PGC-Atan demodulation method and system for directly calculating phase modulation depth

Abstract

The invention relates to a PGC-Atan demodulation method and system for directly calculating phase modulation depth, and belongs to the technical field of sensor phase demodulation, the method is based on the corresponding relation between the phase change caused by laser modulation and the interference light intensity, and the phase modulation depth is calculated by monitoring the intensity change of interference signals under different laser modulation parameters. And the phase modulation depth is directly calculated. The demodulation system carries out high-frequency modulation on a laser light source by adopting an internal modulation mode, and eliminates the influence of associated amplitude modulation by utilizing synchronous A / D (Analog to Digital) acquisition. The obtained interference signals are mixed and multiplied with carrier frequency-doubled sine signals, carrier frequency-doubled cosine signals and carrier frequency-doubled cosine signals respectively, and a pair of orthogonal signals containing the phase of the signal to be measured is obtained through low-pass filtering and signal processing. And performing arc tangent operation and high-pass filtering on the orthogonal signal to realize accurate demodulation of the signal to be measured. According to the invention, accompanying amplitude modulation elimination and direct calculation and compensation of carrier modulation depth and phase difference are carried out, and the demodulation accuracy is obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sensor phase demodulation, and in particular to a PGC-Atan demodulation method and system for directly calculating phase modulation depth. Background Art

[0002] In the field of high-precision measurement, Phase Generated Carrier (PGC) demodulation technology is favored because it can transmit information through high-frequency carriers, especially for fiber optic sensors and precision measurement systems. This technology is used in a variety of sensors, including but not limited to temperature, pressure, displacement and strain sensors, which rely on phase changes to detect changes in physical quantities. PGC technology transmits information by introducing high-frequency carriers in optical signals, achieving high-precision detection of small changes, which is crucial to improving the sensitivity and resolution of measurements.

[0003] Among the traditional PGC demodulation algorithms, PGC-DCM and PGC-Atan are two common methods. The PGC-DCM algorithm first differentiates the carrier signal, then cross-multiplies it with the original signal, and extracts the phase information to be measured through signal operation. Since the differentiation process will amplify the noise in the signal, the demodulation accuracy of the PGC-DCM algorithm is restricted by the light intensity fluctuation or the stability of the light source. The PGC-Atan algorithm eliminates the influence of light intensity disturbance by performing an appropriate linear transformation on the demodulated signal and then applying the inverse tangent function to obtain the phase information. However, the traditional PGC-Atan algorithm is affected by inherent factors such as carrier phase modulation depth deviation, associated amplitude modulation, and carrier phase delay. In practical applications, its demodulation accuracy and stability need to be improved. Therefore, in order to meet the requirements of high precision, high stability and real-time performance, the traditional PGC-Atan algorithm is improved so that it can effectively resist the interference of inherent factors, improve the resolution and accuracy of the measurement, and is conducive to improving the performance of optical fiber sensors and precision measurement systems, and enhancing their adaptability and reliability under various environmental conditions. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and propose a PGC-Atan demodulation method and system for directly calculating the phase modulation depth. Based on the correspondence between the phase change caused by high-frequency carrier modulation and the light intensity in the interference spectrum, the present invention obtains the range of variation of the interference signal voltage intensity by changing the modulation parameters, and directly calculates the phase modulation depth. At the same time, the modulated light is split, and the influence of the associated amplitude modulation caused by the internal modulation of the laser is eliminated by synchronous A / D acquisition and signal calculation; the phase difference between the two signals is compensated by mixing and filtering the interference signal and the frequency-doubled signal. Therefore, compared with the traditional PGC demodulation algorithm, the present invention comprehensively considers the interference of phase modulation depth calculation, associated amplitude modulation, and carrier delay, and proposes an improved demodulation algorithm and system, which is beneficial to improving the demodulation accuracy of the interferometric fiber optic sensor.

[0005] The present invention provides a PGC-Atan demodulation method for directly calculating the phase modulation depth, comprising the following steps:

[0006] Step S1, internally modulate the laser light source so that it carries a high-frequency carrier signal; use an optical fiber coupler to divide the modulated laser light source into two paths, one of which enters the sensor and generates an interference light signal I containing the phase information of the signal to be measured. i (t); Considering the change of laser output power caused by internal modulation, that is, the influence of associated amplitude modulation, after photoelectric conversion, the interference signal expression is:

[0007] ,

[0008] in, is the associated amplitude modulation term, m is the laser modulation depth, ω0 is the high-frequency carrier frequency, A and B are constant terms related to the interference light signal, C is the phase modulation depth of the high-frequency carrier, assuming that the initial phase of the high-frequency carrier is 0, is the phase generated by carrier modulation, φ(t) is the phase to be measured;

[0009] Step S2, after the other modulated optical signal I0(t) undergoes photoelectric conversion, its electrical signal V0(t) carries information related to the laser current modulation depth m. AD ​​acquisition and phase division operations are performed on the above two signals to obtain the interference signal expression that eliminates the influence of the associated amplitude modulation:

[0010] ,

[0011] Step S3, when no signal to be tested is applied, the modulation parameters of the laser are adjusted to gradually increase the modulation depth of the carrier signal, and the intensity change of the interference signal V(t) is observed; when the carrier modulation depth increases to a certain extent, the voltage intensity will reach an extreme value. , From the perspective of interference spectroscopy, this means that the phase modulation generated by the carrier has reached or even exceeded π; the maximum voltage variation range during the recording adjustment process ; is the maximum value of V(t), is the minimum value of V(t);

[0012] Step S4, set appropriate high-frequency carrier modulation parameters, and observe the waveform of the interference signal V(t), and record the peak-to-peak value of the waveform as ΔV current ; ΔV current The physical meaning of is the voltage change of the interference signal caused by the phase modulation of the incident light when the carrier modulation depth is C. Therefore, the phase modulation depth C can be directly calculated using the following formula:

[0013] ,

[0014] Step S5: The interference signal V(t) is combined with the carrier frequency-doubled cosine signal Multiply and low-pass filter to obtain the signal P(t) containing the phase sine term to be measured; add the interference signal V(t) to the carrier double frequency cosine signal Multiply and low-pass filter to obtain the signal Q(t) containing the phase cosine term to be measured; considering that there is a phase difference θ between the interference signal and the carrier frequency multiplication signal when the signals are multiplied, the corrected signals P(t) and Q(t) are:

[0015] ,

[0016] Wherein, G and H are the amplitudes of the carrier frequency-doubled and frequency-doubled signals, respectively, and G=H; J1(C) and J2(C) are the first-order and second-order first-kind Bessel function values ​​about C, respectively, and when the C value is calculated in step S4, both are constant terms;

[0017] Step S6: The interference signal V(t) is combined with the carrier frequency-doubled sinusoidal signal Multiply and low-pass filter to obtain the signal R(t) containing the sinusoidal term of the phase difference θ; divide the signal R(t) by the inverted signal P(t), and then perform an inverse tangent operation to obtain the phase difference θ:

[0018] ,

[0019] Step S7, combining the two orthogonal signals P(t) and Q(t) obtained in step S5 and step S6 and the phase difference θ, finally solving the phase φ(t) to be measured:

[0020] .

[0021] The present invention also proposes a PGC-Atan demodulation system for directly calculating the phase modulation depth. The modulation module performs internal modulation on the laser light source so that the output light carries a high-frequency carrier and is divided into two paths after passing through the optical fiber coupler. One path generates interference light after entering the sensor, and the other path is used as a reference signal for the change in the intensity of the modulated light, and performs synchronous A / D acquisition with the interference light. The two signals are respectively connected to a first divider to obtain an interference signal V(t) that eliminates the associated amplitude modulation. The parameters of the modulation module are adjusted and the changes in the interference signal are recorded. The data on the changes in the interference signal are input into a phase modulation depth solver to directly calculate the phase modulation depth C. The carrier-frequency-doubled sinusoidal signal and the interference signal V(t) are respectively connected to a first multiplier, and the output results thereof are connected to a first low-pass filter to obtain a signal R(t). The sine signal and the interference signal V(t) are respectively connected to the second multiplier, and the output results thereof are connected to the second low-pass filter to obtain the signal P(t); the carrier double frequency cosine signal and the interference signal V(t) are respectively connected to the third multiplier, and the output results thereof are connected to the third low-pass filter to obtain the signal Q(t); the output end of the first low-pass filter and the inverted output end of the second low-pass filter are respectively connected to the second divider, and the output results thereof are input to the first inverse tangent operator to calculate the phase difference θ; the output end of the second low-pass filter and the output end of the third low-pass filter are respectively connected to the third divider, and the output results thereof and the compensation coefficient term solver are respectively connected to the fourth multiplier; the output end of the fourth multiplier is connected to the second inverse tangent operator, and the output result thereof is output after passing through a high-pass filter to output the final phase φ(t) to be measured.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention is based on the correspondence between the phase change caused by high-frequency carrier modulation and the light intensity change in the interference spectrum. By monitoring the voltage intensity change range of the interference signal under different modulation parameters, the carrier phase modulation depth is solved and corrected; the modulated laser light source is split by an optical fiber coupler to obtain a reference signal carrying the laser current modulation information, and the influence of the associated amplitude modulation caused by the internal modulation of the laser is eliminated by synchronous A / D acquisition and signal operation; the phase difference of the two signals and the orthogonal signal compensation coefficient are calculated by mixing and filtering the interference signal and the frequency-doubled signal. The improved algorithm and system proposed by the present invention are conducive to improving the PGC-Atan demodulation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flowchart of a PGC-Atan demodulation method for directly calculating the phase modulation depth;

[0025] Figure markings: 1-modulation module; 2-A / D acquisition module; 3-first divider; 4-phase modulation depth solver; 5-carrier one-time sine signal generator; 6-first multiplier; 7-carrier one-time cosine signal generator; 8-second multiplier; 9-carrier two-time cosine signal generator; 10-third multiplier; 11-first low-pass filter; 12-second low-pass filter; 13-third low-pass filter; 14-second divider; 15-first inverse tangent operator; 16-third divider; 17-fourth multiplier; 18-compensation coefficient term solver; 19-second inverse tangent operator; 20-high-pass filter. DETAILED DESCRIPTION

[0026] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms, and the present disclosure should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0027] like Figure 1 As shown, the present invention provides a PGC-Atan demodulation method and system for directly calculating the phase modulation depth. The functions and implementation processes of each part of the system are as follows:

[0028] First, the modulation module 1 performs internal modulation on the laser light source so that the output light carries a high-frequency carrier, and connects the modulated laser to the optical fiber coupler to be divided into two paths. One path generates interference light after entering the sensor, and the other path is used as a reference signal for the intensity change of the modulated light. The two signals are synchronously collected by the A / D acquisition module 2 and respectively connected to the first divider 3 to obtain the interference signal V(t) that eliminates the associated amplitude modulation; adjust the laser drive current and temperature and other parameter settings in the modulation module 1, read the voltage change of the interference signal, input the relevant data to the phase modulation depth solver 4, and directly calculate the phase modulation depth C; then the carrier-frequency-doubled sine signal generator 5 and the interference signal V(t) are respectively connected to the first multiplier 6, and the output result thereof is connected to the first low-pass filter 11 to obtain a signal R(t) containing the phase difference θ term; the carrier-frequency-doubled cosine signal generator 7 and the interference signal V(t) are respectively connected to the second multiplier 8, and the output result thereof is connected to the first low-pass filter 11 to obtain the signal R(t) containing the phase difference θ term. The second low-pass filter 12 obtains a signal P(t) containing the sine term of the phase to be measured; the carrier double frequency cosine signal generator 9 and the interference signal V(t) are respectively connected to the third multiplier 10, and the output results thereof are connected to the third low-pass filter 13 to obtain a signal Q(t) containing the cosine term of the phase to be measured; then the output end of the first low-pass filter 11 and the inverted output end of the second low-pass filter 12 are respectively connected to the second divider 14, and the output results thereof are input to the first inverse tangent operator 15, so as to calculate the phase difference θ; the output end of the second low-pass filter 12 and the output end of the third low-pass filter 13 are respectively connected to the third divider 16, and the output results thereof and the compensation coefficient term solver 18 are respectively connected to the fourth multiplier 17, so as to obtain a pair of orthogonal signals containing the phase information to be measured; finally, the output end of the fourth multiplier 17 is connected to the second inverse tangent operator 19, and then passes through the high-pass filter 20 to solve the phase φ(t) to be measured.

[0029] In the implementation process of the demodulation system, the demodulation algorithm principle and process involved can be summarized as the following steps:

[0030] Step S1, internally modulate the laser light source to make it carry a high-frequency carrier signal; use an optical fiber coupler to divide the modulated laser light source into two paths, one of which enters the sensor and generates an interference light signal I i (t); Since the modulation in the light source causes the high-frequency change of the light frequency, the output light intensity will also change, that is, there is an associated amplitude modulation term; therefore, after the interference light is converted into photoelectric light, the expression of its electrical signal is:

[0031] ,

[0032] in, is the associated amplitude modulation term, m is the laser modulation depth, ω0 is the high-frequency carrier frequency, A and B are constant terms related to the interference light signal, C is the phase modulation depth of the high-frequency carrier, assuming that the initial phase of the high-frequency carrier is 0, is the phase generated by carrier modulation, φ(t) is the phase to be measured;

[0033] In step S2, the other modulated optical signal I0(t) does not enter the sensor, but only represents the change of the light intensity after modulation. Its electrical signal V0(t) carries information related to the laser current modulation depth m. Therefore, this optical signal is directly photoelectrically converted, and the above two signals are synchronously AD-collected. After the signal division operation, the influence of the associated amplitude modulation can be eliminated in real time, and the expression of the interference signal is corrected to:

[0034] ,

[0035] Step S3, when no signal to be tested is applied, the modulation parameters of the laser are adjusted to gradually increase the modulation depth of the carrier signal, and the intensity change of the interference signal V(t) is observed; when the carrier modulation depth increases to a certain extent, the voltage intensity will reach an extreme value. , From the perspective of interference spectroscopy, this means that the phase modulation generated by the carrier has reached or even exceeded π; the maximum voltage variation range during the recording adjustment process ; is the maximum value of V(t), is the minimum value of V(t);

[0036] Step S4, set appropriate high-frequency carrier modulation parameters, and observe the waveform of the interference signal V(t), and record the peak-to-peak value of the waveform as ΔV current ; ΔV current The physical meaning of is the voltage change of the interference signal caused by the phase modulation of the incident light when the carrier modulation depth is C. Therefore, the phase modulation depth C can be directly calculated using the following formula:

[0037] ,

[0038] Step S5: The interference signal V(t) is combined with the carrier frequency-doubled cosine signal Multiply and low-pass filter to obtain the signal P(t) containing the phase sine term to be measured; add the interference signal V(t) to the carrier double frequency cosine signal Multiply and low-pass filter to obtain the signal Q(t) containing the phase cosine term to be measured; considering that there is a phase difference θ between the interference signal and the carrier frequency multiplication signal when the signals are multiplied, the corrected signals P(t) and Q(t) are:

[0039] ,

[0040] Wherein, G and H are the amplitudes of the carrier frequency-doubled and frequency-doubled signals, respectively. For the convenience of calculation, G=H can be set; J1(C) and J2(C) are the first-order and second-order first-kind Bessel function values ​​about C, respectively. When the C value is calculated in step S4, both are constant terms;

[0041] Step S6: The interference signal V(t) is combined with the carrier frequency-doubled sinusoidal signal Multiply and low-pass filter to obtain the signal R(t) containing the sinusoidal term of the phase difference θ; divide the signal R(t) by the inverted signal P(t), and then perform an inverse tangent operation to obtain the phase difference θ:

[0042] ,

[0043] Step S7, combining the two orthogonal signals P(t) and Q(t) obtained in step S5 and step S6 and the phase difference θ, finally solving the phase φ(t) to be measured:

[0044] ,

[0045] It should be noted that since the value range of the inverse tangent operation is (-π / 2, π / 2), phase unwrapping is required to obtain a complete phase signal; after that, high-pass filtering is used to eliminate low-frequency interference to complete the entire PGC-Atan demodulation operation.

[0046] Furthermore, the modulation parameters mainly refer to the driving current of the laser. The rationality of the parameter setting lies in adjusting the bias and amplitude of the driving current so that the V(t) signal presents a relatively regular cosine waveform and the voltage intensity corresponding to the peak does not exceed V max , the voltage intensity corresponding to the trough is not less than V max , so the peak-to-peak value ΔV can be read accurately current .

[0047] Furthermore, the core component of the modulation module 1 is the laser light source driving circuit board, which is equipped with other components such as a signal generator, a current driver, a temperature controller, etc. to realize the laser internal modulation function.

[0048] Obviously, the above embodiments are only examples for clear explanation and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description, and the changes or modifications derived therefrom are still within the protection scope of the invention.

Claims

1. A PGC-Atan demodulation method for directly calculating the phase modulation depth, characterized in that: The following steps are involved: Step S1, internally modulate the laser light source so that it carries a high-frequency carrier signal; use an optical fiber coupler to divide the modulated laser light source into two paths, one of which enters the sensor and generates an interference light signal I containing the phase information of the signal to be measured. i (t); Considering the change of laser output power caused by internal modulation, that is, the influence of associated amplitude modulation, after photoelectric conversion, the interference signal expression is: ， in, is the associated amplitude modulation term, m is the laser modulation depth, ω0 is the high-frequency carrier frequency, A and B are constant terms related to the interference light signal, C is the phase modulation depth of the high-frequency carrier, assuming that the initial phase of the high-frequency carrier is 0, is the phase generated by carrier modulation, φ(t) is the phase to be measured; Step S2, after the other modulated optical signal I0(t) undergoes photoelectric conversion, its electrical signal V0(t) carries information related to the laser current modulation depth m. AD ​​acquisition and signal division operations are performed on the above two signals to obtain the interference signal expression that eliminates the influence of the associated amplitude modulation: ， Step S3, when no signal to be tested is applied, the modulation parameters of the laser are adjusted to gradually increase the modulation depth of the carrier signal, and the intensity change of the interference signal V(t) is observed; when the carrier modulation depth increases to a certain extent, the voltage intensity will reach an extreme value. , From the perspective of interference spectroscopy, this means that the phase modulation generated by the carrier has reached or even exceeded π; the maximum voltage variation range during the recording adjustment process ; is the maximum value of V(t), is the minimum value of V(t); Step S4, set appropriate high-frequency carrier modulation parameters, and observe the waveform of the interference signal V(t), and record the peak-to-peak value of the waveform as ΔV current ; ΔV current The physical meaning is that when the carrier modulation depth is C, the voltage change of the interference signal caused by the phase modulation of the incident light can be directly calculated using the following formula: ， Step S5: The interference signal V(t) is combined with the carrier frequency-doubled cosine signal Multiply and low-pass filter to obtain the signal P(t) containing the phase sine term to be measured; add the interference signal V(t) to the carrier double frequency cosine signal Multiply and low-pass filter to obtain the signal Q(t) containing the phase cosine term to be measured; considering that there is a phase difference θ between the interference signal and the carrier frequency multiplication signal when the signals are multiplied, the corrected signals P(t) and Q(t) are: ， Wherein, G and H are the amplitudes of the carrier frequency-doubled and frequency-doubled signals, respectively, and G=H; J1(C) and J2(C) are the first-order and second-order first-kind Bessel function values ​​about C, respectively, and when the C value is calculated in step S4, both are constant terms; Step S6: The interference signal V(t) is combined with the carrier frequency-doubled sinusoidal signal Multiply and low-pass filter to obtain the signal R(t) containing the sinusoidal term of the phase difference θ; divide the signal R(t) by the inverted signal P(t), and then perform an inverse tangent operation to obtain the phase difference θ: ， Step S7, combining the two orthogonal signals P(t) and Q(t) obtained in step S5 and step S6 and the phase difference θ, finally solving the phase φ(t) to be measured: 。 2. A PGC-Atan demodulation method for directly calculating phase modulation depth as claimed in claim 1, characterized in that: The modulation parameter in step S4 is the driving current of the laser. The rationality of setting this parameter lies in adjusting the bias and amplitude of the driving current so that the V(t) signal presents a relatively regular cosine waveform and the voltage intensity corresponding to the peak does not exceed V max , the voltage intensity corresponding to the trough is not less than V max , and then read the peak-to-peak value ΔV current .

3. A PGC-Atan demodulation system for directly calculating the phase modulation depth, characterized in that: The modulation module performs internal modulation on the laser light source so that the output light carries a high-frequency carrier and is divided into two paths after passing through the fiber coupler; one path generates interference light after entering the sensor, and the other path is used as a reference signal for the intensity change of the modulated light and performs A / D acquisition synchronously with the interference light; the two signals are respectively connected to the first divider to obtain the interference signal V(t) that eliminates the associated amplitude modulation; Adjust the parameters of the modulation module and record the changes of the interference signal. Input the data of the changes of the interference signal into the phase modulation depth solver to directly calculate the phase modulation depth C. The carrier frequency-doubled sine signal and the interference signal V(t) are respectively connected to the first multiplier, and the output results are connected to the first low-pass filter to obtain the signal R(t). The carrier frequency-doubled cosine signal and the interference signal V(t) are respectively connected to the second multiplier, and the output results are connected to the second low-pass filter to obtain the signal P(t). The carrier frequency-doubled cosine signal and the interference signal V(t) are respectively connected to the third multiplier. Its output result is connected to the third low-pass filter to obtain the signal Q(t); the output end of the first low-pass filter and the inverted output end of the second low-pass filter are respectively connected to the second divider, and the output results are input to the first inverse tangent operator to calculate the phase difference θ; the output end of the second low-pass filter and the output end of the third low-pass filter are respectively connected to the third divider, and the output results and the compensation coefficient term solver are respectively connected to the fourth multiplier; the output end of the fourth multiplier is connected to the second inverse tangent operator, and the output result is output after passing through the high-pass filter to output the final phase φ(t) to be measured.

4. The system according to claim 3, characterized in that The modulation module refers to a laser light source driving circuit board, which is equipped with a signal generator, a current driver, and a temperature controller to realize the laser internal modulation function.

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