Crosstalk between WDM channels in double pumped fiber optic parametric amplifier F. A. Callegari (1), J. M. Chavez Boggio (2), P. Dainese (3), H. L. Fragnito (4) 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. pdainese@ifi.unicamp.br, 4 : Unicamp. hugo@ifi.unicamp.br Abstract We analyze the amplification of WDM signals in two-pump optical parametric amplifier with several modulated signal channels, we show that crosstalk can be mitigated by adjusting the pump power and fiber length. Introduction Two-pump fiber optical parametric amplifiers (2P- FOPA) [1-4] provide flatter and broader bandwidth than one-pump FOPA (1P-FOPA). 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 demonstrated 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 -1 , attenuation coefficient α = 0.2 dB/km, zero dispersion wavelength λ 0 = 1568 nm, dispersion slope, S 0 = 0.07 ps nm -2 Km - 1 . 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 bit long word). Fig1 shows the setup. PM indicates the phase modulators. The signals are multiplexed (MUX) and placed at the imput of fiber with the pumps through a coupler. At the output of the system, the channels are optically filtered with a Bessel filter of order 10 and bandwidth of four times the bit rate. Fig. 1. Schematic used in the simulations, symbols are explained in text. Then the optical signal is converted electrically through a p-i-n photodiode receiver, 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. 2 shows the input (as seen at the monitor port of Fig.1) and output spectra with 0.1 nm resolution, obtained for the in-line amplifier case. We have a net gain of ~22 dB (25 dB parametric gain  3 dB input coupler loss), and approximately constant throughout the system band. Fig. 2. Simulated spectra obtained for in-line case. PUMPS λ 2 λ 2 λ 1 λ 1 SIGNALS λλ 1 λ 2 λ Ν Nx1 MUX P M P M INPUT OUTPUT MONITOR 3dB 3dB PUMPS λ 2 λ 2 λ 1 λ 1 SIGNALS λλ 1 λ 2 λ Ν Nx1 MUX P M P M INPUT OUTPUT MONITOR 3dB 3dB 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 Monitor 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 Monitor Output λ 0