In this paper, a digitalized polarization fading suppression and phase demodulation technique for a phase-sensitive optical time-domain reflectometry (φ-OTDR) sensing system utilizing polarization diversity virtual coherence is proposed, in which virtual cross-coherence between the polarization diversity digital signals is employed for simultaneous fading noise suppression and phase demodulation. The principle of the proposed demodulation algorithm is presented and analyzed. Based on this, the practicability and validity of the proposed demodulation method for fading noise suppression and distributed vibration sensing are confirmed through experiments. The experimental results indicate that the proposed demodulation scheme can effectively reduce the polarization fading noise caused by the polarization mismatch between the probe light and the reference light, and the phase changes induced by external interference can also be accurately recovered with a signal-to-noise ratio (SNR) of vibration signal localization of 27.14 dB and an SNR of vibration signal phase demodulation of 47.88 dB, which provides a simplified method for simultaneous polarization fading suppression and the phase demodulation of the φ-OTDR system.

In this paper, a fiber optic acoustic sensor with continuously adjustable membrane stress technology is proposed, in which the stress exerted on the membrane can be flexibly adjusted by employing the inverse piezoelectric effect of lead zirconate titanate (PZT) tubular pedestal. First, the response mechanism of stress on the membrane is investigated theoretically. Based on this principle, the effect of adjustable stress on the flat response region and sensitivity of a single mode-multimode-single mode (SMS) fiber optic acoustic sensor are studied experimentally. The experimental results reveal that the flat response region of the sensor extends from 250 Hz to 450 Hz following the continuous increase in the membrane stress by changing the positive direct current voltage applied on PZT from 0 V to 100 V; meanwhile, the sensitivity decreases gradually from 336.5 mV Pa⁻¹ to 162.7 mV Pa⁻¹. The results also verify that the average minimum detectable pressure of the sensor is maintained at 0.54 mPa Hz^−1/2 with a fluctuation of 0.08 mPa Hz^−1/2 during the tuning process of membrane stress, which provides a flexible method for performance and applicability improvement of membrane-based fiber optic acoustic sensors.

In this paper, the response mechanisms of erbium-doped fiber (EDF)-based fiber-optic temperature sensors and the influence of nonradiative transitions on sensor sensitivity are experimentally investigated for the first time, and a sensitivity enhancement technology based on the lifetime differentiation of dual EDF is also proposed. First, the fluorescence temperature sensing mechanism and the influence of nonradiative transitions on the response characteristics of EDF-based fiber-optic temperature sensors are analyzed theoretically. Subsequently, experiments were conducted to further explore the properties of the fluorescence lifetime of EDF in response to temperature under the influence of nonradiative transitions by varying the length of the EDF to adjust the proportion of nonradiative transition. The experimental results demonstrate that the fluorescence lifetime of EDF exhibits non-monotonic changes under the influence of nonradiative transitions, and the sensitivity of the EDF-based fiber-optic temperature sensor also changes greatly from −0.00070 to 0.00054ms/^∘C as the EDF length varies from 20 to 500 cm. Based on the influence mechanisms of nonradiative transitions on EDF-based fiber-optic temperature sensors, a sensitivity enhancement method is proposed by differentiating the fluorescence lifetimes of two segments of erbium-doped fibers with different lengths and opposite sensitivities, by which a measurement error of 2°C and sensitivity of −0.00135ms/^∘C can be finally achieved within the temperature range from 37 to 223°C. This study provides insights into the influence mechanisms of nonradiative transitions on the fluorescence lifetime of EDF and contributes to the performance improvement of EDF-based fiber-optic temperature sensors.

Bearing-fault diagnosis based on single-modal signals is often constrained by incomplete fault information, whereas existing multimodal fusion methods often suffer from feature redundancy and a heavy preprocessing burden. To overcome these limitations, a vibro-acoustic channel fusion convolutional neural network model that employs channel-level fusion within an end-to-end one-dimensional framework, enhanced by wavelet packet decomposition and a squeeze-and-excitation mechanism, is proposed in this study. This method achieves mean diagnostic accuracies of 99.77% and 98.98% on a self-collected dataset and on the public MAFAULDA dataset, respectively. Additional experimental results indicate that the model maintains strong diagnostic performance under additive white Gaussian noise and variable-load conditions.