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In this letter, we proposed an improved polarization compensation method to eliminate polarization-induced phase shift and polarization-induced fading and enhance the positioning accuracy of interferometric fiber-optic intrusion sensor based on dual Mach–Zehnder interferometry. The implement scheme employs two polarization controllers (PC) to compensate the polarizations of light beams before they interfere at beam combiner. The compensation strategy of optimum polarization adjustment is based on the directed compensation of the state of polarization (SOP) and it has the advantages of fast PC adjustment and fine synchronization of the interference light beams. We also experimentally demonstrated the efficiency of our proposed method with a positioning error within ±30 m. [ABSTRACT FROM PUBLISHER]

This paper proposes a hybrid feature extraction-based intrusion discrimination scheme for an optical fiber perimeter security system, which concurrently possesses high classification rate and high efficiency. The high classification rate lies in two aspects: On one hand, plentiful contents (including bandwidth segmentation in frequency domain, kurtosis in statistics, and the zero-crossing rate in time domain) are incorporated into the proposed hybrid feature vector; on the other hand, a configurable filter bank is adopted to reduce the intercoupling between features in the hybrid vector. The high efficiency also arises for two reasons: For one thing, the configurable filter bank works in a pipeline stream; for another, an efficient support vector machine is employed to classify hybrid vectors. Experiments demonstrated that the proposed scheme can accurately identify four common intrusions (fence climbing, knocking the cable, waggling, and fence cutting) with an average recognition rate higher than 94%. Moreover, the recognition efficiency is also high. [ABSTRACT FROM PUBLISHER]

A de-noising algorithm based on ensemble empirical mode decomposition (EEMD) method is employed in this paper for Raman-based distributed temperature sensor (RDTS). We first decompose the noisy signal using the EEMD and find local maxima on each intrinsic mode function (IMF) whose zero contour line is used to determine noise interval. The signal is then de-noised and reconstructed by removing the noise components of each IMF. The experimental results demonstrated that the proposed de-noising algorithm can enhance the signal-to-noise ratio by 8.8 dB while maintaining spatial resolution. The temperature error reduction of 3.2 °C can be achieved at 10 km using conventional RDTS without losing any detail. [ABSTRACT FROM PUBLISHER]

In this paper, an improved positioning algorithm is proposed for a long-range asymmetric perimeter security system. This algorithm employs zero-crossing rate to detect the disturbance starting point, and then utilizes an improved empirical mode decomposition to obtain the effective time-frequency distribution of the extracted signal. In the end, a cross-correlation is used to estimate the time delay of the effective extracted signal. The scheme is also verified and analyzed experimentally. The field test results demonstrate that the proposed scheme can achieve a detection of 96.60% of positioning errors distributed within the range of \rm0\-- \pm 20\,m at the sensing length of 75 km, which significantly improves the positioning accuracy for the long-range asymmetric fence perimeter application. [ABSTRACT FROM PUBLISHER]

This paper put forward an endpoint detection scheme consisting of fast Fourier transform analysis, signal filtering, and threshold judgement. Due to incorporation of a novel amplitude–frequency characteristic compensation based high-pass filter (HPF) design, this scheme concurrently possesses high accuracy and high efficiency. Its high accuracy lies in adapting the cutoff frequency of a low-ordered HPF to the field environmental interference. Meanwhile, its high efficiency attributes to the merit that this HPF can be rapidly configured in closed form. Field experimental results demonstrated that the proposed scheme can achieve acceptable detection accuracy only consuming dozens of multipliers, which presents a vast potential in intrusion-detection-related applications. [ABSTRACT FROM PUBLISHER]

We propose a time delay estimation (TDE) method based on a continuous wavelet transform (CWT), which can be applied to the different-wavelength-based fiber interferometric vibration sensors. Using a CWT-based characteristic extraction algorithm, we successfully eliminate the asymmetry of the interference outputs that would seriously deteriorate the positioning accuracy of the sensor. A positioning measurement experiment using an asymmetric dual Mach-Zehnder interferometric sensor was carried out to verify the effectiveness of the proposed method. The experiment achieved a positioning accuracy of 0.029% at the sensing length of 85 km, with a mean processing time of 591.2 ms. [ABSTRACT FROM PUBLISHER]

To meet the growing demand of event discrimination in a dual Mach–Zehnder Interferometry (DMZI) vibration sensing system, this paper proposes a novel scheme of distinguishing invasion events. This scheme consists of three stages: endpoint detection, filter-bank-based feature extraction, and radial-basis-function neural network classification. As the hard core, the proposed filter bank, which is derived from the classical frequency-sampling-based filter design method, greatly suppresses the interchannel interference and, thus, provides accurate feature description for the radial basis function (RBF)-based classifier. Moreover, we also derive the closed-form formula of the filter coefficients and, thus, design a pipeline structure for the filter bank, which brings the advantages of high accuracy, high flexibility, great rapidity, and low cost. Simulation verifies the proposed filter bank's superiority in separating different frequency bands. Field experiments also show that the proposed event discrimination scheme cannot only eliminate some false alarms caused by noninvasion events but can discriminate two common invasion events (climbing the fence and knocking the cable) with high recognition accuracy as well. [ABSTRACT FROM PUBLISHER]

This paper proposes an integrated scheme to distinguish invasive events in optical fiber dual Mach–Zehnder Interferometry based perimeter security system. This algorithm combined empirical mode decomposition, kurtosis characteristics with radial basis function neural network, which can improve the recognition rate of event discrimination and increase the variety of intrusion events. Several experiments demonstrate that the proposed scheme can discriminate four common invasive events (climbing the fence, knocking the cable, cutting the fence, and waggling the fence) with an average recognition rate above 85.75%, which can satisfy actual application requirements. [ABSTRACT FROM PUBLISHER]

An improved positioning algorithm for dual Mach–Zehnder interferometry (DMZI) disturbance sensing system is proposed. We employ zero-crossing method, which can be computed easily to extract the disturbance signal segment with maximum zero-crossing rate. Meanwhile, we use general cross correlation based on Wiener filtering and Gnn subtraction weighting function (WG-GCC) to estimate the time delay of the extracted signal, which is robust to the correlated noise. Finally, we experimentally demonstrate that the proposed positioning algorithm can greatly improve the positioning accuracy with positioning error of ±20 m. Compared with the traditional positioning algorithm, the positioning error has been reduced by an order of magnitude. This algorithm has a promising potential in real-time fence perimeter applications. [ABSTRACT FROM PUBLISHER]

A low-frequency (20–80 kHz) tube plasma source was designed for plasma beam generation at low pressure. In the atmosphere of pure nitrogen, the plasma source exhibited two distinct discharge states. The discharge sustained at low current (G mode) was a capacitive discharge and transited into a resistive discharge self-pulsing mode (SP mode) when the current exceeded a critical level. The SP-mode discharge was identified to be a mixing discharge consisting of continuous discharge and periodic sparks or pulsing arcs. Powered with 10–110 W, the SP-mode discharge created a plasma plume with high electron density (0.9– 5.1\times 10^11~\mathrmcm^\mathrm -3) and relatively low electron temperature (1.62–0.55 eV). The vibrational and rotational temperatures of the SP-mode plasma in the tube were determined to be $\sim 5000$ K and 350–700 K by fitting the optical emission spectra, respectively, distinguishing from those of the G-mode discharge. [ABSTRACT FROM PUBLISHER]

We proposed an improved polarization control method to reduce polarization-induced phase shift (PIPS) and polarization-induced fading (PIF) in a dual Mach–Zehnder interferometry (DMZI) disturbance sensing system. PIPS and PIF will seriously affect the positioning accuracy of the DMZI sensor. This polarization control method uses two PCs to control the state of polarization at the inputs of clockwise Mach–Zehnder interferometer and counter-clockwise Mach–Zehnder interferometer, respectively, based on chaotic particle swarm optimization algorithm, which has advantages of high speed and easy implementation. We experimentally demonstrated that the polarization method can overcome the effect of PIPS and PIF, improve the positioning accuracy of the DMZI sensor efficiently with positioning error of ±20 m after polarization control. Compared with the traditional polarization control method in DMZI based on the criterion of visibility, the positioning error of the sensor using our proposed method has been reduced at least an order of magnitude. [ABSTRACT FROM PUBLISHER]