Mach-Zehnder interferometer concatenated fiber loop mirror based gain equalization filter for an EDFA

An all-fiber interferometric technique for gain flattening of amplitude spontaneous emission (ASE) response of an erbium doped fiber amplifier (EDFA) is presented. In the proposed method, a single-stage Mach-Zehnder interferometer (MZI) is cascaded to a fiber loop mirror configuration with polarization controllers incorporated inside the loop. By the mean of variation in polarization controller's orientation and number of fiber loops in it, it is possible to tune and modify the sliced wavelength spectrum of a single-stage MZI for achieving equalization of the EDFA gain spectrum. The present scheme has many advantages for being low loss, polarization independent, easy to tune and is demonstrated through simulation study and verified by experiments. The flattened ASE gain spectrum of an EDF over wavelength range of 35 nm with peak to peak difference of ±0.4 dB is obtained.