MZI strain sensor based on spiral fiber core and manufacturing and using method thereof

Abstract

The invention relates to the technical field of optical fiber interference sensors, in particular to an MZI strain sensor based on a spiral fiber core and a manufacturing and using method of the MZI strain sensor. The strain sensor comprises a light injection area, a light splitting area, a core shift spiral area, a light combination area and a light receiving area which are sequentially arranged on an optical fiber, the fiber core of the core shift spiral area is in a spiral shape, and the path length of light propagating in the fiber core is larger than the path length of light propagating in the cladding; the core shift spiral area can be formed by a D-shaped optical fiber or a core shift optical fiber in a spiral mode, and the cladding is in a thread shape or a cylindrical shape; the screw pitch of the spiral fiber core in the core shift spiral area is larger than 400 microns, the screw pitch of the spiral fiber core is inversely proportional to the strain sensitivity, and the strain sensitivity of the sensor is adjusted by selecting the screw pitch of the spiral fiber core. The problems that in the sensitization process of an existing MZI strain sensor, the limitation of the material elasto-optical effect cannot be broken through, and the strain sensitivity is low are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber interference sensors, and in particular to an MZI strain sensor based on a spiral fiber core and a manufacturing and using method thereof. Background Art

[0002] According to the strain detection mechanism of MZI sensors, most of the sensitivity enhancement research focuses on increasing the influence of the photoelastic effect on strain detection, but due to the limitation of the photoelastic coefficient of optical fiber materials, the sensitivity enhancement effect is limited. Therefore, it is necessary to conduct in-depth research to continue to break through the sensitivity limit of optical fiber MZI strain sensors that respond to the photoelastic effect with other mechanisms and realize high-sensitivity strain MZI.

[0003] When MZI is subjected to strain, the interference wavelength shift is determined by both the photoelastic effect and the strain effect. Since the amount of interference wavelength shift caused by the photoelastic effect is much greater than that caused by the strain effect, the influence of the strain effect on its strain detection can be ignored, and strain sensitivity can be achieved by strengthening the photoelastic effect. The photoelastic effect is determined by the product of the change in the refractive index difference between the fiber core and the cladding and the difference in the sensing path length between the core and the cladding. Therefore, the strain sensitivity of the fiber MZI can be studied starting from these two factors. At present, the research on the strain sensitivity of the fiber MZI focuses on increasing the change in the refractive index difference between the core mode and the cladding mode during the strain process, which is often achieved by exciting high-order cladding modes and strain concentration. For example, Bianchetti et al. spliced ​​a single-mode fiber between two single-mode fibers by offset fusion splicing, and increased the change in the core-cladding mode refractive index difference by exciting the high-order cladding mode, thereby increasing the strain detection sensitivity to 7.46 pm / με (SUSANA AVILA-GARCIA M, BIANCHETTI M, LE CORRE R, et al. High sensitivity strain sensors based on single-mode-fiber core-offset Mach-Zehnder interferometers[J]. Optics and Lasers in Engineering, 2018, 107: 202-6.); André et al. tapered the multimode fiber in the middle of the single-multi-single structure to enhance the influence of the elastic-optic effect on strain detection by strain concentration, and the strain detection sensitivity of the sensor was increased to 23.69 pm / με (ANDRE RM, BIAZOLI CR, SILVA SO, et al. Strain-Temperature Discrimination Using Multimode Interference in Tapered Fiber[J]. IeeePhotonics Technology Letters, 2013, 25(2): 155-8.). Some researchers have also combined the two methods of exciting high-order cladding modes and strain concentration to enhance the response of the elastic-optical effect to strain. For example, Dong et al. spliced ​​two single-mode optical fibers in the middle.

[0004] Hollow core fiber, and the hollow core fiber is tapered, with a strain sensitivity of 2.7pm / με (DONG L, GANG T, BIAN C, et al. A high sensitivity optical fiber strain sensor based on hollow core tapering [J]. Optical Fiber Technology, 2020, 56.). However, due to the limitation of the optical fiber material's elastic coefficient, the optical fiber effect has limited response to strain detection, and it is difficult to further improve the sensitivity of the optical fiber MZI strain sensor.

[0005] In summary, although there are some methods for enhancing the sensitivity of MZI strain sensors, the current sensitization methods cannot break through the limitation of the material's elastic-optical coefficient on the sensitivity of MZI strain sensors. The strain sensitization effect of MZI is limited, and it is difficult to achieve a highly sensitive MZI strain sensor. Summary of the invention

[0006] The main purpose of the present invention is to provide an MZI strain sensor based on a spiral fiber core and a method for manufacturing and using the same, so as to solve the technical problem of insufficient strain sensitivity of the existing MZI strain sensor.

[0007] In order to solve the above problems, the present application provides an MZI strain sensor based on a spiral fiber core, comprising a light injection zone, a light splitting zone, an eccentric spiral zone, a light combining zone, and a light receiving zone sequentially arranged on the optical fiber; the length of the optical fiber in the eccentric spiral zone is 2cm-4cm, the core is in a spiral shape, and the path length of light propagating in the core is greater than the path length of light propagating in the cladding; the spiral core in the eccentric spiral zone can be formed by a D-shaped optical fiber or an eccentric optical fiber spiral, and the cladding is threaded or cylindrical; the pitch of the spiral core in the eccentric spiral zone is greater than 400μm, wherein the pitch of the spiral core is inversely proportional to the strain sensitivity, and the strain sensitivity of the sensor is adjusted by selecting the pitch of the spiral core.

[0008] The pitch of the spiral core in the eccentric spiral region of the sensor is greater than 400μm. When the pitch is less than 400μm, the bending degree of the core is too large and the light beam cannot be transmitted in the core. When the length of the eccentric spiral region is constant, the smaller the pitch of the spiral core, the longer the sensing length of the optical fiber core, and the sensing length of the optical fiber cladding remains unchanged, resulting in a longer path length for light propagating in the core, while the path length for light propagating in the cladding remains unchanged. The greater the difference between the path length for light propagating in the core and the path length for light propagating in the cladding, the higher the strain sensitivity of the sensor. The sensitivity of the sensor can be adjusted by adjusting the pitch of the spiral core in this area.

[0009] Mach-Zehnder interferometer (MZI) follows the principle of double-beam interference, and its interference wavelength can be expressed as:

[0010]

[0011] in and Represent the effective refractive index of the core and cladding of the optical fiber, L core and L clad denote the sensing path lengths of the core and cladding, respectively.

[0012] When using MZI for strain detection, its strain sensitivity can be expressed as, that is, the derivative of equation (1) with respect to strain:

[0013]

[0014] The first two terms are determined by the photoelastic effect of the optical fiber, and the last two terms are determined by the elastic deformation of the optical fiber, that is, the strain effect. For the MZI strain sensor, the interference wavelength shift caused by the photoelastic effect is much larger than the interference wavelength shift caused by the strain effect, so the last two terms in the above formula can be ignored, that is:

[0015]

[0016] From formula (3), we can know that by increasing the change of the effective refractive index difference between the core and the package (i.e. ) and the length difference between the core and cladding paths in the sensing area (i.e., L core -L clad ) to achieve strain sensitivity. The greater the difference between the path length of light propagating in the fiber core and the path length of light propagating in the cladding in the sensing area, the higher the strain sensitivity.

[0017] The length of the eccentric spiral region of the sensor determines the free spectral range of the interference spectrum. In order to produce a stable interference spectrum in the 1510nm-1610nm band, the length of the eccentric spiral region can be set to 2cm-4cm; when the pitch of the spiral fiber core is constant, the longer the length of the eccentric spiral region, the greater the difference between the path of light propagating in the fiber core and the path of light propagating in the cladding, and the higher the strain sensitivity; the strain sensitivity of the sensor can be adjusted by adjusting the length of the eccentric spiral region in this area.

[0018] As a preferred solution, when the eccentric spiral region is formed by a D-shaped optical fiber spiral, when the D-shaped optical fiber is connected to the multimode optical fiber in the light splitting region, the geometric center axes of the two completely coincide, and the optical fiber cladding is a threaded structure.

[0019] As a preferred solution, when the eccentric spiral region of the sensor is formed by a D-shaped optical fiber spiral, the D-shaped optical fiber is made by side polishing of a single-mode optical fiber, the core diameter of the single-mode optical fiber is 9μm, and the cladding diameter is 125μm. The upper half of the single-mode optical fiber is polished and removed by an optical fiber side polishing machine to form a D-shaped optical fiber, and then a spiral fiber core structure is formed by hydrogen-oxygen flame spiral processing; the optical fiber cladding of the eccentric spiral region is a threaded structure, and the thread diameter is 70μm-90μm. The core is in a spiral shape, and since the spiral shape increases the path length of light propagating in the core, the path length of light propagating in the cladding remains unchanged, resulting in the path length of light propagating in the core being greater than the path length of light propagating in the cladding.

[0020] When the eccentric spiral area of ​​the sensor is formed by a D-shaped optical fiber spiral, the optical fiber cladding is in a threaded shape, and the thread diameter determines the strain sensitivity of the sensor. In order to ensure that obvious threads are formed on the optical fiber cladding without damaging the optical fiber core, the thread diameter of the eccentric spiral area can be set to 70μm-90μm. The smaller the thread diameter, the more concentrated the strain of the sensor is in the thread area during the strain process, the greater the strain on the thread area, and the greater the strain sensitivity of the sensor. The strain sensitivity of the sensor can be adjusted by adjusting the thread diameter within this range.

[0021] As a preferred solution, when the eccentric spiral zone is formed by an eccentric optical fiber spiral, the outer surfaces of the claddings of the eccentric optical fiber and the multimode optical fiber in the light splitting zone are completely overlapped when the eccentric optical fiber is connected, and the optical fiber cladding is a cylindrical structure.

[0022] As a preferred solution, when the eccentric spiral region of the sensor is formed by the spiral of an eccentric optical fiber, the core diameter of the eccentric optical fiber is 9 μm, the core is 30.5 μm away from the optical fiber axis, and the spiral core structure is formed by hydrogen-oxygen flame spiral processing. The core is in a spiral shape, and the spiral shape increases the path length of light propagating in the core, while the path length of light propagating in the cladding remains unchanged, resulting in the path length of light propagating in the core being greater than the path length of light propagating in the cladding.

[0023] As a preferred solution, the sensor's light injection area and light receiving area are composed of single-mode optical fiber, the single-mode optical fiber has a core diameter of 9μm, a cladding diameter of 125μm, and a coating diameter of 250μm; the light splitting area and light combining area are composed of step-index multimode optical fiber, the multimode optical fiber length is 1mm-2mm, the step-index multimode optical fiber has a core diameter of 105μm, a cladding diameter of 125μm, and a coating diameter of 250μm; the length of the sensor's eccentric spiral area is 2cm-4cm, and the core is spiral in shape. Since the spiral shape increases the path length of light propagating in the core, the path length of light propagating in the cladding remains unchanged, resulting in the path length of light propagating in the core being greater than the path length of light propagating in the cladding.

[0024] The length of the multimode optical fiber used in the light-splitting and light-combining areas of the sensor determines the loss, position and stability of the interference spectrum. If the length of the multimode optical fiber is too long, it will lead to excessive mode dispersion and loss, and the stability of the interference spectrum will deteriorate; if the length of the multimode optical fiber is too short, various cladding modes cannot be excited and the interference effect is not obvious. In order to produce a stable interference spectrum in the 1510nm-1610nm band, the length of the multimode optical fiber can be set to 1mm-2mm.

[0025] Another object of the present invention is to provide a method for manufacturing an MZI strain sensor based on a helical fiber core. When the eccentric helical region is formed by a D-shaped optical fiber helix, the method for manufacturing the sensor is:

[0026] First, use Miller pliers to strip the coating on the surface of single-mode fiber and step-index multimode fiber. After cleaning with alcohol, use a fiber cleaver to cut the fiber end face flat, weld the single-mode fiber and multimode fiber face to face, and cut the multimode fiber to a fixed length of 1mm-2mm in the fiber fixed-length cutting device; use Miller pliers to strip the coating on the middle part of another single-mode fiber, clamp it on the bare fiber side polishing machine, and polish and remove the upper half of the single-mode fiber to form a D-shaped fiber. Polish until the short diameter of the D-shaped fiber is 70μm-90μm, and the length of the polishing area is set to 5cm. The polished D-shaped optical fiber is fused to one end of the multimode optical fiber of the spliced ​​single-mode-multimode optical fiber. During the fusion, the geometric center of the D-shaped optical fiber needs to coincide with the central axis of the multimode optical fiber; then the D-shaped single-mode optical fiber is cut to a fixed length of 2cm-4cm; then another section of single-mode optical fiber is coaxially fused with the multimode optical fiber, and the multimode optical fiber is cut to 1mm-2mm and fused with the other end of the D-shaped single-mode optical fiber to form a single-mode-multimode-D-shaped single-mode-multimode-single-mode optical fiber structure. Finally, the middle D-shaped single-mode optical fiber is twisted into a spiral core shape. The detailed steps are as follows: Put the fused sensor into the hydrogen-oxygen flame spiral processing machine, install the rotating fixture at one end and the magnetic fixture at the other end, and adjust the position of the sensor so that the middle of the D-shaped single-mode optical fiber is located directly below the flame nozzle. Light the flame nozzle and set it to the left and right scanning burning mode. After heating, twist the fixture. The twisted fiber core pitch is greater than 400μm, and the thread diameter is 70μm-90μm, and the sensor is completed.

[0027] Another object of the present invention is to provide a method for manufacturing an MZI strain sensor based on a spiral fiber core. When the eccentric spiral region is formed by an eccentric fiber spiral, the method for manufacturing the sensor is:

[0028] First, use Miller pliers to strip the coating on the surface of single-mode fiber and step-index multimode fiber. After cleaning with alcohol, use a fiber cleaver to cut the fiber end face flat, weld the single-mode fiber and multimode fiber face to face, and cut the multimode fiber to a fixed length of 1mm-2mm in the fiber fixed-length cutting device; use Miller pliers to strip the coating of the middle part of the eccentric fiber, and weld the eccentric fiber to a section of the multimode fiber of the spliced ​​single-mode-multimode fiber. When welding, the eccentric fiber needs to completely overlap the outer surface of the cladding of the multimode fiber, and then cut the eccentric fiber to a fixed length of 2cm-4cm; then coaxially weld another section of single-mode fiber to the multimode fiber, cut the multimode fiber to 1mm-2mm and weld it to the other end of the eccentric fiber, forming a single-mode-multimode-eccentric-core single-mode-multimode-single-mode fiber structure. Finally, the eccentric fiber in the middle is twisted into a spiral core shape. The detailed steps are as follows: put the fused sensor into the hydrogen-oxygen flame spiral processing machine, install one end into the rotating fixture, and the other end into the magnetic fixture, and adjust the position of the sensor so that the center of the eccentric fiber is located directly below the flame nozzle. Light the flame nozzle and set it to the left and right scanning burning mode. After heating, twist the fixture. The twisted fiber core pitch is greater than 400μm, and the sensor is completed.

[0029] As a preferred solution, the method of using the MZI strain sensor is as follows: the light injection area of ​​the sensor is connected to the light source, and the light receiving area is connected to the spectrometer. After the connection is completed, the two ends of the sensor are clamped in the optical fiber clamps at both ends of the strain table, and the strain table is controlled to move to both sides by the strain controller, strain is applied to the sensor, the interference wavelength under different strain states is recorded, and the actual strain size is obtained by demodulation based on the interference wavelength.

[0030] As a preferred solution, the performance adjustment method of the MZI strain sensor is as follows: for the MZI strain sensor, the length of the eccentric spiral zone of the sensor is 2cm-4cm, and the free spectral range and strain sensitivity of the interference spectrum are adjusted by changing the length of the eccentric spiral zone; the cladding of the sensor is threaded, and the diameter of the threaded cladding is 70μm-90μm, and the sensitivity of the sensor is selected by selecting the diameter of the threaded cladding; the core pitch of the eccentric spiral zone of the sensor is greater than 400μm, and the sensitivity of the sensor is adjusted by selecting the pitch of the spiral core.

[0031] The beneficial effects of the present invention are:

[0032] 1. This application increases the difference between the sensing length of the optical fiber core and the sensing length of the optical fiber cladding in the MZI sensing area, thereby increasing the difference between the path length of light propagating in the core and the path length of light propagating in the cladding, thereby achieving high sensitivity of the MZI strain sensor.

[0033] 2. The D-shaped optical fiber solution of the present application achieves high sensitivity of the MZI strain sensor by concentrating the strain in the sensing area during the strain process, thereby increasing the strain on the optical fiber sensing area.

[0034] 3. The MZI strain sensor manufactured by the present application has a difference between the core sensing length and the cladding sensing length in the sensing area. The strain sensitivity of the sensor can be increased by increasing the length of the sensing area, thereby realizing the adjustable sensitivity of the MZI strain sensor.

[0035] 4. The MZI strain sensor manufactured in the present application can use a single-mode optical fiber to be side-cast and then spirally formed into an eccentric thread structure, and does not require expensive D-shaped special optical fiber to manufacture the sensor, thereby reducing the manufacturing cost of the sensor.

[0036] 5. The MZI strain sensor made of optical fiber in this application breaks through the limitation of the material's elastic-optical coefficient on the sensitivity of the MZI strain sensor that the current sensitization method cannot break through, and further realizes the adjustable sensitivity of the strain sensor. The strain sensor, as the core element for detecting deformation, can convert mechanical strain into electrical signals through different physical effects (such as resistance, capacitance, fiber grating, etc.), and is widely used in sensors such as mechanical sensors, velocity sensors and electrical sensors. It can be integrated into medical devices, electronic chips, aerospace precision instruments, intelligent manufacturing and robots, and scenarios where the measured object has a small structure and weak strain fluctuations, for real-time and high-sensitivity strain monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0038] Figure 1 The overall composition diagram of the MZI strain sensor based on the spiral core of the present invention is shown, wherein the eccentric spiral region is formed by a D-shaped optical fiber or an eccentric core optical fiber spiral;

[0039] Figure 2 It is a schematic diagram of the strain calibration device of the present invention;

[0040] Figure 3 This is a graph showing the relationship between transmission loss and wavelength under different strain conditions of the sensor when the eccentric helical region is formed by a D-shaped optical fiber helix;

[0041] Figure 4 This is the sensor strain detection data diagram when the eccentric spiral area is formed by a D-shaped optical fiber spiral. DETAILED DESCRIPTION

[0042] 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 illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0043] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0044] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0045] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0046] The present invention can be implemented in the following ways:

[0047] like Figure 1 As shown, this embodiment provides an MZI strain sensor based on a spiral core, comprising a light injection area 1, a light splitting area 2, an eccentric spiral area 3, a light combining area 4, and a light receiving area 5 which are sequentially arranged on the optical fiber.

[0048] in, Figure 1 The light injection area 1 and the light receiving area 5 of the middle sensor are both composed of single-mode optical fibers. The core diameter of the single-mode optical fiber is 9 μm, the cladding diameter is 125 μm, and the coating diameter is 250 μm.

[0049] Among them, the splitting area 2 and the combining area 4 are both composed of step-index multimode optical fiber, the length of the multimode optical fiber is 1mm-2mm, and the preferred length in this embodiment is 1mm. The core diameter of the step-index multimode optical fiber is 105μm, the cladding diameter is 125μm, and the coating diameter is 250μm.

[0050] Among them, the length of the optical fiber in the eccentric spiral zone 3 is 2cm-4cm, preferably 2cm in this embodiment, the core is in a spiral shape, and the path length of light propagating in the core is greater than the path length of light propagating in the cladding; the spiral core of the eccentric spiral zone 3 can be formed by a D-shaped optical fiber or an eccentric optical fiber spiral.

[0051] In this embodiment, when the spiral core of the eccentric spiral region 3 is formed by the back spiral of the D-shaped optical fiber, the geometric center axes of the D-shaped optical fiber and the multimode optical fiber are completely overlapped when they are connected, and the optical fiber cladding has a threaded structure. The D-shaped optical fiber of the eccentric spiral 3 of the sensor is made by side polishing of a single-mode optical fiber, the core diameter of the single-mode optical fiber is 9μm, and the cladding diameter is 125μm. The upper half of the single-mode optical fiber is polished and removed by an optical fiber side polishing machine to form a D-shaped optical fiber, and then a spiral core structure is formed by hydrogen-oxygen flame spiral processing; the optical fiber cladding of the eccentric spiral region 3 has a threaded structure, and the thread diameter is 70μm-90μm, preferably 70μm in this embodiment. The strain sensitivity of the sensor can be adjusted by the thread diameter. The strain magnitude of the sensor sensing area increases with the decrease of the thread diameter, and the strain sensitivity of the sensor increases with the decrease of the thread diameter.

[0052] The pitch of the spiral core of the eccentric spiral region 3 is greater than 400 μm, and is preferably 485 μm in this embodiment. The strain sensitivity of the sensor can be adjusted by the pitch of the spiral core. The difference between the path length of light propagating in the core and the path length of light propagating in the cladding increases as the pitch of the spiral core decreases, and the strain sensitivity of the sensor increases as the pitch of the spiral core decreases. The pitch of the spiral core is inversely proportional to the strain sensitivity, and the strain sensitivity of the sensor is adjusted by selecting the pitch of the spiral core.

[0053] In this embodiment, when the spiral core of the eccentric spiral region 3 is formed by the back spiral of the D-shaped optical fiber, the core diameter of the eccentric optical fiber is 9 μm, the core is 30.5 μm away from the optical fiber axis, and the spiral core structure is formed by hydrogen-oxygen flame melting spiral processing.

[0054] The length of the eccentric spiral region 3 of the sensor is 3 cm, and the core is in a spiral shape. Since the spiral shape increases the path length of light propagating in the core, the path length of light propagating in the cladding remains unchanged, resulting in the path length of light propagating in the core being greater than the path length of light propagating in the cladding; the strain sensitivity of the sensor can be adjusted by the length of the eccentric spiral region 3, and the difference between the path length of light propagating in the core and the path length of light propagating in the cladding increases with the increase of the length of the eccentric spiral region, and the strain sensitivity of the sensor increases with the length of the eccentric spiral region 3.

[0055] This solution also provides a method for manufacturing the above-mentioned MZI strain sensor based on a spiral fiber core. When the eccentric spiral region 3 is formed by a D-shaped optical fiber spiral, the specific manufacturing steps are as follows:

[0056] S1: First, use Miller pliers to strip off the coating on the surface of the single-mode optical fiber and the step-index multimode optical fiber. After cleaning with alcohol, use a fiber optic cutter to cut the optical fiber end face flat, and weld the single-mode optical fiber and the multimode optical fiber directly. Use a fiber optic fixed-length cutting device to cut the multimode optical fiber to a fixed length of 1mm-2mm, preferably 1mm, to complete the connection between the light injection area 1 and the light splitting area 2.

[0057] S2: Use Miller pliers to strip the coating layer of the middle part of another single-mode optical fiber, clamp it on the bare optical fiber side polishing machine, polish and remove the upper half of the single-mode optical fiber to form a D-shaped optical fiber, polish until the short diameter of the D-shaped optical fiber is 70μm-90μm, preferably 70μm, and the length of the polishing area is set to 5cm; the polished D-shaped optical fiber is fused to one end of the multimode optical fiber of the spliced ​​single-mode-multimode optical fiber, and the central axis of the D-shaped optical fiber needs to coincide with the multimode optical fiber during fusion; then the D-shaped single-mode optical fiber is cut to a fixed length of 2cm-4cm, preferably 3cm.

[0058] S3: Then, another section of single-mode optical fiber is coaxially welded with the multi-mode optical fiber, and the multi-mode optical fiber is cut to 1mm-2mm, preferably 1mm, and welded with the other end of the D-shaped single-mode optical fiber to form a single-mode-multi-mode-D-shaped single-mode-multi-mode-single-mode structure, completing the connection between the light combining area 4 and the light receiving area 5.

[0059] S4: Finally, the D-shaped single-mode optical fiber in the middle is twisted into a spiral core shape. The detailed steps are as follows: Place the fused sensor into the hydrogen-oxygen flame spiral processing machine, install one end into the rotating fixture, and the other end into the magnetic fixture, and adjust the position of the sensor so that the middle of the D-shaped single-mode optical fiber is located directly below the flame nozzle. Light the flame nozzle and set it to the left and right scanning burning mode. Set the rotation speed of the rotating fixture to 12000μm / s, twist the fixture after heating, and the twisted fiber core pitch is greater than 400μm, preferably 485μm, and the thread diameter is 70μm-90μm, preferably 70μm, to complete the sensor.

[0060] When the eccentric helical region 3 is formed by a D-shaped optical fiber helix, the specific manufacturing steps of the manufacturing method of the MZI strain sensor based on the helical fiber core are as follows:

[0061] S1: The cutter cuts the fiber end face flat, welds the single-mode fiber and the multi-mode fiber face to face, cuts the multi-mode fiber into fixed lengths of 1mm-2mm, preferably 1mm, in the fiber fixed-length cutting device, and completes the connection between the light injection area 1 and the light splitting area 2.

[0062] S2: Use Miller pliers to strip off the coating layer of the middle part of the eccentric optical fiber, and fuse the eccentric optical fiber to a section of the multimode optical fiber of the spliced ​​single-mode-multimode optical fiber. During the fusion, the eccentric optical fiber needs to completely overlap with the outer surface of the cladding of the multimode optical fiber, and then the eccentric optical fiber is cut to a fixed length of 2cm-4cm, preferably 3cm.

[0063] S3: Then, another section of single-mode optical fiber is coaxially fused with the multi-mode optical fiber, and the multi-mode optical fiber is cut into 1mm-2mm and fused with the other end of the eccentric optical fiber to form a single-mode-multi-mode-eccentric single-mode-multi-mode-single-mode optical fiber structure.

[0064] S4: Twist the eccentric optical fiber in the middle into a spiral core shape. The detailed steps are as follows: Place the fused sensor into a hydrogen-oxygen flame spiral processing machine, install one end into a rotating fixture, and the other end into a magnetic fixture, and adjust the position of the sensor so that the middle of the eccentric optical fiber is located directly below the flame nozzle; ignite the flame nozzle, set it to the left and right scanning burning mode, twist the fixture after heating, and the twisted fiber core pitch is greater than 400μm, preferably 485μm, to complete the sensor production.

[0065] In this scheme, the sensor is subjected to a strain detection experiment. The strain detection experimental device is as follows: Figure 2 As shown, it includes a light source, a spectrometer and two optical fiber clamps. The light injection area 1 of the sensor is connected to the light source, and the light receiving area 5 is connected to the spectrometer. After the connection is completed, the two ends of the sensor are clamped in the optical fiber clamps at both ends of the strain table. The strain table is controlled to move to both sides by the strain controller, and strain is applied to the sensor. The interference wavelength under different strain states is recorded, and the actual strain size is obtained by demodulation according to the interference wavelength.

[0066] This solution also provides a method for using the MZI strain sensor based on the spiral fiber core, specifically: when the eccentric spiral region is formed by a D-shaped optical fiber spiral, the specific method for using the MZI strain sensor is: the applied strain increases from 0με to 450με, specifically as follows Figure 3 As shown. When the step size is set to 50με, the resonant wavelength of the sensor changes as follows Figure 4 As shown, as the strain at both ends of the sensor increases, its interference wavelength regularly blue-shifts; the applied strain is fitted with the resonant wavelength, and the strain sensitivity is calculated to be 27.6pm / με.

Claims

1. MZI strain sensor based on helical fiber core, characterized by: It includes a light injection area, a light splitting area, an eccentric spiral area, a light combining area, and a light collecting area which are sequentially arranged on the optical fiber; the length of the optical fiber in the eccentric spiral area is 2cm-4cm, the core is in a spiral shape, and the path length of light propagating in the core is greater than the path length of light propagating in the cladding; the spiral core of the eccentric spiral area can be formed by a D-shaped optical fiber or an eccentric optical fiber spiral, and the cladding is in a threaded or cylindrical shape; the pitch of the spiral core of the eccentric spiral area is greater than 400μm, wherein the pitch of the spiral core is inversely proportional to the strain sensitivity, and the strain sensitivity of the sensor is adjusted by selecting the pitch of the spiral core.

2. The helical core MZI strain sensor according to claim 1, characterized in that: When the eccentric spiral area is formed by a D-shaped optical fiber spiral, the geometric center axes of the D-shaped optical fiber and the multimode optical fiber in the light splitting area are completely overlapped when they are connected, and the optical fiber cladding is a threaded structure.

3. The helical core MZI strain sensor according to claim 2, characterized in that: When the eccentric spiral area of ​​the sensor is formed by a D-shaped optical fiber spiral, the D-shaped optical fiber is made by side polishing of a single-mode optical fiber, the core diameter of the single-mode optical fiber is 9μm, and the cladding diameter is 125μm. The upper half of the single-mode optical fiber is polished and removed by a fiber side polishing machine to form a D-shaped optical fiber, and then a hydrogen-oxygen flame melting spiral processing is performed to form a spiral core structure; the optical fiber cladding of the eccentric spiral area has a threaded structure, and the thread diameter is 70μm-90μm.

4. The helical core MZI strain sensor according to claim 1, characterized in that: When the eccentric helical region is formed by the eccentric optical fiber helix, the outer surfaces of the claddings of the eccentric optical fiber and the multimode optical fiber in the light splitting region are completely overlapped when the eccentric optical fiber is connected, and the optical fiber cladding is a cylindrical structure.

5. The helical core MZI strain sensor according to claim 4, characterized in that: When the eccentric spiral region of the sensor is formed by an eccentric optical fiber spiral, the core diameter of the eccentric optical fiber is 9 μm, the core is 30.5 μm away from the optical fiber axis, and the spiral core structure is formed by hydrogen-oxygen flame melting spiral processing.

6. The helical core MZI strain sensor according to claim 1, characterized in that: The sensor's light injection area and light receiving area are both composed of single-mode optical fiber, the single-mode optical fiber has a core diameter of 9μm, a cladding diameter of 125μm, and a coating diameter of 250μm; the sensor's light splitting area and light combining area are both composed of step-index multimode optical fiber, the multimode optical fiber has a length of 1mm-2mm, the step-index multimode optical fiber has a core diameter of 105μm, a cladding diameter of 125μm, and a coating diameter of 250μm.

7. A method for manufacturing the sensor as claimed in claim 1, characterized in that: When the eccentric helical region is formed by a D-shaped optical fiber helix, the manufacturing method of the sensor is: Use Miller pliers to strip the coating on the surface of the single-mode fiber and the step-index multimode fiber. After cleaning with alcohol, use a fiber cleaver to cut the fiber end face flat, weld the single-mode fiber and the multimode fiber face to face, and cut the multimode fiber to a fixed length of 1mm-2mm in the fiber fixed length cutting device; use Miller pliers to strip the coating of the middle part of another single-mode fiber, clamp it on the bare fiber side polishing machine, polish and remove the upper half of the single-mode fiber to form a D-shaped fiber, polish until the short diameter of the D-shaped fiber is 70μm-90μm, and the length of the polishing area is set to 5cm; weld the polished D-shaped fiber to the multimode fiber end of the spliced ​​single-mode-multimode fiber. When welding, the geometric center of the D-shaped fiber needs to coincide with the central axis of the multimode fiber; cut the D-shaped single-mode fiber to a fixed length. 2cm-4cm; then coaxially fuse another section of single-mode optical fiber with the multi-mode optical fiber, and cut the multi-mode optical fiber to 1mm-2mm and fuse it with the other end of the D-shaped single-mode optical fiber to form a single-mode-multi-mode-D-shaped single-mode-multi-mode-single-mode optical fiber structure; twist the middle D-shaped single-mode optical fiber into a spiral core shape. The detailed steps are as follows: put the fused sensor into the hydrogen-oxygen flame spiral processing machine, install one end into the rotating fixture, and the other end into the magnetic fixture, adjust the position of the sensor so that the middle of the D-shaped single-mode optical fiber is located directly below the flame nozzle; ignite the flame nozzle, set it to the left and right scanning burning mode, twist the fixture after heating, the twisted fiber core pitch is greater than 400μm, and the thread diameter is 70μm-90μm, and the sensor is completed.

8. A method for manufacturing the sensor as claimed in claim 1, characterized in that: When the eccentric helical region is formed by an eccentric optical fiber helix, the manufacturing method of the sensor is: Use Miller pliers to strip the coating on the surface of the single-mode fiber and the step-index multimode fiber. After cleaning with alcohol, use a fiber cleaver to cut the fiber end face flat, weld the single-mode fiber and the multimode fiber directly, and cut the multimode fiber to a fixed length of 1mm-2mm in the fiber fixed length cutting device; use Miller pliers to strip the coating of the middle part of the eccentric fiber, and weld the eccentric fiber to a section of the multimode fiber of the spliced ​​single-mode-multimode fiber. When welding, the eccentric fiber needs to completely overlap with the outer surface of the cladding of the multimode fiber, and then cut the eccentric fiber to a fixed length of 2cm-4cm; then coaxially weld another section of single-mode fiber to the multimode fiber. Then, cut the multimode optical fiber into 1mm-2mm and fuse it with the other end of the eccentric-core optical fiber to form a single-mode-multimode-eccentric-core single-mode-multimode-single-mode optical fiber structure; twist the eccentric-core optical fiber in the middle into a spiral core shape. The detailed steps are as follows: put the fused sensor into the hydrogen-oxygen flame spiral processing machine, install one end into the rotating fixture, and the other end into the magnetic fixture, adjust the position of the sensor so that the middle of the eccentric-core optical fiber is located directly below the flame nozzle; ignite the flame nozzle, set it to the left and right scanning burning mode, twist the fixture after heating, and the twisted fiber core pitch is greater than 400μm, completing the sensor.

9. A method for using the sensor as claimed in claim 1, characterized in that: The light injection area of ​​the sensor is connected to the light source, and the light receiving area is connected to the spectrometer. After the connection is completed, the two ends of the sensor are clamped in the optical fiber clamps at the two ends of the strain table. The strain table is controlled to move to both sides by the strain controller, strain is applied to the sensor, the interference wavelength under different strain states is recorded, and the actual strain size is obtained by demodulation according to the interference wavelength.

10. A method for adjusting the performance of a sensor as claimed in claim 1, characterized in that: The length of the eccentric spiral zone of the sensor is 2cm-4cm, and the free spectral range and strain sensitivity of the interference spectrum are adjusted by changing the length of the eccentric spiral zone; the cladding of the sensor is threaded, and the diameter of the threaded cladding is 70μm-90μm, and the sensitivity of the sensor is selected by selecting the diameter of the threaded cladding; the core pitch of the eccentric spiral zone of the sensor is greater than 400μm, and the sensitivity of the sensor is adjusted by selecting the pitch of the spiral core.

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