Gain flattening of an erbium-doped fiber amplifier using a high-birefringence fiber loop mirror

We propose a flexible method for flattening the gain profile of an erbium-doped fiber amplifier (EDFA). The method is based on a high-birefringence fiber loop mirror (HiBi-FLM), which contains a number of high-birefringence fiber sections and polarization controllers. We show that, by setting the polarization controllers properly, the reflection spectrum of the loop mirror can be adjusted to compensate for the variations in the gain profile of the EDFA. The method is demonstrated experimentally by using a single-section HiBi-FLM and a two-section HiBi-FLM, respectively. With a two-section HiBi-FLM, we are able to flatten the gain profile of an EDFA to within +/- 0.9 dB over a bandwidth of 33 mn at the center wavelength of 1543 mn, under different operating conditions of the EDFA.