We propose and demonstrate a method to generate a flat broadband chaotic laser by using an active optical feedback loop combined with a high nonlinear fiber. The feedback strength and nonlinear effect, especially the four-wave mixing effect of high nonlinear fiber, are studied to improve the bandwidth and flatness of chaos. When the feedback strength is 6.6 and injected fiber power is 1.0 W, a chaotic signal with a frequency range over 50 GHz, 80% bandwidth of 38.9 GHz, and flatness of 4.2 dB are experimentally achieved.

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Chaotic laser generated by semiconductor lasers has been attached great importance in areas of secure communication, random number generation, and optical sensing. This article mainly reviews the research progress in the performance improvement of chaotic laser, including bandwidth enhancement and time-delay signature suppression. First, the methods of chaotic laser generation and the existing problems are briefly introduced. Then, innovative methods for the optimization of chaotic characteristics are analyzed and discussed. The integrated chaotic semiconductor lasers are also discussed. At last, avenues for the development trends and future applications of chaotic semiconductor lasers are prospected.