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

Abstract

The invention discloses a method and device for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor, and relates to the fiber application technology, and the method comprises the steps: respectively welding a first hollow-core photonic crystal fiber ring and a second hollow-core photonic crystal fiber ring to two tail fibers of a Y waveguide; applying a modulation signal to the lock-in amplifier and the Y waveguide through a signal generator, and recording the change of a first output value of the lock-in amplifier; intercepting the first hollow-core photonic crystal fiber ring and the second hollow-core photonic crystal fiber ring, reserving melting points on two tail fibers of the Y waveguide, applying the modulation signal to the lock-in amplifier and the Y waveguide through a signal generator, and recording the change of a second output value of the lock-in amplifier; and calculating a second-order backscattering coherence error according to the deviation between the two measurement results of the phase-locked amplifier. According to the invention, a coherent detection method based on backscattering secondary waves is adopted, a common adaptive coherent error measurement method is provided, and the measurement precision is improved.

Description

Technical Field

[0001] The present application relates to the field of optical fiber application technology, and in particular to a method and device for measuring the second-order backscattering coherence error of a hollow-core photonic crystal optical fiber sensor. Background Art

[0002] As a rapidly developing inertial angular velocity sensor, fiber optic gyroscope has been widely used in various fields due to its unique technical and performance advantages, such as all-solid-state structure, high reliability, long life; fast startup speed, short response time; large measurement range, wide dynamic range; resistance to shock, vibration, and chemical corrosion; small size, light weight, low cost; and suitability for mass production.

[0003] Optical fiber is the primary transmission medium in fiber-optic gyros (FOGs). Existing FOGs typically use conventional polarization-maintaining (PM) fiber. Its wave-guiding properties are sensitive to external physical fields, such as temperature and electromagnetic fields, resulting in poor environmental adaptability. Currently, this issue is primarily addressed through passive protection measures, such as the addition of protective covers. While these measures can improve the FOG's environmental adaptability to a certain extent, they also come with side effects, such as increased size, weight, power consumption, and cost. Hollow-core photonic crystal fiber (HCPCF) utilizes a periodic arrangement of SiO2 and air holes to form a two-dimensional photonic crystal structure, generating a photonic bandgap effect that restricts light propagation within the central air hole defect (fiber core). This is why it is also known as hollow-core photonic crystal fiber (HCPCF). The unique structure and light-guiding mechanism of HCPCF give it numerous properties distinct from traditional optical fibers, such as low sensitivity to environmental factors such as temperature, electromagnetic fields, and space radiation, and insensitivity to bending. Therefore, HCPCF is an ideal choice for addressing the environmental adaptability issues of FOGs and represents a future development trend for FOGs. The hollow core photonic crystal fiber gyroscope fiber ring is wound by hollow core photonic crystal fiber, and the hollow core photonic crystal fiber ring and the Y waveguide pigtail are fused by fiber fusion splicing.

[0004] However, the introduction of hollow-core photonic crystal fiber (HCF) increases the intensity of the backscattered secondary waves in fiber optic gyros. On the one hand, the rough inner wall of the HCF core causes the fiber ring to generate a large number of distributed backscattered secondary waves, whose intensity is far greater than that of traditional optical fibers. On the other hand, the difference in refractive index between the PBG fiber and the traditional optical fiber core leads to strong backscattered secondary waves at the coupling point. Interference occurs between the backscattered secondary waves in the HCPF gyroscope, and the resulting interference error seriously restricts the improvement of the PBF gyroscope's accuracy. Currently, there are corresponding measurement methods for the backscattered reflection coherence error caused by the interference between the backscattered secondary waves and the backscattered reflection secondary waves. However, the second-order backscattered coherence error caused by the interference between the backscattered secondary waves is difficult to distinguish from the gyro signal and the backscattered reflection coherence error, and there is a lack of corresponding measurement methods. Summary of the Invention

[0005] The embodiments of the present application provide a method and device for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor, which adopts a coherent detection method based on backscattering secondary waves, proposes a universally applicable coherent error measurement method and improves measurement accuracy.

[0006] The present invention provides a method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor, comprising: The first hollow-core photonic crystal fiber ring 5 and the second hollow-core photonic crystal fiber ring 6 are fused to the two pigtails of the Y-waveguide 1 respectively. 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. The coupler 8 is also connected to the ASE light source 7. Applying a modulation signal to the lock-in amplifier 10 and the Y-waveguide 1 through the signal generator 11, and recording the change of the first output value of the lock-in amplifier 10; 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; According to the deviation between the two measurement results of the lock-in amplifier 10, the second-order backscatter coherence error coefficient is determined to calculate the second-order backscatter coherence error.

[0007] The present invention provides a device for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor, comprising: A Y-waveguide 1, with a first hollow-core photonic crystal fiber ring 5 and a second hollow-core photonic crystal fiber ring 6 fused to its two pigtails, respectively. The Y-waveguide 1 is connected to a lock-in amplifier 10 via a coupler 8 and a detector 9. The coupler 8 is connected to an ASE light source 7; a signal generator 11 connected to the lock-in amplifier 10 and the Y-waveguide 1, applying a modulation signal to the lock-in amplifier 10 and the Y-waveguide 1 through the signal generator 11, and recording a change in a first output value of the lock-in amplifier; 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; According to the deviation between the two measurement results of the lock-in amplifier 10, the second-order backscatter coherence error coefficient is determined to calculate the second-order backscatter coherence error.

[0008] The embodiment of the present application designs a coherent detection method based on backscattered secondary waves, proposes a universally applicable coherent error measurement method and improves measurement accuracy.

[0009] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference symbols are used throughout the drawings to represent the same components. In the drawings: Figure 1 This is a schematic diagram of the coherence error of the hollow-core photonic crystal fiber gyroscope according to an embodiment of the present application; Figure 2 This is a schematic diagram of the basic process of the second-order backscattering error measurement method of the hollow-core photonic crystal fiber sensor according to an embodiment of the present application; Figure 3 This is a schematic diagram of the second-order backscattering error measurement principle of the hollow-core photonic crystal fiber gyroscope in an embodiment of the present application; Figure 4 This is a schematic diagram of the backscatter reflection error of the hollow-core photonic crystal fiber gyroscope according to an embodiment of the present application. DETAILED DESCRIPTION

[0011] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although 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 should not be limited by the embodiments set forth herein. Rather, 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.

[0012] Schematic diagram of coherent error of hollow core photonic crystal fiber gyroscope Figure 1As shown, the clockwise primary wave generates a first backreflected secondary wave WA at the first melting point of the Y-waveguide 1 first pigtail 2 and the hollow-core photonic crystal fiber ring 5. Similarly, the counterclockwise primary wave generates a second backreflected secondary wave WB at the first melting point. Due to the length mismatch between the Y-waveguide first pigtail 2 and the Y-waveguide second pigtail 3, WA and WB become decoherent. Consequently, WA and WB interfere with the third and fourth backscattered secondary waves WA1 and WB1 at symmetrical locations with equal optical path lengths, resulting in backscattered reflection coherence errors. Simultaneously, the distributed backscattered secondary waves generated by the clockwise and counterclockwise primary waves at symmetrical locations on the pre-set hollow-core photonic crystal fiber ring 4 also interfere, generating second-order backscattering coherence errors.

[0013] The present invention provides a method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor. Figure 2 As shown, including: In step S101, the first hollow-core photonic crystal fiber ring 5 and the second hollow-core photonic crystal fiber ring 6 are fused to the two pigtails of the Y-waveguide 1 respectively. The Y-waveguide 1 is connected to the phase-locked amplifier 10 through the coupler 8 and the detector 9. The signal generator 11 is connected to the phase-locked amplifier 10 and the Y-waveguide 1. The coupler 8 is also connected to the ASE light source 7.

[0014] In a specific example, Figure 3 As shown, light emitted by the ASE light source 7 passes through the coupler 8 and reaches the Y-waveguide 1. The Y-waveguide 1 splits the light into two paths: one path passes through the Y-waveguide's first pigtail 2 and reaches the first hollow-core photonic crystal fiber ring 5, and the other path passes through the Y-waveguide's second pigtail 3 and reaches 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 are of the same length but are not connected, effectively avoiding the influence of primary wave interference on the measurement of the second-order backscattered secondary wave coherence error. The backreflected secondary wave generated at the connection between the Y-waveguide 1's pigtail and the hollow-core photonic crystal fiber, as well as the backscattered secondary wave generated within the two hollow-core photonic crystal fiber rings, pass through the Y-waveguide 1 and coupler 8 in sequence and reach the detector 9.

[0015] In step S102, a modulation signal is applied to the lock-in amplifier 10 and the Y-waveguide 1 via the signal generator 11, and the change in the first output value of the lock-in amplifier 10 is recorded. Specifically, the signal generator 11 simultaneously transmits the modulation signal to the Y-waveguide 1 and the lock-in amplifier 10, which then records the backscattered secondary wave coherence error intensity. This error includes not only the second-order backscattered reflection coherence error but also the scattered reflection coherence error caused by interference between the backscattered secondary wave and the backscattered secondary wave.

[0016] To separate the two types of errors, the two hollow-core photonic crystal fiber rings are removed, but the first and second melting points are retained. In step S103, the first and second hollow-core photonic crystal fiber rings 5 ​​and 6 are removed, while the melting points on the two pigtails of Y-waveguide 1 are retained. Signal generator 11 applies the modulation signal to lock-in amplifier 10 and Y-waveguide 1, and the change in the second output value of lock-in amplifier 10 is recorded. At this point, the result recorded by lock-in amplifier 10 contains only the backscattered reflection coherence error.

[0017] In step S104 , the second-order backscatter coherence error coefficient is determined based on the deviation between the two measurement results of the lock-in amplifier 10 .

[0018] The embodiment of the present application designs a coherent detection method based on backscattered secondary waves, proposes a universally applicable coherent error measurement method and improves measurement accuracy.

[0019] 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 ring length L of the hollow-core photonic crystal fiber gyroscope 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 ring length L of the hollow-core photonic crystal fiber gyroscope to be measured. The distance between the two fusion points on the two pigtails of the Y-waveguide 1 is greater than the decoherence length.

[0020] In some embodiments, applying a modulation signal to the lock-in amplifier 10 and the Y-waveguide 1 through the signal generator 11 and recording a change in a first output value of the lock-in amplifier 10 includes: The clockwise main wave generates a first back-reflected secondary wave WA at the first pigtail 2 of the Y-waveguide 1 and the first melting point of the hollow-core photonic crystal fiber ring 5, and the counterclockwise main wave generates a second back-reflected secondary wave WB at the first melting point; According to 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 at the symmetrical position with the same optical path, the interference light intensity produces a back-scattered reflection coherence error on the gyroscope, and the generated back-scattered reflection interference light intensity is calculated. I bs.rf.interf for: in, I 0 Indicates the light intensity after the main wave enters the first pigtail and the second pigtail. α other represents the loss from the Y-waveguide pigtail to the detector, α splicing Indicates the loss of hollow core photonic crystal fiber and traditional optical fiber melting point, orfiber.PMF and or fiber.HCPCF are the backscattering coefficients of traditional optical fiber and hollow-core photonic crystal fiber, or fused Indicates the intensity of the back-reflected secondary wave generated by the first melting point and the second melting point, ϕ ( t ) represents the modulation signal applied to the Y waveguide, including square wave and step wave, Δ P 1 ( t ) and Δ P 2 ( t ) is the random phase caused by the environment.

[0021] In some embodiments, applying a modulation signal to the lock-in amplifier 10 and the Y-waveguide 1 through the signal generator 11 and recording a change in the first output value of the lock-in amplifier 10 further includes: According to the distributed backscattered secondary waves generated by the clockwise and counterclockwise main waves at symmetrical positions on the preset hollow core photonic crystal fiber ring 4, interference occurs, where 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, and the interference light intensity produces a second-order backscattered coherent error on the gyroscope. Second-order backscattered interference light intensity I bs.interf.all Expressed as: Where N represents the number of backscatter points, m represents the ordinal number of the backscatter points, α 2Lm Indicates the distance from melting point A or melting point B to the location where the backscattered secondary wave is generated L m And the round-trip loss of returning along the original route, t 2Lm Indicates the location where the primary wave is generated from the Y waveguide to the backscattered secondary wave L m Twice the time, Δ P m ( t ) represents the random phase of the mth point caused by the environment.

[0022] In some embodiments, applying a modulation signal to the lock-in amplifier 10 and the Y-waveguide 1 through the signal generator 11 and recording a change in the first output value of the lock-in amplifier 10 further includes: Let the total error interference intensity coefficient be the sum of the first-type error intensity and the second-type error intensity, that is: Modulation signal ϕ (t) includes two parts: square wave modulation and step wave modulation. The square wave frequency fFiber ring length L The relationship is as follows: Where c is the speed of light, n is the refractive index of the fiber ring core, L is the fiber ring length. Taking a 260m long hollow core photonic crystal fiber gyroscope as an example, since the refractive index of the air core is about 1, the backscattered reflected interference light intensity is I bs.rf.interf The formula calculates that the square wave frequency is 577kHz, 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 cycle. Considering the response speed of the phase-locked amplifier 10 and improving the accuracy, the step wave step height is ϕ s should be much smaller than π, such as ϕ s =π / 10^7, the duration of each step is the transit time t =n L / c, for a hollow-core photonic crystal fiber gyroscope with a ring length of 260m, the transit time t ≈0.87us. At this time, when the step wave changes from 0 to π, the single test time is π t / ϕ s ≈8.7 s. t 2Lm ≤1.74us, much less than 8.7 s, 2[ ϕ (t)+ ϕ (tt 2Lm )]≈4 ϕ (t), so I error.all In a single measurement, there will be a change of 2 cycles. The total error interference intensity coefficient is the maximum value obtained by the lock-in amplifier measurement. I error.all-max and minimum value I error.all-min The relationship between them is: .

[0023] In some embodiments, cutting off the first hollow-core photonic crystal fiber ring 5 and the second hollow-core photonic crystal fiber ring 6 and retaining the melting points on the two pigtails of the Y-waveguide 1 include: The remaining length after cutting off the second hollow core photonic crystal fiber ring 6 ensures that the third backscattered secondary wave WA1 generated in the remaining fiber interferes with the first backreflected secondary wave WA. Figure 4 The first remaining hollow core photonic crystal fiber 12 and the second remaining hollow core photonic crystal fiber 13 are included in the device after the cutting. At this time, the device only contains the backscattered reflected interference light intensity. Ibs.rf.interf , the strength can be calculated using the above method. I bs.rf.interf In a single measurement, two cycles of change will also occur. The lock-in amplifier records the maximum value of the second output value change. I bs.rf.interf-max and minimum value I bs.rf.interf-min , then the relationship between the backscattered reflection interference intensity coefficient and the maximum and minimum values ​​is: .

[0024] In some embodiments, determining the second-order backscatter coherence error coefficient based on the deviation between two measurement results of the lock-in amplifier 10 includes: The difference between the two measurement results of the lock-in amplifier 10 is used to obtain the second-order backscattered interference light intensity coefficient: According to the above formula and the working principle of the gyroscope, the maximum value of the gyroscope second-order backscatter coherent error is: in, α L represents the ring loss of hollow-core photonic crystal fiber, λ represents the wavelength of the light source, L represents the fiber ring length, and D represents the fiber ring diameter.

[0025] The method of the present invention has a simple structure, which is conducive to engineering applications. It uses a coherent detection method based on backscattered secondary waves, which has high measurement accuracy. The method proposed in the present invention can be applied to all types of interferometric fiber optic gyroscopes and has universal applicability.

[0026] The present application also provides a device for measuring the second-order backscattering coherence error of a hollow-core photonic crystal fiber sensor, comprising: A Y-waveguide 1, with a first hollow-core photonic crystal fiber ring 5 and a second hollow-core photonic crystal fiber ring 6 fused to its two pigtails, respectively. The Y-waveguide 1 is connected to a lock-in amplifier 10 via a coupler 8 and a detector 9. The coupler 8 is connected to an ASE light source 7; a signal generator 11 connected to the lock-in amplifier 10 and the Y-waveguide 1, applying a modulation signal to the lock-in amplifier 10 and the Y-waveguide 1 through the signal generator 11, and recording a change in a first output value of the lock-in amplifier; 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; The second-order backscatter coherence error coefficient is determined based on the deviation between the two measurement results of the lock-in amplifier 10.

[0027] It should be noted that, in the various embodiments of the present application, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0028] The serial numbers of the above-mentioned embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0029] Through the description of the above embodiments, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus the necessary general hardware platform. Of course, they can also be implemented by hardware, but in many cases the former is a more preferred embodiment. Based on this understanding, the technical solution of this application, or the part that contributes to the existing technology, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes a number of instructions for enabling a terminal (which can be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in each embodiment of this application.

[0030] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of this application, ordinary technicians in this field can also make many forms without departing from the purpose of this application and the scope of protection of the claims, all of which are protected by this application.

Claims

1. A method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor, characterized in that: include: The first hollow-core photonic crystal fiber ring (5) and the second hollow-core photonic crystal fiber ring (6) are fused to two pigtails of a Y-waveguide (1), respectively; the Y-waveguide (1) is connected to a lock-in amplifier (10) through a coupler (8) and a detector (9); a signal generator (11) is connected to the lock-in amplifier (10) and the Y-waveguide (1); and an ASE light source (7) is also connected to the coupler (8); Applying a modulation signal to the lock-in amplifier (10) and the Y-waveguide (1) through a signal generator (11), and recording a change in a first output value of the lock-in amplifier (10); Cutting off the first hollow-core photonic crystal fiber ring (5) and the second hollow-core photonic crystal fiber ring (6), retaining the melting points on the two pigtails of the Y-waveguide (1), applying the modulation signal to the lock-in amplifier (10) and the Y-waveguide (1) via a signal generator (11), and recording the change in the second output value of the lock-in amplifier (10); According to the deviation between the measurement results of two phase-locked amplifiers (10), a second-order backscattering coherence error coefficient is determined to calculate the second-order backscattering coherence error.

2. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor according to claim 1, wherein: 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 two fusion points on two pigtails of the Y waveguide (1) is greater than the decoherence length.

3. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor according to claim 2, wherein: Applying a modulation signal to the lock-in amplifier (10) and the Y-waveguide (1) through a signal generator (11), and recording a change in a first output value of the lock-in amplifier (10) comprises: The clockwise main wave generates a first back-reflected secondary wave WA at the first pigtail (2) of the Y waveguide (1) and the first melting point of the hollow-core photonic crystal fiber ring (6), and the counterclockwise main wave generates a second back-reflected secondary wave WB at the first melting point; According to the interference between 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 at the same optical path as the first back-reflected secondary wave WA, the back-scattered reflected interference light intensity generated is calculated as follows: in, I 0 Indicates the light intensity after the main wave enters the first pigtail and the second pigtail. α other represents the loss from the Y-waveguide pigtail to the detector, α splicing Indicates the loss of hollow core photonic crystal fiber and traditional optical fiber melting point, η fiber.PMF and η fiber.HCPCF are the backscattering coefficients of traditional optical fiber and hollow-core photonic crystal fiber, η fused Indicates the intensity of the back-reflected secondary wave generated by the first melting point and the second melting point, ϕ (t) represents the modulation signal applied to the Y waveguide, Δ Ψ 1 ( t ) and Δ Ψ 2 ( t ) is the random phase caused by the environment.

4. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor according to claim 3, wherein: Applying a modulation signal to the lock-in amplifier (10) and the Y-waveguide (1) through a signal generator (11), and recording a change in a first output value of the lock-in amplifier (10) further comprises: Interference occurs according to distributed backscattered secondary waves generated by clockwise and counterclockwise main waves at symmetrical positions on a preset hollow-core photonic crystal fiber ring (4), wherein two ends of the preset hollow-core photonic crystal fiber ring (4) are respectively fused to two pigtails of the Y waveguide (1); Calculate the intensity of the second-order backscattered interference light: Where N represents the number of backscatter points, m represents the ordinal number of the backscatter points, α 2Lm Indicates the distance from melting point A or melting point B to the location where the backscattered secondary wave is generated L m And the round-trip loss of returning along the original route, t 2Lm Indicates the location where the primary wave is generated from the Y waveguide to the backscattered secondary wave L m Twice the time, Δ Ψ m ( t ) represents the random phase of the mth point caused by the environment.

5. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor according to claim 4, wherein: Applying a modulation signal to the lock-in amplifier (10) and the Y-waveguide (1) through a signal generator (11), and recording a change in a first output value of the lock-in amplifier (10) further comprises: 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 the maximum value obtained by the lock-in amplifier measurement I error.all-max and minimum value I error.all-min The relationship between them is: 。 6. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor according to claim 5, wherein: Cutting off the first hollow-core photonic crystal fiber ring (5) and the second hollow-core photonic crystal fiber ring (6), and retaining the melting points on the two pigtails of the Y-waveguide (1) include: The remaining length after cutting the second hollow-core photonic crystal fiber ring (6) ensures that the third backscattered secondary wave WA1 generated in the remaining optical fiber interferes with the first backreflected secondary wave WA; The lock-in amplifier (10) records the maximum value of the second output value change I bs.rf.interf-max and minimum value I bs.rf.interf-min , then the relationship between the backscattered reflection interference intensity coefficient and the maximum and minimum values ​​is: 。 7. The method for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor according to claim 6, wherein: Determining the second-order backscatter coherence error coefficient based on the deviation between the two measurement results of the phase-locked amplifier (10) includes: Subtracting the two measurement results of the phase-locked amplifier (10) to obtain the second-order backscattered interference light intensity coefficient; The gyro second-order backscatter coherent error is calculated as: in, α L represents the ring loss of hollow-core photonic crystal fiber, λ represents the wavelength of the light source, L represents the fiber ring length, and D represents the fiber ring diameter.

8. A device for measuring the second-order backscattering error of a hollow-core photonic crystal fiber sensor, characterized in that: include: A Y-waveguide (1), two pigtails of which are fused with a first hollow-core photonic crystal fiber ring (5) and a second hollow-core photonic crystal fiber ring (6), respectively; the Y-waveguide (1) is connected to a lock-in amplifier (10) via a coupler (8) and a detector (9); and 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), applying a modulation signal to the lock-in amplifier (10) and the Y-waveguide (1) through the signal generator (11), and recording a change in a first output value of the lock-in amplifier (10); and Cutting off the first hollow-core photonic crystal fiber ring (5) and the second hollow-core photonic crystal fiber ring (6), retaining the melting points on the two pigtails of the Y-waveguide (1), applying the modulation signal to the lock-in amplifier (10) and the Y-waveguide (1) via a signal generator (11), and recording the change in the second output value of the lock-in amplifier (10); According to the deviation between the measurement results of two phase-locked amplifiers (10), a second-order backscattering coherence error coefficient is determined to calculate the second-order backscattering coherence error.

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