Simultaneous amplification and compression of ultrashort solitons in an erbium-doped nonlinear amplifying fiber loop mirror

Abstract

A simple technique for simultaneous amplification and compression of ultrashort fundamental solitons is proposed. It is based on an erbium-doped nonlinear amplifying fiber loop mirror. Numerical simulations show that, unlike conventional erbium-doped fiber amplifiers in which nonlinear effects lead to serious degradation of pulse quality, the proposed device performs efficient high-quality amplification and compression of ultrashort solitons while nearly preserving the soliton nature of the input pulses. We have also studied the effects of loop characteristics, nonsoliton input pulses, and higher order fiber effects on the device performance and show that the proposed scheme is fairly insensitive to small variations in both the loop and input pulse parameters. Index Terms-Optical fiber amplifiers, optical pulse amplification, optical pulse compression, optical solitons, optical switching. I. INTRODUCTION U LTRASHORT pulse amplification is required in many fields such as ultrafast spectroscopy, optical signal processing, and soliton-based communication systems, etc., because of the relatively low output power levels of commonly used short pulse sources, such as mode-locked semiconductor and fiber lasers. Erbium-doped fiber amplifiers (EDFAs) are widely used for pulse amplification owing to their broad bandwidths (50 nm), high gains (40-dB), and high pulse-saturation energies (1 J). For most applications of ultrashort pulses, the pulse quality is a key factor. It is, therefore, not sufficient to achieve a high gain, but the amplification process must also preserve the pulse quality, which is especially important for soliton-based communication systems. However, distortionless amplification of ultrashort soliton pulses in EDFAs is difficult if fiber nonlinearities such as self-phase modulation (SPM) and Raman self-scattering (RSS) are large [1]-[5]. These nonlinear effects lead to undesirable pulse shaping and serious degradation of the pulse quality. Although adiabatic amplification (small gain) gives high-quality pulses,