Cascade FP cavity vernier effect mechanical sensor and system based on optical fiber

Abstract

The invention provides an optical fiber-based cascaded FP cavity vernier effect mechanical sensor and system, the optical fiber-based cascaded FP cavity vernier effect mechanical sensor comprises a single-mode optical fiber and a 3D micro-nano structure, the 3D micro-nano structure comprises a disc base, a connecting spring and a cylindrical FP cavity, the disc base and the cylindrical FP cavity are connected through the connecting spring to form an adjustable air FP cavity, and the adjustable air FP cavity is connected with the single-mode optical fiber. The adjustable air FP cavity and the cylindrical FP cavity form a cascade FP cavity, one outer wall of the disc base or the outer wall of the cylindrical FP cavity is selected to be connected with the single-mode optical fiber, and the other outer wall receives the action of a force to be measured; the linear response range of the cascaded FP cavity is expanded through the response range of the connecting spring, and high-precision and high-sensitivity mechanical measurement in the expanded range is realized in combination with the vernier effect of the cascaded FP cavity. The cascaded FP cavity vernier effect mechanical sensor based on the optical fiber and the system have high-precision and high-sensitivity mechanical detection in a larger linear response range.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber sensors, and in particular to an optical fiber-based cascaded FP cavity vernier effect mechanical sensor and system. Background Art

[0002] In the field of optics, such as the measurement of light manipulation force, in the field of life sciences, such as the measurement of cell stretching force and gravity, and in the field of materials science, such as the detection of mechanical properties of metamechanical materials, extremely high requirements are placed on the accuracy of mechanical sensors. For example, the force used to stretch cells in cell detection needs to be at the nanonewton level, and the exquisitely designed curved dome-type metamechanical materials can withstand the highest pressure at the millinewton level. For example, the driving force of the gold sheet attached to the surface of the optical fiber is in the range of about piconewtons to micronewtons. Therefore, many fields have an urgent need for high-precision mechanical sensors.

[0003] Optical fiber has the advantages of low attenuation, strong anti-interference, long service life and stable transmission quality. The vernier effect generated by the cascaded FP structure for mechanical sensing has higher measurement accuracy than using a single FP cavity. Therefore, the optical fiber-based cascade FP cavity vernier effect mechanical sensor can combine the advantages of both.

[0004] The existing Vernier effect mechanical sensors prepared based on the fiber splicing method have the problem of complex and time-consuming processes. In addition, due to the limitations of the fixed structure of the optical fiber itself, it is difficult to design a structure suitable for the scene according to different application scenarios. The two-photon printing technology is a 3D printing technology. The use of this technology to prepare cascaded FP cavities can make the structure design flexible, so as to facilitate the use of mechanical sensing in different application scenarios, such as printing a fixed bracket for the cell when measuring cell gravity.

[0005] An ideal sensor should provide an output proportional to the input over its entire operating range. However, many sensors can only maintain good linearity within a specific range of pressure or force. Once this range is exceeded, the output of the sensor may exhibit significant nonlinear behavior, resulting in reduced measurement accuracy, dynamic response distortion, frequent calibration, and data processing complexity caused by compensating for nonlinear errors. The structural design of the spring allows the spring itself to maintain a good linear relationship over a wide range until it reaches its elastic limit.

[0006] Therefore, how to broaden the linear response range of the micro-force sensor and provide a micro-force sensor with high precision and high sensitivity within a wide linear response range is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0007] The first object of the present invention is to provide an optical fiber-based cascaded FP cavity vernier effect mechanical sensor to address the problems in the prior art.

[0008] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions: A cascaded FP cavity vernier effect mechanical sensor based on optical fiber, characterized in that it includes a single-mode optical fiber and a 3D micro-nano structure, wherein the 3D micro-nano structure includes a disc base, a connecting spring and a cylindrical FP cavity, wherein the disc base and the cylindrical FP cavity are connected by a connecting spring to form an adjustable air FP cavity, the adjustable air FP cavity and the cylindrical FP cavity form a cascaded FP cavity, and one of the outer walls of the disc base or the cylindrical FP cavity is selected to be connected to the single-mode optical fiber, and the other outer wall receives the effect of the force to be measured; The linear response range of the cascaded FP cavity is expanded by connecting the spring with a wide response range, and combined with the vernier effect of the cascaded FP cavity, high-precision and high-sensitivity mechanical measurement within the expanded range is achieved.

[0009] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred technical solution of the present invention: the disc base is placed on the end face of the single-mode optical fiber, and its center part is aligned with the core of the single-mode optical fiber, which is used to fix the entire 3D micro-nano structure; the connecting spring is used to connect the cylindrical FP cavity of the disc base, so that an air cavity is formed between the end face of the single-mode optical fiber and the cylindrical FP cavity, and is used to adjust the length of the air cavity; the cylindrical FP cavity is solid, forming a solid cavity and receiving force; Alternatively, the disk base is a ring structure and is placed on the end face of the single-mode optical fiber.

[0010] As a preferred technical solution of the present invention: the cylindrical FP cavity is placed on the end face of the optical fiber to fix the 3D micro-nano structure and form a solid cavity, the connecting spring is used to connect the cylindrical FP cavity and the disc base, so that the side of the cylindrical FP cavity away from the end face of the optical fiber and the side of the disc base close to the end face of the optical fiber form an air cavity and the connecting spring can be used to adjust the length of the air cavity, and the disc base is used to receive the action of force.

[0011] As a preferred technical solution of the present invention: the refractive index of the cylindrical FP cavity is 1.53, the cavity length is 20-30 microns, the optical signal enters the cavity, and forms a Fabry-Perot cavity through optical resonance to produce the free spectral range required to form the vernier effect, which serves as a vernier effect reference cavity.

[0012] As a preferred technical solution of the present invention: the refractive index of the adjustable air FP cavity is 1, and the cavity length is 75-85 microns. The optical signal enters the cavity and forms a Fabry-Perot cavity through optical resonance, which is used to generate the free spectral range required to form the Vernier effect, as a Vernier effect sensing cavity; The disk base has a diameter of 50-80 microns and a thickness of only 2 microns, so that its modulation of the optical signal will not affect the generation of the cursor signal, wherein the diameter of the cylindrical FP cavity is the same as the diameter of the disk base; The diameter of the cylindrical FP cavity is the same as the diameter of the disk base, and both match the mode field diameter of the single-mode optical fiber to ensure that the light wave can effectively propagate in the cavity and form an interference pattern.

[0013] As a preferred technical solution of the present invention: the 3D micro-nano structure is prepared by two-photon polymerization 3D printing.

[0014] The second object of the present invention is to provide an optical fiber-based cascaded FP cavity Vernier effect mechanical sensor system in response to the problems in the prior art.

[0015] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions: An optical fiber-based cascade FP cavity Vernier effect mechanical sensor system, comprising: The tunable laser is used as a light source to provide light waves of a specific wavelength to stimulate the interference phenomenon in the fiber FP cavity; The optical power meter measures the optical power reflected from the cascaded FP cavity to detect the change in light intensity caused by the force to be measured; Optical fiber-based FP cavity mechanical sensor: Accurately measure changes in external pressure through the vernier effect.

[0016] The first end of the optical fiber connector is connected to the tunable laser, the second end of the optical fiber connector is connected to the optical fiber-based FP cavity refractive index sensor, and the third end of the optical fiber connector is connected to the optical power meter to form a mechanical sensor system.

[0017] Compared with the existing design, the present invention provides an optical fiber-based cascade FP cavity vernier effect mechanical sensor and system, which utilizes a cylindrical FP cavity to form a vernier effect reference cavity, utilizes one end face of the cylindrical FP cavity and the end face of a disk base to form a vernier effect sensing cavity, utilizes the free spectral range difference of the cascaded FP cavity to generate a vernier effect, and improves the sensing accuracy and sensitivity. At the same time, the vernier effect sensing cavity is utilized as an adjustable spring cavity, and the linear response range is expanded by connecting the spring synchronously, thereby realizing high-precision and high-sensitivity mechanical detection within a larger linear response range. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the first configuration structure of an optical fiber-based cascaded FP cavity Vernier effect mechanical sensor provided by the present invention; Figure 2 A schematic diagram of a second configuration structure of an optical fiber-based cascaded FP cavity Vernier effect mechanical sensor provided by the present invention; Figure 3 A schematic diagram of the change in the length of the air cavity after the surface of the optical fiber-based cascade FP cavity vernier effect mechanical sensor provided by the present invention is subjected to pressure; Figure 4 A schematic diagram of the translation of a spectral vernier signal after the surface of a cascaded FP cavity vernier effect mechanical sensor based on optical fiber provided by the present invention is subjected to pressure; Figure 5 It is a schematic diagram of the preparation process of an optical fiber-based cascade FP cavity Vernier effect mechanical sensor of the present invention; Figure 6 A graph showing the measurement results of the interferometric spectroscopy vernier effect of the mechanical sensor provided by the present invention; In the attached drawings, there are a disc base 1, a connecting spring 2, a cylindrical FP cavity 3, and a single-mode optical fiber 4. DETAILED DESCRIPTION

[0019] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] The present invention provides a cascade FP cavity vernier effect mechanical sensor based on optical fiber. The key structure for realizing sensing is a micro-spring type cascade FP cavity structure prepared on the end face of the optical fiber. By designing the spring structure parameters and the ratio of the cascade FP cavity length, a wide linear response range is achieved while realizing the vernier effect to achieve high detection sensitivity and ensure the stability of the overall structure.

[0021] The present invention provides a method for preparing a cascade FP cavity by two-photon printing technology. Thanks to the advantages of additive manufacturing, the cascade FP cavity structure can be personalized according to different application scenarios. The appropriate laser power and scanning speed are adjusted according to the cascade FP cavity structure. High-efficiency preparation is achieved while avoiding burning and bubble generation. The collapse of the cascade FP cavity structure can be avoided by selecting a suitable post-processing solution.

[0022] In order to achieve the above object, the present invention adopts the following technical scheme: The present invention provides a first micro-spring type cascade FP cavity structure construction form including a circular ring base, a connecting spring 2 and a cylindrical FP cavity 3. The circular ring base is placed on the end face of a single-mode optical fiber 4, and its center portion is aligned with the core of the single-mode optical fiber 4, and is used to fix the entire 3D micro-nano structure. The connecting spring 2 is used to connect the circular ring base cylindrical FP cavity 3, so that an air cavity is formed between the end face of the single-mode optical fiber 4 and the cylindrical FP cavity 3, and is used to adjust the length of the air cavity. The cylindrical FP cavity 3 is solid, and is used to form a solid cavity and receive the effect of force.

[0023] The present invention provides a second structural form of a micro-spring cascade FP cavity structure, including a cylindrical FP cavity 3, a connecting spring 2 and a disc base 1. The cylindrical FP cavity 3 is placed on the end face of the optical fiber to fix the entire 3D micro-nano structure and form a solid cavity. The connecting spring 2 is used to connect the cylindrical FP cavity 3 and the disc base 1, so that the side of the cylindrical FP cavity 3 away from the end face of the optical fiber and the side of the disc base 1 close to the end face of the optical fiber form an air cavity, and the connecting spring 2 can be used to adjust the length of the air cavity. The disc base 1 is used to receive the action of force.

[0024] The present invention forms a cascade FP cavity by placing an air cavity and a solid cavity in series, and through calculation, the refractive index of the cylindrical FP cavity 3 is 1.53, the refractive index of the air cavity is 1, the cavity length of the solid cavity of the cascade FP cavity is set at 20-30 microns, and the air cavity is set at 75-85 microns. The solid cavity produces a larger free spectral range (FSR) than the air cavity, thereby generating a first-order vernier effect, thereby improving the mechanical sensing sensitivity compared to the single FP cavity structure.

[0025] The present invention broadens the linear response range of the cascade FP cavity mechanical sensing by setting the connecting structure of the air cavity as a connecting spring 2, and then calculates through the spring sensitivity calculation formula to set the cross-section of the spring wire to a rectangle, and sets the length of the rectangle to 3-5 microns, the width to 3-5 microns, and the radius formed by the spring wire to 20-50 microns, so that the cylindrical FP cavity 3 and the disc base 1 are consistent with the spring radius, so that the connecting spring 2 can have the highest possible sensitivity and stability on the basis of successful preparation.

[0026] The present invention provides a method for preparing a cascade FP cavity by two-photon printing technology. The two-photon laser parameters are: wavelength of 700-1000nm; laser power of 35-45mW; laser scanning speed of 1000-3000μm / s, so as to achieve the fastest possible preparation speed while avoiding burning and bubble generation.

[0027] The present invention sets the surface of the two forms of micro-spring cascade FP cavity structures that receive mechanical signals as a plane. Thanks to the two-photon printing technology as an additive manufacturing technology, the plane can be used as a design base surface. Different structures can be designed on the surface according to different application scenarios to meet the requirements of different application scenarios.

[0028] The present invention avoids structural collapse during the post-processing process by selecting propylene glycol methyl ether acetate (PGMEA) as the developer used for development and methyl nonafluorobutyl ether (MNE) as the cleaning liquid in the post-processing development, cleaning and curing steps, setting the ultraviolet light wavelength to 400-500 nm, the curing temperature to 30-40°C, and the curing time to 10-15 minutes during the curing process.

[0029] The present invention provides a system structure of a cascaded FP cavity vernier effect mechanical sensor based on optical fiber, which includes a tunable laser, an optical fiber connector, an optical power meter, and a cascaded FP cavity vernier effect mechanical sensor based on optical fiber. The tunable laser emits an optical signal, which reaches the mechanical sensor through the optical fiber connector. The mechanical sensor receives the mechanical signal, converts the mechanical signal into a vernier signal through the cascaded FP cavity structure on the mechanical sensor, and then transmits the vernier signal back to the optical fiber connector through the single-mode optical fiber 4 of the mechanical sensor, and finally transmits it back to the optical power meter. By observing the movement of the spectrum line on the optical power meter, the relationship between the movement of the spectrum line and the mechanical signal is established to achieve mechanical sensing.

[0030] Because the spring satisfies Hooke's law, there is a linear relationship between the detected force and the length change. Therefore, the cascade FP cavity introduces a spring structure. When the detected force causes the spring length to change, the optical path of the FP cavity formed by the spring connection in the cascade FP cavity also changes, effectively linking the optical effect with the mechanical effect.

[0031] In summary, the optical fiber-based cascaded FP cavity vernier effect mechanical sensor provided by the present invention has the following characteristics and advantages compared with the prior art: one of the cavities in the cascaded FP cavity structure is set as a spring cavity, and the linear response range is expanded by taking advantage of the wide response range of the spring; the cascaded FP cavity structure utilizes the vernier effect, and can achieve higher precision and sensitivity compared with the single FP cavity structure; the cascaded FP cavity structure can be prepared by two-photon printing technology, and has flexibility in structural design. In addition, the present invention provides a method for preparing the sensor cascaded FP cavity structure on the end face of an optical fiber, so that it can achieve high precision, sensitivity and high preparation efficiency on the basis of successful preparation. Example 1

[0032] The present invention provides two structural forms for the micro-spring cascade FP cavity structure. The first one is as follows: Figure 1As shown, the cylindrical FP cavity 3 is on the top and the connecting spring 2 is on the bottom. Figure 2 As shown, the connecting spring 2 is on the top and the cylindrical FP cavity 3 is on the bottom. The difference between the two is that the solid cavity formed by the cylindrical FP cavity 3 and the air cavity formed by the spring are placed in different positions. In essence, they are both cascade FP cavities. Figure 1 Take the structure as an example and describe it in detail.

[0033] The present invention prepares a disc base 1, the inner diameter of which is 45 , the outer diameter is 50 , thickness is 10 .

[0034] The present invention prepares a connecting spring 2, wherein the spring wire has a rectangular cross section, a length of 4.5 microns and a width of 5.5 microns, a spring wire pitch of 70 microns, and a diameter of 50 microns.

[0035] The present invention prepares a cylindrical FP cavity 3 with a diameter of 50 microns and a length of 25 microns.

[0036] F=k•

[0037] Among them, k is called the elastic coefficient, which determines the sensitivity of the spring and can be adjusted by designing the structure of the spring. k can be expressed by the formula:

[0038] G is the elastic modulus of the spring material. The spring wire in the present invention is set as a spring wire with a rectangular cross section, w and t are the length and width of the cross-sectional rectangle, γ is the Poisson's ratio of the spring, n is the effective number of turns of the spring, and R is the radius of the spring.

[0039] The free spectral range of a single FP cavity can be expressed as the formula,

[0040] n is the refractive index of the cavity, and Indicates two consecutive maxima or minima of the spectrum curve, l indicates the cavity length. If this formula is used to calculate the FSR range of the air cavity, if it is applied to Figure 1 In the configuration shown, l represents the distance between the top surface of the cylinder and the bottom surface of the disk. If applied to Figure 2 In the configuration shown, l represents the distance between the optical fiber end face and the bottom surface of the cylinder.

[0041] If two cascaded FP cavities are to produce a vernier effect, the free spectral range (FSR) of the two FP cavities needs to meet the following conditions: KFSR1=[(i+1)k+1]FSR2 i represents the order of the cursor effect to be generated, and K represents the free spectral range (FSR) of the cursor signal envelope. envelope ) contains the number of FSR1, which must be an integer. envelope It can be expressed as follows:

[0042] The magnification M can be expressed by the formula:

[0043] The relationship between the change in the length of a single FP cavity Δl and the spectrum shift distance Δλ can be expressed as:

[0044] Therefore, the relationship between the mechanical action and the moving distance of the cursor signal spectrum can be established.

[0045] like Figure 4 The figure shows the schematic diagram of the translation of the spectral cursor signal after the surface is subjected to pressure.

[0046] like Figure 5 The figure shows the preparation process and finished product schematic diagram of the present invention.

[0047] In the preparation process using the two-photon printing technology of the present invention, the two-photon laser parameters adopted are: wavelength of 780nm; laser power of 40mW; laser scanning speed of 2000μm / s.

[0048] In the present invention, the developer used for development is propylene glycol methyl ether acetate (PGMEA); the cleaning solution used for cleaning is methyl nonafluorobutyl ether (MNE).

[0049] In the present invention, the ultraviolet (external) light wavelength used is 365nm.

[0050] In the present invention, the curing temperature is 25° C. and the curing time is 15 minutes.

[0051] like Figure 6 As shown, the vernier effect signal is measured by the mechanical sensing system provided by the present invention for the structure prepared by the above process.

[0052] The present invention provides an optical fiber-based cascaded FP cavity Vernier effect mechanical sensor system, comprising: The tunable laser is used as a light source to provide light waves of a specific wavelength to stimulate the interference phenomenon in the fiber FP cavity; The optical power meter measures the optical power reflected from the cascaded FP cavity to detect the change in light intensity caused by the force to be measured; Optical fiber-based FP cavity mechanical sensor: Accurately measure changes in external pressure through the vernier effect.

[0053] The first end of the optical fiber connector is connected to the tunable laser, the second end of the optical fiber connector is connected to the optical fiber-based FP cavity refractive index sensor, and the third end of the optical fiber connector is connected to the optical power meter to form a mechanical sensor system.

[0054] The above-mentioned specific implementation methods are used to explain the present invention and are only preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. An optical fiber-based cascaded FP cavity Vernier effect mechanical sensor, characterized in that: The invention comprises a single-mode optical fiber and a 3D micro-nano structure, wherein the 3D micro-nano structure comprises a disc base, a connecting spring and a cylindrical FP cavity, wherein the disc base and the cylindrical FP cavity are connected by the connecting spring to form an adjustable air FP cavity, the adjustable air FP cavity and the cylindrical FP cavity form a cascade FP cavity, and an outer wall of the disc base or the cylindrical FP cavity is selected to be connected to the single-mode optical fiber, and the other outer wall receives the effect of the force to be measured; The linear response range of the cascaded FP cavity is expanded by connecting the spring with a wide response range, and combined with the vernier effect of the cascaded FP cavity, high-precision and high-sensitivity mechanical measurement within the expanded range is achieved.

2. The optical fiber-based cascaded FP cavity Vernier effect mechanical sensor as claimed in claim 1, characterized in that: The disc base is placed on the end face of the single-mode optical fiber, and its center part is aligned with the core of the single-mode optical fiber, which is used to fix the entire 3D micro-nano structure. The connecting spring is used to connect the cylindrical FP cavity of the disc base, so that an air cavity is formed between the end face of the single-mode optical fiber and the cylindrical FP cavity, and is used to adjust the length of the air cavity. The cylindrical FP cavity is solid, forming a solid cavity and receiving force. Alternatively, the disk base is a ring structure and is placed on the end face of the single-mode optical fiber.

3. The optical fiber-based cascaded FP cavity Vernier effect mechanical sensor as described in claim 1, characterized in that: The cylindrical FP cavity is placed on the end face of the optical fiber to fix the 3D micro-nano structure and form a solid cavity. The connecting spring is used to connect the cylindrical FP cavity and the disc base, so that the side of the cylindrical FP cavity away from the end face of the optical fiber and the side of the disc base close to the end face of the optical fiber form an air cavity and the connecting spring can be used to adjust the length of the air cavity. The disc base is used to receive the action of force.

4. The optical fiber-based cascaded FP cavity Vernier effect mechanical sensor as claimed in claim 1, characterized in that: The cylindrical FP cavity has a refractive index of 1.53 and a cavity length of 20-30 microns. An optical signal enters the cavity and forms a Fabry-Perot cavity through optical resonance to generate a free spectral range required for forming a vernier effect, serving as a vernier effect reference cavity.

5. The optical fiber-based cascaded FP cavity Vernier effect mechanical sensor as claimed in claim 1, characterized in that: The refractive index of the adjustable air FP cavity is 1, and the cavity length is 75-85 microns. The optical signal enters the cavity and forms a Fabry-Perot cavity through optical resonance, which is used to generate the free spectrum range required to form the Vernier effect, and serves as a Vernier effect sensing cavity; The disk base has a diameter of 50-80 microns and a thickness of only 2 microns, so that its modulation of the optical signal will not affect the generation of the cursor signal, wherein the diameter of the cylindrical FP cavity is the same as the diameter of the disk base; The diameters of the cylindrical FP cavity, the disk base and the spring structure are larger than the diameter of the optical fiber core to ensure that the light waves can effectively propagate in the cavity and form an interference pattern.

6. The optical fiber-based cascaded FP cavity Vernier effect mechanical sensor as claimed in claim 1, characterized in that: The 3D micro-nano structure is prepared by two-photon polymerization 3D printing.

7. A mechanical sensor system using the optical fiber-based cascaded FP cavity Vernier effect mechanical sensor according to any one of claims 1 to 6, characterized in that: include The tunable laser is used as a light source to provide light waves of a specific wavelength to stimulate the interference phenomenon in the cascaded FP cavity; The optical power meter measures the optical power reflected from the cascaded FP cavity to detect the change in light intensity caused by the force to be measured; Optical fiber-based FP cavity mechanical sensor: accurately measures changes in external pressure through the vernier effect; The first end of the optical fiber connector is connected to the tunable laser, the second end of the optical fiber connector is connected to the optical fiber-based FP cavity refractive index sensor, and the third end of the optical fiber connector is connected to the optical power meter to form a mechanical sensor system.

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