CN111504351A - Device and method for online correcting phase demodulation error of 3 × 3 coupler - Google Patents
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- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
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Abstract
The invention discloses a device for online correcting phase demodulation errors of a 3 × coupler, wherein a reference arm optical fiber is wound on a piezoelectric ceramic tube, the laser signal output end of a narrow linewidth laser is connected with the input end of a 1 × coupler, the first output end of a 1 × coupler is connected with one end of a delay optical fiber, the other end of the delay optical fiber is connected with the first signal input end of a 3 × coupler, the second signal input end of a 3 × coupler is suspended, the second output end of a 1 × coupler is connected with one end of the reference arm optical fiber, the other end of the reference arm optical fiber is connected with the third signal input end of a 3 × coupler, the sine excitation signal output end of a signal source generator is connected with the control signal input end of the piezoelectric ceramic tube, and the three output ends of a 3 × coupler are respectively connected with three optical signal input and output corresponding to a three-channel photoelectric detector.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a device and a method for online correcting phase demodulation errors of a 3 × 3 coupler.
Technical Field
The phase demodulation technology is one of the key technologies of the interference type optical fiber sensor, and can be divided into an active type and a passive type according to whether a phase demodulation system is active or not, and typical representatives of the two types of demodulation technologies are Phase Generation Carrier (PGC) demodulation and 3 × 3 coupler phase demodulation respectively.
The 3 × coupler is an important passive device, is especially widely applied to an interference type optical fiber sensing signal demodulation system, and compared with a dual 2 × coupler Mach-Zehnder interferometer (MZ interferometer) used in the early period, the interferometer formed by the coupler has the obvious advantages of high sensitivity, capability of tracking phase change direction, realization of high dynamic range through phase unwrapping and the like.
In practical applications, however, both classical MZ interferometers and interferometric distributed fiber grating demodulation systems suffer from inevitable polarization-induced signal fading, which is caused by inherent structural defects and interference from external factors such as temperature, stress, vibration, etc., and random variations, and polarization of input light causes polarization-induced signal fading (references: Kersey a D, Marrone M J, Dandridge a, et al. optimization and stabilization of polarization-induced interference control J. Journal of L interferometric Technology,1988,6 (16010): 1599;) so that the direct and alternating current coefficients in the three-way interference signals of the 3-intensity 3 × 3 coupler change, and if the fixed-mode method is adopted, the phase-induced demodulation system is applied to large-scale fiber grating demodulation systems with serious limitations.
Disclosure of Invention
The invention aims to provide a device and a method for online correcting phase demodulation errors of a 3 × coupler, which aim to solve the technical problems, the invention takes a most basic MZ interferometer as a research model by taking the thought of a phase generation carrier active demodulation technology as reference, introduces a piezoelectric ceramic tube as a phase modulator into a MZ interferometer reference arm, and utilizes the phase modulator to perform high-frequency modulation on a phase sensing system so as to achieve the aim of observing the polarization state and the interference effect of the interferometer in real time at the output end of the 3 × coupler.
In order to achieve the purpose, the device for online correcting the phase demodulation error of the 3 × 3 coupler comprises a narrow-linewidth laser, a 1 × 2 coupler, a delay optical fiber, a piezoelectric ceramic tube, a signal source generator, a 3 × 3 coupler, a three-channel photodetector and a three-channel data acquisition card, wherein a reference arm optical fiber is wound on the piezoelectric ceramic tube, the laser signal output end of the narrow-linewidth laser is connected with the input end of the 1 × 2 coupler, the first output end of the 1 × 2 coupler is connected with one end of the delay optical fiber, the other end of the delay optical fiber is connected with the first signal input end of the 3 × 3 coupler, the second signal input end of the 3 × 3 coupler is suspended, the second output end of the 1 × 2 coupler is connected with one end of the reference arm optical fiber, the other end of the reference arm optical fiber is connected with the third signal input end of the 3 × 3 coupler, the sinusoidal excitation signal output end of the signal source generator is connected with the control signal input end of the piezoelectric ceramic tube, the three output ends of the 3 × 3 coupler are respectively connected with the three optical signal input ends of the three-channel photodetector, and the three signal input ends of the three-channel data acquisition card are connected with the three.
Compared with the prior art, the invention has the following remarkable effects:
1. the method uses the thought of active demodulation of phase generation carrier waves, and adopts the piezoelectric ceramic tube to perform high-frequency modulation on the reference arm of the interference system, so that the phase dynamic range of the system is kept at a high amplitude level, and a guarantee is provided for the 3 × 3 coupler L issajous ellipse fitting estimation phase demodulation;
2. considering the phase demodulation error of the 3 × 3 coupler caused by the factors of asymmetry of the 3 × 3 coupler, unstable light source output power, inconsistent working efficiency of a photoelectric detector, element coupling loss in a light path, interference polarization induced fading and the like, the invention adopts a L issajous ellipse fitting method based on least square to realize the parameter estimation of the output phase characteristic of the 3 × 3 coupler, and the precision of the coupling output phase difference of the 3 × 3 coupler is controlled within 0.2 degrees;
3. the invention uses the thought of the phase generation carrier active demodulation technology for reference, adds a piezoelectric ceramic tube on a reference arm in the original interference system, applies high-frequency excitation to carry out high-frequency modulation on the phase of light waves in an optical fiber of the reference arm, improves the phase dynamic range of the 3 × 3 coupler to a large-amplitude level, and combines a L issajous ellipse fitting parameter estimation phase demodulation method to refresh fitting ellipse parameters in real time, eliminates random errors caused by demodulation parameter changes of the 3 × 3 coupler due to factors such as polarization induced fading and the like, and improves the phase demodulation precision of the 3 × 3 coupler.
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FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a L issajous diagram formed by the first path of interference light and the second path of interference light of the coupler 3 × 3;
FIG. 3 is a L issajous diagram of the second path of interference light and the third path of interference light of the 3 × 3 coupler.
Wherein, I1 is the first path of interference light intensity, I2 is the second path of interference light intensity, and I3 is the third path of interference light intensity.
The optical fiber laser comprises a 1-narrow linewidth laser, a 2-1 × 2 coupler, a 3-time delay optical fiber, a 4-piezoelectric ceramic tube, a 4.1-reference arm optical fiber, a 5-signal source generator, a 6-3 × 3 coupler, a 7-three-channel photoelectric detector and an 8-three-channel data acquisition card.
Detailed Description
The invention is described in further detail below with reference to the following figures and examples:
the device for online correction of phase demodulation errors of a 3 × coupler as shown in fig. 1 comprises a narrow-linewidth laser 1, a 1 × 2 coupler 2, a delay fiber 3, a piezoelectric ceramic tube 4, a signal source generator 5, a 3 3503 coupler 6, a three-channel photodetector 7 and a three-channel data acquisition card 8, wherein a reference arm fiber 4.1 is tightly and uniformly wound on the piezoelectric ceramic tube 4, a laser signal output end of the narrow-linewidth laser 1 is connected with an input end of the 1 × coupler 2, a first output end of the 1 × 2 coupler 2 is connected with one end of the delay fiber 3, the other end of the delay fiber 3 is connected with a first signal input end of a 3 × coupler 6, a second signal input end of the 3 × coupler 6 is suspended, a second output end of the 1 × coupler 2 is connected with one end of the reference arm fiber 4.1, the other end of the reference arm fiber 4.1 is connected with a third signal input end of a 3 × coupler 6, an excitation signal output end of the signal generator 5 is connected with a sinusoidal signal control input end of a sinusoidal tube 4, a phase demodulation signal control signal of the 3, an on-phase demodulation error control signal detector of a three-phase demodulation optical fiber 3, and a three-path optical fiber optical detector are connected with a three-phase demodulation optical fiber optical detector, and a three-phase demodulation optical fiber optical detector, the three-phase demodulation optical fiber optical interference detector, the three-phase demodulation optical interference detector is designed for the three-phase.
In the above technical solution, the 1 × 2 coupler 2, the delay fiber 3, and the reference arm fibers 4.1 and 3 × 3 coupler 6 form a dual beam MZ interferometer structure, which is an important component of a fiber interferometer sensing demodulation system, wherein the delay fiber 3 is used to make the length of the interferometer signal arm where the delay fiber is located equal to the length of the interferometer reference arm fiber 4.1 where the piezoelectric ceramic tube 4 is located, so as to form an equal arm interferometer, thereby reducing the influence of wavelength fluctuation of the light source and external interference.
In the above technical solution, the narrow linewidth laser 1 (linewidth 100kHz) is configured to emit continuous narrow linewidth laser to the 1 × 2 coupler 2, and serve as a light source of a dual-beam interference system, the 1 × 2 coupler 2 is configured to divide laser power of the continuous narrow linewidth laser into two parts (to implement dual-beam interference), and the two parts reach the 3 × 3 coupler 6 through the delay fiber 3 and the reference arm fiber 4.1 tightly and uniformly wound on the piezoelectric ceramic tube 4, and generate a dual-beam interference effect at the 3 × 3 coupler 6, so as to implement a basic dual-beam interference function of the MZ interferometer.
In the above technical solution, the signal source generator 5 is configured to perform sinusoidal excitation (frequency is set to 1kHz) on the piezoelectric ceramic tube 4 to enable the piezoelectric ceramic tube 4 to generate an electrostrictive effect, so that the length of the reference arm optical fiber 4.1 wound around the piezoelectric ceramic tube 4 is periodically changed, and further, the high-frequency modulation of the carrier frequency of 1kHz is performed on the optical phase of the reference arm optical fiber 4.1, so that the signal to be measured is located on the side band of the carrier modulation signal, and thus the phase dynamic range of the 3 × 3 coupler is improved to a large-amplitude level, which is beneficial to subsequent phase correction.
In the above technical solution, the three-channel data acquisition card 8 is configured to acquire the three-channel interference light intensity signals of the 3 × 3 coupler 6 through the three-channel photodetector 7, and perform subsequent phase demodulation on the three-channel interference light intensity signals by using the characteristic that the three-channel output phase difference of the 3 × 3 coupler 6 is constant.
In the above technical solution, the first path of interference light intensity signal (X axis) and the second path of interference light intensity signal (Y axis), the second path of interference light intensity signal (X axis) and the third path of interference light intensity signal (Y axis) in the three paths of interference light intensity signals respectively form two L issajous graphs (corresponding ellipses are drawn through the X axis and the Y axis), the graphs are elliptical, and the least square ellipse fitting algorithm is used to respectively calculate the elliptical parameters of the two L issajous graphs (5 parameters in the elliptical equation are generally required for determining an ellipse, such as the elliptical equation X in fig. 2 and 32+Axy+By2In the + Cx + Dy + E ═ 0, x and y respectively represent any two paths of light intensity signals output by the 3 × 3 coupler, the solution of the demodulation parameters A-E of the elliptic equation is established on the basis of elliptic fitting, and the elliptic synthesis follows the ellipseFollowing the nature and regularity of lissajous figures, relevant reports are found in the references (reference: application of ellipse parameter estimation in optical fiber interference sensing system [ J]The technical innovation and application are that 2015(18):6-7.), phase demodulation output characteristic parameters of three paths of interference light of a 3 × 3 coupler 6 are determined through elliptic parameters of two L issajous graphs and are used for phase accurate demodulation, in addition, demodulation signals (carrier frequency is 1kHz) carrying piezoelectric ceramic tube modulation signals are demodulated according to the phase demodulation output characteristic parameters of the three paths of interference light, and finally high-frequency carrier modulation signals in the demodulation signals can be filtered through low-pass filtering, so that phase change information of interferometer arm length difference caused by external stress or vibration is obtained (external change causes phase fluctuation in signal arm optical fibers, and therefore intensity change of the interference signals is caused).
A method for correcting phase demodulation errors of a 3 × 3 coupler based on the device is characterized by comprising the following steps:
step 2, the signal source generator 5 carries out sinusoidal excitation on the piezoelectric ceramic tube 4, so that the piezoelectric ceramic tube 4 generates an electrostrictive effect, the length of a reference arm optical fiber 4.1 wound on the piezoelectric ceramic tube 4 is changed periodically, and then the high-frequency modulation of the carrier frequency of 1kHz is carried out on the optical wave phase in the reference arm optical fiber 4.1, so that a signal to be detected is positioned on the side band of a carrier modulation signal, and the phase dynamic range of the 3 × 3 coupler is improved to a large-amplitude level;
step 3, the three-channel data acquisition card 8 acquires three channels of interference light intensity signals of the 3 × 3 coupler 6 through the three-channel photoelectric detector 7;
and 5, in order to realize the real-time correction effect, repeatedly executing the step 4 (repeatedly executing the steps of monitoring the change of the polarization state caused by factors such as external stress, vibration and the like) at intervals of preset time (such as 1 minute), namely demodulating phase change information of the current moment by using the 'L issajous diagram, parameter estimation, signal demodulation and low-pass filtering' in the step 4, realizing online observation of the polarization effect of the MZ interferometer, namely visibility of interference fringes by using the shape of the L issajous diagram in the step 4 (the larger the ellipse is, the thinner the side line is, the better the interference effect is), and realizing real-time correction of the phase demodulation error of the 3 × 3 coupler according to the ellipse parameters of the two L issajous diagrams at the current moment.
The invention solves the problem of real-time online demodulation error of the existing 3 × 3 coupler 6, provides a more effective method, adds a piezoelectric ceramic tube 4 to the reference arm in the original interference system, applies high-frequency excitation to perform high-frequency modulation on the phase of light waves in the optical fiber of the reference arm, improves the phase dynamic range of the 3 × 3 coupler 6 to a large-amplitude level, and realizes real-time correction of the phase demodulation error of the 3 × 3 coupler 6 by combining a L issajous ellipse fitting parameter estimation phase demodulation method.
Details not described in this specification are within the skill of the art that are well known to those skilled in the art.
Claims (8)
1. The device for online correcting the phase demodulation error of the 3 × coupler is characterized by comprising a narrow-linewidth laser (1), a 1 × 2 coupler (2), a delay optical fiber (3), a piezoelectric ceramic tube (4), a signal source generator (5), a 3 × coupler (6) and a three-channel photoelectric detector (7), wherein a reference arm optical fiber (4.1) is wound on the piezoelectric ceramic tube (4), the laser signal output end of the narrow-linewidth laser (1) is connected with the input end of the 1 × 2 coupler (2), the first output end of the 1 × 2 coupler (2) is connected with one end of the delay optical fiber (3), the other end of the delay optical fiber (3) is connected with the first signal input end of the 3 × coupler (6), the second signal input end of the 3 × 3 coupler (6) is suspended, the second output end of the 1 × 2 coupler (2) is connected with one end of the reference arm (4.1), the other end of the reference arm optical fiber (4.1) is connected with the third signal input end of the 3 × coupler, and the three signal input ends of the three-channel optical detectors (×) are respectively connected with the three excitation signal input ends of the three-channel optical fiber (3) and the three-3 optical.
2. The device for online correction of phase demodulation errors of the 3 × 3 coupler according to claim 1, wherein the delay fiber (3) is used to make the length of the interferometer signal arm where the delay fiber is located equal to that of the interferometer reference arm fiber (4.1) to form an equal arm interferometer.
3. The device for online correction of phase demodulation error of 3 × 3 coupler according to claim 1, wherein the narrow linewidth laser (1) is used to emit continuous narrow linewidth laser to the 1 × 2 coupler (2), the 1 × 2 coupler (2) is used to divide the laser power of the continuous narrow linewidth laser into two parts, which reach the 3 × 3 coupler (6) through the delay fiber (3) and the reference arm fiber (4.1) wound on the piezo-ceramic tube (4), and the double beam interference effect occurs at the 3 × 3 coupler (6).
4. The device for online correction of the phase demodulation error of the 3 × 3 coupler according to claim 1, wherein the signal source generator (5) is configured to perform sinusoidal excitation on the piezoceramic tube (4) to generate an electrostrictive effect on the piezoceramic tube (4), so that the length of the reference arm optical fiber (4.1) wound around the piezoceramic tube (4) is periodically changed, and thus the modulation of the optical wave phase in the reference arm optical fiber (4.1) is achieved.
5. The device for online correction of the phase demodulation error of the 3 × 3 coupler according to claim 1, further comprising a three-channel data acquisition card (8), wherein three signal input terminals of the three-channel data acquisition card (8) are connected to three electrical signal output terminals corresponding to the three-channel photodetector (7), and the three-channel data acquisition card (8) is used for acquiring the three-way interference light intensity signal of the 3 × 3 coupler (6) through the three-channel photodetector (7).
6. The device for online correction of the phase demodulation error of the 3 × 3 coupler according to claim 5, wherein the first path of interference light intensity signal and the second path of interference light intensity signal in the three paths of interference light intensity signals, the second path of interference light intensity signal and the third path of interference light intensity signal respectively form two L issajous graphs, the ellipse parameters of the two L issajous graphs are calculated by using a least square ellipse fitting algorithm, the phase demodulation output characteristic parameters of the three paths of interference light of the 3 × 3 coupler (6) are determined according to the ellipse parameters of the two L issajous graphs and are used for phase demodulation, in addition, the demodulation signal carrying the piezoelectric ceramic tube modulation signal is demodulated according to the phase demodulation output characteristic parameters of the three paths of interference light, and finally the corresponding modulation signal in the demodulation signal can be filtered through low-pass filtering, so as to obtain the phase change information of the arm length difference of the interferometer caused by external stress or vibration.
7. The device for online correction of phase demodulation errors of a 3 × 3 coupler according to claim 1, wherein the 1 × 2 coupler (2), the delay fiber (3), the reference arm fiber (4.1), and the 3 × 3 coupler (6) form a dual-beam MZ interferometer.
8. A method for correcting phase demodulation errors of a 3 × 3 coupler based on the apparatus of claim 1, comprising the steps of:
step 1, the narrow linewidth laser (1) emits continuous narrow linewidth laser to a 1 × 2 coupler (2), the 1 × 2 coupler (2) divides the laser power of the continuous narrow linewidth laser into two parts, the two parts respectively reach a 3 × 3 coupler (6) through a delay optical fiber (3) and a reference arm optical fiber (4.1) wound on a piezoelectric ceramic tube (4), and a double-beam interference effect is generated at the 3 × 3 coupler (6);
step 2, the signal source generator (5) carries out sinusoidal excitation on the piezoelectric ceramic tube (4), so that the piezoelectric ceramic tube (4) generates an electrostrictive effect, the length of a reference arm optical fiber (4.1) wound on the piezoelectric ceramic tube (4) is changed periodically, and further the modulation of the optical wave phase in the reference arm optical fiber (4.1) is realized, so that a signal to be measured is positioned on the side band of a carrier modulation signal, and the phase dynamic range of the 3 × 3 coupler is improved;
step 3, the three-channel data acquisition card (8) acquires three channels of interference light intensity signals of the 3 × 3 coupler (6) through the three-channel photoelectric detector (7);
step 4, firstly, respectively forming two L issajous graphs for a first path of interference light intensity signal and a second path of interference light intensity signal, and a second path of interference light intensity signal and a third path of interference light intensity signal in three paths of interference light intensity signals, secondly, respectively calculating elliptical parameters of two L issajous graphs by using a least square method ellipse fitting algorithm, determining phase demodulation output characteristic parameters of the three paths of interference light of a 3 × 3 coupler (6) according to the elliptical parameters of the two L issajous graphs, then demodulating a demodulation signal carrying a piezoelectric ceramic tube modulation signal according to the phase demodulation output characteristic parameters of the three paths of interference light, and finally, filtering a corresponding modulation signal in the demodulation signal through low-pass filtering to obtain phase change information of interferometer arm length difference caused by external stress or vibration;
and 5, in order to realize the real-time correction effect, repeatedly executing the step 4 at intervals of preset time, namely the L issajous diagram, the parameter estimation, the signal demodulation and the low-pass filtering in the step 4, demodulating the phase change information at the current moment, realizing the online observation of the polarization effect of the MZ interferometer, namely the visibility of interference fringes, by the shape of the L issajous diagram in the step 4, and realizing the real-time correction of the phase demodulation error of the 3 × 3 coupler according to the elliptic parameters of the two L issajous diagrams at the current moment.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112097813A (en) * | 2020-09-14 | 2020-12-18 | 中国人民解放军国防科技大学 | 3X3 coupler photoelectric detection method and device based on optical frequency modulation |
| CN112815970A (en) * | 2021-01-05 | 2021-05-18 | 安徽大学 | High-precision ellipse fitting device and ellipse fitting method in interference system |
| CN112857207A (en) * | 2021-03-09 | 2021-05-28 | 哈尔滨工业大学 | Single-beam three-degree-of-freedom homodyne laser interferometer based on array detector |
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| CN112857207A (en) * | 2021-03-09 | 2021-05-28 | 哈尔滨工业大学 | Single-beam three-degree-of-freedom homodyne laser interferometer based on array detector |
| CN112857207B (en) * | 2021-03-09 | 2022-12-16 | 哈尔滨工业大学 | Single-beam three-degree-of-freedom homodyne laser interferometer based on array detector |
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