Femtosecond laser processed seawater temperature and salinity F-P (Fabry-Perot) microcavity sensor and preparation method thereof

Abstract

The invention provides a femtosecond laser processed seawater temperature and salinity F-P microcavity sensor and a preparation method thereof, and relates to the technical field of optical fiber sensing, the F-P microcavity sensor provided by the invention is a single-mode optical fiber provided with a microstructure cavity, the distance between the first end of the single-mode optical fiber and the microstructure cavity is a preset value, and the first end of the single-mode optical fiber is connected with the microstructure cavity. The length of the microstructure cavity is a preset length, the preset length is smaller than the length of the single-mode optical fiber, and the width of the microstructure cavity is smaller than the diameter of the single-mode optical fiber. According to the preparation method of the seawater temperature and salinity F-P micro-cavity sensor processed by femtosecond laser, the F-P micro-cavity sensor is obtained by performing laser etching on the single-mode optical fiber through femtosecond laser, so that the open micro-cavity is manufactured only by using a femtosecond laser micro-nano processing technology, and the manufacturing process is simple. Through the microstructure cavity, direct contact between a sensing light beam in the F-P interference structure and seawater can be ensured, and seawater temperature sensing and salinity measurement are realized.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing, in particular to a femtosecond laser processed seawater temperature and salinity FP microcavity sensor and a preparation method thereof. Background Art

[0002] The ocean is one of the most important ecosystems on Earth. The temperature and salinity of seawater are key factors affecting the marine environment, climate change, and biodiversity. Accurately measuring the temperature and salinity of seawater is of great significance for marine research, the establishment of climate models, and ecological protection. Therefore, the development of efficient and stable seawater temperature and salinity measurement technology has become an important topic in current scientific research.

[0003] Traditional methods of measuring seawater temperature and salinity usually rely on electronic sensing technology, such as resistance thermometers and conductivity salinometers. Although these electronic sensors can provide relatively accurate measurements in laboratory environments, they face many challenges in actual ocean monitoring. First, the measurement accuracy of electronic sensors is often affected by environmental factors, such as water flow velocity, temperature fluctuations, and salinity changes. In addition, these sensors may experience electrode corrosion, salt deposition, and other phenomena during long-term use, resulting in measurement drift, which in turn affects the reliability of the data. At the same time, traditional electronic sensors are usually large in size, and their deployment and maintenance are relatively complex, making it difficult to achieve high-density real-time monitoring in complex marine environments. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to propose a femtosecond laser processed seawater temperature and salinity FP microcavity sensor. The FP microcavity sensor is a single-mode optical fiber provided with a microstructure cavity. The distance between the first end of the single-mode optical fiber and the microstructure cavity is a preset value, and the length of the microstructure cavity is a preset length, which is smaller than the length of the single-mode optical fiber. The width of the microstructure cavity is smaller than the diameter of the single-mode optical fiber.

[0005] Optionally, the microstructure cavity penetrates the single-mode optical fiber from the cylindrical side of the single-mode optical fiber, and the penetration depth is a preset height. The FP microcavity sensor has four planes at the microstructure cavity, including a first plane, a second plane, a third plane and a fourth plane. The first plane is parallel to the second plane, and the distance between the first plane and the second plane is the width of the microstructure cavity. The third plane is perpendicular to both the first plane and the second plane, the fourth plane is perpendicular to both the first plane and the second plane, the third plane and the fourth plane are parallel, the distance between the third plane and the first end of the single-mode optical fiber is a preset value, and the distance between the third plane and the fourth plane is the length of the microstructure cavity.

[0006] Optionally, the fourth plane of the microstructure cavity is the first end face M1 of the FP microcavity sensor, the third plane of the microstructure cavity is the second end face M2 of the FP microcavity sensor, the first end of the single-mode optical fiber is the third end face M3 of the FP microcavity sensor, an air cavity FPI1 is formed between the first end face M1 and the second end face M2, a glass cavity FPI2 is formed between the second end face M2 and the third end face M3, and a composite cavity FPI3 is formed between the first end face M1 and the third end face M3.

[0007] A method for preparing a seawater temperature and salinity FP microcavity sensor processed by a femtosecond laser, which is used to prepare a seawater temperature and salinity FP microcavity sensor processed by a femtosecond laser, comprising:

[0008] Step 1: Use a fusion splicer to connect the second end of the single-mode optical fiber to the single-mode patch cord, use a cutter to cut the single-mode optical fiber of a set length, and cut the first end of the single-mode optical fiber flat, and use it as the input single-mode optical fiber;

[0009] Step 2: Fix the input single-mode optical fiber on a glass slide with tape, place the glass slide on a 3D mobile work platform, use a three-port circulator, connect the input end of the three-port circulator to an ASE light source and a spectrum analyzer, respectively, and connect the output end to a single-mode jumper of the input single-mode optical fiber;

[0010] Step 3: Adjust the Y and Z directions of the 3D mobile work platform to focus the light spot of the femtosecond laser on the core of the input single-mode optical fiber; adjust the X direction of the 3D mobile work platform to control the distance between the light spot of the femtosecond laser and the first end of the input single-mode optical fiber, so that the distance between the light spot of the femtosecond laser and the first end of the input single-mode optical fiber is a preset value, and set the parameters for etching the microstructure cavity, wherein the parameters for etching the microstructure cavity include the etching length and etching width of the microstructure cavity;

[0011] Step 4: For the input single-mode optical fiber, the processing software is used to control the speed of the micro-processing platform, and laser etching is performed according to the set parameters of the micro-structure cavity to complete the production of the FP micro-cavity sensor.

[0012] Optionally, in step 3, the frequency of laser etching is set to 10 kHz, the objective lens is 20×, and the laser power is about 95 μw.

[0013] Optionally, the etching length of the microstructure cavity is 40 μm, 70 μm, 100 μm or 130 μm, the etching width of the microstructure cavity is 55 μm, and the preset value is 100 μm.

[0014] Optionally, the seawater temperature and salinity FP microcavity sensor processed by femtosecond laser detects seawater temperature and salinity through the three-port circulator, ASE light source and spectrometer.

[0015] The beneficial effects of adopting the above technical solution are:

[0016] The present invention uses only femtosecond laser micro-nano processing technology to realize the production of an open microcavity, and the production process is simple. By constructing a microstructure open cavity, the direct contact between the sensing beam and the seawater in the FP interference structure is ensured, and seawater temperature sensing and salinity measurement are realized. The present invention also uses a simple single-mode-cavity-single-mode structure to design an integrated integrated multi-FP interference structure, which is a reflective sensor and can be plug-and-play. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is one of the structural schematic diagrams of a seawater temperature and salinity FP microcavity sensor processed by a femtosecond laser in an embodiment of the present invention;

[0018] Figure 2 FIG2 is a second schematic diagram of the structure of a femtosecond laser processed seawater temperature and salinity FP microcavity sensor in an embodiment of the present invention, wherein FIGa is a cross-sectional view of a microstructure cavity portion in the FP microcavity sensor, FIGb is a schematic diagram of the structure of a microstructure cavity length of 40 μm in the FP microcavity sensor, FIGc is a schematic diagram of the structure of a microstructure cavity length of 70 μm in the FP microcavity sensor, FIGd is a schematic diagram of the structure of a microstructure cavity length of 100 μm in the FP microcavity sensor, and FIGe is a schematic diagram of the structure of a microstructure cavity length of 130 μm in the FP microcavity sensor;

[0019] Figure 2 In: 11, first plane; 12, second plane; 13, third plane with a microstructure cavity length of 40 μm; 14, fourth plane with a microstructure cavity length of 40 μm; 15, first end of a single-mode optical fiber with a microstructure cavity length of 40 μm; 23, third plane with a microstructure cavity length of 70 μm; 24, fourth plane with a microstructure cavity length of 70 μm; 25, first end of a single-mode optical fiber with a microstructure cavity length of 70 μm; 33, third plane with a microstructure cavity length of 100 μm; 34, fourth plane with a microstructure cavity length of 100 μm; 35, first end of a single-mode optical fiber with a microstructure cavity length of 100 μm; 43, third plane with a microstructure cavity length of 130 μm; 44, fourth plane with a microstructure cavity length of 130 μm; 45, first end of a single-mode optical fiber with a microstructure cavity length of 130 μm;

[0020] Figure 3 A physical diagram of a femtosecond laser processing process in an embodiment of the present invention;

[0021] Figure 4 It is a structural schematic diagram of an experimental test system in an embodiment of the present invention;

[0022] Figure 5 This is a diagram of the seawater salinity measurement result of the FP microcavity sensor in an embodiment of the present invention;

[0023] Figure 6 This is a diagram of the temperature measurement results of the FP microcavity sensor in the embodiment of the present invention in seawater bathing. DETAILED DESCRIPTION

[0024] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0025] In view of the limitations of traditional electronic sensing methods, fiber optic sensing technology has gradually become an ideal alternative. Fiber optic sensors use the transmission characteristics of optical signals and have the advantages of high sensitivity, anti-electromagnetic interference, small size, and easy deployment. Fiber optic sensors can achieve long-term and stable temperature and salinity monitoring in harsh marine environments, and can obtain data in real time and continuously, thereby providing more reliable marine environmental information.

[0026] In view of the problems existing in the prior art, the present invention provides a seawater temperature and salinity FP microcavity sensor processed by a femtosecond laser. Figure 1 The FP microcavity sensor is a single-mode optical fiber provided with a microstructure cavity. The distance between the first end of the single-mode optical fiber and the microstructure cavity is a preset value, which is 100 μm in the present invention. The length of the microstructure cavity is a preset length, which is 40 μm or 70 μm or 100 μm or 130 μm in the present invention. The preset length is smaller than the length of the single-mode optical fiber. The width of the microstructure cavity is smaller than the diameter of the single-mode optical fiber. The width of the microstructure cavity in the present invention is 55 μm.

[0027] It should be noted that the preset length is adjustable. The preset length in the present invention is 40 μm, 70 μm, 100 μm or 130 μm. In the specific implementation process, the preset length can also be adjusted according to actual needs. The present invention prepares FP microcavity sensors with four preset lengths.

[0028] Figure 2Figure a is a cross-sectional view of the microstructure cavity portion in the FP microcavity sensor, and Figure b is a schematic structural diagram of a microstructure cavity length of 40 μm in the FP microcavity sensor. Combining Figure a and Figure b, the microstructure cavity penetrates the single-mode optical fiber from the cylindrical side of the single-mode optical fiber, and the penetration depth is a preset height. The FP microcavity sensor has four planes at the microstructure cavity, including a first plane 11, a second plane 12, a third plane 13 with a microstructure cavity length of 40 μm, and a fourth plane 14 with a microstructure cavity length of 40 μm. The first plane 11 and the second plane 12 are parallel, and the distance between the first plane 11 and the second plane 12 is the width of the microstructure cavity. The third plane 13 with a cavity length of 40 μm is perpendicular to the first plane 11 and the second plane 12, the fourth plane 14 with a microstructure cavity length of 40 μm is perpendicular to the first plane 11 and the second plane 12, the third plane 13 with a microstructure cavity length of 40 μm and the fourth plane 14 with a microstructure cavity length of 40 μm are parallel, the distance between the third plane 13 with a microstructure cavity length of 40 μm and the first end 15 of the single-mode optical fiber with a microstructure cavity length of 40 μm is a preset value, and the distance between the third plane 13 with a microstructure cavity length of 40 μm and the fourth plane 14 with a microstructure cavity length of 40 μm is the length of the microstructure cavity, which is 40 μm.

[0029] Figure 2 Figure c is a schematic diagram of the structure of the FP microcavity sensor with a microstructure cavity length of 70 μm. Combined with Figure a and Figure c, the microstructure cavity penetrates the single-mode optical fiber from the cylindrical side of the single-mode optical fiber, and the penetration depth is a preset height. The FP microcavity sensor has four planes at the microstructure cavity, including a first plane 11, a second plane 12, a third plane 23 with a microstructure cavity length of 70 μm, and a fourth plane 24 with a microstructure cavity length of 70 μm. The first plane 11 is parallel to the second plane 12, and the distance between the first plane 11 and the second plane 12 is the width of the microstructure cavity. The third plane 23 with a microstructure cavity length of 70 μm is parallel to the second plane 12. The distance between the first plane 11 and the second plane 12 is the width of the microstructure cavity. The surface 23 is perpendicular to both the first plane 11 and the second plane 12, the fourth plane 24 with a microstructure cavity length of 70 μm is perpendicular to both the first plane 11 and the second plane 12, the third plane 23 with a microstructure cavity length of 70 μm and the fourth plane 24 with a microstructure cavity length of 70 μm are parallel, the distance between the third plane 23 with a microstructure cavity length of 70 μm and the first end 25 of the single-mode optical fiber with a microstructure cavity length of 70 μm is a preset value, and the distance between the third plane 23 with a microstructure cavity length of 70 μm and the fourth plane 24 with a microstructure cavity length of 70 μm is the length of the microstructure cavity, which is 70 μm.

[0030] Figure 2Figure d in the middle is a schematic diagram of the structure of the FP microcavity sensor with a microstructure cavity length of 100 μm. Combining Figures a and d, the microstructure cavity penetrates the single-mode optical fiber from the cylindrical side of the single-mode optical fiber, and the penetration depth is a preset height. The FP microcavity sensor has four planes at the microstructure cavity, including a first plane 11, a second plane 12, a third plane 33 with a microstructure cavity length of 100 μm, and a fourth plane 34 with a microstructure cavity length of 100 μm. The first plane 11 is parallel to the second plane 12, and the distance between the first plane 11 and the second plane 12 is the width of the microstructure cavity. The third plane 33 with a microstructure cavity length of 100 μm is parallel to the second plane 12. The distance between the first plane 11 and the second plane 12 is the width of the microstructure cavity. 3 is perpendicular to both the first plane 11 and the second plane 12, the fourth plane 34 with a microstructure cavity length of 100 μm is perpendicular to both the first plane 11 and the second plane 12, the third plane 33 with a microstructure cavity length of 100 μm is parallel to the fourth plane 34 with a microstructure cavity length of 100 μm, the distance between the third plane 33 with a microstructure cavity length of 100 μm and the first end 35 of the single-mode optical fiber with a microstructure cavity length of 100 μm is a preset value, and the distance between the third plane 33 with a microstructure cavity length of 100 μm and the fourth plane 34 with a microstructure cavity length of 100 μm is the length of the microstructure cavity, which is 100 μm.

[0031] Figure 2 Figure e is a schematic diagram of the structure of the FP microcavity sensor with a microstructure cavity length of 130 μm. Combining Figure a and Figure e, the microstructure cavity penetrates the single-mode optical fiber from the cylindrical side of the single-mode optical fiber, and the penetration depth is a preset height. The FP microcavity sensor has four planes at the microstructure cavity, including a first plane 11, a second plane 12, a third plane 43 with a microstructure cavity length of 130 μm, and a fourth plane 44 with a microstructure cavity length of 130 μm. The first plane 11 is parallel to the second plane 12, and the distance between the first plane 11 and the second plane 12 is the width of the microstructure cavity. The third plane 43 with a microstructure cavity length of 130 μm is 130 μm. 3 is perpendicular to both the first plane 11 and the second plane 12, the fourth plane 44 with a microstructure cavity length of 130 μm is perpendicular to both the first plane 11 and the second plane 12, the third plane 43 with a microstructure cavity length of 130 μm is parallel to the fourth plane 44 with a microstructure cavity length of 130 μm, the distance between the third plane 43 with a microstructure cavity length of 130 μm and the first end 45 of the single-mode optical fiber with a microstructure cavity length of 130 μm is a preset value, and the distance between the third plane 43 with a microstructure cavity length of 130 μm and the fourth plane 44 with a microstructure cavity length of 130 μm is the length of the microstructure cavity, which is 130 μm.

[0032] Combination Figure 1, the fourth plane of the microstructure cavity is the first end face M1 of the FP microcavity sensor, the third plane of the microstructure cavity is the second end face M2 of the FP microcavity sensor, the first end of the single-mode optical fiber is the third end face M3 of the FP microcavity sensor, an air cavity FPI1 is formed between the first end face M1 and the second end face M2, a glass cavity FPI2 is formed between the second end face M2 and the third end face M3, and a composite cavity FPI3 is formed between the first end face M1 and the third end face M3. Specifically, when light is incident on the FP microcavity sensor, the intensity of the incident light is I0. After passing through the first end face M1 of the FP microcavity sensor, the light beam is transmitted and reflected. The intensity of the reflected light is recorded as I01, and the intensity of the transmitted light is recorded as I10. The transmitted light I10 continues to propagate toward the second end face M2 of the optical fiber. At the M2 end face, transmission and reflection phenomena also occur. The intensity of the reflected light is marked as I02, and the intensity of the transmitted light is marked as I20. The reflected light I01 and the reflected light I02 are coherently superimposed to form an air cavity FPI1. The transmitted light I20 passes through the third end face M3 of the optical fiber, where the light beam undergoes transmission and reflection again. The intensity of the reflected light is recorded as I03, and the intensity of the transmitted light is recorded as I30. The reflected light I02 and the reflected light I03 are coherently superimposed to form a glass cavity FPI2. The reflected light I01 is also coherently superimposed with the reflected light I03 to form a composite cavity FPI3.

[0033] The FP microcavity sensor structure can be regarded as the interference superposition of the reflected light beams of three FP structures. The three FP interferences are integrated in a compact optical fiber sensor structure. When the salinity and temperature of seawater change, the optical path difference of multiple FPIs will change, which will cause the trough of the reflection spectrum to drift.

[0034] The method for preparing the seawater temperature and salinity FP microcavity sensor processed by femtosecond laser is used to prepare the seawater temperature and salinity FP microcavity sensor processed by femtosecond laser in claim 1, comprising:

[0035] Step 1: Use a fusion splicer to connect the second end of the single-mode optical fiber to the single-mode patch cord, use a cutter to cut the single-mode optical fiber of a set length, and cut the first end of the single-mode optical fiber flat, and use it as the input single-mode optical fiber;

[0036] In the present invention, the cutting knife cuts the single-mode optical fiber of set length 8.2 μm / 125 μm, and the fusion splicer model is Fujikawa fusion splicer, model S179C.

[0037] Step 2: Fix the input single-mode optical fiber on a glass slide with tape, place the glass slide on a 3D mobile work platform, use a three-port circulator, connect the input end of the three-port circulator to an ASE light source and a spectrum analyzer, respectively, and connect the output end to a single-mode jumper of the input single-mode optical fiber;

[0038] Step 3: Adjust the Y and Z directions of the 3D mobile work platform to focus the light spot of the femtosecond laser on the core of the input single-mode optical fiber; adjust the X direction of the 3D mobile work platform to control the distance between the light spot of the femtosecond laser and the first end of the input single-mode optical fiber, so that the distance between the light spot of the femtosecond laser and the first end of the input single-mode optical fiber is a preset value, and set the parameters for etching the microstructure cavity, wherein the parameters for etching the microstructure cavity include the etching length and etching width of the microstructure cavity;

[0039] Among them, the frequency of laser etching in step 3 is set to 10kHz, the objective lens is 20×, the laser power is about 95μw, and the sensing optical fiber is placed on a glass slide during the microstructure cavity processing to avoid optical fiber shaking caused by excessive power during the processing.

[0040] Step 4: For the input single-mode optical fiber, the processing software is used to control the speed of the micro-processing platform, and laser etching is performed according to the set parameters of the micro-structure cavity to complete the production of the FP micro-cavity sensor.

[0041] The processing software in this embodiment uses Newport μFab, and laser etching is performed at a speed of 180 μm / s according to the set parameters.

[0042] The seawater temperature and salinity optical fiber FP microcavity sensor designed in this embodiment is processed by femtosecond laser. The femtosecond laser processing process is as follows: Figure 3 As shown, the lengths of the microstructure cavities are 40 μm, 70 μm, 100 μm, and 130 μm, respectively, the width is 55 μm, the height is 125 μm, and the length of the end single-mode optical fiber is 100 μm.

[0043] The femtosecond laser processed seawater temperature and salinity FP microcavity sensor detects seawater temperature and salinity through the three-port circulator, ASE light source and spectrum analyzer. The specific detection process refers to the experimental test system, such as Figure 4 As shown in the figure, the test system mainly includes ASE light source, spectrum analyzer (OSA: YOKOGAWA, AQ6370D), three-port circulator, and thermostatic seawater sample bath. The ASE light source enters the sensor structure through the circulator, reflects in the three FP cavities, and enters the spectrum analyzer through the circulator again. Since the design is a reflective sensor structure, the seawater sample is placed in a beaker and a thermostatic seawater bath, so that the seawater sample completely enters the microstructure cavity and ensures the stability of the measurement environment. The entire experiment is carried out at room temperature to avoid interference from temperature changes.

[0044] Since the longer cavity length increases the propagation path of light, it makes the response to external changes (such as temperature, salinity, etc.) more sensitive, while not introducing too much light loss or noise due to the excessive cavity length. Therefore, the sensor with a cavity length of 100μm achieves the best balance between optimizing the interference effect and avoiding excessive loss, thus providing the best sensitivity.

[0045] The FP microcavity sensor with a cavity length of 100 μm exhibited high sensitivity and linear response in seawater salinity measurement, such as Figure 5 As shown in Figure 2, with the increase of salinity, the reflection spectrum trough undergoes an obvious red shift phenomenon. When the salinity increases from 0‰ to 60‰, the wavelength eventually moves to 1596.15nm based on the initial interference wavelength of 1588.42nm, with a total displacement of 7.73nm and a sensitivity of 0.13nm / ‰ (fitting degree R 2 =0.9970). In addition, the initial interference wavelength was 1592.82 nm, the total wavelength shift was 7.79 nm, the sensitivity was maintained at 0.13 nm / ‰, and the fitting degree R 2 is 0.9974.

[0046] Under different temperature conditions, the reflection spectrum trough of the FP microcavity sensor shows a trend of blue shifting with increasing temperature, such as Figure 6 In a seawater environment of 25°C to 65°C, with the interference wavelength of 1592.33nm at 25°C as the reference, the trough eventually moves to 1588.69nm, with a total displacement of 3.64nm, showing a sensitivity of -0.071nm / °C (fitting degree R 2 =0.9988). The total displacement was 4.00 nm with a sensitivity of -0.081 nm / °C and a fitting degree of R 2 =0.9997.

[0047] Since the interference fringes respond differently to changes in seawater temperature and salinity, the sensitivity matrix can be used to achieve simultaneous measurement of seawater temperature and salinity. Within the target wavelength range, the wavelength shift of the two interference fringes can be expressed in matrix form as:

[0048]

[0049] Among them, ΔS and ΔT are the changes in seawater salinity and temperature, respectively, K is the sensitivity matrix, and the sensitivity coefficient K iS and K iT (i=1,2) is Figure 5 , Figure 6 The obtained linear fitting coefficients.

[0050] Select Dip1 and Dip2 for measurement, combined with Figure 5 and Figure 6 The experimental fitting coefficients can be used to calculate the response of the FP microcavity sensor to changes in seawater temperature and salinity:

[0051]

[0052] By measuring the displacement of the trough of the reflection spectrum, we can obtain the changes in seawater salinity and temperature respectively.

[0053] The key points of the present invention are:

[0054] (1) The present invention realizes the fabrication of an open microcavity using only femtosecond laser micro-nano processing technology, and the fabrication process is simple.

[0055] (2) The present invention ensures direct contact between the sensing beam and seawater in the FP interference structure by constructing a microstructure open cavity, thereby realizing seawater temperature sensing and salinity measurement.

[0056] (3) The present invention designs an integrated multi-FP interference structure using a simple single-mode-cavity-single-mode structure. The structure is a reflective sensor that can be plug-and-play.

[0057] The present invention provides a femtosecond laser processed seawater temperature and salinity FP microcavity sensor and a preparation method thereof, and the FP microcavity sensor is used for seawater temperature sensing and salinity measurement. The sensor has the advantages of simple manufacturing process, compact structure, low cost, high stability, etc., and can realize real-time, online, and rapid detection of weakly changing physical quantities.

[0058] The above description is only a preferred embodiment of the present disclosure and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the above-mentioned inventive concept. For example, the above-mentioned features are replaced with the technical features with similar functions disclosed in the embodiments of the present disclosure (but not limited to) to form a technical solution.

Claims

1. Femtosecond laser processed seawater temperature and salinity FP microcavity sensor, characterized in that: The FP microcavity sensor is a single-mode optical fiber provided with a microstructure cavity, the distance between the first end of the single-mode optical fiber and the microstructure cavity is a preset value, the length of the microstructure cavity is a preset length, the preset length is smaller than the length of the single-mode optical fiber, and the width of the microstructure cavity is smaller than the diameter of the single-mode optical fiber.

2. The femtosecond laser processed seawater temperature and salinity FP microcavity sensor according to claim 1, characterized in that: The microstructure cavity penetrates the single-mode optical fiber from the cylindrical side of the single-mode optical fiber, and the penetration depth is a preset height. The FP microcavity sensor has four planes at the microstructure cavity, including a first plane, a second plane, a third plane and a fourth plane. The first plane and the second plane are parallel, and the distance between the first plane and the second plane is the width of the microstructure cavity. The third plane is perpendicular to both the first plane and the second plane. The fourth plane is perpendicular to both the first plane and the second plane. The third plane and the fourth plane are parallel. The distance between the third plane and the first end of the single-mode optical fiber is a preset value, and the distance between the third plane and the fourth plane is the length of the microstructure cavity.

3. The femtosecond laser processed seawater temperature and salinity FP microcavity sensor according to claim 2, characterized in that: The fourth plane of the microstructure cavity is the first end face M1 of the FP microcavity sensor, the third plane of the microstructure cavity is the second end face M2 of the FP microcavity sensor, the first end of the single-mode optical fiber is the third end face M3 of the FP microcavity sensor, an air cavity FPI1 is formed between the first end face M1 and the second end face M2, a glass cavity FPI2 is formed between the second end face M2 and the third end face M3, and a composite cavity FPI3 is formed between the first end face M1 and the third end face M3.

4. A method for preparing a seawater temperature and salinity FP microcavity sensor processed by femtosecond laser, characterized in that: The femtosecond laser processed seawater temperature and salinity FP microcavity sensor for preparing claim 1 comprises: Step 1: Use a fusion splicer to connect the second end of the single-mode optical fiber to the single-mode patch cord, use a cutter to cut the single-mode optical fiber of a set length, and cut the first end of the single-mode optical fiber flat, and use it as the input single-mode optical fiber; Step 2: Fix the input single-mode optical fiber on a glass slide with tape, place the glass slide on a 3D mobile work platform, use a three-port circulator, connect the input end of the three-port circulator to an ASE light source and a spectrum analyzer, respectively, and connect the output end to a single-mode jumper of the input single-mode optical fiber; Step 3: Adjust the Y and Z directions of the 3D mobile work platform to focus the light spot of the femtosecond laser on the core of the input single-mode optical fiber; adjust the X direction of the 3D mobile work platform to control the distance between the light spot of the femtosecond laser and the first end of the input single-mode optical fiber, so that the distance between the light spot of the femtosecond laser and the first end of the input single-mode optical fiber is a preset value, and set the parameters for etching the microstructure cavity, wherein the parameters for etching the microstructure cavity include the etching length and etching width of the microstructure cavity; Step 4: For the input single-mode optical fiber, the processing software is used to control the speed of the micro-processing platform, and laser etching is performed according to the set parameters of the micro-structure cavity to complete the production of the FP micro-cavity sensor.

5. The method for preparing the seawater temperature and salinity FP microcavity sensor processed by femtosecond laser according to claim 4, characterized in that: In step 3, the frequency of laser etching is set to 10 kHz, the objective lens is 20×, and the laser power is about 95 μw.

6. The method for preparing the seawater temperature and salinity FP microcavity sensor processed by femtosecond laser according to claim 4, characterized in that: The etching length of the microstructure cavity is 40 μm, 70 μm, 100 μm or 130 μm, the etching width of the microstructure cavity is 55 μm, and the preset value is 100 μm.

7. The method for preparing the seawater temperature and salinity FP microcavity sensor processed by femtosecond laser according to claim 4, characterized in that: The seawater temperature and salinity FP microcavity sensor processed by femtosecond laser detects seawater temperature and salinity through the three-port circulator, ASE light source and spectrum analyzer.

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