| Laser chaos has attracted extensively attention because it provides some promising applications such as high-speed secure communications, high-rate physical random key generation, and high-resolution lidar ranging. External-cavity feedback semiconductor lasers (ECLs) are the first candidate as chaotic light source for the above applications, because of simple configuration and complex dynamics. However, chaos in ECLs has two inherent defects:First, laser relaxation oscillation dominates the chaotic oscillation in ECL and results in a sharp spectrum. The sharp spectrum not only limits the effective bandwidth but also restrains energy of the low-frequency components. The latter will set a limit to the practical application system based on chaotic light because most electronic acquisition devices act as a low-pass filter.Second, external-cavity resonance makes the ECL chaos has time-delay signature and implicit periodicity. This feature will increase the probability that chaos system is cracked and will also degrade the randomness and reliability of the random key extracted from the ECL chaos.Moreover, chaotic ECL actually is not suitable for application in free-space lidar due to its low output power.Aiming at the issues mentioned above, we explore some methods in this Thesis to generate broadband chaos with a flat spectrum and depressed time- delay signature, and study how to use chaotic laser to diagnose fiber faults, i.e., chaos optical time-domain reflectometry (OTDR). The main work and results are summarized as follows.1) We experimentally enhanced the bandwidth of a chaotic ECL about3times to17GHz by using optical injection method; and we also experimentally and numerically uncovered the underlying physics that the unlocking injection induces high-frequency oscillations.2) We proposed a fiber ring resonator equipped with an optical filter as a "bandwidth amplifier" for chaotic laser light, and experimentally achieved a chaotic light with a flat spectrum exceeding over26.5GHz and fluctuating in±1.5dB. In addition, we also revealed the physical mechanism by experimental and theoretical research, and found this method can tune the bandwidth and keep the spectral flatness.3) We found in experiments and simulations, that the delayed self-interference (DSI) of a chaotic ECL can yield a wideband chaos with a depressed time-delay signature. Especially, DSI enhances the low-frequency components and eliminates the domination of laser relaxation oscillation in laser chaos.4) Inspired by the DSI, we proposed a method to generate a physical chaos with a white spectrum, named white chaos, by using optical heterodyne of two chaotic ECLs. The heterodyne method can eliminate the signatures of time delay and of relaxation oscillation. A white chaotic spectrum with1-dB fluctuation in a band of11GHz was experimentally obtained.5) The application of chaotic ECL in OTDR was explored. We utilized a single-mode laser to generate a chaotic light with a fixed wavelength for diagnosing a single fiber link, and employed a multimode FP laser with filtered feedback to generate wavelength-tunable chaotic light for detecting a fiber network. We experimentally achieved a centimeter-range resolution which is independent of measure distance. In addition, we also developed a prototype of chaos OTDR, in which the chaotic light source is improved by the fiber ring resonator we proposed.6) We also developed a prototype of random bit generator based on a chaotic ECL, which can generate physical random bits with a maximum rate of4.5Gbit/s in real time. In addition, we also examined the promotion given by the DSI signal of an ECL onto the random bit generation, and found it can improve the radom-bit speed5/3times for the quantization scheme using multi-bit ADC. |
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