8 results about "Bragg resonance" patented technology

The present invention belongs to the technical field of optical fiber sensing. Provided are a ring-type small-period long-period fiber grating sensor, and a preparation method therefor and the application thereof. A ring-type small-period long-period fiber grating provided in the present invention matches the cross-sectional shape of an optical fiber, and rings can more effectively expand the area of each refractive index modulation region in the cross section of the optical fiber, such that the ring-type grating has large refractive index modulation regions in both the axial direction and longitudinal direction of the optical fiber, and the intensities of a Bragg resonance peak and a cladding mode resonance peak can thus be simultaneously enhanced. Therefore, the Bragg resonance peak and the cladding mode resonance peak can be simultaneously observed in a transmission spectrum of the ring-type grating, such that simultaneous measurement of an ambient refractive index and temperature can be realized, and there is no longer a need to observe a reflection peak, thereby simplifying multi-parameter sensing test steps of the small-period long-period fiber grating.

The application discloses a simulation method for imaging sea surface in a region of interest of variable-beam SAR, and belongs to the technical field of radar signal simulation processing. In order to solve the problem of improving the fidelity of echo signal simulation, the application comprises the following steps: constructing a sea surface movement model of a coastal zone; constructing a Kirchhoff mirror reflection model; constructing a Bragg resonance scattering model; performing echo simulation and simulation of the sea surface of the variable-beam SAR, including updating the space-varying scattering grid by using the sea surface movement model of the coastal zone and updating the instantaneous sea surface movement state, calculating the backscattering intensity of each scattering facet in the time domain by using the Kirchhoff mirror reflection model and the Bragg resonance scattering model, then calculating the space-varying azimuth two-way pattern at each distance unit of the scattering facet at the same azimuth position, weighting the echo of each scattering facet, and then traversing the non-uniform sampling time to obtain an echo matrix of the variable-beam high-resolution wide-width SAR. The application can significantly improve the fidelity of echo signal simulation.

The application discloses a high-sensitivity high-temperature high-pressure sensor based on a high-birefringence grating, which comprises a microstructure optical fiber, the microstructure optical fiber comprises a fiber core and a cladding layer, the fiber core is located at the center of the cladding layer, the microstructure optical fiber has a first polarization direction and a second polarization direction on a radial plane, the first polarization direction is perpendicular to the second polarization direction, symmetrical air hole channels are arranged in the cladding layer on both sides of the fiber core along the first polarization direction, and the air hole channels are parallel to the fiber core; and a high-birefringence grating is formed in the fiber core or the cladding layer of the microstructure optical fiber through periodic refractive index modulation. The high-sensitivity high-temperature high-pressure sensor can directly form two separated Bragg resonance peaks, does not need to use any polarization device for demodulation, and can simultaneously measure temperature and pressure, has high sensitivity to pressure, and can work in a high-temperature environment.

A method, device and equipment for calculating hydrodynamic characteristics of a flexible Bragg submerged dike based on frequency band control and a computer storage medium relate to the technical field of coast and ocean engineering, and the method comprises the following steps: constructing a flexible structure-water wave complete coupling mathematical model; the structural natural vibration frequency and the Bragg resonance frequency of the flexible Bragg submerged dike are calculated to determine a core wave absorption frequency band, and frequency band control conditions of the flexible Bragg submerged dike are formed; weighting the transmission coefficient, the energy loss and the wave load on the basis of a frequency band control condition in combination with a target sea condition spectrum to form a comprehensive evaluation factor, and representing the comprehensive wave dissipation performance and the structural stress performance of the submerged dike; according to the scheme provided by the invention, the hydrodynamic characteristics of the flexible Bragg submerged embankment can be accurately calculated, a scientific basis is provided for reasonable design and arrangement of the flexible Bragg submerged embankment in ocean engineering, and the wave dissipation performance and comprehensive benefits of the submerged embankment are improved.

This invention provides a Bragg resonance breakwater design method and breakwater. The Bragg resonance breakwater design method includes acquiring wave field characteristic parameters of the target sea area and determining the target wave frequency band based on the wave field characteristic parameters; determining the target wave frequency of each resonant unit based on the target wave frequency band, and determining the geometric parameters of the resonant cavity of the resonant unit based on the target wave frequency, so that the inherent resonant frequency of the resonant cavity matches the target wave frequency; determining the reflection coefficient index to characterize the wave dissipation effect based on the target wave frequency band, and determining the arrangement parameters of each resonant unit based on the reflection coefficient index under the premise of satisfying preset constraints, wherein the arrangement parameters change stepwise along the incident wave propagation direction; and outputting the resonant cavity geometric parameters and arrangement parameters corresponding to each resonant unit to form a Bragg resonance breakwater design scheme.

An annular small-period-long-period fiber grating (SP-LPG) sensor, a preparation method and applications thereof are provided. The annular (SP-LPG) sensor matches the cross-section shape of the optical fibers, the annulus can expand the area of the refractive index modulation region more effectively in the section of the optical fibers, so that the annular grating has a large refractive index modulation region in both the axial and longitudinal directions of the optical fibers, which can simultaneously enhance the intensity of the Bragg resonance peak and the resonance peaks of the cladding modes. Therefore, the Bragg resonance peak and the resonance peaks of the cladding modes can be observed simultaneously in the transmission spectra. It can realize the simultaneous measurement of the refractive index and temperature of the surrounding environment without the need to observe the reflection peak, which simplifies the multi-parameter sensing test steps of the (SP-LPG) sensor.

A method and apparatus for inscribing a Bragg grating in the core of an optical waveguide. Electromagnetic radiation at a chosen wavelength passes through a diffractive optical element optimized for the wavelength such that a beam is generated on the waveguide having an interference pattern so as to form a Bragg grating in the core of the optical waveguide, the beam being sufficiently intense to cause a permanent (Type II) change in the index of refraction in the core in the form of at least one elongated micropore. The Bragg grating period can be selected to promote coupling of guided light into a radiation mode for detection by a detector to form a spectrometer. The Bragg grating is characterized by a scattering loss less than 10−5 dB per grating period at the Bragg resonance but outcoupling efficiency at visible wavelengths of 0.03% per grating period.

The high-sensitivity high-temperature and high-pressure sensor comprises a microstructure optical fiber, the microstructure optical fiber comprises a fiber core and a cladding, the fiber core is located in the center of the cladding, and the microstructure optical fiber has a first polarization direction and a second polarization direction on a radial plane. The first polarization direction is perpendicular to the second polarization direction, symmetrical air hole channels are arranged in the cladding on the two sides of the fiber core along the first polarization direction, and the air hole channels are parallel to the fiber core; and a high-birefringence grating is formed in a fiber core or a cladding of the microstructure optical fiber through periodic refractive index modulation. The high-sensitivity high-temperature and high-pressure sensor can directly form two separated Bragg harmonic peaks, does not need to use any polarization device for demodulation, can measure the temperature and the pressure at the same time, is high in pressure sensitivity, and can work in a high-temperature environment.