.3 Experimental setup for harmonically mode-locked fiber 2
AM [6][7] (a) Waveform (b) Spectral profile (c) Extracted clock signal (d) Output pulse trains Fig.5 Output Waveform, spectral profile, extraction clock spectrum, and output pulse trains. [8][9] [10][11] 10GHz 10GHz Fig.4 10GHz µ Fig.4 Experimental setup for harmonically and regeneratively mode-locked fiber at 10GHz 10GHz 10GHz 10GHz Fig.5(a) 1.0ps Fig.5(b) 3
1550nm 2.7nm 10GHz ( 0.08nm) 0.34 sech Fig.5 (c) 1 10GHz 70dBm Fig.5(d) Fig.6 The bit error rate vs. time of the regeneratively mode-locked fiber laser and a conventional fiber laser 100ps 10GHz 2.0mW 2.5W using a synthesizer. 1 PLL 10GHz PLL Fig.7 PLL 2 23 1 ( ) 10Gbit/s (DBM Double Balanced Mixer) Fig.6 µ 10 30 Fig.6 30 Fig.7 Experimental setup for PLL, regeneratively mode-locked fiber laser 4
10GHz 10-9 Fig.8 Change in repetition-rate frequency with time (PZT Piezoelectric Transducer) DSF PZT RF ( T/T) ( ) 1 T / T = ( 2πn) {( P ) } 1/ 2 2 / P1 f J / f res (3) n P 1 P 2 PZT f J f res 1 (10GHz) RF Fig.9 Fig.9 PLL PLL 5KHz 30Hz (b) RF PLL 500V P2 / P1 n= 1 = 3.0 10 100kHz DSF PLL 6 ( ) f J = 600Hz (3) T / T = 1.2 10-3 1MHz T 100ps PLL 120fs 0.9MHz 10GHz PLL (SSB) Fig.10 10GHz PLL SSB Fig.10 Fig.8 PLL SSB ( ) (a) 180fs PLL 120fs 5
FFPI transmission FSR ~ q f 0 (a) (b) Fig.9 RF spectrum of repetition-rate-frequency (a) Synthesizer (b) PLL, regeneratively mode-locked fiber laser Fig.10 SSB noise at 10GHz carrier frequency (a) Synthesizer (b) PLL, regeneratively mode-locked fiber laser f 0 Longitudinal mode Fig.11 illustration of Supermode noise f 0 ( ) q (q ) q f 0 q (Fig.11) 1 PLL PLL PZT khz 10ms ω FFPI FFPI 1 FP (Fiber Fabry-Perot Interferometer FFPI) [12][13] Fig.12 Fig.13 FFPI [14][15] PLL PZT (a) FFPI [16] (b) FFPI FFPI 6
(a) (b) Fig.12 mode-locked pulse trains (a)without FFPI, and RF Power [db] -20-40 -60-80 9.6 9.8 10.0 10.2 10.4 RF Frequency [GHz] (a) (b)with FFPI. RF Power [db] -20-40 -60-80 9.6 9.8 10.0 10.2 10.4 RF Frequency [GHz] (b) Fig.13 RF spectrum of mode-locked fiber laser. (a) (b) Fig.14 RF spectrum of fiber lasers a. Mode-locked laser b. Regeneratively mode-locked laser GHz Fig.14 (a) (b) 4.2 PLL PZT 14kHz Fig.15 PZT (a) (b) 7
(a) (b) Fig.15 RF spectrum of mode-locked fiber laser (a) Without tone (b) With tone pulse phase locking, Electron Lett., Vol.28, No.2, pp.182-184, 1992. [11] E.Yoshida, et al, Wavelength tunable 1.0ps pulse OTDM generation in 1.530-1.555µm region from PLL, regen- eratively modelocked fibre laser, Electron Lett., Vol.34, No.18, pp.1753-1754, 1998. [1] M.Nakazawa, Mode-Locked Fiber Laser Technology for Ultrahigh-Speed TDM Optical Transmission, NTT R&D, Vol48, No.1, pp59-66, 1999. [2] H.Takara, et al, 20GHz transform-limited optical pulse gereration and bit-error-free operation using a tunable, actively modelocked Er-doped fibre ring laser, Electron. Lett., 29, No.13, pp.1149-1150, 1993. [3] Th.Preiffer, et al, 40GHz pulse generation using a widely tunable all-polarization preserving erbium fibre ring laser, Electron Lett., 29, No.21, pp.1849-1850, 1993. [4] T.F.Carruthers and I.N.During, 10-GHz, 1.3-ps erbium fiber laser employing soliton pulse shortening, Optics Letters., 21, No.23, pp.1927-1929, 1996. [5],, pp.28-29.70-71,, 1998. [6] Govind P. Agrawal, Applications of Nonlinear Fiber Optics, pp.218-229, Academic Press. [7] Anthony E. Siegman, Lasers, pp.1056-1058, University Science Books. [8] M.Nakazawa, et al, Ultrastable harmonically and regeneratively modelocked polarization-maintaining erbuim fibre ling laser, Electron.Lett., Vol.30, No19, pp1603-1605, 1994. [9] E.Yoshida, et al, Femutosecond Fiber Laser at 10GHz and Its Application as a Multi-Wavelength Optical Pulse Source, C-1, Vol.J-80-C-1, No.2, pp.70-77, 1997. [10] X.Shan, et al, Stabilising Er fibre soliton laser with [12] Shinji Yamashita, Rie Hayashi, and Takashi Saida, Multiwavelength, Actively Mode-Locked Polarization-Maintaining Fiber Laser at 10GHz, OFC 2003, TuL6, March 2003. [13] G.T.Harvey, L.F.Mollenauer, Harmonically mode-locked fiber ring laser with an internal Fabry-Perot stasbilizer for soliton transmission, Optics Lett., Vol.18, No.2, pp.107, 1993. [14] P.V.Mamyshev, All-optical data regeneration based on self-phase modulation effect, ECOC 98, pp.475-476. 20-24 September 1998. [15] M.Nakazawa, et al, Supermode noise suppression in a harmonically modelocked fibre laser by selfphase modulation and spectral filtering, Electron. Lett., Vol.32, No.5, pp.461-463, 1996. [16] X.Shan and D.M.Spirit, Novel method to suppress noise in harmonically modelocked erbium fibre lasers, Electron. Lett.,Vol.29, No.11, pp.979-981, 1993. 8