CN116683997A - Method for demodulating low-frequency signal by improving phase generation carrier algorithm - Google Patents
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Abstract
The invention belongs to the technical fields of optical fiber interferometry and phase generation carrier demodulation, and particularly relates to a method for demodulating a low-frequency signal by improving a phase generation carrier algorithm, which comprises the following steps: and generating carrier mixing based on the frequency tripling phase, demodulating the low-frequency signal by using an arctangent algorithm, and combining with an ellipse fitting algorithm to correct the non-orthogonal signal and compensate the linear error in real time. In the process of demodulating the low-frequency signal, the method is not influenced by the modulation depth of the carrier and the disturbance of the light intensity, meanwhile, the problem of direct current drift existing in the traditional PGC-DCM in the process of demodulating the low-frequency signal is avoided, the accuracy of a demodulation result is improved, and the interference of error factors is reduced.
Description
Technical Field
The invention belongs to the technical fields of optical fiber interferometry and phase generation carrier demodulation, is used for signal demodulation of an interference type optical fiber sensing system, and particularly relates to a method for demodulating a low-frequency signal by improving a phase generation carrier algorithm.
Background
For an interference type optical fiber sensing system, a light intensity signal is usually directly obtained, and the phase measurement change is inverted by demodulating a phase signal in the light intensity to realize indirect measurement of a physical quantity to be measured, so that the phase demodulation method is particularly important. The demodulation techniques commonly used at present can be classified into active homodyne, closed loop operating point control, 3×3 coupler polyphase detection and Phase Generation Carrier (PGC) demodulation methods.
The active homodyne detection belongs to a closed loop test scheme, and stronger low-frequency noise can be introduced in the process of loading a compensation signal to a modulator; the closed loop working point control is a pseudo zero difference method, and when the system is applied to a low frequency band, the detection signal is the same as the external interference frequency band, so that the system is not suitable for low frequency signal detection; the demodulation method for the 3×3 coupler multiphase detection has the advantages of simplicity, large dynamic range and suitability for low-frequency signals, but under the low-frequency condition, the system is more easily interfered and influenced by external low-frequency due to the lack of a modulation process for processing and protecting the signals.
The phase-generating carrier (PGC) demodulation algorithm is an active passive homodyne demodulation algorithm for demodulating the sensing signal of the interferometric fiber optic sensor. This demodulation algorithm converts the variation of the interference light intensity into a variation of the phase amplitude. The method is suitable for low-frequency signal detection, and has the advantages of strong anti-interference capability, high modulation efficiency and good signal quality. The PGC demodulation method changes a field signal to be detected into a sideband of a carrier signal by applying a high-frequency carrier modulation signal, and then removes the interference of noise signals through operations such as low-pass filtering, mixing, high-pass filtering and the like, and extracts the intensity and phase information of a low-frequency weak signal from the carrier signal. In terms of demodulation, the differential cross-multiplication algorithm (PGC-DCM) and the arctangent algorithm (PGC-Arctan) are one of the most commonly used algorithms.
From the demodulation result, the PGC-DCM algorithm is affected by factors such as interference visibility, light intensity, modulation depth and the like. In addition, an integrator is arranged in the demodulation process, a direct current term is inevitably introduced, and because the field signal to be detected is a low-frequency signal, the signal cannot be filtered by using a high-pass filter, and the direct current drift of a demodulation result can be caused. The PGC-Arctan algorithm is not affected by the instability of the light source, but can demodulate the low frequency signal without distortion only when the modulation depth is 2.63 rad.
Disclosure of Invention
The invention aims to provide a method for demodulating a low-frequency signal by improving a phase generation carrier algorithm aiming at the influence of factors such as interference visibility, light intensity, modulation depth and the like of a GC-DCM algorithm.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
a method for demodulating a low-frequency signal by improving a phase-generating carrier algorithm, which applies a high-frequency carrier modulation signal to change a field signal to be detected into sidebands of the carrier signal and multiplies a frequency-doubled carrier signal Gcos omega c Frequency doubling carrier signal Hcos2 omega c Frequency tripled carrier signal Dcos3 omega c Respectively multiplying the interference output signals, and respectively performing low-pass filtering on the obtained results to obtain I 1 、I 2 And I 3 Will I 3 Way signal and I 1 Result sum I of the path signals subtracted 2 And carrying out modulation depth estimation and correction on the path signals through ellipse fitting, dividing the corrected orthogonal signals, and carrying out arctangent calculation to obtain the low-frequency signals to be detected.
The interference output signal is:
a is DC bias, B is AC amplitude,for the phase of the signal to be measured, C is the modulation depth of the phase modulator, cos omega c t is a phase carrier signal;to multiply carrier signal Gcos omega by one frequency c Frequency doubling carrier signal Hcos2 omega c Frequency tripled carrier signal Dcos3 omega c Respectively mixing with an interferometer output signal I, and passing through a low-pass filter with cut-off frequency between the frequency of a signal to be detected and the carrier frequency after mixing:
wherein J is 1 (C) As a first-order Bessel function, J 2 (C) As a second order Bessel function of the first kind, J 3 (C) Is a third-order bezier function of the first type.
Will I 3 (t)-I 1 (t) obtaining:
let L 2 (t)＝I 2 (t) mixing L with 1 (t) divided by L 2 (t) obtaining
In practical applications, factors such as carrier phase delay, light intensity disturbance, modulation depth fluctuation, non-ideal performance of a low-pass filter and the like, all cause dynamic changes of direct current offset and alternating current amplitude of the quadrature signal. L (L) 1 (t) and L 2 General expression of (t)The rewrites are:
L 1 (t)＝a(t)+b(t)cosθ(t)
L 2 (t)＝c(t)+d(t)cos[θ(t)+δ]
wherein a (t) and c (t) are DC offset, b (t) and d (t) are AC amplitude, θ (t) is signal to be measured,delta is the phase difference of two paths of signals, L 1 (t) and L 2 (t) fitting to an ellipse x 2 +A 1 xy+A 2 y 2 +A 3 x+A 4 y+A 5 =0, get a from the fitting result 1 -A 5 Is a value of (a).
Calculation ofAnd feeding back the final demodulation amplitude to improve demodulation accuracy.
Will L 1 (t) and L 2 (t) signal correction is:
cosθ(t)＝[L 1 (t)-a]/b
finally, dividing and arctangent calculating two paths of orthogonal signals to obtain a low-frequency signal to be detected
The optical signal is converted into an electric signal by the optical fiber interference sensing system output signal through the photoelectric detector, the data acquisition card is used for acquiring the signal and inputting the signal to the FPGA high-speed data processing platform for phase generation carrier algorithm demodulation. The optical fiber interference sensing system signal measuring device comprises a laser, an optical fiber coupler, a sensing optical fiber, a reference optical fiber, a phase modulator, a Faraday rotating mirror, a photoelectric detector, a data acquisition card and an FPGA high-speed data processing platform.
The output port of the laser is connected with a 2X 2 optical fiber coupler 2, the 2X 2 optical fiber coupler divides an optical signal into two paths, the first path is reflected back to the 2X 2 optical fiber coupler 2 through a Faraday rotating mirror at the tail end of a sensing optical fiber, the second path is reflected through the Faraday rotating mirror at the tail end of the reference optical fiber after being subjected to phase modulation by a phase modulator along a reference optical fiber, and finally interference occurs between the second path and the first path at the 2X 2 optical fiber coupler 2; when an external low-frequency signal acts on the sensing optical fiber, the optical phase in the sensing optical fiber is modulated, the phase difference of the optical signals in the corresponding sensing optical fiber and the reference optical fiber is changed, the phase difference is finally reflected to the light intensity change detected by the photoelectric detector, the data acquisition card is used for acquiring the signal and inputting the signal to the FPGA high-speed data processing platform, and the carrier algorithm is generated by utilizing the improved phase to demodulate.
The FPGA high-speed data processing platform comprises: the DDS sine signal generator, the mixer, the multiplier, the low-pass filter, the subtracter, the ellipse fitting module, the divider and the arctangent module.
The improved phase-generating carrier demodulation comprises the steps of:
(1) Acquiring interference light intensity signals after carrier modulation;
(2) The DDS sinusoidal signal generator generates a fundamental frequency carrier signal, a double frequency carrier signal and a triple frequency carrier signal; the fundamental frequency carrier signal, the frequency doubling carrier signal and the frequency tripling carrier signal are mixed with the interference signal respectively;
(3) The mixed signal passes through a low-pass filter with cut-off frequency between the frequency of the signal to be detected and the carrier frequency;
(4) Processing the output signal of the low-pass filter according to the Bessel function recurrence principle, demodulating the phase modulation depth in real time through ellipse fitting, and generating two paths of orthogonal signals;
(5) And finally, obtaining the low-frequency signal to be detected by dividing and arctangent calculation of the two paths of orthogonal signals.
The invention has the beneficial effects that:
the invention discloses a method for demodulating a low-frequency signal by improving a phase generation carrier algorithm. The method is characterized in that frequency tripling mixing is combined with an elliptic fitting algorithm, the method is analyzed from a demodulation result, is not influenced by modulation depth and light intensity disturbance, and is analyzed from the process, an integrator module which is necessary in a PGC-DCM demodulation algorithm is not used in the method, the problem of direct current offset for demodulating a low-frequency signal is avoided, and an elliptic fitting algorithm module is utilized for correcting a non-orthogonal signal and compensating amplitude linear errors, so that accurate demodulation of the low-frequency signal is realized. In the low frequency band (20 Hz-1 kHz), the total harmonic distortion of the demodulation signal is 0.04%, the susceptance ratio is 65.77dB, and the amplitude root mean square error is 0.002rad.
Drawings
FIG. 1 shows a signal measuring device of an optical fiber Michelson interference sensing system
FIG. 2 is a method for demodulating a low frequency signal by an improved phase-generated carrier algorithm
FIG. 3 is a sum spectrum of the interference signals output by the interferometric sensor system
FIG. 4 is a spectrum diagram of signal demodulation
Detailed Description
The technical scheme of the present invention will be clearly and completely described in the following examples. It will be apparent that the embodiments described herein represent only a portion of the invention, but not all embodiments. On the basis of the invention, the person skilled in the art can obtain all other embodiments without inventive work, which are also protected by the invention.
The invention is further described below with reference to the drawings and examples.
Example 1:
the optical fiber interference sensing system output signal is converted into an electric signal through a photoelectric detector, the data acquisition card is used for acquiring the signal and inputting the signal to the FPGA high-speed data processing platform for carrying out phase generation carrier algorithm demodulation, and the phase generation carrier demodulation module comprises a DDS sine signal generator, a mixer, a multiplier, a low-pass filter, an ellipse fitting module, a divider and an arc tangent module;
the optical fiber interference sensing system mainly comprises a laser, an optical fiber coupler, a phase modulator, a sensing optical fiber, a reference optical fiber, a Faraday rotating mirror, a photoelectric detector, a data acquisition card and an FPGA high-speed data processing platform;
the output port of the laser is connected with a 2X 2 coupler, the 2X 2 optical fiber coupler divides an optical signal into two paths, one path is reflected back to the 2X 2 optical fiber coupler through a Faraday rotating mirror at the tail end of the sensing optical fiber along the sensing optical fiber, the other path is subjected to phase modulation through a phase modulator along a reference optical fiber, and interference finally occurs at the 2X 2 coupler through the Faraday rotating mirror at the tail end of the reference optical fiber to form a Michelson interferometer; the interference signal reaches the detector through the optical fiber coupler. The intensity of the optical interference signal is related to the phase difference of the two beams. When an external low-frequency weak signal acts on the sensing optical fiber, the phase of light in the sensing optical fiber is modulated, and the phase difference of the light signals in the corresponding sensing optical fiber and the reference optical fiber is also changed;
the phase modulator is PZT piezoelectric ceramics, and the function generator generates a high-frequency carrier signal to be applied to the PZT piezoelectric ceramics by winding a single-mode fiber in the interference arm so as to perform phase modulation on the interference output signal.
Specifically, the interference output signals I are respectively identical to the frequency-doubled carrier signals Gcos omega c Frequency doubling carrier signal Hcos2 omega c Triple frequency carrier signalNumber Dcos3 omega c Multiplying, and respectively performing low-pass filtering on the obtained results to obtain I 1 、I 2 、I 3 Will I 3 Way signal and I 1 Result sum I of the path signals subtracted 2 The method comprises the steps that modulation depth estimation and correction are carried out on a path signal through an ellipse fitting module, and the corrected orthogonal signals are divided and subjected to arc tangent module calculation to obtain a low-frequency signal to be detected;
specifically, the output signal of the interferometer is:
a is DC bias, B is AC amplitude,for the phase of the signal to be measured, C is the modulation depth of the phase modulator, cos omega c t is the phase carrier signal. Demodulation of the phase by means of a phase-generating carrier algorithm can be calculated +.>To multiply carrier signal Gcos omega by one frequency c Frequency doubling carrier signal Hcos2 omega c Frequency tripled carrier signal Dcos3 omega c Respectively mixing with an interferometer output signal I, and passing through a low-pass filter with cut-off frequency between the frequency of a signal to be detected and the carrier frequency after mixing:
wherein J is 1 (C) As a first-order Bessel function of the first kind，J 2 (C) As a second order Bessel function of the first kind, J 3 (C) As the third-order Bezier function of the first class, according to the Bezier function recurrence relation:will I 3 (t)-I 1 (t) obtaining:
let L 2 (t)＝I 2 (t) mixing L with 1 (t) dividing L 2 (t) obtaining:
in practical applications, factors such as electronic noise, such as non-ideal performance, all cause dynamic changes in the dc offset and ac amplitude of the quadrature signal. Thus, L 1 (t) and L 2 The general expression of (t) can be rewritten as:
L 1 (t)＝a(t)+b(t)cosθ(t)
L 2 (t)＝c(t)+d(t)cos[θ(t)+δ]
wherein a (t) and c (t) are DC offset, b (t) and d (t) are AC amplitude, θ (t) is signal to be measured,delta is the phase difference of the two signals. Thus, L 1 (t) and L 2 (t) can be fit to an ellipse and expressed as:
x 2 +A 1 xy+A 2 y 2 +A 3 x+A 4 y+A 5 ＝0
a (t), b (t), c (t) and d (t) can be calculated:
the role of ellipse fitting here:
(1) Calculation ofAnd feeding back the final demodulation amplitude to improve demodulation accuracy.
(2) Will L 1 (t) and L 2 (t) signal correction is:
cosθ(t)＝[L 1 (t)-a]/b
finally, dividing and arctangent calculating two paths of orthogonal signals to obtain a low-frequency signal to be detected
Example 2:
referring to fig. 1, a signal measuring device of an optical fiber michelson interference sensing system is provided, which comprises a laser 1, an optical fiber coupler 2, a sensing optical fiber 3, a reference optical fiber 5, a phase modulator 6, faraday rotation mirrors 4 and 7, a photoelectric detector 8, a data acquisition card 9 and an fpga high-speed data processing platform 10;
in this embodiment, the output port of the laser 1 is connected to the 21 port of the 2×2 optical fiber coupler 2, the 2×2 optical fiber coupler 2 splits the optical signal into two paths, one path is along the sensing optical fiber 3, reflected back to the 2×2 optical fiber coupler 2 through the faraday rotator 4 at the end of the sensing optical fiber 3, and the other path is along the reference optical fiber 5, phase-modulated by the phase modulator 6, reflected through the faraday rotator 4 at the end of the reference optical fiber 5, and finally interfered at the 2×2 optical fiber coupler 2. The intensity of the optical interference signal is related to the phase difference of the two beams. When an external low-frequency signal acts on the sensing optical fiber 3, the optical phase in the sensing optical fiber 3 is modulated, the phase difference of the optical signals in the corresponding sensing optical fiber 3 and the reference optical fiber 5 is also changed, and finally the phase difference is reflected to the light intensity change detected by the photoelectric detector 8, the data acquisition card 9 is used for acquiring the signal and inputting the signal to the FPGA high-speed data processing platform 10, and the phase generation carrier algorithm is improved by the invention for demodulation;
in this embodiment, the phase modulator 6 is a PZT piezoelectric ceramic, and a single-mode fiber is wound around the PZT piezoelectric ceramic, so that a function generator generates a high-frequency carrier signal to be applied to the PZT piezoelectric ceramic, and further, the interference output signal is phase-modulated.
In the embodiment, the photoelectric detector 8 outputs an interference signal and is acquired by a data acquisition card 9 with 16 bits, the sampling frequency is 1M/s and the storage depth is 64M;
the system output interference light intensity acquired by the data acquisition card 9 is as follows:
a is DC bias, B is AC amplitude, and is the phase of the signal to be measured, C is the modulation depth of the phase modulator, cos omega c t is the phase carrier signal.
As shown in FIG. 2, the FPGA high-speed data processing platform 10 comprises a fundamental frequency carrier signal 10-1, a frequency doubling carrier signal 10-2, a frequency tripling carrier signal 10-3, multipliers 10-4, 10-5 and 10-6, low-pass filters 10-7, 10-8 and 10-9, a subtracter 10-10, an ellipse fitting module 10-11, a divider 10-12 and an arctangent module 10-13.
In the embodiment, a DDS sinusoidal signal generator is utilized to generate a fundamental frequency carrier signal, a double frequency carrier signal and a triple frequency carrier signal; the fundamental frequency carrier signal, the frequency doubling carrier signal and the frequency tripling carrier signal are mixed with the interference signal respectively, and after mixing, the interference signal passes through a low-pass filter with cut-off frequency between the frequency of the signal to be detected and the carrier frequency:
wherein J is 1 (C) As a first-order Bessel function, J 2 (C) As a second order Bessel function of the first kind, J 3 (C) As the third-order Bezier function of the first class, according to the Bezier function recurrence relation:will I 3 (t)-I 1 (t) obtaining:
let L 2 (t)＝I 2 (t) mixing L with 1 (t) dividing L 2 (t) obtaining:
in practical applications, factors such as electronic noise, such as non-ideal performance, all cause dynamic changes in the dc offset and ac amplitude of the quadrature signal. Thus, L 1 (t) and L 2 The general expression of (t) can be rewritten as:
L 1 (t)＝a(t)+b(t)cosθ(t)
L 2 (t)＝c(t)+d(t)cos[θ(t)+δ]
wherein a (t) and c (t) are DC offset, b (t) and d (t) are AC amplitude, θ (t) is signal to be measured,delta is the phase difference of the two signals. Thus, L 1 (t) and L 2 (t) can be fit to an ellipse and expressed as:
x 2 +A 1 xy+A 2 y 2 +A 3 x+A 4 y+A 5 ＝0
thus a (t), b (t), c (t) and d (t) can be calculated:
the effect of the ellipse fitting here is:
(1) Calculation ofAnd feeding back the final demodulation amplitude to improve demodulation accuracy.
(2) Will L 1 (t) and L 2 (t) signal correction is:
cosθ(t)＝[L 1 (t)-a]/b
finally, dividing and arctangent calculating two paths of orthogonal signals to obtain a low-frequency signal to be detected
The PGC algorithm demodulates the device selection and parameters of the low frequency signal testing device as follows:
(1) Laser 1: a narrow linewidth laser with a central wavelength of 1550nm, an output power of 12m and a linewidth of about 0.0179nm;
(2) Optical fiber coupler 2: operating wavelength 1550nm, spectral ratio 50%:50%, the insertion loss is less than or equal to 3.7dB;
(3) Sensing optical fiber 3:10m magnetically folded doped fiber;
(4) Faraday rotation mirror 4:1550nm optical fiber Faraday rotary mirror, single pass rotary angle 45 DEG, maximum insertion loss 0.6dB (environment at 25 ℃);
(5) Phase modulator 6: the PZT piezoelectric ceramic phase modulator has an optical phase modulation constant of 6rad/V at a resonance frequency (27-32 kHz) and 0.3rad/V at a non-resonance frequency;
(6) Photodetector 8: type InGaAs/PIN photodetector, connection mode is of the type
FC/APC type, working wavelength of 1200-1700 nm, total output voltage noise<9mV RMS ；
(7) Data acquisition card 9: sampling rate 1MS/s,4 paths of synchronous 16-bit analog quantity input, input voltage amplitude + -10V, sampling clock as the internal clock of the acquisition card, memory depth 64M, input impedance 10 mu M omega;
experiments were performed using the optical fiber michelson interferometric sensor system signal measuring device of fig. 1. One path of the sensing optical fiber 3 applies a 20Hz sensing signal to the PZT piezoelectric ceramic with a high-frequency carrier wave with the frequency of 1kHz, and the spectrum of the acquired interference signal is shown in figure 3. The 20Hz signal is annihilated in the low frequency band and extraction of the low frequency signal cannot be achieved with a spectrum analyzer.
Therefore, the algorithm of the invention is adopted to demodulate the signal, the demodulation result is shown in fig. 4, and the 20Hz sensing signal is effectively extracted.
The above embodiment is only a preferred embodiment of the present invention, but it is not intended to limit the present invention. Various changes and modifications may be made by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present invention. Therefore, all the technical schemes obtained by adopting the equivalent substitution or equivalent transformation are within the protection scope of the invention.
Claims (10)
1. A method for demodulating a low frequency signal by improving a phase-generating carrier algorithm, comprising the steps of: by applying a high-frequency carrier modulation signal, the field signal to be detected is changed into the sideband of the carrier signal, and the fundamental frequency carrier signal Gcos omega c Frequency doubling carrier signal Hcos2 omega c Frequency tripled carrier signal Dcos3 omega c Respectively multiplying the interference output signals, and respectively performing low-pass filtering on the obtained results to obtain I 1 、I 2 And I 3 Will I 3 Way signal and I 1 Result sum I of the path signals subtracted 2 And carrying out modulation depth estimation and correction on the path signals through ellipse fitting, dividing the corrected orthogonal signals, and carrying out arctangent calculation to obtain the low-frequency signals to be detected.
2. The method of improving a phase generating carrier algorithm for demodulating a low frequency signal according to claim 1 wherein the interference output signal is:
a is DC bias, B is AC amplitude,for the phase of the signal to be measured, C is the modulation depth of the phase modulator, cos omega c t is a phase carrier signal; will base frequency carrier signal Gcos omega c Frequency doubling carrier signal Hcos2 omega c Frequency tripled carrier signal Dcos3 omega c Respectively mixing with an interferometer output signal I, and passing through a low-pass filter with cut-off frequency between the frequency of a signal to be detected and the carrier frequency after mixing:
wherein J is 1 (C) As a first-order Bessel function, J 2 (C) As a second order Bessel function of the first kind, J 3 (C) Is a third-order bezier function of the first type.
3. The method of improving a phase-generating carrier algorithm for demodulating a low frequency signal according to claim 2 wherein: will I 3 (t)-I 1 (t) obtaining:
let L 2 (t)＝I 2 (t) mixing L with 1 (t) dividing L 2 (t) obtaining:
4. a method for demodulating a low frequency signal using an improved phase-generated carrier algorithm as claimed in claim 3 wherein L 1 (t) and L 2 The general expression of (t) is rewritten as:
L 1 (t)＝a(t)+b(t)cosθ(t)
L 2 (t)＝c(t)+d(t)cos[θ(t)+δ]
wherein a (t) and c (t) are DC offset, b (t) and d (t) are AC amplitude, θ (t) is signal to be measured,delta is the phase difference of two paths of signals, L 1 (t) and L 2 (t) fitting to an ellipse x 2 +A 1 xy+A 2 y 2 +A 3 x+A 4 y+A 5 ＝0,
a(t)＝(2A 2 A 3 -A 1 A 4 )/(A 1 2 -4A 2 )
c(t)＝(2A 4 -A 1 A 3 )/(A 1 2 -4A 2 )
5. The method of demodulating a low frequency signal using an improved phase-generated carrier algorithm according to claim 4 wherein: calculation ofFeedback of final demodulationThe amplitude is used to improve the demodulation accuracy,
will L 1 (t) and L 2 (t) signal correction is:
cosθ(t)＝[L 1 (t)-a]/b
finally, dividing and arctangent calculating two paths of orthogonal signals to obtain a low-frequency signal to be detected
6. The method of demodulating a low frequency signal using an improved phase generating carrier algorithm according to any one of claims 1-5, wherein: the optical signal is converted into an electric signal by the optical fiber interference sensing system output signal through the photoelectric detector, the data acquisition card is used for acquiring the signal and inputting the signal to the FPGA high-speed data processing platform for phase generation carrier algorithm demodulation.
7. The method of improving a phase generating carrier algorithm for demodulating a low frequency signal according to claim 6 wherein: the optical fiber interference sensing system signal measuring device comprises a laser, an optical fiber coupler, a sensing optical fiber, a reference optical fiber, a phase modulator, a Faraday rotating mirror, a photoelectric detector, a data acquisition card and an FPGA high-speed data processing platform.
8. The method of improving a phase generating carrier algorithm for demodulating a low frequency signal according to claim 7 wherein: the output port of the laser is connected with a 2X 2 optical fiber coupler 2, the 2X 2 optical fiber coupler divides an optical signal into two paths, the first path is reflected back to the 2X 2 optical fiber coupler 2 through a Faraday rotating mirror at the tail end of a sensing optical fiber, the second path is reflected through the Faraday rotating mirror at the tail end of the reference optical fiber after being subjected to phase modulation by a phase modulator along a reference optical fiber, and finally interference occurs between the second path and the first path at the 2X 2 optical fiber coupler 2; when an external low-frequency signal acts on the sensing optical fiber, the optical phase in the sensing optical fiber is modulated, the phase difference of the optical signals in the corresponding sensing optical fiber and the reference optical fiber is changed, the phase difference is finally reflected to the light intensity change detected by the photoelectric detector, the data acquisition card is used for acquiring the signal and inputting the signal to the FPGA high-speed data processing platform, and the carrier algorithm is generated by utilizing the improved phase to demodulate.
9. The method for demodulating a low-frequency signal with an improved phase-generating carrier algorithm according to claim 8, wherein the FPGA high-speed data processing platform comprises: the DDS sine signal generator, the mixer, the multiplier, the low-pass filter, the subtracter, the ellipse fitting module, the divider and the arctangent module.
10. A method of demodulating a low frequency signal in accordance with claim 9 wherein said method is used to improve a phase-generating carrier algorithm. Wherein said improved phase-generating carrier demodulation comprises the steps of:
(1) Acquiring interference light intensity signals after carrier modulation;
(2) The DDS sinusoidal signal generator generates a fundamental frequency carrier signal, a double frequency carrier signal and a triple frequency carrier signal; the fundamental frequency carrier signal, the frequency doubling carrier signal and the frequency tripling carrier signal are mixed with the interference signal respectively;
(3) The mixed signal passes through a low-pass filter with cut-off frequency between the frequency of the signal to be detected and the carrier frequency;
(4) Processing the output signal of the low-pass filter according to the Bessel function recurrence principle, demodulating the phase modulation depth in real time through ellipse fitting, and generating two paths of orthogonal signals;
(5) And finally, obtaining the low-frequency signal to be detected by dividing and arctangent calculation of the two paths of orthogonal signals.
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| CN117201250B (en) * | 2023-11-07 | 2024-01-23 | 武汉能钠智能装备技术股份有限公司 | Phase generation carrier demodulation method and device, electronic equipment and storage medium |
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