162results about How to "Improve demodulation accuracy" patented technology

An automatic frequency controller includes a frequency offset estimating section that calculates phase distortion quantities and the average thereof from known signals contained in a received signal. The frequency offset estimating section obtains, from the average distortion quantity, signal powers corresponding to a plurality of candidate frequency offsets set at frequency offset estimation accuracy intervals in a frequency offset estimation range. The frequency offset estimating section looks at the signal powers through a frequency window with a frequency width corresponding to a transmission path state. This makes it possible to maximize the signal power of a frequency of a radio wave or radio waves corresponding to the transmission path state, and to place the radio wave or radio waves corresponding to the transmission path state as a frequency controlled object. This can improve demodulation accuracy. Fine adjustment of the candidate frequency offsets can improve the estimation accuracy of the frequency offset without changing the frequency offset estimation range.

The invention discloses a fiber laser static-state strain beat frequency demodulation system based on single-sideband frequency sweep modulation. The system comprises a pumped source, a coupler, a first wavelength division multiplexer, a second wavelength division multiplexer, a first polarization controller, a second polarization controller, a sensing fiber laser, a reference fiber laser, a first isolator, a second isolator, a first beam combiner, a second beam combiner, a first broadband photoelectric detector, a second broadband photoelectric detector, a control processor, a narrow linewidth laser light source, a third isolator, a third polarization controller, a third beam combiner, a suppressed carrier single-sideband modulator, a fourth beam combiner, a frequency sweep signal generator, a phase modulator, a radio frequency signal generator, a frequency stabilization source and a photoelectric detector. The system provided by the invention realizes high-precision static-state strain measurement of the fiber lasers and solves the problems of incapacity of realizing high-precision static-state strain measurement, influences exerted by tunable laser frequency sweep non-linearity on demodulation precision, and the like by use of a conventional fiber laser demodulation technology.

The invention relates to an implementation method for processing an FBG (fiber bragg grating) sensing signal based on a three-point peek-seeking algorithm. The method comprises the steps of providing a peek-seeking processing flow, and giving three elements influencing the peek-seeking accuracy according to the flow, wherein reasonable selection of a window size is a key point for improving the peek-seeking accuracy, and the size of a spectral processing window is determined by adopting a derivation method; the spectrum in the window is resampled by arranging sampling intervals, and sparse spectrum data is acquired and subjected to polynomial fitting; a proper wavelength interval delta lambda is selected according to the fitting result, the coordinates of three points can be determined, the peak value of the FBG reflectance spectrum is detected, so that the central wavelength can be acquired, and external physical parameters can be demodulated.

The present invention discloses an F-P and FBG fiber sensor demodulation system, and aims to provide an F-P/FBG demodulation system which is high in wavelength resolution, and enables the demodulation precision to be improved. The F-P/FBG fiber sensor demodulation system of the present invention is realized by the following technical scheme that under the control of an operation control unit, a tunable laser emits out a beam of C-wave band laser of a constant wavelength, by an optical amplifier SOA and/or an optical isolator, and by being divided equally via a beam splitter, the incident light respectively irradiates to n F-P/FBG sensors in one-to-one correspondence, the light reflected by the F-P/FBG sensors is coupled to n phototriodes in one-to-one correspondence by n optical couplers, the optical power is converted into an optical current, the optical current is converted into an optical voltage entering an analog-digital converter by a logarithmic amplifier, the wavelength-reflection optical voltage digital quantity acquired in a time-sharing manner is stored in a memorizer of the operation control unit, the operation control unit carries out the fast Fourier transform on a sampled spectrum, the types of the F-P/FBG sensors are distinguished, and a peak searching demodulation algorithm is carried out to obtain a gradient value containing the cavity length information.

The invention discloses a method and device for demodulating a distributed optical fiber vibration sensing system. The method comprises that two continuous ultra-narrow linewidth lasers with the sameoptical power are subjected to acousto-optic modulation and electro-optic modulation to be converted into two pulsed light signals; the two pulsed light signals are input into a sensing fiber at an interval of set pulse width; the backward Rayleigh scattered light of the two pulsed light signals generate a set frequency difference such that the returned Rayleigh light signals exhibit sinusoidal interference fringes; when a disturbance signal has an effect on the sensing fiber, the phase difference of the returned Rayleigh light signals changes, and the vibration waveform and position sensed bythe sensing fiber are obtained according to the phase difference. When the disturbance signal appears, a detector can quickly obtain the position of the disturbance signal and the intensity of the disturbance signal, which solves the problem that the demodulation algorithm of a [phi]-OTDR system is complex and a laser frequency drifts, and guarantees that the positioning error of the system is within +/-1m.

The invention discloses a multi-channel high-precision fiber grating sensor demodulation device. The quantity of fiber grating sensor channels is increased and large-capacity multi-channel high-precision fiber grating demodulation is realized by combining an optical switch, a beam splitter and a beam combiner on the premise that the quantities of photoelectric detectors, signal amplifiers and AD acquisition channels are not increased and even reduced; the temperature of a tunable filter and an etalon is controlled via a TEC (Thermoelectric Cooler) temperature control module, thereby reducing the nonlinear influence of temperature on the output wavelength of the tunable filter and the influence of temperature on comb-like spectral line offset of the etalon, and improving the demodulation precision of the fiber grating demodulation device.

The invention discloses a self-mixing interference orthogonal detection vibration measuring device and method. A single-mode semiconductor laser diode adjustable in constant current source control outputs incidence laser, one part of the incidence laser is reflected to a second photoelectric diode, and optical signals are converted into current signals which are detected by a second photoelectricdetection module and fed back to a collecting module; the other part of the incidence laser is irradiated on the surface of a to-be-detected object and is reflected to a first photoelectric diode according to the original path, and the optical signals are converted into the current signals which are detected by a first photoelectric detection module and fed back to the collecting module. Comparedwith a traditional self-mixing measuring device, the self-mixing interference orthogonal detection vibration measuring device has the advantages that the orthogonal self-mixing signals can be acquired, inverse tangent demodulation of the vibration signals is completed, signal demodulation difficulty of the system is reduced, high displacement resolution is achieved, demodulation precision of the vibration signals of the system is improved, and real-time and online measuring can be realized.

The invention discloses a method and device for digitally demodulating a phase generated carrier by adopting analog front end. The device is characterized by consisting of analog demodulation, digital compensation and digital demodulation modules. The method comprises four steps of frequency mixing of an interference signal with a primary-frequency carrier signal and a doubled-frequency carrier signal respectively and carrying out of low-pass filtering, digital compensation, elimination of random phase fading, reduction of a detected signal, and the like. Compared with an existing digital demodulation method, the method can be used for obviously reducing a demodulation response time; a frequency mixing algorithm and a low-pass filtering algorithm in the existing digital demodulation are removed; the algorithm complexity is decreased; the demodulation precision is improved; the problem that a dynamic range is limited by the existing digital demodulation method is solved.

The invention relates to a fiber Bragg raster sensing device based on a high-speed pulse laser. The fiber Bragg raster sensing device includes the high-speed pulse laser, a dispersion module, a fiber Bragg raster array, a data acquisition module, and a data processing module. Based on the high-speed pulse laser, the narrow pulse being broad in band and high in repetition rate is provided, and the demodulation rate and the dynamic range of a fiber Bragg raster sensing demodulation system is greatly improved. Through the adoption of a photon time stretching method, the measurement of the wavelength shift of the optical fiber Bragg raster in the frequency domain is converted to the measurement of the time shift in the time domain, and the signal processing precision of the time domain is higher. Therefore, the demodulation precision of fiber Bragg sensing system can be significantly improved, and the requirement on the sampling rate of the data acquisition and processing modules is also reduced.

The invention relates to a recursion demodulation method for an electrical tomography system, which is characterized by comprising the following steps: (1) establishing an initial equation and a recursion equation according to an excitation frequency f and a sampling frequency f s of a system; (2) taking a zero phase moment of an excitation signal as an initial moment, and calculating initial values of a data matrix B and a state matrix P based on an initial equation in step (1) according to two sampling point data of a measurement signal immediately after the initial moment; (3) substituting the initial values of the data matrix B and the state matrix P as well as newly added sampling point data into the recursion equation in step (1) so as to update B and P; and (4) judging whether a demodulation result meets the accuracy requirement of the system or not, if not, returning to step (3), and if so, finishing demodulation and outputting the amplitude and phase data of the measurement signal. The recursion demodulation method only needs at least two sampling point data, and can improve demodulation accuracy and anti-noise ability by adding sampling points.

The invention discloses a grating sensing device based on a Brillouin filter. The grating sensing device comprises a broadband light source, a first circulator, a sensing optical fiber grating, the Brillouin filter, a synchronization signal module, a photoelectric detector and a signal acquisition and processing module. The Brillouin filter comprises an optical fiber section generating the stimulated Brillouin scattering SBS effect, a second circulator and a narrow linewidth tunable light source. Broad spectrum continuous signal light outputted by the broadband light source is outputted to the sensing optical fiber grating through the first circulator, and the reflected light meeting the Bragg's condition of reflection is generated and outputted to the optical fiber section through the first circulator. The narrow linewidth tunable light source outputs frequency sweep light to be outputted to the optical fiber section through the second circulator. The reflected light and the frequency sweep light are reversely transmitted in the optical fiber section to generate the SBS effect, and the amplified reflected light is outputted to demodulate the central reflection wavelength of the sensing optical fiber grating. The invention also discloses a method of the grating sensing device based on the Brillouin filter. The device is simple in structure and high in measurement precision.

The invention relates to an optical fiber temperature and pressure composite sensor, in particular to an optical fiber temperature and pressure composite sensor which can be used for simultaneous measurement of the temperature, absolute pressure or relative pressure of liquid and gas, and belongs to the field of optical fiber sensing technology. The sensor realizes simultaneous measurement of thetemperature and pressure through a simple two-layer structure, a transmission optical fiber with collimated microlenses on its end faces is used to enhance the signal quality of the sensor, two spectral analysis modules containing optical wedges with different thicknesses are used to demodulate a pressure sensing cavity length and a temperature sensing cavity length respectively, interference signals of the two cavities are separated through the one-to-one correspondence between the wedge thicknesses and the cavity lengths, in this way, the data processing steps are simplified, the demodulation speed is increased, and the measurement of dynamic pressure and temperature signals facilitated.

The present invention relates to an optical fiber pressure sensor based on a micro ellipsoidal air cavity and a manufacturing method of an optical fiber pressure sensor based on a micro ellipsoidal air cavity, belonging to the technical field of optical fiber pressure sensors. The optical fiber pressure sensor comprises a single-mode optical fiber and a pressure-sensitive film; the upper end of the single-mode optical fiber is fixedly connected with the lower end of the pressure-sensitive film; and the single-mode optical fiber and the pressure-sensitive film are connected with an air Fabry-Perot cavity. The materials of the optical fiber pressure sensor are silicon dioxide, so that the thermal expansion coefficients of the optical fiber pressure sensor are the same, thereby avoiding structural failure due to high temperature mismatch of different materials and achieving small temperature crosstalk and low cost. The manufacturing process of the sensor head only needs welding, cutting and grinding, and the process is simple; the confocal Fabry-Perot cavity in the device has the advantages of small interference cavity loss and high interference fringe contrast ratio and high demodulation precision compared with the Fabry-Perot cavity made by the etching process or the femtosecond laser in the prior art.

The invention discloses a method used for array waveguide optical grating demodulating system temperature compensation in smart clothes. The central wavelength lambda i of all channel output spectrums of an array waveguide optical grating has a temperature drift phenomenon, when human body temperature measurement is carried out through an array waveguide optical grating demodulating system in the smart clothes, due to the fact that the temperature difference among the left chest, the right chest, the left axilla, the right axilla and the back in the human body is within the range of 1.7 DEG C, the temperature variation value delta T of the array waveguide optical grating and a fiber bragg grating is considered to be integrated, the central wavelength is replaced with a relational expression containing the delta T, and an array waveguide optical grating temperature demodulating formula with the temperature compensation is derived. According to the method, the result of temperature demodulating shows that a kind of stable linear relation exists between a temperature value and a light intensity comparison value, temperature sensitivity is 0.25733 dB/ DEG C, and demodulating precision of the array waveguide optical grating demodulating system used for the human body temperature measurement in the smart clothes can be effectively improved.

The invention relates to a non-scanning demodulation system based on an optical fiber Fabry-Perot sensor, whichbelongs to the technical field of optical fiber sensing. The system comprises a positivelens, a first free-form surface reflector, a second free-form surface reflector, an optical wedge, a plano-convex cylindrical lens, a linear array CCD and a data processor. The positive lens is used for receiving light with cavity length information obtained from the optical fiber Fabry-Perot sensor, and the light is emitted to the positive lens through the optical fiber and is diffused into parallel light; the first free-form surface reflector is used for receiving the parallel light diverged by the positive lens and converting the parallel light into flat-topped light; the second free-form surface reflector is used for collimating the emergent direction of the flat-topped light to ensure that the signal light incident to the optical wedge is perpendicular to the surface of the second free-form surface reflector; the plano-convex cylindrical lens is used for converting the rectangular light spot transmitted by the optical wedge into one-dimensional linear light; and the linear array CCD is used for detecting the one-dimensional linear light passing through the plano-convex cylindrical lens and outputting a voltage signal. The signal contrast can be effectively demodulated, and thedemodulation precision of a demodulation system can be improved.

The invention relates to a multi-frequency recursive demodulation method for electrical tomographic systems. The method is characterized by comprising the following steps: (1) establishing an original equation and a recursive equation according to m component frequencies of an excitation signal and the sampling frequency of a system; (2) with a zero-phase time of the excitation signal as a starting time, according to data of 2m sampling points a measuring signal, which are closely following the starting time, calculating the initial values of a data matrix B and a state matrix P according to the original equation in the step (1); (3) substituting the initial values and the new sample point data into the recursive equation in the step (1) so as to update B and P; and (4) judging whether a demodulation result meets the accuracy requirements of the system, if so, completing the demodulation operation, and outputting the amplitude values and phase data of m frequency components of the measuring signal; otherwise, returning to the step (3). By using the recursive demodulation method disclosed by the invention, data of at least 2m sampling points is required, and due to the increase of the number of sampling points, the demodulation accuracy and the anti-noise capacity can be improved.