A novel approach to extract edge features from wideband echo is proposed. The set of extracted features not only represents the echo waveform in a concise way, but also is sufficient and well suited for classification...A novel approach to extract edge features from wideband echo is proposed. The set of extracted features not only represents the echo waveform in a concise way, but also is sufficient and well suited for classification of non-stationary echo data from objects with different property.The feature extraction is derived from the Discrete Dyadic Wavlet Transform (DDWT) of the echo through the undecimated algorithm. The motivation we use the DDWT is that it is time-shift-invariant which is beneficial for localization of edge, and the wavelet coefficients at larger scale represent the main shape feature of echo, i.e. edge, and the noise and modulated high-frequency components are reduced with scale increased. Some experimental results using real data which contain 144 samples from 4 classes of lake bottoms with different sediments are provided. The results show that our approach is a prospective way to represent wideband echo for reliable recognition of nonstationary echo with great variability.展开更多
In the fields of light manipulation and localization,quasiperiodic photonic crystals,or photonic quasicrystals[PQs],are causing an upsurge in research because of their rotational symmetry and long-range orientation of...In the fields of light manipulation and localization,quasiperiodic photonic crystals,or photonic quasicrystals[PQs],are causing an upsurge in research because of their rotational symmetry and long-range orientation of transverse lattice arrays,as they lack translational symmetry.It allows for the optimization of well-established light propagation properties and has introduced new guiding features.Therefore,as a class,quasiperiodic photonic crystal fibers,or photonic quasicrystal fibers[PQFs],are considered to add flexibility and richness to the optical properties of fibers and are expected to offer significant potential applications to optical fiber fields.In this review,the fundamental concept,working mechanisms,and invention history of PQFs are explained.Recent progress in optical property improvement and its novel applications in fields such as dispersion control,polarization-maintenance,supercontinuum generation,orbital angular momentum transmission,plasmon-based sensors and filters,and high nonlinearity and topological mode transmission,are then reviewed in detail.Bandgap-type air-guiding PQFs supporting low attenuation propagation and regulation of photonic density states of quasiperiodic cladding and in which light guidance is achieved by coherent Bragg scattering are also summarized.Finally,current challenges encountered in the guiding mechanisms and practical preparation techniques,as well as the prospects and research trends of PQFs,are also presented.展开更多
文摘A novel approach to extract edge features from wideband echo is proposed. The set of extracted features not only represents the echo waveform in a concise way, but also is sufficient and well suited for classification of non-stationary echo data from objects with different property.The feature extraction is derived from the Discrete Dyadic Wavlet Transform (DDWT) of the echo through the undecimated algorithm. The motivation we use the DDWT is that it is time-shift-invariant which is beneficial for localization of edge, and the wavelet coefficients at larger scale represent the main shape feature of echo, i.e. edge, and the noise and modulated high-frequency components are reduced with scale increased. Some experimental results using real data which contain 144 samples from 4 classes of lake bottoms with different sediments are provided. The results show that our approach is a prospective way to represent wideband echo for reliable recognition of nonstationary echo with great variability.
基金supported by the Changsha Municipal Natural Science Foundation(No.kq2202295)the Scientific Research Foundation of Hunan Provincial Education Department(Nos.22B0273 and 21A0013)+1 种基金the National Natural Science Foundation of China(Nos.61405058 and 62075059)the Natural Science Foundation of Hunan Province(Nos.2017JJ2048 and 2020JJ4161)。
文摘In the fields of light manipulation and localization,quasiperiodic photonic crystals,or photonic quasicrystals[PQs],are causing an upsurge in research because of their rotational symmetry and long-range orientation of transverse lattice arrays,as they lack translational symmetry.It allows for the optimization of well-established light propagation properties and has introduced new guiding features.Therefore,as a class,quasiperiodic photonic crystal fibers,or photonic quasicrystal fibers[PQFs],are considered to add flexibility and richness to the optical properties of fibers and are expected to offer significant potential applications to optical fiber fields.In this review,the fundamental concept,working mechanisms,and invention history of PQFs are explained.Recent progress in optical property improvement and its novel applications in fields such as dispersion control,polarization-maintenance,supercontinuum generation,orbital angular momentum transmission,plasmon-based sensors and filters,and high nonlinearity and topological mode transmission,are then reviewed in detail.Bandgap-type air-guiding PQFs supporting low attenuation propagation and regulation of photonic density states of quasiperiodic cladding and in which light guidance is achieved by coherent Bragg scattering are also summarized.Finally,current challenges encountered in the guiding mechanisms and practical preparation techniques,as well as the prospects and research trends of PQFs,are also presented.
