Dual-parameter measurement fiber sensor based on harmonic vernier effect and manufacturing method thereof

Abstract

The application provides a two-parameter measurement optical fiber sensor based on harmonic vernier effect and a manufacturing method, and belongs to the field of optical communication.The sensor comprises, from the incident end to the emission end, an incident single-mode optical fiber, a first multi-mode optical fiber, a first ring-core optical fiber, a third multi-mode optical fiber, a second ring-core optical fiber, a second multi-mode optical fiber and an emission single-mode optical fiber arranged in sequence.The adjacent optical fibers are fused, the cross sections of the cores of the multi-mode optical fibers are all larger than those of the adjacent other optical fibers, and the cross section of the core of the ring-core optical fiber is larger than that of the core of the single-mode optical fiber.The length of the first ring-core optical fiber is such that the reflected light of the first end face and the reflected light of the second end face form a Fabry-Perot interference, and the proportion of the first ring-core optical fiber to the second ring-core optical fiber is such that a harmonic vernier or a basic vernier is generated.The two interferometers of the sensor share the same optical fiber structure, the cascaded double chambers generate the harmonic vernier effect, the sensitivity of the sensor is improved, and the different responses of the FPI and the MZI to the external temperature and strain are utilized, so that the dual-parameter sensing function is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical communication, and in particular to a dual-parameter measurement optical fiber sensor based on harmonic vernier effect and a manufacturing method thereof. BACKGROUND

[0002] In the past few decades, optical fiber sensors have been widely used due to their unique advantages. With the rapid development of various fields, the demand for precise measurement and multi-parameter sensing has significantly increased, and thus the demand for new sensors has also grown. Compared with traditional optical fiber sensors, these new sensors can not only achieve higher sensitivity, but also can simultaneously measure.

[0003] The introduction of vernier effect in optical fiber sensors has been proven to be an effective tool to improve sensing performance. Optical vernier effect can be generated by combining two interferometers with slightly different free spectral range (FSR). By superimposing two interference spectra, a modulated spectrum with an envelope can be obtained. With the change of external parameters, the envelope shifts more than a single interference spectrum, thus amplifying the sensitivity of the sensor based on vernier effect. Using optical vernier effect, many different fiber interferometers with approximately but not equal FSR are combined together to manufacture sensing devices with enhanced sensitivity capability. For example, Fabry-Perot interferometer (FPI), Mach-Zehnder interferometer (MZI), Sagnac interferometer (SI), etc., are usually integrated in cascade or parallel to produce vernier effect.

[0004] However, despite the great efforts made to develop fiber sensors based on vernier effect, they still cannot fully meet the growing demand for precise measurement and multi-parameter sensing. For example, most vernier effect sensors are composed of two independent interferometers, one of which is used as a sensing unit and the other as an interference unit. The reference unit needs to be placed in an environment with good isolation, which constitutes a major challenge in practical applications. More importantly, this type of sensor is difficult to achieve multi-parameter sensing. SUMMARY

[0005] In view of the problems existing in the prior art, the present application provides a dual-parameter measurement optical fiber sensor based on harmonic vernier effect and a manufacturing method thereof.

[0006] The application provides a dual-parameter measurement optical fiber sensor based on a harmonic vernier effect, which comprises, from the direction of an incident end to an exit end, an incident single-mode optical fiber, a first multi-mode optical fiber, a first ring-core optical fiber, a third multi-mode optical fiber, a second ring-core optical fiber, a second multi-mode optical fiber and an exit single-mode optical fiber arranged in sequence; adjacent optical fibers are fused; the cross section of the core of each multi-mode optical fiber is larger than the cross section of the core of the adjacent optical fiber; the length of the first ring-core optical fiber is such that the reflected light of the first end face and the reflected light of the second end face form a Fabry-Perot interference; wherein the first end face is the interface between the first multi-mode optical fiber and the first ring-core optical fiber, and the second end face is the interface between the first ring-core optical fiber and the other multi-mode optical fiber adjacent thereto, and the ratio of the second ring-core optical fiber to the first ring-core optical fiber makes the optical fiber sensor generate a harmonic vernier or a basic vernier.

[0007] According to the dual-parameter measurement optical fiber sensor based on the harmonic vernier effect provided by the application, the ratio of the second ring-core optical fiber to the first ring-core optical fiber is determined according to the ratio of the free spectral range sizes of the Mach-Zehnder interference and the Fabry-Perot interference; when a third-order harmonic vernier, a second-order harmonic vernier, a first-order harmonic vernier or a basic vernier is generated, the ratio of the free spectral range sizes of the Mach-Zehnder interference and the Fabry-Perot interference is 4, 3, 2 and 1 respectively.

[0008] According to the dual-parameter measurement optical fiber sensor based on the harmonic vernier effect provided by the application, when a third-order harmonic vernier is generated, the length of the second ring-core optical fiber is 0, and correspondingly, the length of the third multi-mode optical fiber is also 0.

[0009] According to the dual-parameter measurement optical fiber sensor based on the harmonic vernier effect provided by the application, the determination method of the free spectral ranges of the Mach-Zehnder interference and the Fabry-Perot interference comprises:

[0010]

[0011] wherein, FSR MZI is the free spectral range of the Mach-Zehnder interference, FSR FPI is the free spectral range of the Fabry-Perot interference, λ is the wavelength of the input light, n1 and n2 are the refractive indexes of air and silicon dioxide respectively, L1 is the length of the first ring-core optical fiber, and L2 is the length of the second ring-core optical fiber.

[0012] According to the dual-parameter measurement optical fiber sensor based on the harmonic vernier effect provided by the application, the length of the first multi-mode optical fiber is less than or equal to 100 microns.

[0013] The application provides a dual-parameter measurement optical fiber sensor based on harmonic vernier effect, wherein the core diameter of a single-mode optical fiber is 8.2 microns, the cladding diameter is 125 microns, the multi-mode optical fiber is a step multi-mode optical fiber, the core diameter is 105 microns, the cladding diameter is 125 microns, the air core diameter of a ring core optical fiber is 53 microns, the ring core diameter is 65 microns, and the cladding diameter is 125 microns.

[0014] The application provides a dual-parameter measurement optical fiber sensor based on harmonic vernier effect, wherein when the third-order harmonic vernier is generated, the length of the first ring core optical fiber is 720 microns; when the second-order harmonic vernier is generated, the length of the first ring core optical fiber is 770 microns and the length of the second ring core optical fiber is 420 microns; when the first-order harmonic vernier is generated, the length of the first ring core optical fiber is 750 microns and the length of the second ring core optical fiber is 850 microns; and when the basic harmonic vernier is generated, the length of the first ring core optical fiber is 752 microns and the length of the second ring core optical fiber is 2541 microns.

[0015] The application further provides a manufacturing method of the dual-parameter measurement optical fiber sensor based on harmonic vernier effect, which comprises the following steps: placing an incident single-mode optical fiber and a first multi-mode optical fiber in a fiber fusion machine to perform discharge fusion, placing the fused optical fiber under a fiber knife, controlling the length of the first multi-mode optical fiber and cutting a flat end face to obtain a first fused optical fiber; fusing the first fused optical fiber with a first ring core optical fiber, cutting the first ring core optical fiber at a preset length through an optical magnifying glass to obtain a second fused optical fiber; if a second ring core optical fiber exists, fusing the other end face of the first ring core optical fiber with a third multi-mode optical fiber and fusing the other end face of the third multi-mode optical fiber with the second ring core optical fiber to obtain a second fused optical fiber; fusing the ring core port of the second fused optical fiber or the second fused optical fiber with a second multi-mode optical fiber to obtain a third fused optical fiber, and fusing the multi-mode optical fiber port of the third fused optical fiber with an incident single-mode optical fiber; wherein the cross section of each multi-mode optical fiber core is larger than the cross section of the adjacent other optical fiber core; the preset length makes the reflected light of the first end face and the reflected light of the second end face form a Fabry-Perot interference; wherein the first end face is the interface between the first multi-mode optical fiber and the first ring core optical fiber, and the second end face is the interface between the first ring core optical fiber and the other multi-mode optical fiber adjacent thereto; the ratio of the first ring core optical fiber and the second ring core optical fiber makes the optical fiber sensor generate a harmonic vernier or a basic vernier.

[0016] The application provides a manufacturing method of the dual-parameter measurement optical fiber sensor based on harmonic vernier effect, wherein the ratio of the second ring core optical fiber and the first ring core optical fiber is determined according to the free spectral range size ratio of Mach-Zehnder interference and Fabry-Perot interference.

[0017] The free spectral range size ratios of the Mach-Zehnder interference and the Bragg-Perot interference are 4, 3, 2 and 1 respectively when the third-order harmonic vernier, the second-order harmonic vernier, the first-order harmonic vernier or the base vernier is generated.

[0018] According to the application, the length of the second ring core fiber is 0 when the third-order harmonic vernier is generated, and correspondingly, the length of the third multimode fiber is also 0.

[0019] The application provides a double-parameter measurement fiber sensor based on the harmonic vernier effect and a manufacturing method thereof, and a bidirectional sensing structure is introduced, the Mach-Zehnder interferometer is combined with the Fabry-Perot interferometer in the transmission direction and the reflection direction respectively, and the two interferometers share the same fiber structure. The cascaded double chambers generate the harmonic vernier effect due to the same free spectral range, and the sensitivity of the sensor is improved. In addition, the different responses of the FPI and the MZI to the external temperature and the strain can realize the double-parameter sensing function. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0021] Figure 1 Fig. 1 is a structural schematic diagram of the double-parameter measurement fiber sensor based on the harmonic vernier effect provided by the application;

[0022] Figure 2 Fig. 2 is another structural schematic diagram of the double-parameter measurement fiber sensor based on the harmonic vernier effect provided by the application;

[0023] Figure 3 Fig. 3 is a micrograph of the fiber structure of the double-parameter measurement fiber sensor based on the harmonic vernier effect provided by the application;

[0024] Figure 4 Fig. 4 is a micrograph of the end face of each fiber of the double-parameter measurement fiber sensor based on the harmonic vernier effect provided by the application;

[0025] Figure 5 Fig. 5 is a device connection diagram provided by the application. DETAILED DESCRIPTION

[0026] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below in combination with the drawings in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present application.

[0027] The present application provides a Vernier-effect fiber sensor based on a bidirectional FPI-MZI structure, which can detect temperature and strain, and comprises a forward MZI and a reverse FPI. The FPI and the MZI share a ring core (RCF) fused between two segments of multimode fiber (MMF). When light is transmitted forward, a MZI sensing spectrum is obtained, and when light is transmitted reversely, a FPI sensing spectrum is obtained. The forward and reverse optical coupling produces a Vernier effect. In order to make the FSRs of the MZI and the FPI similar and flexibly control the magnification of the Vernier effect, a segment of RCF is added behind the incident MMF segment to adjust the spectral density of the MZI. By controlling the length of the added RCF segment, the magnification can be arbitrarily adjusted.

[0028] The contributions of the present application can be summarized as three main points: 1. The forward and reverse spectra of the same structure are used to produce a Vernier effect; 2. An FSR tuning fiber (added RCF) is introduced, which can arbitrarily adjust the magnification by adjusting the length of the FSR tuning fiber; 3. The responses of the FPI and the MZI to temperature and strain are different. Among them, the FPI is only sensitive to temperature and has no response to the change of refractive index, while the MZI has responses to both temperature and refractive index, so this structure can realize dual-parameter sensing.

[0029] The present application will be described below in combination with Figures 1-5 The present application provides a dual-parameter measurement fiber sensor based on harmonic Vernier effect and a manufacturing method. Figure 1 is one of the flowcharts of the dual-parameter measurement fiber sensor based on harmonic Vernier effect provided by the present application, as Figure 1 shown, the present application provides a dual-parameter measurement fiber sensor based on harmonic Vernier effect, comprising:

[0030] The lead-in single-mode fiber, the first multi-mode fiber, the first ring-core fiber, the third multi-mode fiber, the second ring-core fiber, the second multi-mode fiber and the lead-out single-mode fiber are arranged in sequence from the light beam incident end to the light beam exit end. Adjacent optical fibers are fused, the cross section of the core of each multi-mode fiber (the first, second or third multi-mode fiber) is larger than the cross section of the core of the adjacent other optical fiber (including the single-mode fiber and the ring-core fiber), and the cross section of the core of the ring-core fiber is larger than the cross section of the core of the single-mode fiber; the length of the first ring-core fiber is such that the reflected light of the first end face and the reflected light of the second end face form a Fabry-Perot interference (FPI), and in addition, the difference in refractive index between the air core and the ring core causes the light beams entering the multi-mode fiber (the third multi-mode fiber for the second multi-mode fiber in the third-order vernier mode, and the third multi-mode fiber for the second multi-mode fiber in the second-order, first-order or fundamental vernier mode) from the air core and the ring core of the first ring-core fiber to produce a Mach-Zehnder interference (MZI); the first end face is the interface between the first multi-mode fiber and the first ring-core fiber, and the second end face is the interface between the first ring-core fiber and the other multi-mode fiber adjacent thereto; the ratio of the second ring-core fiber to the first ring-core fiber causes the optical fiber sensor to generate a harmonic vernier or a fundamental vernier. When applied to the third-order harmonic vernier, the second end face is the interface between the first ring-core fiber and the second multi-mode fiber, and when applied to the second-order, first-order harmonic vernier or fundamental vernier, the second end face is the interface between the first ring-core fiber and the third multi-mode fiber.

[0031] Specifically, the light beam first enters the sensor through the lead-in single-mode fiber, and then is transmitted to the first multi-mode fiber segment MMF1. Since the MMF is a multi-mode fiber with a large core area, it diffuses the light intensity into the air core and the ring core of the ring-core fiber (such as RCF1). Part of the light is reflected from the interface between the core of MMF1 and RCF1, and the remaining light beam is transmitted from the surface of MMF1, entering the air core and the ring core region of RCF.

[0032] Since part of the light is confined in the air core region of RCF1, this part of the light is reflected again from the end face of RCF1 and the exit MMF2. Therefore, a circulator can be added at the incident end to observe the FPI interference fringes formed by the interference of the double-reflected light beams. At the same time, the light in RCF1 exits the air core and the ring core to enter the subsequent multi-mode fiber segment for coupling. Due to the effective refractive index difference between the air core and the ring core of RCF1, the two transmitted light beams are coupled to form MZI interference fringes. Coupling the FPI and MZI light can realize the vernier effect.

[0033] The embodiment of the present application adds a section of MMF-RCF (denoted as MMF3 and RCF2) between the MMF2 (second multi-mode fiber) and RCF1 (first ring-core fiber) at the light output end to increase the optical path of the MZI, which can combine Figure 3 , the light beam enters through the incident single-mode fiber SMF, then transmits into the air core and ring core region of the first multi-mode fiber MMF1 section, after which the light in the RCF1 exits the air core and ring core of the RCF1 and enters the MMF3 section, where a part of the air core and ring core light will be coupled. Since the core diameter of the RCF is smaller than that of the MMF, another part of the light will continue to enter the air core and ring core of the RCF2, and the light is coupled at the MMF2. By adjusting the length ratio of the MMF3-RCF2, third-order harmonic verniers, second-order harmonic verniers, first-order harmonic verniers and base verniers can be generated respectively, and the fiber end faces are as shown in Figure 4 , a, b and c are single-mode fiber, multi-mode fiber and ring-core fiber respectively.

[0034] The total light intensity of the FPI interference fringes generated by the emitted light and the MZI interference fringes generated by the transmitted light can be expressed as:

[0035]

[0036] where φ MZI and φ FPI are the phase differences of the MZI and the FPI respectively, and I1, I2, I3 represent the output light intensities of the three ports of the circulator (see Figure 5 port of the circulator). A small part of the MMF is only used as a coupling part, and the light beam propagating in the RCF1 constitutes a hybrid interferometer. The phase difference of the MZI and the FPI can be defined as:

[0037]

[0038] where λ is the wavelength of the input light, n1 and n2 are the refractive indices of air and silica respectively, and L is the length of the RCF1. Since the values of n2 and n1 are fixed, the free spectral range (FSR) of the FPI and the FSR of the MZI are equal, so the ratio of the FSR of the FPI to the FSR of the MZI is fixed.

[0039] The dual-parameter measurement optical fiber sensor based on the harmonic vernier effect of the present application introduces a bidirectional sensing structure, in which the Mach-Zehnder interferometer is combined with the Fabry-Perot interferometer in the transmission direction and the reflection direction respectively. The two interferometers share the same fiber structure. The cascaded double chambers produce a harmonic vernier effect due to the same free spectral range, thereby improving the sensitivity of the sensor. In addition, the different responses of the FPI and the MZI to external temperature and strain can realize the dual-parameter sensing function.

[0040] The interference signals from the two structures are cleverly superimposed to produce a vernier effect. By carefully adjusting the interference spectral line period of the MZI, the present application can realize the basic vernier effect and the incident, outgoing and third-order harmonic vernier. The harmonic vernier effect fiber sensor constructed by combining FPI and MZI can be used for dual-parameter sensing, and the vernier effect is generated by the interference between the spectra of FPI and MZI. The harmonic vernier effect fiber sensor improves the sensitivity and realizes accurate measurement of temperature and strain. The bidirectional structure of the sensor refers to the ability to measure parameters in both forward and reverse directions, and this bidirectional structure allows simultaneous measurement in both forward and reverse directions, which enhances the versatility of the sensor by adapting to scenarios where parameters change in both directions, ensuring comprehensive monitoring and analysis of the target system. By combining the advantages of harmonic vernier effect and bidirectional FPI and MZI structure, this dual-parameter sensor provides a powerful and efficient solution for accurate and simultaneous measurement of multiple physical parameters.

[0041] In one embodiment, the ratio of the second ring core fiber and the first ring core fiber is determined according to the size ratio of the free spectral range of Mach-Zehnder interference and Bragg-Parry interference; when used to generate a third-order harmonic vernier, a second-order harmonic vernier, a first-order harmonic vernier or a basic vernier, the size ratio of the free spectral range of Mach-Zehnder interference and Bragg-Parry interference is 4, 3, 2 and 1 respectively.

[0042] In one embodiment, when a third-order harmonic vernier is generated, the length of the second ring core fiber is 0, and correspondingly, the length of the second multi-mode fiber is also 0. When the size ratio of the free spectral range of Mach-Zehnder interference and Bragg-Parry interference is 4, the length of RCF2 can be set to 0, that is, when applied to generate a third-order vernier, the length of the second ring core fiber RCF2 is 0, at this time MMF3 and MMF2 are integrated, without the need to set two multi-mode fibers, one multi-mode fiber MMF2 can be used, as shown in Figure 2 .

[0043] In some embodiments, the determination of the free spectral range of Mach-Zehnder interference and Bragg-Parry interference includes:

[0044]

[0045] wherein FSR MZI is the free spectral range of Mach-Zehnder interference, FSR FPI is the free spectral range of Bragg-Parry interference, λ is the wavelength of input light, n1 and n2 are the refractive indices of air and silicon dioxide respectively, and L1 is the length of the first ring core fiber and L2 is the length of the second ring core fiber.

[0046] It is worth noting that because the principle of FPI is to interfere with reflected light, there will be transmission loss in the process of light transmission in the sensor. The transmission loss of light at the interface between the core and the air cavity is 0.5, so when the light is reflected at the interface between MMF3-RCF2, the loss of light reflected through three interfaces is negligible, and the optical path difference of FPI has not increased. Therefore, the new phase difference can be defined as:

[0047]

[0048] Where L1 and L2 are the cavity lengths of RCF1 and RCF2 respectively, and according to FSR = λ / OPD (OPD is the optical path difference), the FSR of MZI and FPI is determined by the above equations (5) and (6) respectively.

[0049] In the above embodiment, the electric field intensity of the input light is E in , T0 = DH / DM, DH and DM are the inner diameter of the hollow tube and the core diameter of the multi-mode optical fiber respectively. Therefore, the electric field intensity E Fin of the part of the light used to form FPI interference can be represented as:

[0050] E Fin = T0E in (9)

[0051] The two reflecting surfaces of the FPI interferometer are formed at both ends of the air cavity. Assuming that the input light electric field intensity of the FPI interferometer is E in , the electric field intensity of the two reflected lights of the two reflecting surfaces of the FPI interferometer is:

[0052]

[0053] Where T F is the transmission matrix of FPI, is the phase difference between the two reflected light beams. Where n and L F are the refractive index and length of the FPI cavity respectively, and λ is the wavelength.

[0054]

[0055] After being reflected by the FPI, the total reflected electric field can be written as:

[0056]

[0057] The transmitted light beams propagate along two paths of the air cavity and the capillary tube wall respectively, forming a MZI. The electric field of the two light beams constituting the MZI can be represented as:

[0058]

[0059] is the transmission matrix of MZI, which can be expressed as:

[0060]

[0061] where T1 and T2 are the amplitude splitting ratio of the two beams of light propagating in MZI, and is the cumulative phase shift of light propagating in air hole and silica wall. The cumulative phase difference between the beams propagating along the air hole and the silica wall is where Δn is the effective index difference between the air hole and the silica cladding of HCF, L M is the interference length of MZI, i.e. the length of HCF in MZI. The output electric field of MZI can be obtained as:

[0062]

[0063] After passing through the bidirectional interferometer structure, FPI and MZI can be obtained simultaneously. In order to improve the sensing performance, a 3dB coupler is used to combine the bidirectional optical signals. The transmission matrix of a general coupler is:

[0064]

[0065] where r is the splitting ratio of the coupler; σ=(1-μ)1 / 2; μ is the additional loss of the coupler. For a 3dB coupler, r=0.5, and the additional loss of the coupler is usually ignored in calculation, so μ=0, σ=1. The output electric field of the coupler can be expressed as:

[0066]

[0067] Finally, the total light intensity output is:

[0068]

[0069] FPI and MZI can be used as sensing units to perceive environmental parameters, respectively. The movement of the FPI and MZI interference spectrum trough caused by external factors can be expressed as:

[0070]

[0071] where λ F (m) and λ M (m) are the wavelengths of the mth trough of FPI and MZI, respectively.

[0072] According to the optical vernier theory, when the free spectral range (FSR) of two groups of interferometers are similar but not the same, an optical vernier spectrum will be generated. The vernier effect spectrum contains a series of fringes modulated by a vernier envelope, and the mth trough wavelength and FSR of the vernier envelope are respectively:

[0073]

[0074] where FSR F and FSR M are the free spectral ranges of the FPI and MZI respectively. Correspondingly, the movement of the trough of the vernier envelope caused by external factors can be expressed as:

[0075]

[0076] According to formulas (21), (22) and (25), the relationship between the wavelength shift of the vernier envelope and the wavelength shift of the FPI and MZI troughs can be arranged as:

[0077] Δλ E = |M F Δλ-M M Δλ M | (26)

[0078] where M F and M M are the sensitivity amplification factors of the vernier effect compared with the FPI and MZI respectively.

[0079]

[0080] For the FPI and MZI generated by the same hollow fiber structure, the optical path lengths are respectively:

[0081]

[0082] where n is the refractive index of the air cavity, n = 1; Δn is the refractive index difference between the fiber wall and the air cavity, Δn = 0.4685; L F = L M in the same structure, so ΔL F is about 4 times ΔL M .

[0083] When the optical path length of one interferometer in the two groups of interferometers generating the vernier effect increases by an integer multiple of the optical path length of the other interferometer, the basic optical vernier spectrum will be converted into a harmonic vernier spectrum. The FSR of the vernier envelope spectrum described by formula (22) can be written in a more general form as:

[0084]

[0085] The spectrum with harmonic Vernier effect, the inner envelope spectrum is obtained by fitting the maximum group in the harmonic spectrum, the FSR of the inner envelope can be expressed as

[0086]

[0087] The corresponding sensitivity amplification factor of harmonic Vernier effect can be expressed as:

[0088]

[0089] In an embodiment, the length of the first multimode fiber is less than or equal to 100 microns. In order to avoid exciting too many modes, a short segment of MMF is used, with a length less than or equal to 100 μm.

[0090] In an embodiment, the single-mode fiber has a core diameter of 8.2 μm, a cladding diameter of 125 μm, the first multimode fiber is a step multimode fiber with a core diameter of 105 μm, a cladding diameter of 125 μm, the first and second ring-core fibers have an air-core diameter of 53 μm, a ring-core diameter of 65 μm, a cladding diameter of 125 μm.

[0091] For the core diameter and the cladding diameter, the incident single-mode fiber and the exit single-mode fiber are the same, and the first, second and third multimode fibers are also the same. For the air-core diameter, the ring-core diameter and the cladding diameter, the first and second ring-core fibers are also the same.

[0092] In some embodiments, for generating the third-order harmonic Vernier, the length of the first ring-core fiber is 720 microns; for generating the second-order harmonic Vernier, the length of the first ring-core fiber is 770 microns, and the length of the second ring-core fiber is 420 microns; for generating the first-order harmonic Vernier, the length of the first ring-core fiber is 750 microns, and the length of the second ring-core fiber is 850 microns; for generating the fundamental harmonic Vernier, the length of the first ring-core fiber is 752 microns, and the length of the second ring-core fiber is 2541 microns.

[0093] The dimensions are shown in Table 1, and only RCF1 is used for generating the third-order harmonic Vernier, and no RCF2 is used, which can be seen from Figure 1 and Figure 2 .

[0094] Sensor RCF1 RCF2 Third order vernier 720 μm \ Second order vernier 770 μm 420 μm First order vernier 750 μm 850 μm Base vernier 752 μm 2541 μm

[0095] According to the values in Table 1, RCF1 and RCF2 are cut to the calculated lengths, i.e., the third-order harmonic Vernier, the second-order harmonic Vernier, the first-order harmonic Vernier and the fundamental harmonic Vernier are respectively manufactured. Finally, the system can be connected to a broadband light source and a spectrometer for detection, such as Figure 5As shown in the figure, OSA is a spectrum analyzer, coupler is a coupler, circulator is a circulator, and BBS is a broadband light source.

[0096] The method for manufacturing the dual-parameter measurement optical fiber sensor based on the harmonic Vernier effect provided by the present application is described below, and the method for manufacturing the dual-parameter measurement optical fiber sensor based on the harmonic Vernier effect described below can be correspondingly referred to the dual-parameter measurement optical fiber sensor based on the harmonic Vernier effect described above. The method for manufacturing the dual-parameter measurement optical fiber sensor based on the harmonic Vernier effect comprises:

[0097] S1, placing the incident single-mode optical fiber and the first multi-mode optical fiber in the optical fiber fusion machine for discharge fusion, and placing the fused optical fiber under the optical fiber knife, controlling the length of the first multi-mode optical fiber and cutting the flat end face to obtain the first fused optical fiber;

[0098] S2, fusing the first fused optical fiber with the first annular core optical fiber, cutting the first annular core optical fiber at a preset length through an optical magnifying glass to obtain the second fused optical fiber; if there is a second annular core optical fiber, fusing the other end face of the first annular core optical fiber with the third multi-mode optical fiber, and fusing the other end face of the third multi-mode optical fiber with the second annular core optical fiber to obtain the second fused optical fiber;

[0099] S3, fusing the annular core port of the second fused optical fiber or the second fused optical fiber with the second multi-mode optical fiber to obtain the third fused optical fiber, and fusing the multi-mode optical fiber port of the third fused optical fiber with the incident single-mode optical fiber;

[0100] The cross section of the first or second multi-mode optical fiber core is larger than the cross section of the adjacent other optical fiber core, and the cross section of the annular core optical fiber core is larger than the cross section of the single-mode optical fiber core.

[0101] The preset length makes the reflected light of the first end face and the reflected light of the second end face form a Fabry-Perot interference, wherein the first end face is the interface between the first multi-mode optical fiber and the first annular core optical fiber, and the second end face is the interface between the first annular core optical fiber and the other multi-mode optical fiber adjacent thereto, and the ratio of the first annular core optical fiber and the second annular core optical fiber makes the optical fiber sensor generate a harmonic Vernier or a fundamental Vernier.

[0102] In some embodiments, the ratio of the second annular core optical fiber and the first annular core optical fiber is determined according to the size ratio of the free spectral range of the Mach-Zehnder interference and the Fabry-Perot interference; when a third-order harmonic Vernier, a second-order harmonic Vernier, a first-order harmonic Vernier or a fundamental Vernier is generated, the size ratio of the free spectral range of the Mach-Zehnder interference and the Fabry-Perot interference is 4, 3, 2 and 1, respectively.

[0103] In some embodiments, when generating a third-harmonic vernier, the length of the second ring core fiber is 0, and correspondingly, the length of the third multimode fiber is also 0. That is, after obtaining the second fusion fiber, it is not necessary to add MMF3 and RCF2 to create the second fusion fiber for growth.

[0104] To fabricate a three-section harmonic vernier effect sensor, first, use wire strippers to remove the coating of the SMF (Superficial Fiber Medium) and then use a fiber optic cleaver to cut the end face of the SMF flat. Repeat the same steps to remove the coating of the MMF (Medium-Medium Fiber Medium). Clean the fiber surface and cut the end face to ensure it is flat. Place the SMF and MMF in a fiber optic fusion splicer for discharge splicing. Place the spliced ​​SMF+MMF under the fiber optic cleaver, controlling the length of the MMF to cut its end face flat, and then splice the MMF and RCF (Rectangular Fiber Medium). After splicing, place the spliced ​​fiber under the fiber optic cleaver and use an optical magnifying glass to cut the RCF to the required length. Because the sensor is symmetrical, the remaining parts can be manufactured in the same way. Because the interference fringes of MZI and FPI are both formed by light transmitted through the RCF ring core and air core, and the effective refractive index of the ring core and the effective refractive index of the air core are fixed, and the cavity length of the two interference cavities corresponds to the length of the RCF, the FSR of the generated MZI is always kept at about four times that of the FSR of the FPI, and the superimposed harmonic vernier can only be a third-order harmonic vernier.

[0105] When a second-order harmonic vernier, a first-order harmonic vernier, or a basic vernier is required, before fusing the loop core port of the second fusion splice fiber with the second multimode fiber, the other end face of the first loop core fiber is fused with the third multimode fiber; the other end face of the third multimode fiber is then fused with the second loop core fiber to obtain a new growing second fusion splice fiber; correspondingly, the loop core port of the growing second fusion splice fiber is then fused with the second multimode fiber.

[0106] Specifically, the embodiments of the present invention are in Figure 2 Based on the existing structure, an optical path is added to the MZI. The manufacturing process of this sensor differs slightly from that of the third-harmonic vernier sensor. First, the coatings on the SMF and MMF are stripped, and the cut ends are flattened before fusing them together. Then, the coating on the RCF is stripped and fused onto the SMF+MMF. The fused structure is placed under an optical magnifying glass, and the RCF is cut using precise measurements. A section of MMF is then fused onto the SMF+MMF+RCF. After fusing the MMF, its length is controlled and cut. A second section of RCF is then fused onto this structure. After fusing the second RCF section, it is cut to maintain the calculated length. Finally, this section of fiber is fused to the MMF and cut to the appropriate length. Finally, the SMF is fused on top. This yields the sensor we have fabricated.

[0107] The manufacturing method embodiment provided by the embodiment of the application is to realize the above-mentioned device embodiments, and the specific process and detailed content are referred to the above-mentioned device embodiments, which will not be repeated here.

[0108] The implementation principle and the produced technical effects of the manufacturing method of the dual-parameter measurement optical fiber sensor based on the harmonic vernier effect are the same as those of the above-mentioned dual-parameter measurement optical fiber sensor based on the harmonic vernier effect, and for brief description, the part of the manufacturing method of the dual-parameter measurement optical fiber sensor based on the harmonic vernier effect that is not mentioned in the above-mentioned dual-parameter measurement optical fiber sensor based on the harmonic vernier effect can be referred to the corresponding content in the above-mentioned dual-parameter measurement optical fiber sensor based on the harmonic vernier effect.

[0109] The device embodiments described above are only schematic, wherein the units described as separate components can or can not be physically separate, and the components displayed as units can or can not be physical units, that is, can be located in one place, or can be distributed on a plurality of network units. Part or all of the modules can be selected according to actual needs to achieve the purpose of the embodiment scheme. Those skilled in the art can understand and implement without creative labor.

[0110] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the application, but not to limit it; although the application has been described in detail with reference to the above-mentioned embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the above-mentioned embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the application.

Claims

1. A dual-parameter measurement optical fiber sensor based on harmonic Vernier effect, characterized in that, Comprise: sequentially arranged from the incident end to the exit end of the light beam are an incident single-mode optical fiber, a first multi-mode optical fiber, a first annular core optical fiber, a third multi-mode optical fiber, a second annular core optical fiber, a second multi-mode optical fiber and an exit single-mode optical fiber; adjacent optical fibers are fusion spliced, the cross section of the core of each multi-mode optical fiber is larger than the cross section of the core of the adjacent other optical fiber, and the cross section of the core of the annular core optical fiber is larger than the cross section of the core of the single-mode optical fiber; the length of the first annular core optical fiber is such that the reflected light of the first end face and the reflected light of the second end face form a Fabry-Perot interference; wherein the first end face is the interface between the first multi-mode optical fiber and the first annular core optical fiber, the second end face is the interface between the first annular core optical fiber and the other multi-mode optical fiber adjacent thereto, and the ratio of the second annular core optical fiber to the first annular core optical fiber causes the optical fiber sensor to generate a harmonic Vernier or a fundamental Vernier; the ratio of the free spectral range sizes of the Mach-Zehnder interference and the Fabry-Perot interference is determined according to the ratio of the free spectral range sizes of the Mach-Zehnder interference and the Fabry-Perot interference; when generating a third-order harmonic Vernier, a second-order harmonic Vernier, a first-order harmonic Vernier or a fundamental Vernier, the ratio of the free spectral range sizes of the Mach-Zehnder interference and the Fabry-Perot interference is 4, 3, 2 and 1 respectively, and when generating a third-order harmonic Vernier, the length of the second annular core optical fiber is 0, and correspondingly, the length of the third multi-mode optical fiber is also 0.

2. The dual-parameter measurement fiber sensor based on harmonic Vernier effect according to claim 1, characterized in that, The determination method of the free spectral range of the Mach-Zehnder interference and the Fabry-Perot interference comprises: ; ; wherein, is a free spectral range of Mach-Zehnder interference, is a free spectral range of Bragg-Perot interference, λ is a wavelength of input light, n1 and n2 are refractive indexes of air and silica respectively, L1 is a length of the first ring core fiber, and L2 is a length of the second ring core fiber.

3. The dual-parameter measurement fiber sensor based on harmonic Vernier effect according to claim 1, characterized in that, the length of the first multi-mode optical fiber is less than or equal to 100 microns.

4. The dual-parameter measurement fiber sensor based on harmonic Vernier effect according to claim 1, characterized in that, The core diameter of the single-mode optical fiber is 8.2 microns, the cladding diameter is 125 microns, the multi-mode optical fiber is a step multi-mode optical fiber, the core diameter is 105 microns, the cladding diameter is 125 microns, the air core diameter of the annular core optical fiber is 53 microns, the annular core diameter is 65 microns, and the cladding diameter is 125 microns.

5. The dual-parameter measurement optical fiber sensor based on the harmonic Vernier effect according to claim 1, characterized in that: when generating a third-order harmonic Vernier, the length of the first annular core optical fiber is 720 microns; when generating a second-order harmonic Vernier, the length of the first annular core optical fiber is 770 microns, and the length of the second annular core optical fiber is 420 microns; when generating a first-order harmonic Vernier, the length of the first annular core optical fiber is 750 microns, and the length of the second annular core optical fiber is 850 microns; when generating a fundamental harmonic Vernier, the length of the first annular core optical fiber is 752 microns, and the length of the second annular core optical fiber is 2541 microns.

6. A method for manufacturing a dual-parameter measurement fiber sensor based on the harmonic Vernier effect according to any one of claims 1-5, characterized in that, Comprise: placing the incident single-mode optical fiber and the first multi-mode optical fiber in a fiber fusion splicer for discharge fusion splicing, and placing the fused optical fiber after fusion splicing under a fiber knife to control the length of the first multi-mode optical fiber and cut a flat end face to obtain a first fused optical fiber; fusing the first fused optical fiber with the first annular core optical fiber, and cutting the first annular core optical fiber at a preset length through an optical magnifying glass to obtain a second fused optical fiber; If the second annular core optical fiber exists, the other end face of the first annular core optical fiber is fused with a third multimode optical fiber, and the other end face of the third multimode optical fiber is fused with the second annular core optical fiber to obtain a second fused optical fiber; the annular core port of the second fused optical fiber or the second fused optical fiber is fused with a second multimode optical fiber to obtain a third fused optical fiber, and the multimode optical fiber port of the third fused optical fiber is fused with the exit single-mode optical fiber; Wherein, the cross section of each multimode optical fiber core is larger than the cross section of the adjacent other optical fiber core, and the cross section of the annular core optical fiber core is larger than the cross section of the single-mode optical fiber core; The preset length is such that the reflected light of the first end face and the reflected light of the second end face form a Fabry-Perot interference; Wherein, the first end face is the interface between the first multimode optical fiber and the first annular core optical fiber, and the second end face is the interface between the first annular core optical fiber and another multimode optical fiber adjacent thereto; the ratio of the first annular core optical fiber and the second annular core optical fiber makes the optical fiber sensor generate a harmonic vernier or a basic vernier.

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