We propose a method to flatten Raman gain by using a polarization independent filter. It is formed by a fiber loop mirror contains a number of high birefringence fiber sections and polarization controller. The gain profile is observed for one and two sections of polarization maintaining fiber (PMF) with different lengths. By using single pump wavelength at 1455 nm and 5cm length of Hi-Bi FLM, we managed to flatten Raman gain to within ±0.5 dB over a bandwidth of 43 nm at the center wavelength of 1555 nm. By using two sections of Hi-Bi Fiber and longer PMF, which are 5 cm and 8.5 cm PMF in Hi-Bi FLM, we are able to flatten Raman gain to within ±0.5 dB over a bandwidth of 38 nm at the center wavelength of 1555 nm with lower gain suppression from its original gain profile.
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