Polymer waveguide grating based syringe type ultrasonic sensor and preparation method thereof

Abstract

The application discloses an injector type ultrasonic sensor based on a polymer waveguide grating and a preparation method thereof, relates to the technical field of ultrasonic sensors, and is characterized in that a Bragg grating is inscribed on a suspended polymer waveguide to form a polymer waveguide grating; the polymer waveguide grating is connected with a single-mode optical fiber in a core-to-core mode to form an injector type structure; the end face of the single-mode optical fiber and the surface of the polymer waveguide of the injector type structure are coated with waterproof glue to form an injector type ultrasonic sensor; the application provides an injector type ultrasonic sensor based on a polymer waveguide grating for ultrasonic detection of a seismic physical model, overcomes the problem of insufficient sensitivity caused by high Young's modulus and a large sensing diameter of an existing optical fiber ultrasonic sensor, and realizes ultrahigh sensitivity detection of weak echoes of a seismic physical model.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic sensor technology, specifically to a syringe-type ultrasonic sensor based on a polymer waveguide grating and its fabrication method. Background Technology

[0002] Earthquake physical model ultrasonic imaging technology is a seismic simulation method that uses ultrasonic waves to perform forward modeling of seismic exploration work in the laboratory, based on a certain simulation similarity ratio to create a geological model of the geological structures and bodies in the field. The core device in earthquake physical model research is the ultrasonic transducer. Currently, electrical ultrasonic transducers have disadvantages such as narrow bandwidth, susceptibility to electromagnetic interference, insufficient sensitivity, and inconvenience of use. Fiber optic ultrasonic sensors, due to their high sensitivity, wide bandwidth response, small size, and strong resistance to electromagnetic interference, are gradually replacing electrical ultrasonic transducers. Among them, suspended-core fiber ultrasonic sensors can be used for high-sensitivity ultrasonic detection due to their small sensing diameter, but the high Young's modulus of suspended-core fibers (about 70 GPa for quartz fiber) limits their response sensitivity to ultrasonic strain. In addition, polymer fiber ultrasonic sensors have a low Young's modulus, and their large sensing diameter limits the detection resolution and response sensitivity. Therefore, the sensitivity of the sensor can be further improved by constructing small-diameter, low-Young's modulus fibers or waveguides, achieving ultra-high sensitivity ultrasonic detection.

[0003] The suspended or levitated fiber optic sensors developed in OpticsExpress 2018, 26(8), 10820-10832, OpticsExpress 2022, 30(10), 16384-16395, AppliedOptics 2019, 58(13), 3331-3337, and invention patent application 202110223307.8 all exhibit high response sensitivity due to their relatively thin sensing diameter. However, the sensing fiber material is quartz, and quartz fiber has a large Young's mode. The low modulus (approximately 70 GPa) is detrimental to further improving the sensitivity of suspended or levitated fiber optic sensors. The polymer fiber developed in the Journal of Lightwave Technology 2022, 40(15), 5294-5299 exhibits low Young's modulus (MPa level) and good response to ultrasonic strain. However, the polymer waveguide embedded in the capillary has a large diameter (150 μm), which is detrimental to improving sensor sensitivity. Furthermore, sensor fabrication requires fiber nesting and bonding, resulting in insufficient sensor stability. Therefore, a syringe-type ultrasonic sensor based on a polymer waveguide grating and its fabrication method are proposed to address these issues. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a syringe-type ultrasonic sensor based on a polymer waveguide grating and its fabrication method, solving the problem that the high Young's modulus and large sensing size of existing fiber optic ultrasonic sensors are detrimental to sensitivity improvement.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A polymer waveguide comprising: a hollow capillary optical fiber and a polymer adhesive placed in an air hole in the hollow capillary optical fiber; the inner diameter of the capillary optical fiber is 5–15 μm;

[0007] A single-mode optical fiber, which is core-connected to the polymer waveguide;

[0008] A Bragg grating is etched onto the polymer waveguide.

[0009] Furthermore, a method for fabricating a syringe-type ultrasonic sensor based on a polymer waveguide grating includes the following steps:

[0010] Hollow capillary optical fibers with an inner diameter of 5–15 μm are used, and a certain amount of polymer glue is drawn into the air holes of the capillary optical fibers to form a uniform polymer waveguide structure.

[0011] By cutting one end of a capillary fiber filled with polymer colloid flat and then splicing it core-to-core with a section of single-mode fiber with a flat end face, a cascade structure of single-mode fiber and capillary fiber filled with polymer colloid is formed.

[0012] The capillary optical fiber filled with polymer colloid in the cascaded structure is cut again, and the remaining capillary optical fiber after cutting is filled with polymer waveguide of the same length.

[0013] A Bragg grating is inscribed on a polymer waveguide to form a polymer waveguide grating;

[0014] A suspended polymer waveguide grating is obtained by etching a capillary optical fiber filled with a polymer waveguide grating, forming a syringe-type structure.

[0015] Furthermore, the length of the remaining capillary optical fiber in the cascaded structure is 500μm to 1mm.

[0016] Furthermore, the length of the polymer waveguide is 500 μm to 1 mm.

[0017] Furthermore, the Bragg light is inscribed on the polymer waveguide using a femtosecond laser point-by-point inscription method.

[0018] Furthermore, the length of the Bragg grating is the same as the length of the polymer waveguide.

[0019] Furthermore, the etching of the capillary optical fiber filled with polymer waveguide grating is performed by immersion in an acid solution.

[0020] Furthermore, a waterproof adhesive is applied to the single-mode fiber end face and the polymer waveguide surface of the syringe-type structure.

[0021] Furthermore, a waterproof adhesive is applied to the end face of the single-mode fiber and the surface of the polymer waveguide using a pull-out method.

[0022] This invention provides a syringe-type ultrasonic sensor based on a polymer waveguide grating, which has the following advantages:

[0023] 1. The sensing diameter of this invention is in the range of several micrometers. The extremely small sensing diameter can greatly improve the sensor's response sensitivity to ultrasonic strain.

[0024] 2. The sensing material of this invention is a polymer colloid with low Young's modulus, which has a better response to ultrasonic strain than traditional quartz optical fiber.

[0025] 3. This invention provides a syringe-type ultrasonic sensor based on a polymer waveguide grating for ultrasonic detection of earthquake physical models. It overcomes the problem of insufficient sensitivity caused by the high Young's modulus and large sensing size of existing fiber optic ultrasonic sensors, and achieves ultra-high sensitivity detection of weak echoes from earthquake physical models. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a structure according to an embodiment of the present invention;

[0027] Figure 2 A diagram of a test system used to test the present invention;

[0028] Figure 3 The image shows the reflection spectrum of a syringe-type ultrasonic sensor based on a polymer waveguide grating.

[0029] Figure 4 This is an ultrasonic signal diagram of a syringe-type ultrasonic sensor based on a polymer waveguide grating.

[0030] In the diagram: 1-polymer waveguide, 2-Bracket grating, 3-single-mode fiber, 4-waterproof adhesive. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] Please see Figure 1-4 The technical solution provided by this invention:

[0033] A syringe-type ultrasonic sensor based on a polymer waveguide grating is composed of a polymer waveguide 1, a Bragg grating 2, a single-mode optical fiber 3, and a waterproof adhesive 4 connected together (e.g., Figure 1 As shown in the figure, a Bragg grating 2 is inscribed on the suspended polymer waveguide 1 to form a polymer waveguide grating; the polymer waveguide grating is core-connected with a single-mode fiber 3 to form a syringe-type structure; waterproof adhesive 4 is applied to the end face of the single-mode fiber 3 and the surface of the polymer waveguide 1 in the syringe-type structure.

[0034] The sensing laser is transmitted to the polymer waveguide grating via a single-mode fiber 3. When the sensing laser is transmitted in the Bragg grating 2, part of the sensing laser is reflected. The reflected laser is coupled back to the single-mode fiber 3 for output, forming the reflection spectrum of the polymer waveguide grating. The ultrasonic wave acts on the suspended polymer waveguide grating, causing changes in the optical parameters of the Bragg grating 2 inscribed on it, which in turn causes the reflection spectrum of the polymer waveguide grating to drift. Therefore, the ultrasonic signal can be detected by detecting the change in the reflection spectrum.

[0035] A method for fabricating a syringe-type ultrasonic sensor based on a polymer waveguide grating includes the following fabrication steps:

[0036] S1. Select a hollow capillary optical fiber with an inner diameter of 5-15 μm. Utilize the capillary effect to draw a certain amount of polymer adhesive (such as transparent photocurable adhesive) into the air hole of the capillary optical fiber. After the polymer adhesive in the air hole has fully cured, a uniform polymer waveguide structure is formed.

[0037] S2. Cut one end of the capillary fiber filled with polymer colloid flat, and then splice this flattened end face with a single-mode fiber 3 with a flat end face to form a cascade structure of single-mode fiber 3 and capillary fiber filled with polymer colloid.

[0038] S3. The capillary fiber filled with polymer colloid in the cascade structure is cut again. After the cutting is completed, the length of the remaining capillary fiber in the cascade structure is 500μm to 1mm, and it is filled with polymer waveguide 1 of the same length.

[0039] S4. Using a femtosecond laser point-by-point writing method, a Bragg grating 2 is written on the polymer waveguide 1. The length of the Bragg grating 2 is the same as the length of the polymer waveguide 1, i.e., 500μm to 1mm, to form a polymer waveguide grating.

[0040] S5. Immerse the capillary optical fiber filled with polymer waveguide grating into an acid solution. By controlling the immersion depth, make it just submerged in the acid solution. Since the capillary optical fiber is susceptible to acid corrosion, while the polymer waveguide 1 has acid and alkali resistance, a suspended polymer waveguide grating can be obtained after corrosion, forming a syringe-type structure.

[0041] S6. Immerse the syringe-type structure in waterproof adhesive. Apply waterproof adhesive 4 to the end face of the single-mode fiber 3 and the surface of the polymer waveguide 1 by lifting method. Waterproof adhesive 4 has both waterproof function and can improve the stability of the syringe-type structure.

[0042] Example 1:

[0043] S1. Select a hollow capillary optical fiber with an inner diameter of 5μm. Utilize the capillary effect to draw a certain amount of polymer adhesive (such as transparent photocurable adhesive) into the air hole of the capillary optical fiber. After the polymer adhesive in the air hole has fully cured, a uniform polymer waveguide structure is formed.

[0044] S2. Cut one end of the capillary fiber filled with polymer colloid flat, and then splice this flattened end face with a single-mode fiber 3 with a flat end face to form a cascade structure of single-mode fiber 3 and capillary fiber filled with polymer colloid.

[0045] S3. The capillary fiber filled with polymer colloid in the cascade structure is cut again. After the cutting is completed, the remaining capillary fiber in the cascade structure is 500 μm long and is filled with polymer waveguide 1 of the same length.

[0046] S4. Using a femtosecond laser point-by-point writing method, a Bragg grating 2 is written on the polymer waveguide 1. The length of the Bragg grating 2 is the same as the length of the polymer waveguide 1, i.e., 500 μm, to form a polymer waveguide grating.

[0047] S5. Immerse the capillary optical fiber filled with polymer waveguide grating into an acid solution. By controlling the immersion depth, make it just submerged in the acid solution. Since the capillary optical fiber is susceptible to acid corrosion, while the polymer waveguide 1 has acid and alkali resistance, a suspended polymer waveguide grating can be obtained after corrosion, forming a syringe-type structure.

[0048] S6. Immerse the syringe-type structure in waterproof adhesive. Apply waterproof adhesive 4 to the end face of the single-mode fiber 3 and the surface of the polymer waveguide 1 by lifting method. Waterproof adhesive 4 has both waterproof function and can improve the stability of the syringe-type structure.

[0049] Example 2:

[0050] S1. Select a hollow capillary optical fiber with an inner diameter of 15μm. Utilize the capillary effect to draw a certain amount of polymer adhesive (such as transparent photocurable adhesive) into the air hole of the capillary optical fiber. After the polymer adhesive in the air hole has fully cured, a uniform polymer waveguide structure is formed.

[0051] S2. Cut one end of the capillary fiber filled with polymer colloid flat, and then splice this flattened end face with a single-mode fiber 3 with a flat end face to form a cascade structure of single-mode fiber 3 and capillary fiber filled with polymer colloid.

[0052] S3. The capillary fiber filled with polymer colloid in the cascade structure is cut again. After the cutting is completed, the remaining capillary fiber in the cascade structure is 1 mm in length and is filled with polymer waveguide 1 of the same length.

[0053] S4. Using a femtosecond laser point-by-point writing method, a Bragg grating 2 is written on the polymer waveguide 1. The length of the Bragg grating 2 is the same as the length of the polymer waveguide 1, i.e., 1 mm, to form a polymer waveguide grating.

[0054] S5. Immerse the capillary optical fiber filled with polymer waveguide grating into an acid solution. By controlling the immersion depth, make it just submerged in the acid solution. Since the capillary optical fiber is susceptible to acid corrosion, while the polymer waveguide 1 has acid and alkali resistance, a suspended polymer waveguide grating can be obtained after corrosion, forming a syringe-type structure.

[0055] S6. Immerse the syringe-type structure in waterproof adhesive. Apply waterproof adhesive 4 to the end face of the single-mode fiber 3 and the surface of the polymer waveguide 1 by lifting method. Waterproof adhesive 4 has both waterproof function and can improve the stability of the syringe-type structure.

[0056] Example 3:

[0057] S1. Select a hollow capillary optical fiber with an inner diameter of 10μm. Utilize the capillary effect to draw a certain amount of polymer adhesive (such as transparent photocurable adhesive) into the air hole of the capillary optical fiber. After the polymer adhesive in the air hole has fully cured, a uniform polymer waveguide structure is formed.

[0058] S2. Cut one end of the capillary fiber filled with polymer colloid flat, and then splice this flattened end face with a single-mode fiber 3 with a flat end face to form a cascade structure of single-mode fiber 3 and capillary fiber filled with polymer colloid.

[0059] S3. The capillary fiber filled with polymer colloid in the cascade structure is cut again. After the cutting is completed, the length of the remaining capillary fiber in the cascade structure is 610μm, and it is filled with polymer waveguide 1 of the same length.

[0060] S4. Using femtosecond laser point-by-point writing method, Bragg grating 2 is written on polymer waveguide 1. The length of Bragg grating 2 is the same as the length of polymer waveguide 1, i.e., 610μm, to form polymer waveguide grating.

[0061] S5. Immerse the capillary optical fiber filled with polymer waveguide grating into an acid solution. By controlling the immersion depth, make it just submerged in the acid solution. Since the capillary optical fiber is susceptible to acid corrosion, while the polymer waveguide 1 has acid and alkali resistance, a suspended polymer waveguide grating can be obtained after corrosion, forming a syringe-type structure.

[0062] S6. Immerse the syringe-type structure in waterproof adhesive. Apply waterproof adhesive 4 to the end face of the single-mode fiber 3 and the surface of the polymer waveguide 1 by lifting method. Waterproof adhesive 4 has both waterproof function and can improve the stability of the syringe-type structure.

[0063] To verify the beneficial effects of the present invention, an experimental test was conducted using the syringe-type ultrasonic sensor based on a polymer waveguide grating prepared in Example 3 of the present invention:

[0064] like Figure 2 As shown, an ultrasonic generator drives a piezoelectric ultrasonic transducer as the ultrasonic excitation source; a tunable laser is used as the transmission laser source. The sensing laser emitted from the tunable laser is guided into a single-mode fiber 3 via a fiber circulator. The sensing laser is transmitted to a polymer waveguide grating via the single-mode fiber 3. Part of the sensing laser is reflected by a Bragg grating 2, and the reflected laser is coupled back to the single-mode fiber 3 for output. The ultrasonic wave acts on the suspended polymer waveguide grating, causing changes in the optical parameters of the Bragg grating 2 inscribed on it, which in turn causes a shift in the reflection spectrum of the polymer waveguide grating. The reflection spectrum is shown in the figure. Figure 3 As shown, the spectral change information modulated by ultrasound is again fed into a photodetector via an optical fiber circulator, converting the optical signal into an electrical signal. Finally, an oscilloscope is used to acquire the electrical signal. The experimental results are as follows: Figure 4 As shown.

[0065] like Figure 4 As shown, the syringe-type ultrasonic sensor based on polymer waveguide grating detected a 1MHz ultrasonic signal. The sinusoidal signal was smooth and undistorted, while the pulse signal exhibited high signal-to-noise ratio and low resonance characteristics. Experimental results demonstrate that this invention improves sensor sensitivity by constructing a low-Young's modulus waveguide with a small diameter, achieving ultra-high sensitivity ultrasonic detection. This meets the requirements of seismic physics models for sensing weak echoes and has broad application prospects in fields such as oil and gas exploration, microseismic monitoring, and rock engineering.

[0066] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A syringe-type ultrasonic sensor based on a polymer waveguide grating, characterized in that, include: Polymer waveguide (1), comprising: hollow capillary optical fiber and polymer adhesive placed in the air hole of the hollow capillary optical fiber; the inner diameter of the capillary optical fiber is 5~15μm; A single-mode optical fiber (3) is core-connected to the polymer waveguide (1); A Bragg grating (2) is etched on the polymer waveguide (1); The method for preparing the syringe-type ultrasonic sensor includes the following steps: The polymer adhesive is drawn into the air hole of the capillary optical fiber to form a uniform polymer waveguide structure. The inner diameter of the capillary optical fiber is 5~15μm. One end of the capillary fiber filled with polymer colloid is core-spliced ​​with the single-mode fiber (3) to form a cascade structure of the single-mode fiber (3) and the capillary fiber filled with polymer colloid; the capillary fiber filled with polymer waveguide grating is etched by immersion in an acid solution. A Bragg grating (2) is inscribed on the polymer waveguide (1) in the cascaded structure to form a polymer waveguide grating; A suspended polymer waveguide grating is obtained by etching a capillary optical fiber filled with a polymer waveguide grating, forming a syringe-type structure.

2. The syringe-type ultrasonic sensor based on a polymer waveguide grating according to claim 1, characterized in that, The Bragg grating (2) is inscribed on the polymer waveguide (1) using a femtosecond laser point-by-point inscription method.

3. The syringe-type ultrasonic sensor based on a polymer waveguide grating according to claim 1, characterized in that, The length of the Bragg grating (2) is the same as the length of the polymer waveguide (1).

4. The syringe-type ultrasonic sensor based on a polymer waveguide grating according to claim 1, characterized in that, Waterproof adhesive (4) is applied to the end face of the single-mode optical fiber (3) and the surface of the polymer waveguide (1) in the syringe-type structure.

5. A syringe-type ultrasonic sensor based on a polymer waveguide grating according to claim 4, characterized in that, Waterproof adhesive (4) is applied to the end face of the single-mode fiber (3) and the surface of the polymer waveguide (1) using the pull-up method.

6. The syringe-type ultrasonic sensor based on a polymer waveguide grating according to claim 1, characterized in that, The length of the remaining capillary fiber after cutting the capillary fiber filled with polymer colloid in the cascaded structure is a preset length, which is 500μm~1mm.

Images