High gain low noise L band preamplifier with cascade double pass structure

An optimized two-stage-cascade double-pass structure L-band preamplifier was proposed and experimentally studied to overcome the shortcomings of low gain coefficient and high noise figure of L-band erbium-doped fiber amplifier (EDFA). The fiber lengthes of 6.5 and 32.5 m, pump powers of 130 and 119