In order to achieve gain flatness and increase the bandwidth in optical fiber dense wavelength division multiplexing system

we proposed a method to increase the bandwidth by multi-wavelength pump combination

and flat the gain of the Raman Fiber Amplifier（RFA）by cascaded optical fiber.We use different wavelengths of dual pump to pump the same kind of fiber and increase the transmission bandwidth.Linear fitting Raman gain spectrum is applied to achieve pre-amplification and compensation in RFA.Therefore

large light output signal power and good gain flatness are obtained.The transmission bandwidth is doubled compared to the bandwidth of single pump pumping case.The simulation results show that the proposed method can achieve average optical power of 6.2 mW

average gain of 24.48 dB

gain flatness of 0.08 dB

and transmission bandwidth of 25.6 nm.This paper presents a new method to realize gain-flattened broadband RFA.