We demonstrate an optical-fiber recirculating loop for experimental simulation of long-haul optical communication systems using cascaded erbium-doped fiber amplifiers (EDFA's) operating in the gain saturation regime. The loop contains sections of dispersion shifted fibers (DSF's), standard fiber, and a set of in-line devices, such as tuning filters, optical amplifiers, polarization controllers, and a variable attenuator. The main results presented here are related to the observation of the effects due to the slow dynamics of the EDFA. We also discuss the validity of using an optical attenuator to simulate an extra length of fiber. © 1998 IEEE.463253257Mollenauer, L.F., Neubelt, M.J., Evangelides, S.G., Gordon, J.P., Simpson, J.R., Cohen, L.G., Experimental study of soliton transmission over more than 10000 km in dispersion shifted fiber (1990) Opt. Lett., 15 (21), pp. 1203-1205Malyon, D.J., Widdowson, T., Bryant, E.G., Carter, S.F., Wright, J.V., Stalland, W.A., Demonstration of optical pulse propagation over 10000 km of fiber using recirculating loop (1991) Electron. Lett., 27 (2), pp. 120-121Bergano, N., Aspell, J., Davidson, C.R., Trischitta, P.R., Nyman, B.M., Kerfoot, F.W., Bit error rate measurements of 14000 km 5 Gbit/s fiber amplifier transmission system using recirculating loop (1991) Electron Lett., 27 (21), pp. 1889-1890Nakazawa, M., Yamada, E., Kubota, H., Suzuki, K., 10 Gbit/s soliton data transmission over one million kilometers (1991) Electron. Lett., 27 (14), pp. 1270-1272Mazzali, C., Fragnito, H.L., Tunable and high bit rate erbiumdoped fiber ring soliton source Opt. Amplifiers Applicat., Tech. Dig., pp. 239-242. , Optical Society of America, Washington, DC, 1997Desurvire, E., Digonnet, M.J.F., Shaw, H.J., Raman amplification of recirculating pulses in a reentrant fiber loop (1985) Opt. Lett., 10 (2), pp. 83-85Theory and implementation of a Raman active fiber delay line (1986) J. Lightwave Technol, LT-4, pp. 426-443. , AprNakazawa, M., Kubota, H., Yamada, E., Suzuki, K., Infinite-distance soliton transmission with controls in time and frequency domains (1992) Electron. Lett., 28 (12), pp. 1099-1100Mollenauer, L.F., Litchman, E., Neubelt, M.J., Harvey, G.T., Demonstration using sliding frequency guiding filters, of error free soliton transmission over more than 20000 km at 10 Gbit/s, single channel and over more than 13000 km at 20 Gbit/s in a two-channel WDM Opt. Fiber Commun. (OFC/IOOC) Conf., , presented at the Optical Society of America, Washington, DC, 1993, paper PD8Agrawal, G.P., (1992) Fiber-Optic Communication Systems. New York: WileyKeiser, G., (1991) Optical Fiber Communications, 2nd Ed. New York: McGraw-HillGrischowsky, D., Balant, A.C., Optical pulse compression based on enhanced frequency chirping (1982) Appl. Phys. Lett., 41 (1), pp. 1-3Tkach, R.W., Chraplyvy, A.R., Forghieri, F., Gnauck, A.H., Derosier, R.M., Four-photon mixing and high-speed WDM systems (1995) J. Lightwave Technol., 13, pp. 841-849. , May