Method and device for measuring second order backscattering error of hollow core photonic crystal fiber sensor

Abstract

The application discloses a kind of hollow core photonic crystal fiber sensor second-order backscattering error measurement method and device, it is related to optical fiber application technology, comprising: first hollow core photonic crystal fiber ring, second hollow core photonic crystal fiber ring are respectively fused to the two tail fibers of Y waveguide;By signal generator, modulation signal is applied to lock-in amplifier and Y waveguide, and the first output value change of lock-in amplifier is recorded;The first hollow core photonic crystal fiber ring and second hollow core photonic crystal fiber ring are intercepted, and the fusion point on the two tail fibers of Y waveguide is retained, by signal generator, the modulation signal is applied to lock-in amplifier and Y waveguide, and the second output value change of lock-in amplifier is recorded;According to the deviation between the measurement results of two lock-in amplifiers, second-order backscattering coherent error is calculated.This application uses the coherent detection method based on backscattering secondary wave, proposes a kind of universal coherent error measurement method and improves measurement precision.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of optical fiber application, and particularly relates to a method and device for measuring second-order backscattering coherence error of a hollow photonic crystal fiber sensor. BACKGROUND

[0002] As a kind of inertial angular velocity sensor, the fiber optic gyroscope (FOG) has been widely used in various fields due to its unique technical and performance advantages, such as full solid structure, high reliability, long service life, fast start-up speed, short response time, large measurement range, wide dynamic range, impact and vibration resistance, chemical corrosion resistance, small size, light weight, low cost and suitability for mass production.

[0003] The fiber is the most important transmission medium in the fiber optic gyroscope. The conventional panda polarization maintaining fiber is usually used in the existing fiber optic gyroscope, and the waveguide characteristics of the fiber are sensitive to external temperature, electromagnetic and other physical fields, thereby leading to poor environmental adaptability of the fiber optic gyroscope. At present, passive protection measures such as adding a protective cover are mainly taken to solve this problem. Although these measures can improve the environmental adaptability of the fiber optic gyroscope to a certain extent, they also bring some side effects, such as increase in volume, weight, power consumption and cost. The hollow photonic crystal fiber is formed by a two-dimensional photonic crystal structure of SiO2 and air holes, and the photonic bandgap effect is generated to limit the propagation of light in the central air hole defect (core), so it is also called hollow photonic crystal fiber. The unique structure and light guiding mechanism of the hollow photonic crystal fiber make it have many characteristics different from traditional optical fibers, such as low sensitivity to environmental factors such as temperature, electromagnetic field and space radiation, and insensitivity to bending. Therefore, the hollow photonic crystal fiber is an ideal choice to solve the environmental adaptability problem of the fiber optic gyroscope, and it is the future development trend of the fiber optic gyroscope. The hollow photonic crystal fiber ring of the fiber optic gyroscope is wound by the hollow photonic crystal fiber, and the hollow photonic crystal fiber ring and the Y waveguide tail fiber are fused by the fiber fusion.

[0004] However, the introduction of the hollow photonic crystal fiber will increase the intensity of the backscattering secondary wave of the fiber optic gyroscope. On the one hand, the rough inner wall of the hollow photonic crystal fiber core will cause a large number of distributed backscattering secondary waves in the fiber ring, and the intensity is much larger than that of the traditional fiber. On the other hand, the different refractive indices of the photonic bandgap fiber and the traditional fiber core will cause strong backreflection secondary waves at the coupling point. The backscattering secondary waves in the hollow photonic crystal fiber gyroscope will interfere with each other, and the interference error will seriously restrict the improvement of the precision of the photonic bandgap fiber gyroscope. At present, there is a corresponding measurement method for the backscattering reflection coherence error caused by the interference between the backscattering secondary waves and the backreflection secondary waves. However, the second-order backscattering coherence error caused by the interference between the backscattering secondary waves is difficult to distinguish from the gyroscope signal and the backscattering reflection coherence error, and there is a lack of corresponding measurement method. SUMMARY

[0005] The embodiment of the present application provides a kind of hollow core photonic crystal fiber sensor second-order backscattering error measurement method and device, to adopt the coherent detection method based on backscattering secondary wave, propose a kind of universal coherent error measurement method and improve measurement precision.

[0006] The embodiment of the present application provides a kind of hollow core photonic crystal fiber sensor second-order backscattering error measurement method, comprising:

[0007] The first hollow core photonic crystal fiber ring 5, the second hollow core photonic crystal fiber ring 6 are respectively fused to the two pigtail of Y waveguide 1, Y waveguide 1 is connected to lock-in amplifier 10 by coupler 8, probe 9, signal generator 11 is connected to the lock-in amplifier 10 and the Y waveguide 1, still access ASE light source 7 on the coupler 8;

[0008] modulation signal is applied to lock-in amplifier 10 and Y waveguide 1 by signal generator 11, and the first output value change of lock-in amplifier 10 is recorded;

[0009] the first hollow core photonic crystal fiber ring 5 and the second hollow core photonic crystal fiber ring 6 are intercepted, and the fusion point on the two pigtail of Y waveguide 1 is retained, the modulation signal is applied to lock-in amplifier 10 and Y waveguide 1 by signal generator 11, and the second output value change of lock-in amplifier is recorded;

[0010] According to the deviation between the measurement results of lock-in amplifier 10 twice, the second-order backscattering coherent error coefficient is determined, to calculate the second-order backscattering coherent error.

[0011] The embodiment of the present application provides a kind of hollow core photonic crystal fiber sensor second-order backscattering error measurement device, comprising:

[0012] Y waveguide 1, the first hollow core photonic crystal fiber ring 5 and the second hollow core photonic crystal fiber ring 6 are respectively fused to the two pigtail of Y waveguide 1, the Y waveguide 1 is connected to lock-in amplifier 10 by coupler 8, probe 9, ASE light source 7 is accessed on the coupler 8;

[0013] signal generator 11 is connected to the lock-in amplifier 10 and the Y waveguide 1, modulation signal is applied to lock-in amplifier 10 and Y waveguide 1 by signal generator 11, and the first output value change of lock-in amplifier is recorded;And,

[0014] the first hollow core photonic crystal fiber ring 5 and the second hollow core photonic crystal fiber ring 6 are intercepted, and the fusion point on the two pigtail of Y waveguide 1 is retained, the modulation signal is applied to lock-in amplifier 10 and Y waveguide 1 by signal generator 11, and the second output value change of lock-in amplifier is recorded;

[0015] A second-order backscattering coherence error coefficient is determined according to a deviation between two measurement results of the phase-locked amplifier 10, so as to calculate the second-order backscattering coherence error.

[0016] The embodiment of the present application designs a coherent detection method based on backscattering secondary waves, proposes a universal coherent error measurement method and improves the measurement precision.

[0017] The above description is only a summary of the technical solutions of the present application, in order to enable the technical means of the present application to be implemented according to the content of the description, and in order to enable the above and other purposes, characteristics and advantages of the present application to be more apparent and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0018] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments, and are not meant to limit the present application. Moreover, the same reference numerals in the attached drawings refer to the same or similar components. In the drawings:

[0019] Figure 1 The schematic diagram of the coherent error of the hollow core photonic crystal fiber gyroscope according to the embodiment of the present application is shown in

[0020] Figure 2 The basic flowchart of the second-order backscattering error measurement method of the hollow core photonic crystal fiber sensor according to the embodiment of the present application is shown in

[0021] Figure 3 The schematic diagram of the second-order backscattering error measurement principle of the hollow core photonic crystal fiber gyroscope according to the embodiment of the present application is shown in

[0022] Figure 4 The schematic diagram of the backscattering reflection error of the hollow core photonic crystal fiber gyroscope according to the embodiment of the present application is shown in DETAILED DESCRIPTION

[0023] Exemplary embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the present disclosure are shown. It is to be understood that the present disclosure can be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0024] The schematic diagram of the coherent error of the hollow core photonic crystal fiber gyroscope is shown in Figure 1As shown, the clockwise main wave generates a first back-reflection secondary wave WA at the first fusion point of the first tail fiber 2 of the Y waveguide 1 and the first hollow-core photonic crystal fiber ring 5, and the counterclockwise main wave generates a second back-reflection secondary wave WB at the first fusion point. Because the lengths of the first tail fiber 2 of the Y waveguide and the second tail fiber 3 of the Y waveguide are inconsistent, WA and WB are de-coherent, and thus WA and WB interfere with a third back-scattering secondary wave WA1 and a fourth back-scattering secondary wave WB1 at the third back-scattering secondary wave WA1 and the fourth back-scattering secondary wave WB1 at the symmetric position and the light path, to generate a back-scattering reflection coherent error. At the same time, the distributed back-scattering secondary waves generated by the clockwise and counterclockwise main waves at the symmetric position on the preset hollow-core photonic crystal fiber ring 4 also interfere to generate a second-order back-scattering coherent error.

[0025] The embodiment of the present application provides a kind of hollow-core photonic crystal fiber sensor second-order back-scattering error measurement method, such as Figure 2 As shown, comprising:

[0026] In step S101, the first hollow-core photonic crystal fiber ring 5, the second hollow-core photonic crystal fiber ring 6 are fused to the two tail fibers of the Y waveguide 1 respectively, the Y waveguide 1 is connected to the lock-in amplifier 10 by the coupler 8, the detector 9 is connected to the lock-in amplifier 10, and the signal generator 11 is connected to the lock-in amplifier 10 and the Y waveguide 1, and the coupler 8 is also connected to the ASE light source 7.

[0027] In a specific example, as shown in Figure 3 The light emitted by the ASE light source 7 passes through the coupler 8 to reach the Y waveguide 1. The Y waveguide 1 divides the light into two paths, one of which passes through the first tail fiber 2 of the Y waveguide to reach the first hollow-core photonic crystal fiber ring 5, and the other of which passes through the second tail fiber 3 of the Y waveguide to reach the second hollow-core photonic crystal fiber ring 6. The first hollow-core photonic crystal fiber ring 5 and the second hollow-core photonic crystal fiber ring 6 have consistent lengths but are not connected, thereby effectively avoiding the influence of main wave interference on the second-order back-scattering secondary wave coherent error measurement. The back-reflection secondary waves generated at the connection between the tail fibers of the Y waveguide and the hollow-core photonic crystal fiber, and the back-scattering secondary waves generated inside the two hollow-core photonic crystal fiber rings, pass through the Y waveguide 1 and the coupler 8 in turn to reach the detector 9.

[0028] In step S102, a modulation signal is applied to the lock-in amplifier 10 and the Y waveguide 1 by the signal generator 11, and the first output value change of the lock-in amplifier 10 is recorded. That is, the signal generator 11 transmits a modulation signal to the Y waveguide 1 and the lock-in amplifier 10 simultaneously, and the lock-in amplifier 10 records the back-secondary wave coherent error intensity. At this time, the error contains not only the second-order back-scattering reflection coherent error, but also the scattering reflection coherent error caused by the interference between the back-reflection secondary wave and the back-scattering secondary wave.

[0029] To separate the two types of errors, the two hollow core photonic crystal fiber rings need to be removed, but the first fusion point and the second fusion point are retained. In step S103, the first hollow core photonic crystal fiber ring 5 and the second hollow core photonic crystal fiber ring 6 are cut off, and the fusion points on the two tail fibers of the Y waveguide 1 are retained. The modulation signal is applied to the lock-in amplifier 10 and the Y waveguide 1 by the signal generator 11, and the change of the second output value of the lock-in amplifier 10 is recorded. At this time, only the backscattering reflection coherent error is contained in the results recorded by the lock-in amplifier 10.

[0030] In step S104, the second-order backscattering reflection coherent error coefficient is determined according to the deviation between the measurement results of the lock-in amplifier 10 twice.

[0031] The embodiment of the present application designs a coherent detection method based on backscattering secondary waves, proposes a universal coherent error measurement method and improves the measurement accuracy.

[0032] In some embodiments, the lengths of the first hollow core photonic crystal fiber ring 5 and the second hollow core photonic crystal fiber ring 6 are set to correspond to the length L of the hollow core photonic crystal fiber gyroscope ring to be measured, for example, the lengths of the first hollow core photonic crystal fiber ring 5 and the second hollow core photonic crystal fiber ring 6 are consistent with the length L of the hollow core photonic crystal fiber gyroscope ring to be measured. The distance between the two fusion points on the two tail fibers of the Y waveguide 1 is greater than the decorrelation length.

[0033] In some embodiments, the modulation signal is applied to the lock-in amplifier 10 and the Y waveguide 1 by the signal generator 11, and the change of the first output value of the lock-in amplifier 10 is recorded, including:

[0034] Let the clockwise main wave generate a first backscattering secondary wave WA at the first fusion point of the first tail fiber 2 of the Y waveguide 1 and the hollow core photonic crystal fiber ring 5, and the counterclockwise main wave generate a second backscattering secondary wave WB at the first fusion point;

[0035] According to the first backscattering secondary wave WA, the second backscattering secondary wave WB, and the third backscattering secondary wave WA1 and the fourth backscattering secondary wave WB1 at the symmetrical position, the interference light intensity produces a backscattering reflection coherent error to the gyroscope, and the generated backscattering reflection interference light intensity is calculated I bs.rf.interf is:

[0036]

[0037] Wherein, I 0 represents the light intensity after the main wave enters the first tail fiber and the second tail fiber, α other represents the loss from the Y waveguide tail fiber to the detector, αsplicing represents the loss of the fusion point of the hollow-core photonic crystal fiber and the traditional optical fiber, η fiber.PMF and η fiber.HCPCF are the backscattering coefficients of the traditional optical fiber and the hollow-core photonic crystal fiber, respectively, η fused represents the intensity of the back-reflected secondary wave generated by the first fusion point and the second fusion point, ϕ t represents the modulation signal applied to the Y waveguide, containing square waves and step waves, Δ Ψ 1 t ) and Δ Ψ 2 t ) is a random phase caused by the environment.

[0038] In some embodiments, the signal generator 11 applies a modulation signal to the lock-in amplifier 10 and the Y waveguide 1, and records the change of the first output value of the lock-in amplifier 10 further includes:

[0039] According to the interference of the distributed backscattering secondary waves generated by the clockwise and counterclockwise primary waves at the symmetric positions on the preset hollow-core photonic crystal fiber ring 4, wherein the two ends of the preset hollow-core photonic crystal fiber ring 4 are respectively fused to the two pigtails of the Y waveguide 1, the interference light intensity produces a second-order backscattering coherent error to the gyroscope. The second-order backscattering interference light intensity I bs.interf.all represents:

[0040]

[0041] wherein N represents the number of backscattering points, and m represents the serial number of the backscattering point, α 2Lm represents the time from the fusion point A or the fusion point B to the position where the backscattering secondary wave is generated L m and the double-pass loss of the return, t 2Lm represents the time from the Y waveguide to the position where the backscattering secondary wave is generated L m twice the time, Δ Ψ m t represents the random phase of the mth point caused by the environment.

[0042] In some embodiments, the signal generator 11 applies a modulation signal to the lock-in amplifier 10 and the Y waveguide 1, and records the change of the first output value of the lock-in amplifier 10 further includes:

[0043] ​​​​Let the total error interference light intensity coefficient be the sum of the first type of error intensity and the second type of error intensity, that is:

[0044]

[0045] Modulation signal ϕ (t) contains two parts of square wave modulation and step wave modulation, the square wave frequency f and the length of the fiber ring L The relationship is as follows:

[0046]

[0047] Where c is the speed of light, n is the core refractive index of the fiber ring, L is the length of the fiber ring. Taking an air-core photonic crystal fiber gyroscope with a ring length of 260 m as an example, since the air core refractive index is about 1, according to the backscattering reflection interference light intensity I bs.rf.interf The square wave frequency is calculated to be 577 kHz, and the square wave amplitude remains relatively stable in a single measurement. The step wave amplitude gradually changes from 0 to π in a single measurement period. Considering the response speed of the lock-in amplifier 10 and improving the precision, the step height of the step wave ϕ s should be much smaller than π, such as ϕ s =π / 10^7, and the duration of each step is the transit time τ =n L / c. For an air-core photonic crystal fiber gyroscope with a ring length of 260 m, the transit time τ ≈0.87us. When the step wave changes from 0 to π, the single test time is π τ / ϕ s ≈8.7 s. Since t 2Lm ≤1.74us, which is much smaller than 8.7 s, 2[ ϕ (t)+ ϕ (t-t 2Lm )]≈4 ϕ (t), so I error.all there will be a change of 2 cycles in a single measurement. Then the relationship between the total error interference light intensity coefficient and the maximum value I error.all-max and the minimum value I error.all-min measured by the lock-in amplifier is:

[0048] .

[0049] In some embodiments, the cutting off the first hollow core photonic crystal fiber ring 5 and the second hollow core photonic crystal fiber ring 6 and retaining the fusion points on the two pigtails of the Y waveguide 1 comprises:

[0050] The length remaining after cutting off the second hollow core photonic crystal fiber ring 6 ensures that the third backscattering secondary wave WA1 generated in the remaining fiber interferes with the first backscattering secondary wave WA. As shown in the figure, Figure 4 After cutting off, the first remaining hollow core photonic crystal fiber 12 and the second remaining hollow core photonic crystal fiber 13 are included in the cutting off, and at this time, the device only contains the backscattering reflection interference light intensity I bs.rf.interf The intensity can be calculated in the above manner. I bs.rf.interf In a single measurement, 2 cycles of change will also occur. The phase-locked amplifier records the maximum value of the change in the second output value I bs.rf.interf-max And the minimum value I bs.rf.interf-min The relationship between the backscattering reflection interference light intensity coefficient and the maximum value and the minimum value is:

[0051] .

[0052] In some embodiments, the second-order backscattering coherence error coefficient is determined according to the deviation between the measurement results of the phase-locked amplifier 10 twice.

[0053] The measurement results of the phase-locked amplifier 10 twice are subtracted to obtain the second-order backscattering interference light intensity coefficient:

[0054]

[0055] Then, according to the above formula and the working principle of the gyroscope, the maximum value of the second-order backscattering coherence error of the gyroscope is:

[0056]

[0057] Wherein, α L Indicates the loss of the hollow core photonic crystal fiber ring, λ indicates the wavelength of the light source, L indicates the length of the fiber ring, and D indicates the diameter of the fiber ring.

[0058] The method of the application has the advantages of simple structure, high measurement accuracy, and can be applied to all types of interferometric fiber gyroscopes.

[0059] The embodiment of the application also provides a second-order backscattering coherence error measurement device for a hollow core photonic crystal fiber sensor, comprising:

[0060] Y waveguide 1, two pigtail on which are respectively fused with first hollow core photonic crystal fiber ring 5, second hollow core photonic crystal fiber ring 6, the Y waveguide 1 is connected to the lock-in amplifier 10 through the coupler 8, the probe 9, the coupler 8 is accessed with ASE light source 7;

[0061] Signal generator 11, connected to the lock-in amplifier 10 and the Y waveguide 1, through signal generator 11 to lock-in amplifier 10 and Y waveguide 1 apply modulation signal, and record the first output value change of lock-in amplifier;And,

[0062] Cut off the first hollow core photonic crystal fiber ring 5 and the second hollow core photonic crystal fiber ring 6, and keep the fusion point on the two pigtail of Y waveguide 1, through signal generator 11 to lock-in amplifier 10 and Y waveguide 1 apply the modulation signal, record the second output value change of lock-in amplifier;

[0063] According to the deviation between the measurement results of the lock-in amplifier 10 twice, determine the second order backscattering coherent error coefficient.

[0064] It should be noted that in the embodiments of the present application, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0065] The above-mentioned serial numbers of the embodiments of the present application are only for description, not representing the advantages and disadvantages of the embodiments.

[0066] Through the above description of the embodiments, those skilled in the art can clearly understand that the above-mentioned embodiment method can be realized by means of software and necessary general hardware platform, of course, it can also be realized by hardware, but in many cases, the former is a better embodiment. Based on such understanding, the technical solutions of the present application can be embodied in the form of software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), including a plurality of instructions for making a terminal (which can be a mobile phone, computer, server, air conditioner or network equipment, etc.) execute the method described in each embodiment of the present application.

[0067] The embodiments of the present application are described above with reference to the accompanying drawings, but the present application is not limited to the specific embodiments described above, and the specific embodiments described above are merely illustrative, but not restrictive, and a person of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, and these all belong to the protection of the present application.

Claims

1. A method of measuring second order backscatter error in a hollow core photonic crystal fiber sensor, the method comprising: include: The first hollow-core photonic crystal fiber ring (5) and the second hollow-core photonic crystal fiber ring (6) are respectively fused to the two pigtails of the Y waveguide (1). The Y waveguide (1) is connected to the lock-in amplifier (10) through the coupler (8) and the detector (9). The signal generator (11) is connected to the lock-in amplifier (10) and the Y waveguide (1). An ASE light source (7) is also connected to the coupler (8). A modulation signal is applied to the lock-in amplifier (10) and the Y-waveguide (1) by a signal generator (11), and the change in the first output value of the lock-in amplifier (10) is recorded. Cut off the first hollow-core photonic crystal fiber ring (5) and the second hollow-core photonic crystal fiber ring (6), and retain the melting points on the two pigtails of the Y waveguide (1). Apply the modulation signal to the lock-in amplifier (10) and the Y waveguide (1) through the signal generator (11), and record the change of the second output value of the lock-in amplifier (10). Based on the deviation between the two measurement results of the lock-in amplifier (10), the second-order backscattering coherence error coefficient is determined, so as to calculate the second-order backscattering coherence error. The lengths of the first hollow-core photonic crystal fiber ring (5) and the second hollow-core photonic crystal fiber ring (6) are set to correspond to the length L of the hollow-core photonic crystal fiber gyroscope ring to be measured; and The distance between the two fusion points on the two pigtails of the Y waveguide (1) is greater than the decoherence length.

2. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor as described in claim 1, characterized in that, A modulation signal is applied to the lock-in amplifier (10) and the Y-waveguide (1) by a signal generator (11), and the change in the first output value of the lock-in amplifier (10) is recorded, including: The clockwise main wave generates a first back-reflection secondary wave WA at the first melting point of the first pigtail (2) and the second hollow photonic crystal fiber ring (6) of the Y waveguide (1), and the counterclockwise main wave generates a second back-reflection secondary wave WB at the first melting point. The intensity of the backscattered and reflected interference light is calculated based on the interference of the first back-reflected secondary wave WA, the second back-reflected secondary wave WB, and the third back-scattered secondary wave WA1 and the fourth back-scattered secondary wave WB1 located at their symmetrical positions and with equal optical path lengths. wherein, I 0 represents the light intensity after the main wave enters the first and second tail fibers, α other represents the loss from the Y waveguide tail fiber to the detector, α splicing represents the loss of the hollow core photonic crystal fiber and the traditional fiber fusion point, η fiber.PMF and η fiber.HCPCF are the backscattering coefficients of the traditional fiber and the hollow core photonic crystal fiber, respectively, η fused represents the back reflection secondary wave intensity generated by the first and second fusion points, ϕ (t) represents the modulation signal applied on the Y waveguide, Δ Ψ 1 ( t ) and Δ Ψ 2 ( t ) are random phases caused by the environment.

3. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor as described in claim 2, characterized in that, The process of applying a modulation signal to the lock-in amplifier (10) and the Y-waveguide (1) via the signal generator (11) and recording the change in the first output value of the lock-in amplifier (10) also includes: Interference occurs based on the distributed backscattering secondary waves generated at symmetrical positions on the preset hollow photonic crystal fiber ring (4) by the clockwise and counterclockwise main waves, wherein the two ends of the preset hollow photonic crystal fiber ring (4) are respectively fused to the two pigtails of the Y waveguide (1). The calculated intensity of the second-order backscattered interference light is: Where N represents the number of backscattering points, and m represents the ordinal number of the backscattering points. α 2Lm This indicates the location from melting point A or melting point B to where the backscattered secondary wave is generated. L m And the round-trip loss when returning along the same route, t 2Lm This indicates the location from the main waveguide to the backscattered secondary wave generation point. L m Twice the time, Δ Ψ m ( t ) represents the random phase of the m-th point caused by the environment.

4. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor as described in claim 3, characterized in that, The process of applying a modulation signal to the lock-in amplifier (10) and the Y-waveguide (1) via the signal generator (11) and recording the change in the first output value of the lock-in amplifier (10) also includes: Let the total error interference light intensity be the sum of the backscattered reflection interference light intensity and the second-order backscattered interference light intensity; The total error interference intensity coefficient is related to the maximum value measured by the lock-in amplifier. I error.all-max and minimum value I error.all-min The relationship between them is: 。 5. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor as described in claim 4, characterized in that, Cut off the first hollow-core photonic crystal fiber ring (5) and the second hollow-core photonic crystal fiber ring (6), and retain the melting points on the two pigtails of the Y waveguide (1) including: The remaining length after cutting the second hollow photonic crystal fiber ring (6) ensures that the third backscattered secondary wave WA1 generated in the remaining fiber interferes with the first backscattered secondary wave WA. The lock-in amplifier (10) records the maximum value of the change in the second output value. I bs.rf.interf-max and minimum value I bs.rf.interf-min The relationship between the backscattering and reflection interference intensity coefficient and its maximum and minimum values ​​is as follows: 。 6. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor as described in claim 5, characterized in that, Based on the deviation between the two measurement results of the lock-in amplifier (10), the second-order backscattering coherence error coefficients are determined as follows: The difference between the two measurements of the lock-in amplifier (10) is used to obtain the second-order backscattering interference light intensity coefficient; The magnitude of the second-order backscattering coherence error of the gyroscope is calculated as follows: in, α L λ represents the ring loss of the hollow-core photonic crystal fiber, λ represents the wavelength of the light source, L represents the length of the fiber ring, and D represents the diameter of the fiber ring.

7. A device for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor, characterized in that, include: Y-waveguide (1) has a first hollow-core photonic crystal fiber ring (5) and a second hollow-core photonic crystal fiber ring (6) respectively fused to its two pigtails. The Y-waveguide (1) is connected to a lock-in amplifier (10) through a coupler (8) and a detector (9). An ASE light source (7) is connected to the coupler (8). A signal generator (11), connected to the lock-in amplifier (10) and the Y-waveguide (1), applies a modulation signal to the lock-in amplifier (10) and the Y-waveguide (1) via the signal generator (11), and records the first output value change of the lock-in amplifier (10); and, Cut off the first hollow-core photonic crystal fiber ring (5) and the second hollow-core photonic crystal fiber ring (6), and retain the melting points on the two pigtails of the Y waveguide (1). Apply the modulation signal to the lock-in amplifier (10) and the Y waveguide (1) through the signal generator (11), and record the change of the second output value of the lock-in amplifier (10). Based on the deviation between the two measurement results of the lock-in amplifier (10), the second-order backscattering coherence error coefficient is determined, so as to calculate the second-order backscattering coherence error. The lengths of the first hollow-core photonic crystal fiber ring (5) and the second hollow-core photonic crystal fiber ring (6) are set to correspond to the length L of the hollow-core photonic crystal fiber gyroscope ring to be measured; and The distance between the two fusion points on the two pigtails of the Y waveguide (1) is greater than the decoherence length.

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