Optical fiber air pressure sensor based on vernier effect sensitization and detection method

Abstract

The invention discloses an optical fiber gas pressure sensor based on vernier effect sensitization and a detection method, and belongs to the technical field of gas pressure measurement. The first sensing interferometer comprises a first single-mode fiber, a polarization-maintaining photonic crystal fiber, a second single-mode fiber and a gold film which are coaxially arranged in sequence, the two ends of the polarization-maintaining photonic crystal fiber are connected with one end of the first single-mode fiber and one end of the second single-mode fiber in a welding mode, and the gold film is located at the other end of the second single-mode fiber; the second sensing interferometer comprises a third single-mode optical fiber and a quartz tube which are coaxially arranged in sequence, the third single-mode optical fiber is connected with one end of the quartz tube in a welding mode, the quartz tube is provided with a UV film, the welding surface of the third single-mode optical fiber and the quartz tube is a first reflecting surface, and the critical surface of air in the quartz tube and the UV film is a second reflecting surface. According to the invention, the accurate air pressure detection requirement with high sensitivity can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of gas pressure measurement, and in particular to an optical fiber gas pressure sensor and a detection method based on vernier effect sensitivity enhancement. Background Art

[0002] Accurate detection of tiny gas pressure changes is crucial to aerospace, biomedicine, environmental monitoring and other fields. Compared with electronic barometers, fiber optic pressure sensors have attracted much attention from researchers due to their advantages such as anti-electromagnetic interference, corrosion resistance and ability to achieve remote and accurate measurement in extreme environments, and have developed rapidly in recent years.

[0003] Various fiber optic sensors, such as Fabry-Perot interferometer, Mach-Zehnder interferometer, Sagnac interferometer and fiber Bragg grating, have been developed for air pressure detection. However, the detection sensitivity of common fiber optic air pressure sensors can only reach a few nanometers per megapascal, which is difficult to meet the needs of some high-sensitivity air pressure detection fields.

[0004] Therefore, it is necessary to design an air pressure sensor that can achieve high sensitivity, high precision, and detection of tiny air pressure changes. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the present invention provides an optical fiber air pressure sensor and a detection method based on vernier effect sensitivity enhancement, which can meet the requirements of accurate air pressure detection with high sensitivity.

[0006] On one hand, the present invention provides an optical fiber air pressure sensor based on vernier effect sensitivity enhancement, comprising a broadband light source, an optical fiber coupler, a sensor interferometer and a spectrum analyzer, wherein the sensor interferometer comprises a first sensor interferometer and a second sensor interferometer;

[0007] The first sensing interferometer comprises a first single-mode optical fiber, a polarization-maintaining photonic crystal fiber, a second single-mode optical fiber and a gold film which are coaxially arranged in sequence, wherein two ends of the polarization-maintaining photonic crystal fiber are connected to one end of the first single-mode optical fiber and one end of the second single-mode optical fiber by fusion splicing, and the gold film is located at the other end of the second single-mode optical fiber;

[0008] The second sensing interferometer includes a third single-mode optical fiber and a quartz tube coaxially arranged in sequence, the third single-mode optical fiber is connected to one end of the quartz tube by fusion splicing, the quartz tube is provided with a UV film, the fusion surface between the third single-mode optical fiber and the quartz tube is a first reflection surface, and the critical surface between the air in the quartz tube and the UV film is a second reflection surface.

[0009] Furthermore, the polarization-maintaining photonic crystal fiber includes a core with an elliptical cross-section and a cladding covering the outside of the core, the cladding includes array holes and stress holes arranged parallel to the core, the core is located at the center of the array holes, and the stress holes are located at both ends of the short axis of the elliptical cross-section of the core.

[0010] Furthermore, the major axis of the elliptical cross section of the fiber core ranges from 6.4 to 7 μm, the minor axis of the elliptical cross section ranges from 2.5 to 3 μm, the diameter of the stress pores ranges from 4.7 to 5.6 microns, and the diameter of the array pores ranges from 1.8 to 2.1 μm.

[0011] Furthermore, the thickness of the gold film ranges from 50 to 70 nm.

[0012] Furthermore, the length of the second single-mode optical fiber ranges from 0.5 to 1 mm, and the length of the polarization-maintaining photonic crystal optical fiber ranges from 25 to 30 cm.

[0013] Furthermore, the inner diameter of the quartz tube ranges from 50 to 70 μm, and the length of the quartz tube ranges from 200 to 260 μm.

[0014] The second aspect of the present invention provides a method for detecting optical fiber air pressure based on vernier effect sensitivity enhancement, which is implemented based on the optical fiber air pressure sensor based on vernier effect sensitivity enhancement, and includes the following steps:

[0015] The detection light emitted by the broadband light source enters the first single-mode optical fiber through the optical fiber coupler, passes through the polarization-maintaining photonic crystal fiber and the second single-mode optical fiber in sequence, and is reflected at the gold film at the end. The reflected light passes through the second single-mode optical fiber and the polarization-maintaining photonic crystal fiber in sequence and enters the first single-mode optical fiber, and forms the first reflected light in the first single-mode optical fiber. When the air pressure changes, the birefringence coefficient of the polarization-maintaining photonic crystal fiber is changed by force, thereby changing the birefringence coefficient of the first sensor interferometer, and the spectrum of the first sensor interferometer moves accordingly.

[0016] The detection light emitted by the broadband light source enters the quartz tube through the third single-mode optical fiber and is reflected at the first reflection surface and the second reflection surface respectively. The two reflected lights formed by the two reflection surfaces are superimposed in the third single-mode optical fiber to form the second reflected light. When the air pressure changes, the UV film is deformed by force, which changes the cavity length of the second sensor interferometer, and the spectrum of the second sensor interferometer moves accordingly.

[0017] The spectral envelope formed by the superposition of the first reflected light and the second reflected light moves, and the ambient air pressure is measured by detecting the spectral Paul response.

[0018] Furthermore, the spectral envelope shift Δλ Envelope for:

[0019] Δλ Envelope =M·(Δλ SI -Δλ FPI );

[0020] Where M is the amplification factor of the envelope, Δλ SI is the spectral shift of the first sensor interferometer, Δλ FPI is the spectral shift of the second sensor interferometer.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] When the air pressure changes, the birefringence coefficient of the polarization-maintaining photonic crystal fiber in the first sensing interferometer is changed by force, thereby changing the birefringence coefficient of the first sensing interferometer, and the spectrum of the first sensing interferometer moves accordingly; the UV film at the end of the quartz tube of the second sensing interferometer is deformed by force, thereby changing the cavity length of the second sensing interferometer, and the spectrum of the second sensing interferometer moves accordingly. At this time, the spectral envelope of the optical fiber air pressure sensor moves with the air pressure response of the two sensing interferometers. The first optical fiber interferometer and the second optical fiber interferometer are sensing references to each other. When the air pressure changes, the first sensing interferometer and the second sensing interferometer have opposite air pressure responses to realize the enhanced vernier effect, and the traditional vernier effect is secondary sensitized, which increases the accuracy of the air pressure sensor by two to three orders of magnitude. The optical fiber air pressure sensor provided by the present invention has high sensitivity, high accuracy, low temperature crosstalk, and stable structure, and can be used for high-precision air pressure detection.

[0023] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of a hybrid interferometer-enhanced vernier-sensitized optical fiber pressure sensor according to a specific embodiment of the present invention;

[0025] Figure 2 It is a structural schematic diagram of a first sensor interferometer according to a specific embodiment of the present invention;

[0026] Figure 3 A schematic structural diagram of a polarization-maintaining photonic crystal fiber according to a specific embodiment of the present invention;

[0027] Figure 4 It is a structural schematic diagram of a second sensor interferometer according to a specific embodiment of the present invention;

[0028] Figure 5 It is a structural schematic diagram of a quartz tube in a specific embodiment of the present invention;

[0029] Figure 6is a spectrum envelope diagram of a sensor in a specific embodiment of the present invention;

[0030] Figure 7 This is a diagram showing how the spectrum changes with the ambient air pressure in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0032] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner, and thus the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0033] While some exemplary embodiments of the present invention have been described for the purpose of illustration, it should be understood that the present invention may be implemented in other ways not specifically shown in the drawings.

[0034] like Figure 1 As shown, on one hand, the present invention provides a fiber optic pressure sensor based on vernier effect sensitivity enhancement, including a broadband light source, a fiber optic coupler, a sensor interferometer and a spectrum analyzer, wherein the sensor interferometer includes a first sensor interferometer and a second sensor interferometer.

[0035] The optical fiber coupler is provided with a first port, a second port, a third port and a fourth port, the broadband light source is connected to the first port, the spectrum analyzer is connected to the second port, the first sensor interferometer is connected to the third port of the optical fiber coupler through the polarization controller, and the second sensor interferometer is connected to the fourth port.

[0036] like Figure 2As shown, the first sensing interferometer includes a first single-mode optical fiber 1, a polarization-maintaining photonic crystal fiber 2, a second single-mode optical fiber 3 and a gold film 4 connected in sequence, forming a reflective sensing Sagner interferometer with a double optical path. The central axes of the first single-mode optical fiber 1, the polarization-maintaining photonic crystal fiber 2, the second single-mode optical fiber 3 and the gold film 4 are collinear, one end of the first single-mode optical fiber 1 is connected to one end of the polarization-maintaining photonic crystal fiber 2 by fusion splicing, and the other end of the polarization-maintaining photonic crystal fiber 2 is connected to the second single-mode optical fiber 3 by fusion splicing, and the gold film 4 is arranged at the other end of the second single-mode optical fiber 3. In a specific embodiment, the outer diameter of the first sensing interferometer is 125 microns, the diameter range of the first single-mode optical fiber 1 is 8 to 9 microns, and the diameter range of the second single-mode optical fiber 3 is 8 to 9 microns. The first single-mode optical fiber 1 is mainly used to transmit optical signals, and its length is set according to the measurement distance. When remote measurement is required, it can be extended. The length range of the second single-mode optical fiber 3 is 0.5 to 1 mm.

[0037] The characteristics of the cross section of the polarization-maintaining photonic crystal fiber 2 have different effects on the performance of the fiber, such as Figure 3 As shown, the polarization-maintaining photonic crystal fiber 2 includes a core 9 with an elliptical cross-section and a cladding 8 coated on the outside of the core 9. The central axis of the core 9 is collinear with the central axis of the cladding 8. The cladding 8 includes an array pore 11 and two stress pores 10. The cross-sections of the array pores 11 and the stress pores 10 are both circular. The two stress pores 10 are respectively located at the two ends of the short axis of the elliptical core 9. The array pores 11 surround the outside of the core 9 and the stress pores 10. Several array pores 11 are in a hexagonal array structure, and eight array pores 11 are provided on each side of the hexagon. In this embodiment, the birefringence coefficient of the polarization-maintaining photonic crystal fiber 2 is (8.5-9.5)×10 -4 The outer diameter of the polarization-maintaining photonic crystal fiber 2 is 125 microns, and its length ranges from 25 to 30 centimeters. The elliptical major axis length range of the elliptical core 9 of the polarization-maintaining photonic crystal fiber 2 is 6.4 to 7 microns, and its minor axis length ranges from 2.5 to 3 microns. The diameter range of the stress pores 10 of the polarization-maintaining photonic crystal fiber 2 is 4.7 to 5.6 microns, and the diameter range of the array pores 11 of the polarization-maintaining photonic crystal fiber 2 is 1.8 to 2.1 microns. The thickness of the gold film 4 is 50 to 70 nanometers.

[0038] like Figure 4As shown, the second sensing interferometer includes a third single-mode optical fiber 5, a hollow quartz tube 6 and a UV film 7 which are coaxially arranged in sequence. The fusion surface between the third single-mode optical fiber 5 and the quartz tube 6 is a first reflection surface M1, and the critical surface between the air in the quartz tube 6 and the UV film 7 is a second reflection surface M2. At this time, the first reflection surface M1 and the second reflection surface M2 constitute a sensing Fabry-Perot interferometer. The third single-mode optical fiber 5 is connected to one end of the quartz tube 6 by fusion. The quartz tube 6 is provided with a UV film 7. The fusion surface between the third single-mode optical fiber 5 and the quartz tube 6 is a first reflection surface M1, and the critical surface between the air in the quartz tube 6 and the UV film 7 is a second reflection surface M2.

[0039] The cross-sectional schematic diagram of the hollow quartz tube is as follows Figure 5 As shown, it includes a cladding 12 and a central air hole 13, the outer diameter of the second sensor interferometer is 125 microns, the interior of the hollow quartz tube 6 is air, the inner diameter of the central air hole of the quartz tube 6 is in the range of 50 to 70 microns, the length of the quartz tube 6 is in the range of 200 to 260 microns, the thickness of the UV film is in the range of 10 to 20 microns, and the UV film 7 is purchased from Norland, model NOA 68; the third single-mode optical fiber 5 is used for transmitting optical signals, and the length of the third single-mode optical fiber 5 can be set as needed. When remote measurement is required, the length of the third single-mode optical fiber 5 can be extended, and the inner diameter of the third single-mode optical fiber 5 is in the range of 8 to 9 microns.

[0040] Based on the optical fiber pressure sensor based on vernier effect sensitivity enhancement described in the above embodiment, a method for detecting optical fiber pressure based on vernier effect sensitivity enhancement is provided in a specific embodiment, wherein the broadband light source emits a wide spectrum light as the detection light, and the reflected light of the first sensor interferometer and the second sensor interferometer generates periodic interference fringes, and then generates a periodic spectral envelope, and the spectral envelope response of the sensor is detected to achieve the measurement of the ambient air pressure. Specifically, the method comprises the following steps:

[0041] S1, the detection light emitted by the broadband light source enters the first single-mode optical fiber 1 through the optical fiber coupler, the first single-mode optical fiber 1 transmits the optical signal to the polarization-maintaining photonic crystal fiber 2, the spectrum passing through the polarization-maintaining photonic crystal fiber 2 is transmitted through the second single-mode optical fiber 3 to the gold film 4 at the end and is reflected, and the reflected light then passes through the second single-mode optical fiber 3, the polarization-maintaining photonic crystal fiber 2 and the first single-mode optical fiber 1 in sequence to obtain the first reflected light I SI When the air pressure changes, the birefringence coefficient of the polarization-maintaining photonic crystal fiber is changed by force, thereby changing the birefringence coefficient of the first sensor interferometer, and the spectrum of the first sensor interferometer moves accordingly;

[0042] S2, the detection light emitted by the broadband light source enters the quartz tube 6 through the third single-mode optical fiber 5, and the light source spectrum is reflected at the first reflection surface M1 and the second reflection surface M2 to obtain two beams of reflected light. The two beams of reflected light formed by the two reflection surfaces are superimposed in the third single-mode optical fiber 5 to form the second reflected light I FPI When the air pressure changes, the UV film is deformed by force, which changes the cavity length of the second sensor interferometer, and the spectrum of the second sensor interferometer moves accordingly;

[0043] The first reflected light I SI and the second reflected light I FPI They are:

[0044]

[0045] Where a = R1 1 / 2 ; b = (1-α2)(1-R1)R2 1 / 2 , R1 and R2 are the reflection coefficients of the first reflection surface M1 and the second reflection surface M2 respectively, α1 and α2 are the transmission losses of the detection light in the two sensing interferometers respectively; L1 and L2 are the length of the polarization-maintaining photonic crystal fiber 2 and the cavity length of the sensing Fabry-Perot interferometer respectively; B1 is the birefringence coefficient of the polarization-maintaining photonic crystal fiber 2; n1 is the refractive index of the cavity medium of the sensing Fabry-Perot interferometer; λ is the incident wavelength of the detection light;.

[0046] S3, the spectral envelope formed by the superposition of the first reflected light and the second reflected light moves, and the ambient air pressure is measured by detecting the spectral Paul response.

[0047] When the free spectral ranges of the two sensor interferometers are close but not equal, due to the double filtering of the two sensor interferometers, the sensor reflection spectrum produces periodic vernier interference fringes, thereby producing a periodic envelope. In this embodiment, the sensor reflection spectrum envelope is as follows: Figure 6 As shown, the free spectral range of the sensor reflection spectrum envelope is shown in formula (2):

[0048]

[0049] Among them, FSR SI is the free spectral range of the first sensor interferometer reflection spectrum, FSR FPI are the free spectral ranges of the reflection spectrum of the second sensor interferometer, respectively:

[0050]

[0051] M is the enveloping magnification factor, and its value range is 5 to 30. By transforming formula (2), we can get formula (4):

[0052]

[0053] When the ambient air pressure changes, both fiber optic interferometers are used for air pressure detection and serve as sensing references for each other; the birefringence coefficient of the polarization-maintaining photonic crystal fiber 2 of the first sensing interferometer changes under force, thereby changing the birefringence coefficient of the first sensing interferometer, and the spectrum of the first sensing interferometer moves; at the same time, the UV film 7 at the end of the quartz tube 6 of the second sensing interferometer is deformed under force, thereby changing the cavity length of the second sensing interferometer, and the spectrum of the second sensing interferometer also moves accordingly; the spectral envelope of the fiber optic air pressure sensor moves with the air pressure response of the two sensing interferometers; the two sensing interferometers show opposite air pressure responses, thereby realizing the secondary sensitization of the traditional vernier effect and improving the sensor sensitivity by two to three orders of magnitude. The wavelength shift of the reflection spectrum of the two sensing interferometers is shown in formula (5):

[0054]

[0055] Among them, Δλ SI and Δλ FPI are the wavelength shifts of the reflection spectrum of the first sensor interferometer and the second sensor interferometer respectively, ΔB1 ​​is the change in the birefringence coefficient of the polarization-maintaining photonic crystal fiber 2, and ΔL2 is the change in the cavity length of the second sensor interferometer.

[0056] When the ambient air pressure changes, the sensor reflectance spectrum envelope shifts by Δλ Envelope As shown in formula (6):

[0057]

[0058] It can be seen from formula (6) that when the reflection spectra of the two sensor interferometers move with the change of ambient air pressure, the sensor reflection spectrum envelope moves accordingly, and the translation amount is M times the difference of the reflection spectrum translation amounts of the two sensor interferometers. Figure 7 This is a diagram showing the change of spectrum with the change of ambient air pressure in a specific implementation. When the external air pressure changes, the birefringence coefficient of the polarization-maintaining photonic crystal fiber 2 is changed by force, and the reflection spectrum of the first sensor interferometer is red-shifted; the UV film 7 is deformed due to the change of the external air pressure, which changes the cavity length of the Fabry-Perot interferometer, causing the reflection spectrum of the second sensor interferometer to blue-shift; at this time, the spectrum of the sensor is red-shifted. It can be seen that when the ambient air pressure changes, both optical fiber interferometers are used for air pressure detection and serve as sensing references for each other; the two sensor interferometers show opposite air pressure responses, and the sensor's spectral envelope moves with the air pressure response of the two sensor interferometers, and the translation of the sensor's spectral envelope is M times the difference in the translation of the reflection spectrum of the two sensor interferometers.

[0059] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An optical fiber pressure sensor based on vernier effect sensitization, comprising a broadband light source, an optical fiber coupler, a sensor interferometer and a spectrum analyzer, characterized in that: The sensor interferometer comprises a first sensor interferometer and a second sensor interferometer; The first sensing interferometer comprises a first single-mode optical fiber, a polarization-maintaining photonic crystal fiber, a second single-mode optical fiber and a gold film which are coaxially arranged in sequence, wherein two ends of the polarization-maintaining photonic crystal fiber are connected to one end of the first single-mode optical fiber and one end of the second single-mode optical fiber by fusion splicing, and the gold film is located at the other end of the second single-mode optical fiber; The second sensing interferometer includes a third single-mode optical fiber and a quartz tube coaxially arranged in sequence, the third single-mode optical fiber is connected to one end of the quartz tube by fusion splicing, the quartz tube is provided with a UV film, the fusion surface between the third single-mode optical fiber and the quartz tube is a first reflection surface, and the critical surface between the air in the quartz tube and the UV film is a second reflection surface.

2. According to claim 1, a fiber optic air pressure sensor based on vernier effect sensitivity enhancement is characterized in that: The polarization-maintaining photonic crystal fiber includes a core with an elliptical cross-section and a cladding covering the outside of the core. The cladding includes array pores and stress pores arranged parallel to the core. The core is located at the center of the array pores, and the stress pores are located at both ends of the short axis of the elliptical cross-section of the core.

3. A fiber optic pressure sensor based on vernier effect sensitivity enhancement according to claim 2, characterized in that: The long axis of the elliptical cross section of the fiber core is in the range of 6.4 to 7 μm, the short axis of the elliptical cross section is in the range of 2.5 to 3 μm, the diameter of the stress pores is in the range of 4.7 to 5.6 microns, and the diameter of the array pores is in the range of 1.8 to 2.1 μm.

4. The optical fiber air pressure sensor based on vernier effect sensitivity enhancement according to claim 1, characterized in that: The thickness of the gold film ranges from 50 to 70 nm.

5. The optical fiber air pressure sensor based on vernier effect sensitivity enhancement according to claim 1, characterized in that: The length of the second single-mode optical fiber ranges from 0.5 to 1 mm, and the length of the polarization-maintaining photonic crystal optical fiber ranges from 25 to 30 cm.

6. The optical fiber air pressure sensor based on vernier effect sensitivity enhancement according to claim 1, characterized in that: The inner diameter of the quartz tube ranges from 50 to 70 μm, and the length of the quartz tube ranges from 200 to 260 μm.

7. A method for detecting air pressure with optical fiber based on vernier effect sensitization, characterized in that: The optical fiber air pressure sensor based on vernier effect sensitivity enhancement according to any one of claims 1 to 6 is implemented, comprising the following steps: The detection light enters the first sensor interferometer through the optical fiber coupler, and the detection light is reflected at the gold film to form the first reflected light. When the air pressure changes, the birefringence coefficient of the polarization-maintaining photonic crystal fiber is changed by force, thereby changing the birefringence coefficient of the first sensor interferometer, and the spectrum of the first sensor interferometer moves accordingly. The detection light enters the second sensor interferometer, and is reflected at the first reflection surface and the second reflection surface respectively. The two reflected lights formed by the two reflection surfaces are superimposed to form the second reflected light. When the air pressure changes, the UV film is deformed by force, which changes the cavity length of the second sensor interferometer, and the spectrum of the second sensor interferometer moves accordingly. The spectral envelope formed by the superposition of the first reflected light and the second reflected light moves, and the ambient air pressure is measured by detecting the spectral Paul response.

8. The optical fiber air pressure detection method based on vernier effect sensitivity enhancement according to claim 7, characterized in that: The spectral envelope shift Δλ Envelope for: Dl Envelope =M·(Dl SI -Dl FPI ); Where M is the amplification factor of the envelope, Δλ SI is the spectral shift of the first sensor interferometer, Δλ FPI is the spectral shift of the second sensor interferometer.

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