Inhomogeneous MHz-scale intensity noise in double-pass fiber amplifiers

Abstract Here we report about the first demonstration of periodic MHz-scale inhomogeneous relative intensity noise (RIN) induced in double-pass fiber amplifiers. An Er:Yb-doped double-pass fiber amplifier operating near 1570.2 nm and stable continuous-wave single-frequency radiation source are used for the demonstration. The periodic structure of RIN has typical period of units of MHz observed in the range of 0–50 MHz and is formed in the radio-frequency spectrum of the amplified signal. It was found that the key factor influencing period of the RIN structure is spacing between the active fiber and a reflector forming the double-pass amplifier configuration. The population dynamics gratings formed in the active fiber are considered to be responsible for the formation of the periodic RIN structure. Here we investigate an influence of various factors on the period and positions of the RIN structure maxima. The results obtained can be used for designing single-frequency double-pass fiber amplifiers.