Crosstalk mitigation in fiber optic parametric amplifier F. A. Callegari (1), J. M. Chavez Boggio , (2), H. L. Fragnito (3) 1 : Instituto de Fsica Gleb Wataghin Unicamp, 13083-970, CP 6165 Campinas, SP Brazil. andres@ifi.unicamp.br 2 : Unicamp. jmchavez@ifi.unicamp.br 3 : Unicamp. hugo@ifi.unicamp.br Abstract We analyze the amplification of WDM modulated signal channels in two-pump optical parametric amplifiers. Crosstalk between channels can be mitigated by adjusting values of pump power and fiber length. Introduction Two-pump fiber optical parametric amplifiers (2P- FOPAs) [1-4] provide flatter and broader bandwidth than one-pump FOPAs (1P-FOPAs). Recently [4], 6 unmodulated WDM channels were amplified to 40 dB, indicating the potential of 2P-FOPAS for WDM systems. Crosstalk among WDM channels is expected to occur in parametric amplifiers, due to parasite four wave mixing (FWM) between the channels, as observed recently in 1P-FOPA [5]. In 2P-FOPA FWM is better phase matched than in 1P-FOPA. This problem has not been addressed to the present. In this paper, we analyze crosstalk in 2P-FOPAs with 13 WDM signal channels in 2 situations. In a first case, we simulate an in-line amplifier with moderate output powers (~ 0 dBm). We show that for a fixed gain, crosstalk can be reduced using a shorter fiber and larger pump power. In the second case, we simulate a preamplifier with low output power (~ -15 dBm). Our results indicate that 2P-FOPA are good devices as preamplifier but rather limited for in-line amplification. Simulation We solve the non-linear Schordinger equation using the split step Fourier method [6] for a fiber with non linear coefficient γ = 2.1 W -1 /Km, attenuation coefficient α = 0.2 dB/km, zero dispersion wavelength λ 0 = 1568 nm, and dispersion slope, S 0 = 0.07 ps /Km/ nm 2 . Pump lasers (λ 1 and λ 2 ) are set to 1555 nm and 1580 nm, and spectrally broadened by phase modulation to 10 GHz (this is necessary in experiments to prevent stimulated Brillouin scattering). The phase modulations were phased keeping the instantaneous sum of pump frequencies constant [7]. We consider an input of 13 WDM channels, with 100 GHz spacing and 10 Gb/s, uncorrelated random bit patterns (NRZ, 64 bits long word). At the output of the system, the channels are optically filtered with a 10 th filter order and bandwidth of four times the bit rate. Then the optical signal is electrically analyzed, and filtered with a low pass 4 th order Bessel filter with a cutt-off frequency of 0.7 times the bit rate. Results and discussion Fig. 1 shows typical input and output spectra with 0.1 nm resolution, obtained for the in-line amplifier case. Input signal powers are ~ -25 dBm. We have a parametric gain of ~25 dB, approximately constant throughout the system band. Fig 1. Simulated spectra obtained for in-line case We can see at output spectrum the idler waves, which are generate in a symmetrical way respect to signals, relative to λ 0 . Ideal noise figure of 2-PFOPAs is ~3 dB, we have an optical signal to noise ratio at output of ~ 23 dB. Fig.2 shows signal eye diagram obtained at output of fiber used as amplification medium, for channel tuned at 1559.82 nm, for four different choices of pump power (P 1 = P 2 = P) and fiber length (L). In case (a): L = 15 km, P = 18.5 dBm, (b): L = 10 km , P = 19.2 dBm, (c): L = 5 km, P = 21.5 dBm, (d ): L = 2.5 km, P = 24.2 dBm. In all cases, these values maintain the parametric gain fixed to ~25 dB. 1540 1550 1560 1570 1580 1590 -60 -50 -40 -30 -20 -10 0 10 20 Power, (dBm) Wavelength, (nm) λ 1 λ 2 ~25 dB Output λ 0 1540 1550 1560 1570 1580 1590 -60 -50 -40 -30 -20 -10 0 10 20 Power, (dBm) Wavelength, (nm) λ 1 λ 2 ~25 dB Input Output λ 0 1540 1550 1560 1570 1580 1590 -60 -50 -40 -30 -20 -10 0 10 20 Power, (dBm) Wavelength, (nm) λ 1 λ 2 ~25 dB Output λ 0 1540 1550 1560 1570 1580 1590 -60 -50 -40 -30 -20 -10 0 10 20 Power, (dBm) Wavelength, (nm) λ 1 λ 2 ~25 dB Input Output λ 0 2002 IEEE LEOS Europe Meeting - Glasgow, Scotland, UK - Conference Proceedings - Paper WB3