Gain flattened and improved double-pass two-stage EDFA using microbending long-period fiber gratings

An optical gain flattened and improved double-pass two-stage EDFA is proposed using microbending long-period fiber grating (LPFG) filters. This type of filter, based on mechanically induced microbends, has desirable characteristics for gain flattening in an EDFA. As such, it is shown that the incorporation a filter in a reflective EDFA can increase the optical gain, plus the optimum position of the filter is obtained as a function of the pump wavelength and power. Accordingly, when using microbending LPFG filters in the second stage of a double-pass two-stage EDFA, an improved flat gain is obtained with a gain improvement of 2.8 dB and gain flatness of less than 1 dB over a 33-nm wavelength range.