CN111504351A - Device and method for online correcting phase demodulation error of 3 × 3 coupler - Google Patents

Abstract

The invention discloses a device for correcting the phase demodulation error of a 3×3 coupler on-line. The piezoelectric ceramic tube is wound with a reference arm optical fiber, and the laser signal output end of the narrow line width laser is connected to the input of the 1×2 coupler. The first output end of the 1×2 coupler is connected to one end of the delay fiber, the other end of the delay fiber is connected to the first signal input end of the 3×3 coupler, and the second signal input end of the 3×3 coupler is left floating , the second output end of the 1×2 coupler is connected to one end of the reference arm fiber, the other end of the reference arm fiber is connected to the third signal input end of the 3×3 coupler, and the sinusoidal excitation signal output end of the signal source generator is connected to the piezoelectric The control signal input end of the ceramic tube and the three output ends of the 3×3 coupler are respectively connected to the three optical signal outputs and inputs corresponding to the three-channel photodetector. The invention can improve the phase demodulation precision of the 3×3 coupler.

Description

Device and method for online correction of phase demodulation error of 3×3 coupler

technical field

The invention belongs to the technical field of optical fiber sensing, and in particular relates to a device and method for on-line correction of phase demodulation error of a 3×3 coupler.

technical background

Interferometric fiber optic sensors have been widely used in national key fields such as underwater acoustic measurement, structural health monitoring, and geological exploration due to their extremely high sensing sensitivity. Phase demodulation technology is one of the key technologies of interferometric fiber optic sensors. According to whether the phase demodulation system is active or not, it can be divided into two types: active and passive. The typical representatives of the two types of demodulation technology are phase generated carrier (PGC) Demodulation and 3x3 coupler phase demodulation.

The 3×3 coupler is an important passive device, and it is widely used in the interferometric optical fiber sensing signal demodulation system. Compared with the Mach-Zehnder interference of the double 2×2 coupler used in the early stage, the interferometer composed of the 3×3 coupler is widely used. The MZ interferometer has obvious advantages such as high sensitivity, tracking the direction of phase change, and phase unwrapping to achieve high dynamic range. Compared with PGC demodulation, the 3×3 coupler has a simpler system structure, higher dynamic range and faster demodulation method, and at the same time, the laser cost and hardware cost are greatly reduced.

However, in practical applications, both the classical MZ interferometer and the interferometric distributed fiber grating demodulation system will encounter the inevitable problem of polarization-induced signal fading. The polarization state of the laser transmitted and reflected in the optical fiber will be interfered by its own inherent structural defects and external temperature, stress, vibration and other factors, resulting in random changes. At the same time, the polarization of the input light will also cause polarization-induced signal fading (refer to Literature: Kersey A D, Marrone M J, Dandridge A, et al. Optimization and stabilization of visibility ininterferometric fiber-optic sensors using input-polarization control[J]. Journal of Lightwave Technology, 1988, 6(10): 1599-1609.) , so that the DC and AC coefficients in the three-way interference light intensity signal of the 3×3 coupler change accordingly. If the fixed-mode demodulation method is still used, the demodulation accuracy of the fiber phase sensing system will be seriously affected, and it is even more limited. The large-scale promotion and application of interferometric fiber optic sensors in various key fields are presented.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a device and method for online correction of the phase demodulation error of a 3×3 coupler in view of the above-mentioned technical problems. The idea is to introduce a piezoelectric ceramic tube into the reference arm of the MZ interferometer as a phase modulator, and use the phase modulator to perform high-frequency modulation on the phase sensing system, so as to observe the polarization state of the interferometer in real time at the output end of the 3×3 coupler. and interference effects. When the system performs phase demodulation, Lissajous ellipse fitting phase demodulation technology is further used for the three-way output interference light intensity signal to perform accurate real-time phase demodulation, and the fitting ellipse parameters are refreshed in real time to eliminate the polarization-induced fading of the 3×3 coupler. The random error caused by the demodulation parameter change caused by factors such as, greatly improves the phase demodulation accuracy of the 3×3 coupler.

In order to achieve this purpose, a device for on-line correction of phase demodulation error of a 3×3 coupler designed by the present invention includes a narrow linewidth laser, a 1×2 coupler, a time delay fiber, a piezoelectric ceramic tube, and a signal source. generator, 3×3 coupler, three-channel photodetector, and three-channel data acquisition card, among which, the piezoelectric ceramic tube is wound with a reference arm fiber, and the laser signal output end of the narrow linewidth laser is connected to the 1×2 coupler. Input end, the first output end of the 1×2 coupler is connected to one end of the delay fiber, the other end of the delay fiber is connected to the first signal input end of the 3×3 coupler, and the second signal input end of the 3×3 coupler Suspended, the second output end of the 1×2 coupler is connected to one end of the reference arm fiber, the other end of the reference arm fiber is connected to the third signal input end of the 3×3 coupler, and the sinusoidal excitation signal output end of the signal generator is connected to the voltage The control signal input end of the electric ceramic tube, the three output ends of the 3×3 coupler are respectively connected to the three optical signal input ends corresponding to the three-channel photodetector, and the three signal input ends of the three-channel data acquisition card are connected to the three-channel photoelectricity. Three electrical signal output terminals corresponding to the detector.

Compared with the prior art, the present invention has the following remarkable effects:

1. The present invention draws on the idea of phase generation carrier active demodulation, and uses 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 maintained at a high amplitude level, which is a 3×3 coupler Lissajous ellipse The fitting estimation phase demodulation provides a guarantee;

2. The present invention adopts modern digital phase demodulation technology. Compared with the traditional hardware demodulation technology, this method has the advantages of simpler structure, smaller calculation amount and larger dynamic range. Considering the asymmetry of the 3×3 coupler, the unstable output power of the light source, the inconsistent working efficiency of the photodetector, the coupling loss of the components in the optical path, the interference polarization-induced fading and other factors, the phase demodulation error of the 3×3 coupler is calculated. The invention adopts the Lissajous ellipse fitting method based on the least squares to realize the estimation of the output phase characteristic parameters of the 3×3 coupler, and the precision of the coupling output phase difference of the 3×3 coupler is controlled within 0.2°;

3. The present invention draws on the idea of the phase generation carrier active demodulation technology, adds a piezoelectric ceramic tube to the reference arm in the original interference system, and applies high-frequency excitation to perform high-frequency high-frequency excitation on the light wave phase in the reference arm fiber. Modulation, improve the phase dynamic range of the 3×3 coupler to a large level, and combine the Lissajous ellipse fitting parameters to estimate the phase demodulation method, refresh the fitting ellipse parameters in real time, eliminate the polarization-induced fading of the 3×3 coupler, etc. The random error caused by the demodulation parameter change caused by the factor improves the phase demodulation accuracy of the 3×3 coupler.

Description of drawings

Fig. 1 is the structural representation of the present invention;

Fig. 2 is the Lissajous figure formed by the first interference light and the second interference light of the 3×3 coupler;

Fig. 3 is a Lissajous figure formed by the second interference light and the third interference light of the 3×3 coupler.

Among them, I1 is the interference light intensity of the first channel, I2 is the interference light intensity of the second channel, and I3 is the interference light intensity of the third channel.

Among them, 1—narrow linewidth laser, 2—1×2 coupler, 3—delay fiber, 4—piezoelectric ceramic tube, 4.1—reference arm fiber, 5—signal generator, 6—3×3 coupler , 7-three-channel photodetector, 8-three-channel data acquisition card.

Detailed ways

Below in conjunction with accompanying drawing and embodiment, the present invention is described in further detail:

As shown in Figure 1, a device for online correction of phase demodulation error of a 3×3 coupler includes a narrow linewidth laser 1, a 1×2 coupler 2, a delay fiber 3, a piezoelectric ceramic tube 4, and a signal source Generator 5, 3×3 coupler 6, three-channel photodetector 7, three-channel data acquisition card 8, among which, the piezoelectric ceramic tube 4 is tightly and evenly wound with the reference arm fiber 4.1, and the laser signal of the narrow linewidth laser 1 The output end is connected to the input end of the 1×2 coupler 2, the first output end of the 1×2 coupler 2 is connected to one end of the delay fiber 3, and the other end of the delay fiber 3 is connected to the first signal of the 3×3 coupler 6 The input end, 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 to one end of the reference arm fiber 4.1, and the other end of the reference arm fiber 4.1 is connected to the 3×3 coupler 6 The third signal input end of the signal source generator 5 is connected to the control signal input end of the piezoelectric ceramic tube 4, and the three output ends of the 3×3 coupler 6 are respectively connected to the three-channel photodetector 7 corresponding to The three optical signal input ends of the three-channel data acquisition card 8 are connected to the three electrical signal output ends corresponding to the three-channel photodetector 7. The above-mentioned reference arm fiber 4.1 and delay fiber 3 are ordinary single Mode fiber (SMF-28e), the above structure is a double beam interferometer, and the second signal input end of the 3×3 coupler 6 belongs to the useless end. The invention is an improved design based on the double-beam MZ interferometer, so as to study the online correction experiment of the phase demodulation error of the 3×3 coupler.

In the above technical solution, the 1 × 2 coupler 2, the delay fiber 3, the reference arm fiber 4.1, and the 3 × 3 coupler 6 form a double-beam MZ interferometer structure, which is part of a fiber-optic interferometer sensing demodulation system. An important part of. Among them, the delay fiber 3 is used to make the interferometer signal arm where it is located and the interferometer reference arm fiber 4.1 where the piezoelectric ceramic tube 4 is located to be equal in length to form an equal-arm interferometer to reduce the wavelength fluctuation of the light source and the influence of external interference .

In the above technical solution, the narrow linewidth laser 1 (linewidth 100kHz) is used to emit a continuous narrow linewidth laser to the 1×2 coupler 2 as the light source of the double-beam interference system, and the 1×2 coupler 2 is used for The laser power of the continuous narrow linewidth laser is divided into two parts (to realize double-beam interference), and the laser power reaches 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 respectively. , and the double-beam interference effect occurs at the 3×3 coupler 6 to realize the basic double-beam interference function of the MZ interferometer.

In the above technical solution, the signal source generator 5 is used to perform sinusoidal excitation on the piezoelectric ceramic tube 4 (the frequency is set to 1 kHz) to generate an electrostrictive effect on the piezoelectric ceramic tube 4, so that the coils wound on the piezoelectric ceramic tube 4 can be generated. The length of the reference arm fiber 4.1 changes periodically, thereby realizing high-frequency modulation of the light wave phase in the reference arm fiber 4.1 with a carrier frequency of 1 kHz, so that the signal to be measured is located on the sideband of the carrier modulation signal, thereby coupling 3×3 The phase dynamic range of the controller is increased to a large level, which is beneficial to the subsequent phase correction.

In the above technical solution, the three-channel data acquisition card 8 is used to collect the three-channel interference light intensity signals of the 3×3 coupler 6 through the three-channel photodetector 7, and the three-channel output phase difference of the 3×3 coupler 6 is constant. feature to perform subsequent phase demodulation on it.

In the above technical solution, among the three interference light intensity signals, the first interference light intensity signal (X axis) and the second interference light intensity signal (Y axis), the second interference light intensity signal (X axis) and the third interference light intensity signal (X axis) The interference light intensity signal (Y-axis) forms two Lissajous graphs (through the X-axis and Y-axis, the corresponding ellipses are drawn), the graphs are elliptical, and the least squares ellipse fitting algorithm is used to calculate the two Lissajous graphs respectively. The ellipse parameters of the figure (to determine an ellipse generally requires 5 parameters in the ellipse equation, as shown in Figures 2 and 3 in the ellipse equation x ² +Axy+By ² +Cx+Dy+E=0, x, y represent 3× 3. For any two light intensity signals output by the coupler, the solution of the elliptic equation demodulation parameter AE is based on the ellipse fitting, and the ellipse synthesis follows the properties and laws of Lissajous, and there are relevant reports in the reference) (reference Literature: Wang Kai, Wu Shuai, He Shengnan, et al. Application of ellipse parameter estimation in optical fiber interference sensing system [J]. Science and Technology Innovation and Application, 2015(18): 6-7.), through the ellipse of two Lissajous diagrams The parameters determine the phase demodulation output characteristic parameters of the three-way interference light of the 3×3 coupler 6, which are used for accurate phase demodulation. The demodulated signal of the modulated signal (the carrier frequency is 1 kHz), and finally the high-frequency carrier modulated signal in the demodulated signal can be filtered out by low-pass filtering, and the phase of the interferometer arm length difference caused by external stress or vibration can be obtained. Change information (the external changes cause the phase fluctuation in the fiber of the signal arm, thus causing the intensity of the interference signal to change).

A method for correcting the phase demodulation error of a 3×3 coupler based on the above-mentioned device, characterized in that it comprises the following steps:

Step 1: The narrow linewidth laser 1 emits a continuous narrow linewidth laser to the 1×2 coupler 2, and the 1×2 coupler 2 divides the laser power of the continuous narrow linewidth laser into two, respectively after the delay. The optical fiber 3 and the reference arm optical fiber 4.1 wound on the piezoelectric ceramic tube 4 reach the 3×3 coupler 6, and the double-beam interference effect occurs at the 3×3 coupler 6;

Step 2: The signal generator 5 performs sinusoidal excitation on the piezoelectric ceramic tube 4, so that the electric ceramic tube 4 produces an electrostrictive effect, and the length of the reference arm optical fiber 4.1 wound on the piezoelectric ceramic tube 4 changes periodically , and then realize the high-frequency modulation of the light wave phase in the reference arm fiber 4.1 with a carrier frequency of 1 kHz, so that the signal to be measured is located on the sideband of the carrier modulation signal, thereby increasing the phase dynamic range of the 3×3 coupler to a large amplitude Level;

Step 3: The three-channel data acquisition card 8 collects the three-channel interference light intensity signals of the 3×3 coupler 6 through the three-channel photodetector 7;

Step 4: First, form two Lissajous diagrams for the first and second interfering light intensity signals, and the second and third interfering light intensity signals among the three interfering light intensity signals. , as shown in Figure 2, secondly, the ellipse parameters of the two Lissajous graphs are calculated respectively by the least squares ellipse fitting algorithm, and the phase of the three-way interference light of the 3×3 coupler 6 is determined by the ellipse parameters of the two Lissajous graphs Demodulate the output characteristic parameters, and then demodulate the demodulation signal carrying the modulation signal of the piezoelectric ceramic tube according to the phase demodulation output characteristic parameters of the three-way interference light, and finally, filter out the demodulation signal through low-pass filtering. The high-frequency modulation signal (the carrier frequency is 1kHz) in the modulation signal is used to obtain the phase change information of the interferometer arm length difference caused by external stress or vibration;

Step 5: In order to realize the real-time correction effect, step 4 is repeated every preset time (such as 1 minute) (repetition is used to monitor the change of polarization state caused by external stress, vibration and other factors), that is, the The four steps of "Lissajous diagram, parameter estimation, signal demodulation, and low-pass filtering" described above, demodulate the phase change information at the current moment, and realize the polarization effect of the MZ interferometer through the shape of the Lissajous diagram in step 4, that is, the visibility of the interference fringes. (The bigger the ellipse, the thinner the edge, the better the interference effect), and the real-time correction of the phase demodulation error of the 3×3 coupler is realized according to the ellipse parameters of the two Lissajous graphs 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, and applies high frequency excitation, high-frequency modulation of the phase of the light wave in the reference arm fiber, and the phase dynamic range of the 3×3 coupler 6 is increased to a large level. 3 couplers 6 real-time correction of phase demodulation errors.

The content not described in detail in this specification belongs to the prior art 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.

Images