  Since the analogy between laser oscillation and second-order phase transition
was indicated in the 1970s, dynamical fluctuations on lasing threshold inherent
in critical phenomena have gained significant interest. Here, we numerically
and experimentally demonstrate that a semiconductor laser subject to delayed
optical feedback can exhibit unusual large intensity fluctuations characterized
by power-law distributions. Such an intensity fluctuation consists of distinct
intermittent bursts of light intensity, whose peak values attain tens of times
the intensity of the maximum gain mode. This burst behavior emerges when a
laser with a long time delay (over 100 ns) and an optimal feedback strength
operates around the lasing threshold. The intensity and waiting time statistics
follow power-law-like distributions. This implies the emergence of
nonequilibrium critical phenomena, namely self-organized criticality. In
addition to numerical results, we report experimental results that suggest the
power-law intensity dynamics in a semiconductor laser with delayed feedback.
