Extending the flat gain bandwidth of combined Raman-parametric fiber amplifiers using highly nonlinear fiber

Abstract

Optical fiber parametric amplification is combined with Raman amplification to demonstrate the possibility of extending the flat gain bandwidth of Raman fiber amplifiers. Counter propagating pumps separated by over 145 nm are used to pump a section of highly nonlinear fiber. Parametric gain enables an increase in the gain bandwidth by extending the gain region to the long wavelength side of the Raman gain. Gains of nearly 20 dB have been achieved with this configuration. To achieve gain flatness of 5-6 dB, lower peak gains of between 8 and 14 dB are observed where the variations of the gain and gain flatness are controlled by adjusting the two pump powers. Optimal pump powers are determined that result in good performance amplification by characterizing the receiver power penalty of bit error rate measurements. Negligible power penalty is observed in the region of strong Raman gain whereas nearly a 3 dB power penalty is observed in the region of strong parametric gain. An experimental technique is proposed that helps in the understanding of the coupling of the parametric and Raman processes.