EFFECT OF 1/F-TYPE FM NOISE ON SEMICONDUCTOR-LASER LINEWIDTH RESIDUAL IN HIGH-POWER LIMIT

The FM-noise spectrum and the linewidth of 1.3-μm DFB (distributed feedback) semiconductor lasers measured in the high-power state up to 20 mW are discussed. A 5-MHz residual linewidth is observed in the high-power limit. The FM-noise spectrum consists of white noise and 1/f noise. The spectral density of the white noise is reduced by the increase in the output power, whereas that of the 1/f noise is unchanged, which means that the linewidth residual in the high-power limit is caused by the 1/f noise rather than the white noise. The impact of the 1/f-type FM noise on coherent optical communication systems is also discussed.