Characteristics of noise in erbium doped fiber amplifier (EDFA) are theoretically analyzed and experimentally verified. Four discreet energy models are used for erbium ion transition. Spatially varying photon number for traveling optical field was defined in a spatially divided segment with finite length, whose length is decided by property of the spontaneous emission. Quantitative evaluation of the Langevin noise sources becomes possible by this model. The amplified spontaneous emission was included in terms of discrete longitudinal mode, which is defined for whole length of the EDFA. It was found that the relative intensity noise (RIN) in the EDFA hardly changes with noise frequency in the region higher than several kHz. The phase noise in EDFA also hardly changes with the noise frequency. The frequency noise of the signal light in the EDFA increases proportional to squared value of the noise frequency. The amount of RIN and the phase noise decrease in higher input optical power. Good correspondence between theoretical and experimental results was obtained.
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