Theoretical Comparison of Noise Characteristics in Semiconductor and Fiber Optical Amplifiers

Characteristics of the intensity noise, the phase noise, the frequency noise, and the spectral linewidth in the semiconductor optical amplifier (SOA) and the erbium doped fiber amplifier (EDFA) were theoretically examined with a unified analyzing manner. Quantum mechanical fluctuations associating with the optical amplification and the spontaneous emission were taken into account as noise sources on the traveling optical wave. Quantitative calculated results are obtained. As general features, the SOA reveals higher noise than the EDFA, due to larger inclusion of the amplified spontaneous emission, larger value of the optical absorption and larger fluctuation of the injected electron density. However, the SOA has an exceptional feature to suppress the relative intensity noise (RIN) of the output light below the input RIN level under suitable operating condition. The spectrum linewidth hardly increases in both the SOA and the EDFA under linear operation.