Optical lens fiber preparation method, composite sensor and pressure guide wire

Abstract

The invention relates to the technical field of optical fibers, and provides an optical lens optical fiber preparation method, a composite sensor and a pressure guide wire, and the method comprises the steps: S1, carrying out the fusion splicing of a first single-mode optical fiber and a second single-mode optical fiber, and S3, carrying out the arc discharge of the tail end of a coreless optical fiber through an optical fiber fusion splicer, so as to form a lens; s4, inserting the lens end of the coreless optical fiber into the inner cavity of the capillary optical fiber, and discharging and welding; s5, welding the multimode optical fiber and the capillary optical fiber; and S6, cutting and grinding the end face of the multimode optical fiber to form the sensitive diaphragm. During preparation, the length of the capillary optical fiber is controlled through an optical fiber lens focusing theory. According to the invention, the high-performance double-F-P cavity composite sensor can be prepared through cutting, corrosion, welding and grinding processes, so that the composite measurement of two parameters of temperature and pressure is realized, the problem of damage to the optical fiber caused by a femtosecond laser processing process is avoided, and meanwhile, the manufacturing cost of the sensor is also greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of optical fibers, and in particular to a method for preparing an optical lens optical fiber, a composite sensor and a pressure guide wire. Background Art

[0002] With the continuous development of medical technology, interventional minimally invasive surgery has been widely used with the advantages of less trauma, fewer complications and rapid recovery. As an important medical device for evaluating coronary flow reserve fraction (FFR), interventional pressure guidewire measures blood pressure in the coronary artery to assess the degree of vascular stenosis in patients, thereby assisting clinical decision-making. Therefore, accurate measurement of pressure is the key to pressure guidewires, but existing piezoelectric, resistive and other electrical sensors still have disadvantages such as poor biocompatibility and susceptibility to electromagnetic interference. The use of fiber optic sensors is one of the effective means to achieve accurate monitoring in complex vascular environments.

[0003] Fabry-Perot (FP) cavity sensors have been widely used in temperature and pressure monitoring due to their high sensitivity and stability. In order to reduce damage to the sensor and reduce the manufacturing cost of the sensor, people often use a welding and grinding process to prepare the fiber optic Fabry-Perot sensor. For example, the Chinese patent document with publication number CN113188691A provides a fiber optic Fabry-Perot sealed cavity pressure sensor and a preparation method thereof. The sensor consists of a single-mode optical fiber, a quartz capillary and a sealed cavity fixed by one-time welding, and uses CO2 laser welding technology and fine polishing technology.

[0004] Although the preparation process uses CO2 laser welding technology to reduce the cross-sensitivity of temperature and achieve accurate measurement of pressure, based on this type of traditional fiber Fabry-Perot interferometer, when the diaphragm is deformed due to external pressure, the deformation of the diaphragm will affect the quality of its reflection surface, resulting in a decrease in reflection efficiency. Moreover, the reflection surface is far away from the fiber end face, and due to the divergence of the light beam, the intensity of the reflected light will drop rapidly, resulting in a decrease in coupling efficiency. Summary of the invention

[0005] In view of this, the present invention proposes an optical lens fiber preparation method, a composite sensor and a pressure guide wire that can effectively avoid processing damage and ensure fiber performance, thereby solving the problem of affecting fiber performance in the existing fiber preparation process.

[0006] The technical solution of the present invention is achieved in this way:

[0007] In one aspect, the present invention provides a method for preparing an optical lens fiber, comprising the following steps:

[0008] S1, preparing a first single-mode optical fiber and a second single-mode optical fiber, welding the first single-mode optical fiber and the second single-mode optical fiber, and forming an air gap,

[0009] S2, welding one end of the second single-mode optical fiber away from the first single-mode optical fiber to the coreless optical fiber,

[0010] S3, using an optical fiber fusion splicer to perform arc discharge on the end of the coreless optical fiber to form a lens, thereby constituting an optical fiber lens, wherein the optical fiber lens is a semi-spherical structure;

[0011] S4, placing the coreless optical fiber and the capillary optical fiber on an optical fiber fusion splicer, inserting the lens end of the coreless optical fiber into the inner cavity of the capillary optical fiber, and performing discharge fusion splicing;

[0012] S5, preparing a multimode optical fiber, and fusing the multimode optical fiber with the capillary optical fiber by a fiber fusion splicer to form an air cavity;

[0013] S6. Cut and grind the end face of the multimode optical fiber to form a sensitive film.

[0014] During the preparation process, the length of the capillary optical fiber is controlled by the optical fiber lens focusing theory.

[0015] On the basis of the above technical solution, preferably, in step S1, the first single-mode optical fiber and the second single-mode optical fiber are cut and placed in a hydrofluoric acid solution for chemical corrosion treatment, wherein the concentration of the hydrofluoric acid solution is 40% and the corrosion time is 5 minutes;

[0016] When the first single-mode optical fiber and the second single-mode optical fiber are fused together, the discharge intensity is 85 bits, and the discharge time is 1500 ms.

[0017] On the basis of the above technical solution, preferably, the grinding of the multimode optical fiber includes the following steps:

[0018] S61. Use grinding paper with a roughness of 5 μm to roughly grind the end face of the multimode optical fiber, and simultaneously monitor the remaining length of the multimode optical fiber until the length of the multimode optical fiber is ground to 20 μm, and use dust-free paper to wipe off the residues generated during the grinding process;

[0019] S62. Use grinding paper with a roughness of 1 um to grind the multimode optical fiber to a length below 5 um to form a sensitive membrane.

[0020] On the basis of the above technical solution, preferably, the steps of controlling the length of the capillary optical fiber by the optical fiber lens focusing theory are as follows:

[0021] P1. Use the light generated by the ABCD matrix light source to perform trajectory tracking analysis. Assuming that the light beam generated by the light source is a Gaussian beam, use the matrix M LFO To correlate the output light of the single-mode fiber and the fiber lens;

[0022] P2. Obtain the ABCD matrix of the Gaussian beam propagating in the coreless fiber, fiber lens and air cavity, and obtain the system matrix M LFO ;

[0023] P3. Combine steps P1 and P2 to find the optimal focusing range d of the optical fiber lens for light. work , that is, the distance between the output beam waist of the output beam and the tip of the optical lens fiber;

[0024] P4, for the best focus range d work Solve it, combined with matrix M LFO Get the waist size ω of the light beam output by the fiber lens f ;

[0025] P5. Guide the grinding of capillary optical fiber by judging the focusing effect.

[0026] On the basis of the above technical solution, preferably, in the matrix M LFO To correlate the output light of single-mode fiber and fiber lens, the formula is as follows:

[0027]

[0028] Among them, r LFO and r SMF is the position of the light measured from the center axis of the optical fiber, r' LFO and r' SMF is the slope of the light relative to the central axis of the optical fiber.

[0029] On the basis of the above technical solution, preferably, the ABCD matrix of the Gaussian beam propagating in the coreless optical fiber, the optical fiber lens and the air cavity is:

[0030]

[0031] From the above formula, we can get the system matrix M LFO , that is, M LFO =M HCF M lens M CSF ;

[0032]

[0033] Where n1 is the refractive index of single-mode fiber and multimode fiber; d CSF is the length of the coreless optical fiber, which does not include the length of the optical fiber lens; R is the radius of the optical fiber lens; d work M is the working distance of the fiber lens; HCF is the ABCD matrix of propagation in coreless optical fiber; M lens is the ABCD matrix propagating in the fiber lens; M CSFis the ABCD matrix propagating in the air cavity;.

[0034] On the basis of the above technical solution, preferably, the optimal focusing range d work The steps to solve are as follows:

[0035] When the curvature radius of the output beam is infinite, as shown in the following formula,

[0036]

[0037] in, a is the beam parameter, characterizing the beam divergence characteristics; λ is the wavelength of light; n2 is the refractive index of the medium; ω0 is the radius of the Gaussian beam at the beam waist; A, B, C, D are the light transmission matrices, and LFO is the optical lens fiber.

[0038] Solving it, we can get d work The solution is as follows:

[0039]

[0040] Where ω0 is the beam waist radius of the input beam from the single-mode fiber, and λ is the central wavelength of the input Gaussian beam.

[0041] On the basis of the above technical solution, preferably, by d work and M LFO You can get the d work The waist size ω of the light beam output by the optical lens fiber under f ;

[0042]

[0043] When work When working within the range of d0, the output beam has a focusing effect, and the beam waist size ω f When it is at its minimum, the focusing effect is the best. This is used to guide the grinding of the capillary optical fiber. During grinding, the length of the hollow part inside the capillary optical fiber is controlled to be around d1.

[0044] Where ω0 is the radius of the Gaussian beam at the beam waist, n1 is the refractive index of the single-mode fiber and the multimode fiber, and λ is the central wavelength of the input Gaussian beam.

[0045] On the other hand, the present invention provides a composite sensor, which is prepared by the method for preparing an optical lens optical fiber according to any one of claims 1 to 8, wherein the composite sensor comprises a first single-mode optical fiber, a second single-mode optical fiber, a coreless optical fiber, a capillary optical fiber and a multimode optical fiber, wherein:

[0046] One end of the first single-mode optical fiber is fused with one end of the second single-mode optical fiber, and an air gap is formed between the first single-mode optical fiber and the second single-mode optical fiber;

[0047] One end of the second single-mode optical fiber is thermally melted to form an optical fiber lens with a semi-spherical structure, and then inserted into the capillary optical fiber;

[0048] One end of the capillary optical fiber away from the second single-mode optical fiber is fused with the multi-mode optical fiber, and an air cavity is formed between the optical fiber lens and the multi-mode optical fiber.

[0049] In another aspect, the present invention provides a pressure guide wire, comprising the composite sensor as claimed in claim 9, further comprising a head end, a spring hose, a pressure window, a first connecting tube and a second connecting tube, wherein:

[0050] The head end, the spring hose, the first connecting pipe and the second connecting pipe are connected in sequence;

[0051] The pressure window is provided on the first connecting pipe;

[0052] The composite sensor is installed inside the pressure guidewire.

[0053] The optical lens fiber preparation method, composite sensor and pressure guide wire of the present invention have the following beneficial effects compared with the prior art:

[0054] (1) Through cutting, etching, welding and grinding processes, a high-performance dual-FP cavity temperature and pressure composite sensor can be prepared to achieve composite measurement of temperature and pressure dual parameters. This avoids the problem of damage to the optical fiber itself caused by the femtosecond laser processing process, and also greatly reduces the production cost of the sensor;

[0055] (2) By adding a fiber lens structure to shape the light beam, the fiber lens can focus the incident light beam through its curvature, so that the irradiation area of ​​the light beam on the diaphragm is reduced, the light intensity is increased, and the focusing effect can improve the efficiency of the interaction between light and the diaphragm;

[0056] (3) By adding a fiber lens structure to shape the light beam, when the diaphragm is deformed due to external temperature or pressure, its position relative to the optical fiber will also change; since the shape of the fiber lens is similar to a convex lens, it can collect the light reflected back from the fiber even when the diaphragm is displaced;

[0057] (4) By adding a fiber lens structure to shape the light beam, the reflected light can be more effectively coupled back into the single-mode fiber even at long cavity lengths due to the focusing and light collection capabilities of the fiber lens; this means that even if the distance between the diaphragm and the fiber end face changes, the sensor can still capture enough optical power to generate an effective interference signal. In summary, the fiber lens design can collect and focus the reflected light, maintaining a high coupling efficiency even when the diaphragm is deformed. In this way, the sensor can operate at a longer cavity length while maintaining an effective interference signal, thereby improving the sensitivity and accuracy of the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0059] Figure 1 It is a schematic diagram of the structure of the optical lens optical fiber of the present invention;

[0060] Figure 2 It is a schematic diagram of the optical fiber focusing structure of the present invention;

[0061] Figure 3 It is a schematic diagram of the pressure guide wire structure of the present invention;

[0062] Figure 4 A flow chart of etching, welding and cutting of a single-mode optical fiber and a coreless optical fiber of the optical lens optical fiber of the present invention;

[0063] Figure 5 A flow chart of preparing a fiber lens for the coreless light of the optical lens fiber of the present invention and connecting it with a capillary fiber;

[0064] Figure 6 A flow chart of cutting, grinding and cleaning of capillary optical fiber of the optical lens optical fiber of the present invention;

[0065] Figure 7 A flow chart of cutting, grinding and fusing the multimode optical fiber of the optical lens optical fiber of the present invention with the capillary optical fiber;

[0066] In the figure: 1. first single-mode optical fiber; 2. second single-mode optical fiber; 3. coreless optical fiber; 31. optical fiber lens; 4. capillary optical fiber; 5. multimode optical fiber; 100. air gap; 200. air cavity; 101. head end; 102. spring hose; 103. pressure window; 104. first connecting tube; 105. second connecting tube. DETAILED DESCRIPTION

[0067] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] like Figure 2 As shown, the optical lens fiber of the present invention includes a first single-mode optical fiber 1, a second single-mode optical fiber 2, a coreless optical fiber 3, an optical fiber lens 31, a capillary optical fiber 4 and a multimode optical fiber 5.

[0069] The composite sensor of the present invention comprises the above-mentioned optical lens optical fiber, wherein one end of the first single-mode optical fiber 1 is fused with one end of the second single-mode optical fiber 2, and an air gap 100 is formed between the first single-mode optical fiber 1 and the second single-mode optical fiber 2; one end of the second single-mode optical fiber 2 is heat-melted to form a fiber lens 31 with a semi-spherical structure, and is inserted into the capillary optical fiber 4; one end of the capillary optical fiber 4 away from the second single-mode optical fiber 2 is fused with the multimode optical fiber 5, and an air cavity 200 is formed between the fiber lens 31 and the multimode optical fiber 5;

[0070] Specifically, the inner diameter of the capillary optical fiber 4 is 103 μm, the outer diameter is 200 μm, and the diameter of the multimode optical fiber 5 is 200 μm.

[0071] Specifically, the composite sensor is a temperature and pressure sensor, wherein the temperature measurement is realized by a FP interference cavity based on a single-mode optical fiber, the cavity being formed by an air gap 100 between a first single-mode optical fiber 1 and a second single-mode optical fiber 2, and an interface between the second single-mode optical fiber 2 and a capillary optical fiber 4;

[0072] Specifically, the pressure measurement is achieved through an FP interference cavity based on the capillary optical fiber 4 , and the cavity is an air cavity 200 , which is composed of the end face of the optical fiber lens 31 , the capillary optical fiber 4 and the multimode optical fiber 5 .

[0073] like Figure 1 As shown, the pressure guide wire of the present invention includes the above-mentioned composite sensor, and also includes a head end 101, a spring hose 102, a pressure window 103, a first connecting tube 104 and a second connecting tube 105, wherein the head end 101, the spring hose 102, the first connecting tube 104 and the second connecting tube 105 are connected in sequence; the pressure window 103 is opened on the first connecting tube 104; and the composite sensor is installed inside the pressure guide wire;

[0074] As mentioned above, the composite sensor of the present invention has the advantages of small size, anti-electromagnetic interference, biocompatibility, etc., and is applied to interventional pressure guidewires, which increases the accuracy and reliability of pressure monitoring during clinical interventional treatment and is conducive to improving surgical accuracy.

[0075] Specifically, the tip 101 is a hemispherical round head to prevent the guide wire from damaging the inner wall of the blood vessel during the pushing process;

[0076] Specifically, the spring hose 102 can not only be used for buffering, but also be bent to a desired angle to facilitate delivery into the blood vessel;

[0077] Specifically, the pressure window 103 is used for pressure detection to avoid damage to the composite sensor due to the excessive length of the connecting tube.

[0078] Specifically, by adding the structure of the fiber lens 31 to shape the light beam, due to the focusing and light collecting capabilities of the fiber lens 31, the reflected light can be more effectively coupled back into the single-mode optical fiber even at a long cavity length; this means that even if the distance between the sensor diaphragm and the optical fiber end face changes, the sensor can still capture sufficient optical power to generate an effective interference signal.

[0079] In summary, the design of the fiber lens 31 can collect and focus the reflected light, and maintain a high coupling efficiency even when the diaphragm is deformed. In this way, the sensor can operate at a longer cavity length while maintaining an effective interference signal, thereby improving the sensitivity and accuracy of the measurement.

[0080] like Figures 4 to 7 As shown, the method for preparing an optical lens optical fiber of the present invention comprises the following steps:

[0081] S1, preparing a first single-mode optical fiber 1 and a second single-mode optical fiber 2, welding the first single-mode optical fiber 1 and the second single-mode optical fiber 2, and forming an air gap 100,

[0082] Specifically, it includes: etching, placing the two cut single-mode optical fibers in a hydrofluoric acid solution for chemical etching treatment, and the two single-mode optical fibers are respectively recorded as a first single-mode optical fiber 1 and a second single-mode optical fiber 2.

[0083] S2, welding the end of the second single-mode optical fiber 2 away from the first single-mode optical fiber 1 to the coreless optical fiber 3, in this step, using an optical fiber welding machine;

[0084] Specifically, it includes: cutting, with the aid of a microscope, accurately positioning the second single-mode optical fiber 2 after fusion, and then cutting it with a fiber cleaver to reduce the length of the single-mode optical fiber;

[0085] Fusion splicing: precisely splicing one end of the cut second single-mode optical fiber 2 with the coreless optical fiber 3 to achieve a seamless connection between the two optical fibers;

[0086] Cutting: With the help of a microscope, the coreless optical fiber 3 after fusion is precisely positioned, and then cut with a fiber cleaver to reduce the length of the coreless optical fiber 3.

[0087] S3, using an optical fiber fusion splicer to perform arc discharge on the end of the coreless optical fiber 3 to form a lens, thereby forming an optical fiber lens 31, wherein the optical fiber lens 31 is a semi-spherical structure;

[0088] S4, placing the coreless optical fiber 3 and the capillary optical fiber 4 on an optical fiber fusion splicer, inserting the lens end of the coreless optical fiber 3 into the inner cavity of the capillary optical fiber 4, and performing discharge fusion splicing;

[0089] Specifically, it includes: fixing the coreless optical fiber 3 and the capillary optical fiber 4 to corresponding ends of the optical fiber fusion splicer respectively;

[0090] By manual operation, the optical fiber lens 31 of the coreless optical fiber 3 is precisely inserted into the inner cavity of the capillary optical fiber 4;

[0091] After the insertion is completed, the electric shock discharge function of the optical fiber fusion splicer is used to achieve accurate fusion of the coreless optical fiber 3 and the capillary optical fiber 4;

[0092] The diameter of the single-mode optical fiber is 125 μm, and the diameter of the capillary optical fiber 4 is 130 μm.

[0093] Specifically, it also includes: cutting, using a cutting knife to cut the end of the fused capillary optical fiber 4 away from the optical fiber lens 31 to reduce the length of the capillary optical fiber 4;

[0094] Grinding: After the capillary optical fiber 4 is cut, the cut end is finely ground using a grinder.

[0095] Cleaning: After the capillary optical fiber 4 is ground, it is cleaned with an ultrasonic cleaner; this step is to remove optical fiber powder that may be generated during the grinding process, to ensure that there is no residue on the optical fiber surface, thereby improving the cleanliness of the hollow part inside the capillary optical fiber 4.

[0096] S5, preparing a multimode optical fiber 5, and fusing the multimode optical fiber 5 with the capillary optical fiber 4 by a fiber fusion splicer to form an air cavity 200;

[0097] Specifically, it includes: cutting, using a cutting knife to cut the multimode optical fiber 5 to increase the flatness of the end surface of the multimode optical fiber 5;

[0098] Fusion: The cleaned single-mode optical fiber with the capillary optical fiber 4 and the cut multi-mode optical fiber 5 are fixed at both ends of the optical fiber fusion splicer, and the capillary optical fiber 4 is manually fed to contact the multi-mode optical fiber 5; after contact, the electrode discharge of the optical fiber fusion splicer is used to make the multi-mode optical fiber 5 and the capillary optical fiber 4 fuse with each other to form an optical fiber FP cavity, that is, the air cavity 200.

[0099] S6, cutting and grinding the end face of the multimode optical fiber 5 to form a sensitive film;

[0100] Specifically, it includes: cutting, cutting the fused multimode optical fiber 5 to reduce the length of the multimode optical fiber 5;

[0101] Grinding: Grinding the end face of the multimode optical fiber 5 after cutting using a grinder, so that the multimode optical fiber 5 forms a sensitive film.

[0102] In the preparation process, the length of the capillary optical fiber 4 is controlled by the optical fiber lens focusing theory. This step is intended to further reduce the length of the capillary optical fiber 4 and significantly improve the flatness of its end face. By precisely controlling the grinding process, the optical fiber end face is ensured to achieve the required smoothness and parallelism, thereby optimizing the optical performance of the optical fiber and ensuring the reliability of the connection.

[0103] In step S1, the first single-mode optical fiber 1 and the second single-mode optical fiber 2 are cut and placed in a hydrofluoric acid solution for chemical etching, wherein the concentration of the hydrofluoric acid solution is 40% and the etching time is 5 minutes;

[0104] As mentioned above, in the structure of single-mode optical fiber, the chemical composition of the core and cladding is usually slightly different. The core is usually made of doped quartz glass such as germanium to increase the refractive index, while the cladding is made of quartz glass with higher purity. This difference in composition makes the corrosion rate of the core and cladding different when they are in contact with hydrofluoric acid solution. The corrosion rate of the core will be slightly faster than that of the cladding; therefore, it is necessary to accurately control the concentration of the hydrofluoric acid solution and the corrosion time.

[0105] When the first single-mode optical fiber 1 and the second single-mode optical fiber 2 are fused, the discharge intensity is 85 bits and the discharge time is 1500ms;

[0106] As mentioned above, after fusion splicing, the micro air gap 100 between the first single-mode optical fiber 1 and the second single-mode optical fiber 2 acts as a first reflector. When the light source enters the interference cavity, it will be reflected at both ends of the micro air gap 100, namely, the end of the first single-mode optical fiber 1 and the inner surface of the second single-mode optical fiber 2, thereby causing interference.

[0107] Specifically, when preparing the optical fiber lens 31 of the coreless optical fiber 3, the heat generated by the electric arc will melt the glass material at the end 204 of the coreless optical fiber;

[0108] By precisely controlling the time and power of the arc discharge, the molten portion at the end of the coreless optical fiber 3 will form a desired curvature during the cooling process, thereby forming a lens; this lens can focus the incident light and improve the coupling efficiency of the reflected light.

[0109] The grinding of the multimode optical fiber 5 comprises the following steps:

[0110] S61, using grinding paper with a roughness of 5 μm to roughly grind the end face of the multimode optical fiber 5, and simultaneously monitoring the remaining length of the multimode optical fiber 5 until the length of the multimode optical fiber 5 is ground to 20 μm, and using dust-free paper to wipe off the residues generated during the grinding process;

[0111] S62, use grinding paper with a roughness of 1 um to grind the multimode optical fiber 5, and grind its length to less than 5 um to form a sensitive membrane.

[0112] like Figure 3 As shown, the steps of controlling the length of the capillary optical fiber 4 by the optical fiber lens focusing theory are as follows:

[0113] P1. Use the light generated by the ABCD matrix light source to perform trajectory tracking analysis. Assuming that the light generated by the light source is a Gaussian beam, use the matrix M LFO To correlate the output light of the single-mode fiber and the fiber lens;

[0114] P2. Obtain the ABCD matrix of the Gaussian beam propagating in the coreless optical fiber 3, the optical fiber lens 31 and the air cavity 200, and obtain the system matrix M LFO ;

[0115] P3. Combine steps P1 and P2 to find the optimal focusing range d of the optical fiber lens for light. work , that is, the distance between the output beam waist of the output beam and the tip of the optical lens fiber;

[0116] P4, for the best focus range d work Solve it, combined with matrix M LFO Get the waist size ω of the light beam output by the fiber lens f , at the beam waist size ω f When it is smallest, the focusing effect is best;

[0117] PS. By judging the focusing effect, the grinding work of the capillary optical fiber 4 is guided.

[0118] In the matrix M LFO To correlate the output light of single-mode fiber and fiber lens, the formula is as follows:

[0119]

[0120] Among them, rLFO and r SMF is the position of the light measured from the center axis of the optical fiber, r' LFO and r' SMF is the slope of the light relative to the central axis of the optical fiber.

[0121] The ABCD matrix of the Gaussian beam propagating in the coreless optical fiber 3, the optical fiber lens 31 and the air cavity 200 is:

[0122]

[0123] From the above formula, we can get the system matrix M LFO , that is, M LFO =M HCF M lens M CSF ;

[0124]

[0125] Wherein, n1 is the refractive index of the single-mode optical fiber and the multimode optical fiber 5; d CSF is the length of the coreless optical fiber 3, which does not include the length of the optical fiber lens 31; R is the radius of the optical fiber lens 31; d work is the working distance of the optical fiber lens 31; M HCF is the ABCD matrix propagating in the coreless optical fiber 3; M lens is the ABCD matrix propagating in the optical fiber lens 31; M CSF is the ABCD matrix propagating in the air cavity 200;.

[0126] For the best focus range d work The steps to solve are as follows:

[0127] When the curvature radius of the output beam is infinite, as shown in the following formula,

[0128]

[0129] in, a is the beam parameter, characterizing the beam divergence characteristics; λ is the wavelength of light; n2 is the refractive index of the medium; ω0 is the radius of the Gaussian beam at the beam waist; A, B, C, D are the light transmission matrices, and LFO is the optical lens fiber.

[0130] Solving it, we can get d work The solution is as follows:

[0131]

[0132] Where ω0 is the beam waist radius of the input beam from the single-mode fiber, and λ is the central wavelength of the input Gaussian beam.

[0133] By d work and M LFO You can get the d work The waist size ω of the light beam output by the optical lens fiber under f ;

[0134]

[0135] When work When working within the range of d0, the output beam has a focusing effect, and the beam waist size ω f When the minimum, the focusing effect is the best; the incident light is focused onto the diaphragm through the lens fiber, which can increase the optical power density of the light beam on the diaphragm, thereby improving the sensitivity of the sensor to pressure changes. This has a guiding role in the subsequent grinding of the capillary fiber 4, that is, when grinding, the length of the hollow part inside the capillary fiber 4 is controlled to be around d1;

[0136] Wherein, ω0 is the radius of the Gaussian beam at the beam waist, n1 is the refractive index of the single-mode fiber and the multimode fiber 5, and λ is the central wavelength of the input Gaussian beam.

[0137] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an optical lens optical fiber, characterized in that: The following steps are involved: S1, preparing a first single-mode optical fiber (1) and a second single-mode optical fiber (2), fusing the first single-mode optical fiber (1) and the second single-mode optical fiber (2), and forming an air gap (100), S2, fusing one end of the second single-mode optical fiber (2) away from the first single-mode optical fiber (1) with the coreless optical fiber (3), S3, using an optical fiber fusion splicer to perform arc discharge on the end of the coreless optical fiber (3) to form a lens, thereby forming an optical fiber lens (31), wherein the optical fiber lens (31) is a semi-spherical structure; S4, placing the coreless optical fiber (3) and the capillary optical fiber (4) on an optical fiber fusion splicer, inserting the lens end of the coreless optical fiber (3) into the inner cavity of the capillary optical fiber (4), and performing discharge fusion splicing; S5, preparing a multimode optical fiber (5), and fusing the multimode optical fiber (5) and the capillary optical fiber (4) using an optical fiber fusion splicer to form an air cavity (200); S6. Cutting and grinding the end face of the multimode optical fiber (5) to form a sensitive film. During the preparation process, the length of the capillary optical fiber (4) is controlled by the optical fiber lens focusing theory.

2. The method for preparing an optical lens fiber according to claim 1, characterized in that: In the step S1, the first single-mode optical fiber (1) and the second single-mode optical fiber (2) are cut and placed in a hydrofluoric acid solution for chemical etching, wherein the concentration of the hydrofluoric acid solution is 40% and the etching time is 5 minutes; When the first single-mode optical fiber (1) and the second single-mode optical fiber (2) are fused together, the discharge intensity is 85 bits and the discharge time is 1500 ms.

3. The method for preparing an optical lens fiber according to claim 1, characterized in that: The grinding of the multimode optical fiber (5) comprises the following steps: S61, using grinding paper with a roughness of 5 μm to roughly grind the end face of the multimode optical fiber (5), and simultaneously monitoring the remaining length of the multimode optical fiber (5), until the length of the multimode optical fiber (5) is ground to 20 μm, and using dust-free paper to wipe off the residues generated during the grinding process; S62, using grinding paper with a roughness of 1 um to grind the multimode optical fiber (5), grinding its length to less than 5 um to form a sensitive membrane.

4. The method for preparing an optical lens fiber according to any one of claims 1 to 3, characterized in that: The steps of controlling the length of the capillary optical fiber (4) by the optical fiber lens focusing theory are as follows: P1. Use the light generated by the ABCD matrix light source to perform trajectory tracking analysis. Assuming that the light beam generated by the light source is a Gaussian beam, use the matrix M LFO to associate the output light of the single-mode optical fiber and the optical fiber lens (31); P2. Obtain the ABCD matrix of the Gaussian light beam propagating in the coreless optical fiber (3), the optical fiber lens (31) and the air cavity (200), and obtain the system matrix M LFO ; P3. Combine steps P1 and P2 to find the optimal focusing range d of the optical fiber lens (31) for the light beam. work , that is, the distance between the output beam waist of the output beam and the tip of the optical lens fiber; P4, for the best focus range d work Solve it, combined with matrix M LFO Obtain the waist size ω of the light beam output by the optical fiber lens (31) f ; P5. By judging the focusing effect, the grinding work of the capillary optical fiber (4) is guided.

5. The method for preparing an optical lens fiber according to claim 4, characterized in that: In the matrix M LFO To correlate the output light of the single-mode optical fiber and the optical fiber lens (31), the formula is as follows: Among them, r LFO and r SMF is the position of the light measured from the central axis of the optical fiber, r′ LFO and r' SMF is the slope of the light relative to the central axis of the optical fiber.

6. The method for preparing an optical lens fiber according to claim 5, characterized in that: The ABCD matrix of the Gaussian light beam propagating in the coreless optical fiber (3), the optical fiber lens (31) and the air cavity (200) is: From the above formula, we can get the system matrix M LFO , that is, M LFO =M HCF M lens M CSF ; Where n1 is the refractive index of single-mode fiber and multimode fiber; d CSF is the length of the coreless optical fiber (3), which does not include the length of the optical fiber lens (31); R is the radius of the optical fiber lens (31); d work M is the working distance of the optical fiber lens (31); HCF is the ABCD matrix propagating in the coreless optical fiber (3); M lens is the ABCD matrix propagating in the optical fiber lens (31); M CSF is the ABCD matrix propagating in the air cavity (200);.

7. The method for preparing an optical lens fiber according to claim 6, wherein: For the best focus range d work The steps to solve are as follows: When the curvature radius of the output beam is infinite, as shown in the following formula, in, a is the beam parameter, characterizing the beam divergence characteristics; λ is the wavelength of light; n2 is the refractive index of the medium; ω0 is the radius of the Gaussian beam at the beam waist; A, B, C, D are the light transmission matrices, LFO is the optical lens fiber, and π is the pi. Solving it, we can get d work The solution is as follows: Where ω0 is the beam waist radius of the input beam from the single-mode fiber, and λ is the central wavelength of the input Gaussian beam.

8. The method for preparing an optical lens fiber according to claim 7, characterized in that: By d work and M LFO You can get the d work The waist size ω of the light beam output by the optical lens fiber under f ; When work When working within the range of d0, it has a focusing effect on the output beam, and the beam waist size ω f When the value is the smallest, the focusing effect is the best. This is used to guide the grinding of the capillary optical fiber (4). During grinding, the length of the hollow part inside the capillary optical fiber (4) is controlled to be around d1. Wherein, ω0 is the radius of the Gaussian beam at the beam waist, n1 is the refractive index of the single-mode optical fiber and the multimode optical fiber (5), and λ is the central wavelength of the input Gaussian beam.

9. A composite sensor, characterized in that: The composite sensor is manufactured by the method for preparing an optical lens optical fiber according to any one of claims 1 to 8, wherein the composite sensor comprises the first single-mode optical fiber (1), the second single-mode optical fiber (2), the coreless optical fiber (3), the capillary optical fiber (4) and a multimode optical fiber (5), wherein: One end of the first single-mode optical fiber (1) is fused with one end of the second single-mode optical fiber (2), and the air gap (100) is formed between the first single-mode optical fiber (1) and the second single-mode optical fiber (2); One end of the second single-mode optical fiber (2) is melted to form the optical fiber lens (31) with a semi-spherical structure, and is inserted into the capillary optical fiber (4); One end of the capillary optical fiber (4) away from the second single-mode optical fiber (2) is fused to the multimode optical fiber (5), and the air cavity (200) is formed between the optical fiber lens (31) and the multimode optical fiber (5).

10. A pressure guide wire, characterized in that: The composite sensor according to claim 9 further comprises a head end (101), a spring hose (102), a pressure window (103), a first connecting tube (104) and a second connecting tube (105), wherein: The head end (101), the spring hose (102), the first connecting pipe (104) and the second connecting pipe (105) are connected in sequence; The pressure window (103) is opened on the first connecting pipe (104); The composite sensor is installed inside the pressure guide wire.

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