Probe based on vernier effect enhancement, preparation method and ocean temperature sensor

Abstract

The invention belongs to the technical field of optical fiber temperature sensors, and particularly relates to a probe based on an enhanced vernier effect, a preparation method and a marine temperature sensor. A single-mode optical fiber extends to the top end face of a sensor probe base, and the probe base is connected with an open pore microstructure formed by four supporting rods; the supporting rod is also connected with a solid cylindrical structure printed by a polymer material, the first reflecting surface is positioned on the raised upper end surface of the probe base, the second reflecting surface is positioned on the lower end surface of the solid cylindrical structure printed by the polymer material, and a cavity between the first reflecting surface and the second reflecting surface forms a first interference cavity. The third reflecting surface is located on the upper end face of the solid cylindrical structure, and a second interference cavity is formed between the second reflecting surface and the first reflecting surface. The two interference cavities are tightly connected to form a series structure; the device further comprises a vacuumizing unit which is fixed on the optical fiber cable. According to the sensor probe, the signal-to-noise ratio and the sensitivity can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber temperature sensors, and in particular relates to a probe based on an enhanced vernier effect, a preparation method, and an ocean temperature sensor. Background Art

[0002] Temperature monitoring plays a vital role in scientific research and industrial production. Fiber optic temperature sensors have been widely used in fields such as marine research, aerospace, and microfluidic chips due to their compact size, high sensitivity, and strong resistance to electromagnetic interference. In recent years, with the increasing demand for marine environmental monitoring, high-precision measurement of seawater temperature has become of great significance. Therefore, the development of temperature sensors with high sensitivity, high precision, and strong anti-interference capabilities has become particularly important. Today, commonly used fiber optic temperature sensors include temperature sensors based on fiber Bragg gratings, fiber optic temperature sensors based on interferometers, and temperature sensors based on fiber fluorescence effects.

[0003] Existing ocean temperature sensors play an important role in marine environmental monitoring, but they still suffer from the following major drawbacks: Existing thermocouple sensors have low sensitivity: within the range of seawater temperature fluctuations, the thermocouple's output voltage is only approximately 1 millivolt, resulting in low measurement resolution. Existing thermocouple sensor cable material limitations: the detection cable must be made of the same material as the thermocouple, increasing system complexity and cost. Existing thermocouple sensors have low sensitivity. Cold junction compensation requirements: a high-precision cold junction compensator must be included in the secondary instrument; otherwise, errors will be introduced. Existing thermistors (NTCs) have nonlinear characteristics: their resistance and temperature have a nonlinear relationship, and variations in production processes make standardization difficult, requiring complex calibration or compensation circuits. Self-heating errors: they require a current source for power supply, and even small currents can cause self-heating due to power dissipation, affecting measurement accuracy. Mechanical fragility: while small in size and fast in response, they are susceptible to damage from mechanical shock or high temperatures. These shortcomings can affect measurement accuracy, long-term stability, and applicable scenarios. To address this issue, the present invention proposes a probe based on an enhanced vernier effect, a preparation method, and an ocean temperature sensor. Summary of the Invention

[0004] The purpose of the present invention is to provide a probe based on enhanced vernier effect, a preparation method and an ocean temperature sensor, which can effectively improve the signal-to-noise ratio and sensitivity.

[0005] The technical solutions adopted by the present invention are as follows:

[0006] A probe based on enhanced vernier effect, comprising a probe body, an optical fiber cable, and a vacuum unit, wherein the vacuum unit is fixed on the optical fiber cable, and the probe body is located inside the vacuum unit;

[0007] The probe body includes two stacked first probe bases and a second probe base, wherein the diameter of the second probe base is smaller than that of the first probe base, and the second probe base is connected to four support rods, wherein the middle portions of the four support rods form an open-pore microstructure, and the upper ends of the four support rods are connected to a solid cylindrical structure, wherein the solid cylindrical structure is printed from a polymer material;

[0008] The probe body is fixedly arranged on the optical fiber cable; the upper end of the optical fiber cable extends from the inside of the first probe base to the lower end of the second probe base, and the upper end of the optical fiber cable and the open hole microstructure are connected to each other;

[0009] The raised portion in the middle of the second probe base serves as a first reflecting surface, and the lower end surface of the solid cylindrical structure is provided with a second reflecting surface; the cavity between the first reflecting surface and the second reflecting surface constitutes the first interference cavity in the enhanced vernier interferometer dual cavity;

[0010] The upper end surface of the solid cylindrical structure serves as the third reflection surface, and the second interference cavity in the enhanced vernier interference double cavity is formed between the second reflection surface and the third reflection surface; the first interference cavity and the second interference cavity are closely connected to form a series structure.

[0011] Preferably, the vacuum unit includes a temperature sensing tube sleeved on the end of the optical fiber cable, a sealing sleeve is sleeved on the outside of the temperature sensing tube, the probe body is located inside the temperature sensing tube, and a vacuum tube is connected to the outer wall of the sealing sleeve; an air passage is opened on the inner wall of the temperature sensing tube; after the vacuum tube is vacuumed, the vacuum tube is melted and sealed.

[0012] Preferably, the space between the inner wall of the end portion of the temperature sensing tube and the outer wall of the end portion of the optical fiber cable is filled with glass glue, and the space between the temperature sensing tube and the sealing sleeve is filled with a heat-conducting material layer.

[0013] Preferably, the diameter of the first probe base is 150 μm; the diameter of the second probe base is 125 μm. The first probe base and the second probe base are smooth and sturdy, providing good support and stability for the sensor; the diameter of the solid cylindrical structure is 30 μm, and the diameter of the solid cylindrical structure matches the core size of the single-mode optical fiber used in the optical fiber cable, facilitating the transmission of light; the length of the first interference cavity is 70 μm; the length of the second interference cavity is 65 μm.

[0014] Preferably, the first interference cavity formed between the inner walls of the four support rods adopts an open design; the fluid filling time of the cavity is shortened, and its reliability in various environments is improved, especially its adaptability to the marine environment, ensuring that high-precision temperature monitoring tasks can be performed.

[0015] The preparation method of the probe based on the enhanced vernier effect comprises the following steps:

[0016] S1: Print end face processing: Take a single-mode optical fiber SMF-28, strip off the coating, wipe it clean with ethanol solution, use a cleaver to cut the optical fiber end face flat, place the cut single-mode optical fiber SMF in the fusion splicer for observation, and discharge clean the single-mode optical fiber SMF end face; place the treated single-mode optical fiber SMF in the fixture and fix the fixture to the printing equipment;

[0017] S2: Confirm the lens focus and fiber core position, adjust the lens position, focus the lens on the fiber end face, use a 650nm visible light laser light source for fill light processing, and use the micro-displacement platform joystick to adjust the position of the fiber end face; the position of the focused light spot is the position of the fiber core; adjust the micro-displacement platform to adjust the fiber end face to the center position of the printing device;

[0018] S3: Modeling is performed using the SOLIDWORKS software of the 3D printer to obtain a probe design model, which includes a first probe base design model, a second probe base design model, a support rod, and a solid cylindrical structure design model. The support rod and the solid cylindrical structure design model are located between the first probe base design model and the second probe base design model;

[0019] S4: Structural printing: Use a 3D printer to print the probe design model to obtain a probe model. The probe model includes the first probe base and the second probe base design models, a fixedly connected support rod, and a solid cylindrical structure design model. During printing, it is necessary to observe in real time whether the printed structure is at the geometric center of the optical fiber end face and whether it is tilted or broken.

[0020] Preferably, in step 4, the polymer FPI is prepared directly on the tip of a single-mode optical fiber SMF-28 using a MOJI-NANO 3D femtosecond direct laser writing device; during the preparation process, a photoresist is evenly coated on the surface of the substrate, and the photoresist used in the preparation is ATE-DIP-1.52; the FPI area is exposed by ultraviolet light, and after exposure, the photoresist is treated with a developer, which removes the photoresist in the unexposed area, thereby forming the desired pattern.

[0021] The ocean temperature sensor includes a wide spectrum light source, a spectrum demodulator, a fiber optic circulator, and a probe based on an enhanced vernier effect.

[0022] The wide spectrum light source is connected to the first port of the fiber circulator, the spectrum demodulator is connected to the third port of the fiber circulator, and the root of the optical fiber cable on the probe based on enhanced vernier effect is connected to the second port of the fiber circulator.

[0023] The technical effects achieved by the present invention are:

[0024] 1. In the present invention, the sensor probe based on the enhanced vernier effect is constructed as a series structure. Specifically, the first interference cavity formed by the cavity between the first and second reflecting surfaces and the second interference cavity in the enhanced vernier interference dual cavity formed between the second reflecting surface and the first reflecting surface are located on the same straight line. As a result, the two interference cavities can produce a vernier effect during temperature measurement. Furthermore, the two interference cavities are spatially encapsulated within a single probe, thereby allowing the two interference cavities to be in the same measured environment at the same time. In this way, the two interference cavities can remain synchronized when affected by external temperature changes, avoiding the problem of asynchronous temperature response caused by the separation of the main scale cavity and the vernier cavity in other vernier effect temperature measurement schemes, effectively improving the consistency and synchronization of the temperature sensor.

[0025] 2. The sensor probe base and the sensor probe body in the sensor probe of the present application are made of an inert material such as 3D printed polymer. Firstly, the deformation of this inert material caused by temperature change is very small, it is acid-resistant and corrosion-resistant, and has high strength. Secondly, when the sensor probe base and the sensor probe body produce slight deformation due to temperature change, the sensor probe base and the sensor probe body are deformed synchronously, which can greatly offset the deformation caused by temperature change. The two interference cavities are affected by the thermo-optical effect (TOE) and the thermal expansion effect (TEE), respectively. Their spectral interference inclination angles are shifted in opposite directions, achieving an enhanced vernier effect. Specifically, when measuring seawater temperature, the first interference cavity of the cavity structure is filled with seawater, and its medium refractive index decreases with increasing temperature. Therefore, the thermo-optical effect of the medium in the cavity dominates, and the interference spectrum drifts toward short waves. At this time, the thermal expansion effect of the second interference cavity dominates. When the temperature rises, the interference spectrum will drift toward long waves. This unique structure can achieve an enhanced vernier effect and effectively improve the sensitivity of the sensor.

[0026] 3. The sensor probe prepared by the 3D printing-based sensor probe preparation method of this application is directly prepared on the tip of a single-mode optical fiber SMF-28 using the MOJI-NANO3D femtosecond direct laser writing device. Femtosecond laser two-photon polymerization 3D printing technology focuses a femtosecond laser inside a transparent medium and uses the nonlinear two-photon absorption photopolymerization effect of the laser-medium interaction to induce local optical modification of the dielectric material. By precisely controlling the relative movement of the focused laser and the dielectric material, a micromachining technology is achieved that is far less than the diffraction limit. This processing method is point scanning, so it can achieve precise processing of any structure. This technology is a new optical fiber preparation technology with processing accuracy reaching the nanometer level. The resulting sensor probe structure is compact and highly integrated. At the same time, it reduces the dependence of complex optical fiber sensing structures on special optical fibers and can effectively meet the needs of miniaturization of high-refractive index sensor probes.

[0027] 4. Temperature sensors based on the Vernier effect typically require very small detuning to achieve higher sensitivity. The FSR is the wavelength interval between two adjacent interference attenuations, which is affected by the refractive index n and cavity length L of the interferometer cavity. When the temperature changes, the refractive index n and cavity length L of the interferometer cavity also change, causing the FSR to change. When the FSRs of two interferometer cavities connected in series are close, their output spectra overlap to form a large spectral envelope. Temperature changes cause the spectral envelope to be amplified and shifted. The amplification factor is inversely proportional to the absolute value of the difference in the FSRs of the two interferometer cavities. Therefore, when the cavity lengths L of the two interferometer cavities are close, their amplification factor increases, thereby greatly improving the temperature sensitivity of the sensor. Therefore, femtosecond laser 3D printing technology has great advantages in the fabrication of FP microcavities.

[0028] 5. The sensor probe in this application is provided with a vacuum tube 18. After the vacuum tube 18 is evacuated, the vacuum tube 18 is fused and sealed. At this time, the internal vacuum state formed in the sealing sleeve 15 allows the sealing sleeve 15 to remain in a sealed state for a long time. This can effectively eliminate the influence of residual gas in the sealing sleeve, which causes changes in gas density due to thermal expansion and contraction, thereby causing interference errors on the effective cavity length of the series interference cavity. In addition, after the sealing sleeve 15 is evacuated, the influence of external environmental pressure on the various components within the sealing sleeve 15 can be avoided.

[0029] 6. In the present application, the space between the sealing sleeve 15 and the temperature sensing tube 16 is filled with a thermal conductive material layer 14, and then the air inside the sealing sleeve 15 is discharged through the vacuum tube 18, which can effectively ensure that the external temperature is fully conducted in the sensor probe, solving the problem of slow temperature transfer caused by temperature isolation of the vacuum tube, and avoiding the problem of liquid thermal conductive agents such as thermal grease volatilizing in a vacuum state and fluidity contaminating the reflectivity of the interference cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the overall structure of the ocean temperature sensor of the present invention;

[0031] Figure 2 1 is a schematic diagram of the overall structure of the probe body in the probe based on the enhanced vernier effect of the present invention;

[0032] Figure 3 Schematic diagram of the overall structure of the probe based on the enhanced vernier effect of the present invention;

[0033] Figure 4 This is the enhanced composite vernier interferometer cavity spectrum obtained by the ocean temperature sensor of this application at 29℃-35℃;

[0034] Figure 5 This is a temperature calibration test data chart obtained by the ocean temperature sensor of this application under the conditions of 29℃-35℃.

[0035] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0036] 1. Broad-spectrum light source; 2. Spectral demodulator; 3. Fiber circulator; 6. Fiber optic cable; 7. Single-mode fiber core; 8. First probe base; 9. Second probe base; 10. Support rod; 11. Solid cylindrical structure; 12. Open-pore microstructure; 13. Glass glue; 14. Thermal conductive material layer; 15. Sealing sleeve; 16. Temperature sensing tube; 17. Airway. DETAILED DESCRIPTION

[0037] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is described in detail below with reference to the following examples. It should be understood that the following text is only used to describe one or more specific embodiments of the present invention and does not strictly limit the scope of protection of the present invention.

[0038] like Figure 1-Figure 3 As shown, the probe based on the enhanced vernier effect includes a probe body, an optical fiber cable 6 and a vacuum unit, wherein the vacuum unit is fixed on the optical fiber cable 6, and the probe body is located inside the vacuum unit;

[0039] The probe body includes two stacked first probe bases 8 and a second probe base 9. The diameter of the second probe base 9 is smaller than that of the first probe base 8. Four support rods 10 are connected to the second probe base 9. The middle parts of the four support rods 10 form an open-pore microstructure 12. The upper ends of the four support rods 10 are connected to a solid cylindrical structure 11. The solid cylindrical structure 11 is made of a printed polymer material.

[0040] The probe body is fixedly mounted on the optical fiber cable 6 via a seal; the seal can be made of the same material as the sealing sleeve 15; the upper end of the optical fiber cable 6 extends from the inside of the first probe base 8 to the lower end of the second probe base 9, and the upper end of the optical fiber cable 6 is connected to the open microstructure 12;

[0041] The raised portion in the middle of the second probe base 9 serves as a first reflecting surface, and the lower end surface of the solid cylindrical structure 11 is provided with a second reflecting surface; the cavity between the first reflecting surface and the second reflecting surface constitutes the first interference cavity in the enhanced vernier interferometer double cavity;

[0042] The upper end surface of the solid cylindrical structure 11 serves as the third reflection surface, and the second interference cavity in the enhanced vernier interference double cavity is formed between the second reflection surface and the third reflection surface; the first interference cavity and the second interference cavity are closely connected to form a series structure.

[0043] The first interference cavity is the open-pore microstructure 12 . The first interference cavity is the function, and the open-pore microstructure 12 is the definition of its structure.

[0044] Preferably, the vacuum unit includes a temperature sensing tube 16 sleeved on the end of the optical fiber cable 6, a sealing sleeve 15 is sleeved on the outside of the temperature sensing tube 16, the probe body is located inside the temperature sensing tube 16, and a vacuum tube 18 is connected to the outer wall of the sealing sleeve 15; an air duct 17 is opened on the inner wall of the temperature sensing tube 16.

[0045] Preferably, the space between the inner wall of the end of the temperature sensing tube 16 and the outer wall of the end of the optical fiber cable 6 is filled with glass glue 13 , and the space between the temperature sensing tube 16 and the sealing sleeve 15 is filled with a heat conductive material layer 14 .

[0046] After the vacuum tube 18 is evacuated, the vacuum tube 18 is melted and sealed; the sealing sleeve 15 described in this application is made of rubber, the temperature sensing tube 16 is made of beryllium copper alloy material, the thermal conductive material layer 14 is a metal wool layer, and the vacuum unit is fixed to the optical fiber cable 6 with glass glue 13.

[0047] Preferably, the diameter of the first probe base 8 is 150 μm; the diameter of the second probe base 9 is 125 μm. The first probe base 8 and the second probe base 9 are smooth and sturdy in appearance, providing good support and stability for the sensor; the diameter of the solid cylindrical structure 11 is 30 μm, and the diameter of the solid cylindrical structure 11 matches the size of the single-mode optical fiber core 7 used in the optical fiber cable 6, facilitating the transmission of light; the length of the first interference cavity is 70 μm; the length of the second interference cavity is 65 μm.

[0048] Preferably, the first interference cavity formed between the inner walls of the four support rods 10 adopts an open design; the fluid filling time of the cavity is shortened, and its reliability in various environments is improved, especially its adaptability to the marine environment, ensuring that high-precision temperature monitoring tasks can be performed.

[0049] In the present application, the wide-spectrum light source 1 emits a broadband spectrum with a wavelength range of 1100nm-1600nm. The broadband spectrum emitted by the wide-spectrum light source 1 is input into the probe based on the enhanced vernier effect through the optical fiber circulator 3. The first interference cavity and the second interference cavity in the probe based on the enhanced vernier effect are connected in series to form a vernier composite unit. The broadband spectrum input into the probe based on the enhanced vernier effect forms a composite envelope interference spectrum under the action of the vernier composite unit. Then, the composite envelope interference spectrum is transmitted back to the spectrum demodulator 2 through the optical fiber circulator 3 to realize spectrum demodulation.

[0050] In order to verify the temperature sensitivity performance of the ocean temperature sensor of this application, this application conducted a temperature calibration test on the ocean temperature sensor obtained in this embodiment. The test results are as follows: Figure 4 As shown, from Figure 4 It can be seen that the temperature sensitivity of the ocean temperature sensor obtained in this embodiment can reach 43.98nm / ℃. The spectral demodulator 2 in this embodiment adopts the I-MON256OEM demodulation module. The demodulation accuracy of the spectral demodulator 2 is 1pm. According to the demodulation accuracy of the spectral demodulator 2, the temperature sensitivity is calculated. It can be seen that the temperature sensitivity of the ocean temperature sensor of this application can reach 0.000023℃; while in the prior art, the temperature sensitivity of the temperature sensor is usually required to be no higher than 0.005℃ to meet the demand for high-sensitivity ocean temperature detection. That is to say, the sensitivity of the ocean temperature sensor prepared in this application is nearly two orders of magnitude higher than the sensitivity required for high-sensitivity ocean temperature detection in the prior art.

[0051] Example 2:

[0052] The preparation method of the probe based on the enhanced vernier effect comprises the following steps:

[0053] S1: Print end face processing: Take a single-mode optical fiber SMF-28, strip off the coating, wipe it clean with ethanol solution, use a cleaver to cut the optical fiber end face flat, place the cut single-mode optical fiber SMF in the fusion splicer for observation, and discharge clean the single-mode optical fiber SMF end face; place the treated single-mode optical fiber SMF in the fixture and fix the fixture to the printing equipment;

[0054] S2: Confirm the lens focus and fiber core position, adjust the lens position, focus the lens on the fiber end face, use a 650nm visible light laser light source for fill light processing, and use the micro-displacement platform joystick to adjust the position of the fiber end face; the position of the focused light spot is the position of the fiber core; adjust the micro-displacement platform to adjust the fiber end face to the center position of the printing device;

[0055] S3: Modeling is performed using the SOLIDWORKS software of the 3D printer to obtain a probe design model, which includes the design models of the first probe base 8 and the second probe base 9 and the design models of the support rod 10 and the solid cylindrical structure 11. The design models of the support rod 10 and the solid cylindrical structure 11 are located between the design models of the first probe base 8 and the second probe base 9;

[0056] S4: Structure printing: Use a 3D printer to print the probe design model to obtain a probe model. The probe model includes the design models of the first probe base 8 and the second probe base 9, the fixedly connected support rod 10, and the solid cylindrical structure 11. During printing, it is necessary to observe in real time whether the printed structure is in the geometric center of the optical fiber end face, and whether it is tilted or broken.

[0057] Preferably, in step 4, the polymer FPI is prepared directly on the tip of a single-mode optical fiber SMF-28 using a MOJI-NANO 3D femtosecond direct laser writing device; during the preparation process, a photoresist is evenly coated on the surface of the substrate, and the photoresist used in the preparation is ATE-DIP-1.52; the FPI area is exposed by ultraviolet light, and after exposure, the photoresist is treated with a developer, which removes the photoresist in the unexposed area, thereby forming the desired pattern.

[0058] Example 3:

[0059] An ocean temperature sensor comprising: a wide spectrum light source 1, a spectrum demodulator 2, an optical fiber circulator 3, and a probe based on an enhanced vernier effect;

[0060] The wide spectrum light source 1 is connected to the first port of the fiber circulator 3, the spectrum demodulator 2 is connected to the third port of the fiber circulator 3, and the root of the optical fiber cable 6 on the probe based on the enhanced vernier effect is connected to the second port of the fiber circulator 3.

[0061] from Figure 4It can be seen from the changes in the spectrum that as the temperature of the liquid to be measured increases, the peak wavelength of the composite envelope interference spectrum moves toward the long wavelength direction. In other words, as the temperature of the liquid to be measured increases, the peak wavelength of the spectrum of the composite envelope interference light appears to be red-shifted. This shows that the superimposed spectral effect of the first interferometer cavity as the sensing cavity A and the second interferometer cavity as the sensing cavity B has a red-shift trend as the temperature of the liquid to be measured increases, and according to Figure 4 The relationship between the peak wavelength of the composite envelope interference spectrum and the temperature of the liquid to be measured is plotted. Figure 5 .from Figure 5 It can be seen that within the test temperature range of 29℃~35℃, the peak wavelength of the composite envelope interference spectrum is linearly related to the temperature, as shown in formula (1):

[0062] λ=43.98T+24.8 (1)

[0063] In formula (1), λ represents the peak wavelength of the composite envelope interference spectrum, in nm; T represents the temperature of the liquid to be measured, in degrees Celsius.

[0064] In addition, from Figure 5 It can also be seen that the temperature sensitivity of the sensor based on the enhanced vernier effect obtained in the second embodiment of the present invention can reach 43.98nm / °C. The spectrum demodulator 2 in the second embodiment adopts the I-MON 256OEM demodulation module, and the demodulation accuracy of the spectrum demodulator 2 is 1pm. According to the demodulation accuracy of the spectrum demodulator 2, the refractive index sensitivity is calculated. It can be seen that the sensitivity of the high refractive index sensor obtained in the second embodiment of the present application can reach 0.000023°C, which can meet the needs of high-sensitivity temperature detection in fields such as environmental monitoring, food safety, and biomedical testing.

[0065] In addition, due to Figure 5 What is shown is the test result of the temperature sensitivity of the sensor based on the enhanced vernier effect obtained in the second embodiment of the present invention in the temperature range of 29°C to 35°C, which shows that the sensor based on the enhanced vernier effect obtained in the third embodiment of the present invention can adapt to accurate measurement in the temperature range of 29°C to 35°C, that is, the sensor based on the enhanced vernier effect prepared in the present application can measure the liquid temperature with higher sensitivity; moreover, the length of the first interference cavity of the sensor probe based on the enhanced vernier effect prepared in the third embodiment of the present application is 70μm, and the length of the second interference cavity is 65μm. Therefore, the sensor probe based on the enhanced vernier effect prepared in the present application also meets the requirements of miniature.

[0066] In the present invention, the sensor probe based on the enhanced vernier effect is a series structure. Specifically, the first interference cavity formed by the cavity between the first reflecting surface and the second reflecting surface and the second interference cavity in the enhanced vernier interference double cavity formed between the second reflecting surface and the first reflecting surface are located on the same straight line, so that the two interference cavities can produce a vernier effect when measuring temperature. Furthermore, the two interference cavities in the present application are spatially encapsulated in one probe at the same time, so that the two interference cavities can be in the same measured environment at the same time. In this way, the two interference cavities can be synchronized by the influence of external temperature changes, avoiding the problem of asynchronous temperature response caused by the separation of the main scale cavity and the vernier cavity in other vernier effect temperature measurement schemes, and effectively improving the consistency and synchronization of the temperature sensor.

[0067] In the sensor probe of the present application, the sensor probe base and the sensor probe body are both made of an inert material such as 3D printed polymer. Firstly, the deformation of this inert material caused by temperature change is very small, it is acid-resistant and corrosion-resistant, and has high strength; secondly, when the sensor probe base and the sensor probe body produce slight deformation due to temperature change, the sensor probe base and the sensor probe body are deformed synchronously, which can greatly offset the deformation caused by temperature change; the two interference cavities are affected by the thermo-optical effect (TOE) and the thermal expansion effect (TEE), respectively, and their spectral interference inclination angles are shifted in opposite directions, respectively, to achieve an enhanced vernier effect. Specifically, when measuring seawater temperature, the first interference cavity of the cavity structure is filled with seawater, and its medium refractive index decreases with increasing temperature, so the thermo-optical effect of the medium in the cavity dominates, and the interference spectrum drifts toward short waves; at this time, the thermal expansion effect of the second interference cavity dominates, and when the temperature rises, the interference spectrum will drift toward long waves. This unique structure can achieve an enhanced vernier effect and effectively improve the sensitivity of the sensor;

[0068] The sensor probe prepared by the 3D printing-based sensor probe preparation method of this application is prepared directly on the tip of a single-mode optical fiber SMF-28 using a MOJI-NANO3D femtosecond direct laser writing device. Femtosecond laser two-photon polymerization 3D printing technology focuses a femtosecond laser inside a transparent medium and uses the nonlinear two-photon absorption photopolymerization effect of the laser-medium interaction to induce local optical modification of the dielectric material. By precisely controlling the relative movement of the focused laser and the dielectric material, a micromachining technology is achieved that is far less than the diffraction limit. This processing method is point scanning, so it can achieve precise processing of any structure. This technology is a new optical fiber preparation technology with processing accuracy reaching the nanometer level. The resulting sensor probe structure is compact and highly integrated. At the same time, it reduces the dependence of complex optical fiber sensing structures on special optical fibers, and can effectively meet the needs of miniaturization of high-refractive index sensor probes.

[0069] Temperature sensors based on the vernier effect typically require very small detuning to achieve higher sensitivity. The FSR is the wavelength interval between two adjacent interference attenuations, which is affected by the refractive index n and cavity length L of the interferometer cavity. When the temperature changes, the refractive index n and cavity length L of the interferometer cavity also change, causing the FSR to change. When the FSRs of two interferometer cavities connected in series are close, their output spectra overlap to form a large spectral envelope. Temperature changes cause an amplification shift of the spectral envelope, and the amplification factor is inversely proportional to the absolute value of the difference in the FSRs of the two interferometer cavities. Therefore, when the cavity lengths L of the two interferometer cavities are close, their amplification factor increases, greatly improving the temperature sensitivity of the sensor. Therefore, femtosecond laser 3D printing technology has great advantages in the preparation of FP microcavities.

[0070] In the present application, the sensor probe is provided with a vacuum tube 18. After the vacuum tube 18 is evacuated, the vacuum tube 18 is fused and sealed. At this time, the internal vacuum state formed in the sealing sleeve 15 enables the sealing sleeve 15 to remain in a sealed state for a long time, which can effectively eliminate the gas density change caused by thermal expansion and contraction of the gas due to residual gas in the sealing sleeve 15, thereby causing interference error on the effective cavity length of the series interference cavity; in addition, after the sealing sleeve 15 is evacuated, the influence of the external environmental pressure on the various components in the sealing sleeve 15 can be avoided;

[0071] In the present application, the space between the sealing sleeve 15 and the temperature sensing tube 16 is filled with a thermal conductive material layer 14, and then the air inside the sealing sleeve 15 is discharged through the vacuum tube 18, which can effectively ensure that the external temperature is fully conducted in the sensor probe, solving the problem of slow temperature transfer caused by temperature isolation of the vacuum tube, and avoiding the problem of liquid thermal conductive agents such as thermal grease being used for heat conduction and volatilizing in a vacuum state and the problem of fluidity contaminating the reflectivity of the interference cavity.

[0072] The foregoing is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained herein shall, unless otherwise specified or limited, be implemented in accordance with conventional means in the art.

Claims

1. A probe based on enhanced vernier effect, characterized by: It comprises a probe body, an optical fiber cable (6), and a vacuum unit, wherein the vacuum unit is fixed on the optical fiber cable (6), and the probe body is located inside the vacuum unit; The probe body comprises two superimposed first probe bases (8) and a second probe base (9), the diameter of the second probe base (9) being smaller than the diameter of the first probe base (8), four support rods (10) being connected to the second probe base (9), the middle portions of the four support rods (10) forming an open-pore microstructure (12), the upper ends of the four support rods (10) being connected to a solid cylindrical structure (11), the solid cylindrical structure (11) being made by printing a polymer material; The probe body is fixedly arranged on the optical fiber cable (6); the upper end of the optical fiber cable (6) extends inside the first probe base (8) to the lower end of the second probe base (9), and the upper end of the optical fiber cable (6) and the open hole microstructure (12) are connected to each other; The raised portion in the middle of the second probe base (9) serves as a first reflection surface, and the lower end surface of the solid cylindrical structure (11) is provided with a second reflection surface; the cavity between the first reflection surface and the second reflection surface constitutes a first interference cavity in the enhanced vernier interference double cavity; The upper end surface of the solid cylindrical structure (11) serves as a third reflection surface, and the second interference cavity in the enhanced vernier interference double cavity is formed between the second reflection surface and the third reflection surface; the first interference cavity and the second interference cavity are closely connected to form a series structure.

2. The probe based on enhanced vernier effect according to claim 1, characterized in that: The vacuum unit comprises a temperature sensing tube (16) sleeved on the end of the optical fiber cable (6); a sealing sleeve (15) is sleeved on the outside of the temperature sensing tube (16); the probe body is located inside the temperature sensing tube (16); the outer wall of the sealing sleeve (15) is connected to a vacuum tube (18); an air passage (17) is opened on the inner wall of the temperature sensing tube (16); after the vacuum tube (18) is vacuumed, the vacuum tube (18) is melted and sealed.

3. The probe based on enhanced vernier effect according to claim 2, characterized in that: Glass glue (13) is filled between the inner wall of the end of the temperature sensing tube (16) and the outer wall of the end of the optical fiber cable (6), and a heat conductive material layer (14) is filled between the temperature sensing tube (16) and the sealing sleeve (15).

4. The probe based on enhanced vernier effect according to claim 3, characterized in that: The diameter of the first probe base (8) is 150 μm; the diameter of the second probe base (9) is 125 μm; the diameter of the solid cylindrical structure (11) is 30 μm; the diameter of the solid cylindrical structure matches the size of the single-mode optical fiber core (7) used in the optical fiber cable; the length of the first interference cavity is 70 μm; and the length of the second interference cavity is 65 μm.

5. The probe based on enhanced vernier effect according to claim 1, characterized in that: The first interference cavity formed between the inner walls of the four support rods (10) adopts an open design.

6. The method for preparing a probe based on enhanced vernier effect according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: Print end face processing: Take a single-mode optical fiber SMF-28, strip off the coating, wipe it clean with ethanol solution, use a cleaver to cut the optical fiber end face flat, place the cut single-mode optical fiber SMF in the fusion splicer for observation, and discharge clean the single-mode optical fiber SMF end face; place the treated single-mode optical fiber SMF in the fixture and fix the fixture to the printing equipment; S2: Confirm the lens focus and fiber core position, adjust the lens position, focus the lens on the fiber end face, use a 650nm visible light laser light source for fill light processing, and use the micro-displacement platform joystick to adjust the position of the fiber end face; the position of the focused light spot is the position of the fiber core; adjust the micro-displacement platform to adjust the fiber end face to the center position of the printing device; S3: Modeling is performed using the SOLIDWORKS software of the 3D printer to obtain a probe design model, wherein the probe design model includes a first probe base (8) and a second probe base (9) design model and a support rod (10) and a solid cylindrical structure (11) design model, wherein the support rod (10) and the solid cylindrical structure (11) design model are located on the first probe base (8) and the second probe base (9) design model; S4: Structural printing: Printing the probe design model using a 3D printer to obtain a probe model, wherein the probe model includes a first probe base (8) and a second probe base (9) design model, a fixedly connected support rod (10), and a solid cylindrical structure (11) design model.

7. The method for preparing a probe based on enhanced vernier effect according to claim 6, characterized in that: In step 4, the polymer FPI is prepared directly on the tip of a single-mode optical fiber SMF-28 using a MOJI-NANO 3D femtosecond direct laser writing device. During the preparation process, a photoresist is evenly coated on the surface of the substrate, and the FPI area is exposed by ultraviolet light. After exposure, the photoresist is treated with a developer, which removes the photoresist in the unexposed area, thereby forming the desired pattern.

8. Ocean temperature sensor, characterized by: include: A wide spectrum light source (1), a spectrum demodulator (2), an optical fiber circulator (3), and a probe based on an enhanced vernier effect, wherein the probe based on an enhanced vernier effect is the probe based on an enhanced vernier effect according to any one of claims 1 to 7; The wide spectrum light source (1) is connected to the first port of the optical fiber circulator (3), the optical spectrum demodulator (2) is connected to the third port of the optical fiber circulator (3), and the root of the optical fiber cable (6) on the probe based on the enhanced vernier effect is connected to the second port of the optical fiber circulator.

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