Aiming at the problem that Distributed Optical Fiber Acoustic Sensing (DAS) system will misjudge external intrusion signals, an intrusion signal discrimination method based on MFCC-Energy entropy feature and FTO-SVM is proposed. Firstly, the former 13-dimensional Mel-Frequency Cepstral Coefficients (MFCC) is extracted from the collected sound signal, and Principal Component Analysis (PCA) is used to reduce the dimension of MFCC; Secondly, the energy entropy of the collected sound signal is calculated, which fused with the reduced MFCC as the feature parameter of the collected sound signal; Finally, the extracted feature parameters are discriminated by using Support Vector Machine (SVM) with the hyperparameters optimized by the Fibonacci Tree Optimization (FTO) algorithm. The results show that the proposed method can effectively improve the system discrimination accuracy for intrusion signals, and is of great significance to perimeter security and fault diagnosis and other related fields.
In this paper, we propose the simplest one-dimensional grating waveguide to obtain the wideband slow light. An ideal band indicating group index of 18.3 and bandwidth of 10.3 nm is obtained by plane wave expansion method, which is also verified in the finite-difference time-domain numerical simulation when a Gaussian pulse with bandwidth of 10.3
nm is input into the grating waveguide. Thus, this simple one-dimensional grating waveguide is believed to be widely
used as wideband and low loss slow light delay for optical buffering and signal processing.
The area of integrated optical circuits has been undergoing rapid development and gaining a great deal of applications in
fiber communications and optical interconnections. These applications bring a significant challenge to optical circuits
such as increased circuit density and further miniaturized devices. Compact and high performance optical components
are in great demand. This paper present our proposal to use Si based compact diffractive components for coupling,
splitting, and reflection in integrated optical circuits. First, a novel subwavelength grating, binary blazed grating (BBG),
is used as a high efficient vertical coupler from single mode fiber to Si waveguide. By using the strong polarization
dependence of the BBG coupler, a polarization beam splitter (PBS) is proposed to split the polarizations of input light
from fiber into two waveguides separately, during the coupling process. The coupling length is merely 14 μm. The
extinction ratio is better than 20 dB for both polarizations over a 40 nm wavelength range and the coupling efficiencies
for two polarizations are 58% and 50%, respectively. Second, a broadband and high efficient mirror based on the BBG is
designed and fabricated. Up to 96% reflectivity over a wavelength rang of 1.2~1.7um was achieved both theoretically
and experimentally. Finally, a nanoscale pillar waveguide is proposed as an ultra small nanotaper for mode conversion
between fiber and submicron waveguide. It has been demonstrated that a 13 μm long taper is able to convert a mode size
of 4 μm into 1 μm with an efficiency of 85%.
In this paper, we discuss the optimal design of line-tapered multimode interference (MMI) devices using a genetic
algorithm (GA). A 1×4 MMI device is designed as a numerical example. Compared with the conventional design based
on sel-image theory, the GA optimization demonstrates good performances such as a low insertion and small
non-uniformity.
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