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We demonstrate a broadband and wavelength-tunable chaotic laser by using a monolithically integrated wavelength-tunable chaotic semiconductor laser subject to optical feedback. The chip consists of a gain section, a distributed Bragg reflection grating section, a semiconductor optical amplifier section, and a phase section. By applying an optical feedback loop to the chaotic semiconductor laser chip, a nonlinear frequency mixing is stimulated in the laser cavity, and the chaos bandwidth is expanded to 33.6 GHz, which is 4.4 times larger than the bandwidth without optical feedback. Furthermore, the effect of feedback optical power on the bandwidth is investigated. The results show that the wide power spectrum of chaotic laser is available in a large wavelength range from 1556.44 nm to 1566.42 nm. This work explores a broadband and wavelength-tunable chaotic semiconductor laser for the wavelength division multiplexing to enlarge the capacity in chaotic secure optical communications.

The effect of resolution bandwidth (RBW) and video bandwidth (VBW) of a radio-frequency spectrum analyzer on the characteristics of a power spectrum for chaos generated by a semiconductor laser with external optical feedback is investigated experimentally and numerically. We describe the spectral characteristics with effective bandwidth and time-delay signature (TDS) quantificationally. The experimental results demonstrate that the ratio of VBW to RBW has a significant impact on the smoothness of the power spectrum and effective bandwidth of chaos. Meanwhile, the RBW affects the resolution of periodical peaks of the power spectrum and the TDS of chaos, which is obtained by the power spectrum. The incorrect characterization of chaos can be avoided by setting the RBW to no more than 0.1 times as much as the resonance frequency of the external cavity of chaos and setting the VBW/RBW to no more than 0.01. The simulation results qualitatively agree with the analysis of the experiment.

We experimentally observe the local Brillouin dynamic grating (BDG) based on a chaotic laser in a polarization-maintaining fiber for the first time, to the best of our knowledge. The grating length of the chaotic BDG can be adjusted by changing the optical spectral width of the chaotic laser. The characteristics of the reflection spectrum versus the grating length are further analyzed, which agrees with the theory of fiber Bragg grating. Temperature distributed measurements based on the chaotic BDG have been demonstrated with a spatial resolution of an order of centimeter.

We propose a novel, to the best of our knowledge, method to enhance the measurement range of dynamic strain using a single-slope-assisted chaotic Brillouin optical correlation-domain analysis. The broadband chaos provides a Gaussian-shape pump-probe beat spectrum so that not only the centimeter-level spatial resolution is achieved but also the linewidth of the chaotic Brillouin gain spectrum is naturally broadened. Thus, the enlarged linear region could be employed to dynamically measure a large-range stretched strain. This experiment is the first to accurately identify the maximal strain of 1200 µ ε with a high spatial resolution of 3.45 cm using the single-slope-assisted technology. The dynamic frequency is 4.67 Hz in the highest but limited by the practical devices.

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.

A novel Rayleigh noise suppression method is proposed to improve temperature accuracy and resolution for Raman distributed fiber-optics sensors. The proposed temperature demodulation method can eliminate temperature measurement inaccuracy caused by Rayleigh noise. The experimental results indicate that the temperature accuracy is optimized from 6.2°C to 1.7°C at a sensing distance of 9.1 km by using the proposed method, and the temperature resolution leads to about 1.5°C improvement compared with the tradition demodulation method at a sensing distance of 10.0 km. The proposed method provides a robust and reliable high performance for long sensing ranges.

We propose and experimentally demonstrate a novel auto-correction method for improving temperature stability in long-range Raman distributed fiber temperature sensors. The proposed method is based on multi-stage constant temperature control and dynamic gain calibration technology, which can suppress the unstable photoresponsivity and noise of a system. The experimental results indicate that the temperature stability is optimized from ±12.6°C to ±7.2°C at the sensing distance of 30 km for multimode fiber using this method.