Dependence of semiconductor laser linewidth on measurement time: evidence of predominance of 1/ f noise

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Abstract
Linewidths of 1.3 μm InGaAsP lasers were measured by using delayed self-heterodyne set-ups with two different delay-line lengths, i.e. with two equivalent measurement times. It has been found that in high-power operation the linewidth increases as the measurement time becomes longer, and that this dependence is explained well by a calculation assuming that the 1/f noise in the FM noise spectrum is the predominant cause of the spectral broadening. The significance of this fact in coherent optical communications is discussed.