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A novel concept of distributed temperature–strain sensors is proposed using inter-mode Kerr four-wave mixing of polarization-maintaining fiber (PMF), in which the dominated physical mechanism is basically different from reported Brillouin dynamic grating (BDG). The independent measurement for temperature and strain sensitivities (−0.431 MHz °C−1 and 0.067 MHz/10 με) was completed by detecting the change in birefringence under pump-Stokes frequency separation at 370 MHz. As a preliminary proof-of-concept, sensing with a spatial resolution of ∼5 m was demonstrated along ∼210 m PMF. Compared with BDG, the proposed sensor features potential of multiple parameters measurement including temperature–strain and liquid acoustic impedance.

Distributed fiber sensors based on forward stimulated Brillouin scattering (F-SBS) have attracted special attention because of their capability to detect the acoustic impedance of liquid material outside fiber. However, the reported results were based on the extraction of a 1st-order local spectrum, causing the sensing distance to be restricted by pump depletion. Here, a novel post-processing technique was proposed for distributed acoustic impedance sensing by extracting the 2nd-order local spectrum, which is beneficial for improving the sensing signal-to-noise ratio (SNR) significantly, since its pulse energy penetrates into the fiber more deeply. As a proof-of-concept, distributed acoustic impedance sensing along ∼ 1630 m fiber under moderate spatial resolution of ∼ 20 m was demonstrated.

Simultaneous bandwidth (BW) enhancement and time-delay signature (TDS) suppression of chaotic lasing over a wide range of parameters by mutually coupled semiconductor lasers (MCSLs) with random optical injection are proposed and numerically investigated. The influences of system parameters on TDS suppression (characterized by autocorrelation function (ACF) and permutation entropy (PE) around characteristic time) and chaos BW are investigated. The results show that, with the increasing bias current, the ranges of parameters (detuning and injection strength) for the larger BW (> 20 GHz) are broadened considerably, while the parameter range for optimized TDS (< 0.1) is not shrunk obviously. Under optimized parameters, the system can simultaneously achieve two chaos outputs with enhanced BW (> 20 GHz) and perfect TDS suppression. In addition, the system can generate two-channel high-speed truly physical random number sequences at 200 Gbits/s for each channel.

A distributed Brillouin optical time-domain analysis (BOTDA) sensor enhanced by forward stimulated Brillouin scattering (FSBS) based distributed Brillouin amplification (DBA) was proposed and presented. Due to co-propagating of pump and Stokes lights, the Stokes pulse is effectively amplified in front segment of fiber, resulting in flatter gain distribution. As a proof-of-concept, FSBS-DBA based BOTDA sensing with distance of ~74.2 km, Brillouin frequency shift standard deviation of less than ~2 MHz and spatial resolution of ~10 m was demonstrated. This method is compatible and complementary with backward SBS-based DBA, and features better pumping efficiency than Raman amplification.

The influence of the non-local effect on sensing performance in a long-distance Brillouin optical time-domain analyzer (BOTDA) based on bi-directional Raman amplification has been investigated theoretically. The system error induced by the non-local effect worsens with increased powers of probe wave and Raman pump. For smaller Brillouin pump power, the non-local effect is almost independent of Brillouin pump power. For larger Brillouin pump power, the non-local effect deteriorates gradually due to Raman gain saturation and cross-gain modulation (XGM). The purely backward pumping (relative to probe light) is preferable for non-local effect suppression. The frequency-division multiplexing (FDM) and time-division-multiplexing (TDM) technologies exhibit similar performance for suppressing the non-local effect under the same conditions. The sensing range near the far-end (relative to the Brillouin pump) should be appropriately shorter to minimize the non-local effect in FDM and TDM. The physical mechanisms of the non-local effect in long-distance BOTDA with Raman amplification are also shown.