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.

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We demonstrated a structure for extending repeater-less sensing distance of Brillouin optical time-domain analysis enhanced by distributed Brillouin amplification (DBA-BOTDA) through a combination with the Brillouin phase spectrum (BPS), where parallel demodulation of the frequency-comb pump can be realized. The careful structure design is implemented to perfectly suppress the impacts of various phase noises on long-distance BPS extraction. ∼98.9 km sensing distance and ∼6.5 m spatial resolution were demonstrated, with only four times frequency sweeping. The standard deviation of Brillouin frequency shift can be decreased to within ∼2 MHz by a combination of Brillouin gain spectrum and BPS.

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.

The impacts of nonlinear effects on sensing performance of forward stimulated Brillouin scattering (FSBS) were investigated, using opto-mechanical time-domain analysis (OMTDA) sensor as an example. The excitation of FSBS often requires high pulse power (Watt level) because of the lower gain coefficient. Due to the copropagation of reading pulse and scattered light, high-power activation pulses will induce various nonlinear effects in FSBS sensing system. Using the reported method based on activation-reading time-domain separation, the influence of nonlinear effects due to activation pulses can be effectively avoided. However, the nonlinear effects of reading pulses have direct impact on sensing performance. Based on this consideration, we studied the influence of nonlinear effects on FSBS sensing and its physical mechanism under different peak power of reading pulses; the variation process of the 1st- and 2nd-order FSBS spectrums along~4.7 km standard single-mode fiber (SMF) was shown in detail. Finally, the optimization region was found, inside which a perfect FSBS local spectrum was obtained, and the sensing distance extension can be achieved.