Reflection-type optical fiber sensing probe, preparation method thereof and application of reflection-type optical fiber sensing probe in sensor

Abstract

The invention discloses a reflective optical fiber sensing probe, a preparation method thereof and application of the reflective optical fiber sensing probe in a sensor. The reflective optical fiber sensing probe comprises an optical fiber taper, an optical fiber microsphere molten at the conical end of the optical fiber taper, and a PDMS cladding attached to the surface of the optical fiber microsphere. According to the optical fiber sensing probe, the optical fiber microspheres wrapped with the PDMS layers are connected in series with the optical fiber taper, so that an optical fiber Michelson interferometer is formed, finally, simultaneous measurement of temperature and transverse stress can be achieved, temperature crosstalk in stress measurement is effectively avoided, and the optical fiber sensing probe has high mechanical strength.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensors, and in particular relates to a reflective optical fiber sensing probe, a preparation method thereof, and an application in a sensor. Background Art

[0002] Optical fiber sensors have attracted much attention due to their advantages such as low transmission loss, corrosion resistance, large dynamic range of measurement, small size, and resistance to electromagnetic interference. They have been widely used in the fields of physics, chemistry, industry, and biosensing, especially in harsh environments such as flammable, explosive, and strong electromagnetic interference. Optical fiber sensors have great advantages over traditional electrical sensors. Due to their unique advantages, they can measure a variety of physical quantities, such as temperature, refractive index, lateral pressure, strain, humidity, etc.

[0003] The basic working principle of the fiber optic sensor is to send the optical signal from the light source into the modulator through the optical fiber, so that the measured parameter interacts with the light entering the modulation area, causing the optical properties of the light, such as the intensity, wavelength, frequency, phase, polarization state, etc., to change, becoming a modulated signal source, and then sent to the optical detector through the optical fiber, and after demodulation, the measured parameter is obtained. Since optical fiber has many excellent properties, such as: resistance to electromagnetic radiation interference and anti-ion radiation interference, and mechanical properties of thin diameter, soft texture, and light weight; insulation and non-inductive electrical properties; water-resistant, high temperature-resistant, and corrosion-resistant chemical properties, it is very advantageous to introduce it into the sensor.

[0004] At present, there are relatively few studies on low-cost and simple-structured optical fiber sensors. For example, U.S. Patent US6865194B1 and Chinese Patent CN202255683U both disclose an optical fiber sensor. However, these optical fiber sensors all use optical fiber Bragg gratings to monitor temperature, etc. Since the production of optical fiber Bragg gratings usually requires phase mask technology and ultraviolet laser writing, the cost is relatively high and the production process is quite complicated, which is very unfavorable for the widespread promotion of market applications. Therefore, the research and development of new optical fiber sensors with low cost and simple structure has become a top priority. Summary of the invention

[0005] Based on the above technical problems, the present invention provides a reflective fiber optic sensing probe, a preparation method and an application in a sensor. The fiber optic sensing probe utilizes a fiber optic microsphere wrapped with a PDMS layer and a fiber optic cone in series, thereby forming a fiber optic Michelson interferometer, which can ultimately not only achieve simultaneous measurement of temperature and lateral stress, but also effectively avoid temperature crosstalk in stress measurement and has strong mechanical strength.

[0006] The present invention provides a reflective optical fiber sensing probe, which comprises an optical fiber cone, an optical fiber microsphere melted on the conical end of the optical fiber cone, and a PDMS cladding attached to the surface of the optical fiber microsphere.

[0007] Preferably, the tapered region of the optical fiber taper has a length of 130-160 μm and a minimum cross-sectional diameter of 60-80 μm.

[0008] Preferably, the optical fiber microsphere is in the shape of a sphere with a diameter of 120-130 μm.

[0009] Preferably, the PDMS cladding is formed by curing Dow Corning DC184 PDMS optical adhesive and has a thickness of 800-1000 μm.

[0010] The present invention also provides a method for preparing the above-mentioned reflective optical fiber sensing probe, comprising the following steps:

[0011] S1, using optical fiber taper technology to draw the optical fiber into a taper to obtain an optical fiber taper;

[0012] S2, using optical fiber fusion technology to melt the front part of the tapered end of the optical fiber cone, and forming an optical fiber microsphere under natural surface tension after cooling;

[0013] S3, using a coating process to coat PDMS optical glue on the surface of the optical fiber microsphere, and after curing, the reflective optical fiber sensing probe is obtained.

[0014] Preferably, step S1 specifically includes:

[0015] Two sections of single-mode optical fibers with their coating removed are fixed in the V-groove of an optical fiber fusion splicer, and the two sections of single-mode optical fibers are controlled to move closer to each other until their ends touch each other. After discharge to fuse the two sections of single-mode optical fibers, one section of the single-mode optical fiber is stretched unilaterally outward along the axial direction from the fusion point, and the other section of the single-mode optical fiber is stretched into a cone. After being broken, the optical fiber cone is obtained.

[0016] Preferably, step S2 specifically includes:

[0017] The optical fiber cone and the third section of single-mode optical fiber with the coating removed are fixed in the V-groove of an optical fiber fusion splicer so that the optical fiber cone does not contact the end of the third section of single-mode optical fiber. When discharge melts the front part of the tapered end of the optical fiber cone, the third section of single-mode optical fiber is controlled not to advance in the direction of the optical fiber cone. After cooling, the front part of the tapered end of the optical fiber cone forms an optical fiber microball under the action of natural surface tension.

[0018] Preferably, step S3 specifically includes:

[0019] The PDMS optical glue and the curing agent are mixed evenly, and then coated on the surface of the optical fiber microsphere, and heated and cured to obtain the reflective optical fiber sensing probe.

[0020] The present invention also proposes an application of the above-mentioned reflective optical fiber sensing probe in an optical fiber sensor, wherein the optical fiber sensor comprises a broadband light source, the optical fiber sensing probe and a spectrum analyzer;

[0021] Wherein, the emission end of the broadband light source is connected to the input end of the optical fiber sensing probe through a circulator, and the output end of the optical fiber sensing probe is connected to the input end of the optical spectrum analyzer through a circulator.

[0022] Preferably, the optical fibre sensor is used to monitor temperature and / or lateral pressure.

[0023] The specific working principle of the sensor of the present invention is as follows:

[0024] In the reflective optical fiber sensing probe of the present invention, when the incident light reaches the optical fiber cone, the transmitted light is divided into two beams of light and transmitted forward, one part is still transmitted forward along the fiber core, and the other part enters the PDMS cladding for transmission; when it is about to be transmitted to the optical fiber microsphere, since the light propagates in a straight line, part of the light in the free space can be coupled into the optical fiber microsphere to form an echo gallery mode, and part of the light is reflected by the surface of the optical fiber microsphere, so the light beam entering the optical fiber microsphere is reflected by the cladding mode and the core mode, and is transmitted along the core and the cladding; when the core mode and the cladding mode returning along the original path meet the optical fiber cone again, the light in the cladding and the light in the core are coupled and converged to the core for transmission, and finally reach the spectrometer to form a reflection interference spectrum.

[0025] When light waves are transmitted in the sensor, the total light intensity after interference is

[0026]

[0027] In the above formula, I1 and I2 are the light intensity values ​​in the core and cladding respectively, Φ m is the phase difference between the core and the cladding, which can be expressed as:

[0028] Φ m =2πΔn eff L / λ

[0029] In the above formula, Δn eff is the difference between the effective refractive index of the fiber core and the cladding, λ is the central wavelength of the incident light, and L is the interaction length of the sensor, where Δn eff Can be expressed as

[0030] Δn eff =n core -n clad

[0031] In the above formula, n core is the core refractive index, n cladis the cladding refractive index;

[0032] When the phase difference Φ m =(2m+1), m is a constant (0, 1, 2...), and the wavelength of the interference peak and trough will be generated, and its expression is:

[0033]

[0034] As the strain applied to the sensor increases, the effective refractive index difference of the optical fiber will also change, and its effective expression is:

[0035]

[0036] Where Δn e ' ff is the effective refractive index difference when the sensor is subjected to strain, and is the effective refractive index difference of the optical fiber without strain, k is the refractive index strain coefficient, and its value is -0.1649×10 -6 , Δε is the difference between the strains in the core and cladding; therefore, Can be changed to

[0037]

[0038] From the above formula, we can get k, L, and m are constants when the temperature remains unchanged, and the wavelength of the interference peak is only related to the strain and is proportional to it.

[0039] The present invention proposes a reflective optical fiber sensing probe based on a PDMS ball wrapped optical fiber cone, which realizes the simultaneous measurement of lateral stress and temperature. While effectively avoiding temperature crosstalk in stress measurement, the structure has strong mechanical strength because the PDMS firmly wraps the optical fiber cone.

[0040] At the same time, the preparation method of the optical fiber sensing probe is simple. It only requires forming an optical fiber microsphere wrapped with a PDMS layer at the end of the prepared optical fiber cone. The optical fiber cone and the PDMS cladding are combined to form an optical fiber Michelson interferometer MI. The corresponding multiple interference peaks in the reflection interference spectrum respond differently to lateral stress and temperature. In actual operation, two interference peaks can be selected and their changes with lateral stress and temperature can be monitored. The stress sensitivity of the two interference peaks can reach 1.75666nm / N and 1.78371nm / N, respectively, and the temperature sensitivity can reach 910.43pm / ℃ and 680.53pm / ℃, respectively.

[0041] In addition, since the PDMS cladding not only has a smaller Young's modulus but also has a higher thermo-optic coefficient and thermal expansion coefficient, the resulting optical fiber sensing probe has better stress and temperature response characteristics, and the transverse stress and temperature can be measured simultaneously using the sensing matrix method.

[0042] The optical fiber sensing probe described in the present invention has high mechanical strength, low cost, and high sensitivity, and has important application prospects in the fields of safety monitoring, aerospace, and automobile industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 An optical picture of the optical fiber cone with an optical fiber microball at the end of the present invention;

[0044] Figure 2 This is an optical picture of the optical fiber sensing probe of the present invention;

[0045] Figure 3 is the reflection spectrum of the optical fiber sensing probe of the present invention;

[0046] Figure 4 It is a schematic diagram of a temperature and stress testing device based on the optical fiber sensing probe of the present invention;

[0047] Figure 5 is a stress response characteristic diagram of the optical fiber sensing probe of the present invention;

[0048] Figure 6 This is a temperature response characteristic diagram of the optical fiber sensing probe of the present invention. DETAILED DESCRIPTION

[0049] Hereinafter, the present invention will describe the technical solution in detail through specific embodiments, but it should be clearly stated that these embodiments are for illustration only and are not to be construed as limiting the scope of the present invention.

[0050] A reflective optical fiber sensing probe is prepared by the following method:

[0051] (1) Take two sections of single-mode optical fiber (SMF-28e+) of the same length, use a fiber stripping pliers to strip the coating layer at the end to expose the bare layer of the optical fiber, use lens tissue dipped in medical alcohol to wipe off the debris remaining on the surface of the optical fiber, and then put the stripped single-mode optical fiber into the optical fiber cutter for cutting. The optical fiber end face is cut flat; put the two sections of single-mode optical fiber with flat end faces into the V-groove of the optical fiber fusion splicer (KL-300T) and fix them. First, set the discharge mode of the optical fiber fusion splicer to the cleaning mode, and perform a manual cleaning discharge on the optical fiber. The discharge time is 300ms and the discharge intensity is 100bit. The impurities on the optical fiber end face are cleaned; bring the two sections of single-mode optical fiber close to each other until the end faces touch, and press the continue button to use the optical fiber automatic fusion program The welding was performed, and after the welding was completed, manual supplementary discharge was performed, the discharge time was 300ms, and the discharge intensity was 210bit. During the discharge process, one end of the single-mode optical fiber was fixed, and a constant external force was applied to the other end of the single-mode optical fiber, so that the single-mode optical fiber was stretched unilaterally from the fusion point along the axial direction. After 10 discharges, a section of optical fiber long cone (length of about 4mm, waist diameter of about 68μm, double cone structure) was obtained; one end of the waist area of ​​the optical fiber long cone was adjusted to the position of the two electrodes of the optical fiber welding machine, and manual discharge was performed again. During the discharge process, a constant external force was applied to the two sections of optical fiber, and one end of the waist area of ​​the optical fiber long cone was pulled off to obtain an optical fiber cone (the cone area length was about 150μm, and the minimum cross-sectional diameter was 70μm);

[0052] (2) Open the windproof cover of the fiber fusion splicer, adjust the position of the light cone obtained above, so that it is fixed on one side of the V-groove of the fiber fusion splicer, take another section of single-mode optical fiber, and after the same operation as step (1) above, obtain a single-mode optical fiber with a flat end face, and fix it on the other side of the V-groove of the fiber fusion splicer; control the fiber cone and the end face of the single-mode optical fiber not to contact, manually discharge to melt, during the discharge process, control the single-mode optical fiber not to move forward, so that the fiber cone and the single-mode optical fiber are melted separately, after three manual discharges, the front part of the tapered end of the light cone is melted under the high temperature of the discharge, and after cooling, a fiber microsphere is formed at the front part of the tapered end of the fiber cone under the action of natural surface tension, thereby obtaining a fiber cone with a fiber microsphere at the end. Its specific structure can be referred to Figure 1 ,Depend on Figure 1 It can be seen that the optical fiber cone with an optical fiber microball at the end includes an optical fiber cone handle and an optical fiber microball. The diameter of the optical fiber microball is equivalent to the diameter of the optical fiber cladding, and its shape is a sphere with a diameter of 125 μm.

[0053] (3) Take out the fiber cone with the fiber microsphere at the end from the fiber fusion splicer and fix it on the sample holder. TM184 transparent silicone curing agent) is prepared into PDMS optical glue in a ratio of 5:1; the PDMS optical glue is placed on a clean glass slide, and under the lens of the optical fiber precision cutting CCD system (XDC-10A-530HS), the probe of the dispensing instrument is dipped into an appropriate amount of PDMS optical glue and slowly approaches the optical fiber microsphere at the end of the optical fiber cone, and the PDMS optical glue on the dispensing instrument probe is coated on the optical fiber microsphere. Since PDMS is a liquid optical glue with a relatively high viscosity, the optical glue coated on the optical fiber microsphere The liquid will form a PDMS optical adhesive film that completely wraps the optical fiber microsphere; the optical fiber cone coated with the PDMS optical adhesive film is placed in a programmable temperature control box (DHG-9031A) and heated for cross-linking reaction. The heating temperature is set to 160°C and the heating time is 15 minutes. The silicon-oxygen bonds (Si-O-Si) in the PDMS molecules are broken by the cross-linking reaction to form new silicon-oxygen bonds, and finally a three-dimensional network structure is formed. The PDMS also becomes solid to form a PDMS cladding, thereby obtaining the reflective optical fiber sensing probe. The results are as follows Figure 2 shown by Figure 2 It can be seen that in the reflective optical fiber sensing probe, the diameter of the optical fiber microsphere with PDMS cladding is 950 μm, its surface is smooth, and the light transmittance is very good. In addition, the PDMS cladding has good flexibility, so the optical fiber sensing probe can have strong mechanical strength.

[0054] Sensing characteristics test

[0055] The end of the above-mentioned optical fiber sensor probe is connected to a circulator, one end of the circulator is connected to a broadband light source (SC-5-FC), and the other end is connected to a spectrum analyzer (AQ6370D); in the working state, the broadband light source emits broadband light, which is transmitted to the optical fiber sensor probe through the circulator. At this time, after the incident light reaches the optical fiber cone, the transmitted light is divided into two beams of light for forward transmission, one part is still transmitted forward along the core, and the other part enters the PDMS cladding for transmission. When it is about to be transmitted to the optical fiber microsphere, since the light propagates in a straight line, part of the light in the free space can be coupled into the optical fiber microsphere to form an echo gallery mode, and part is reflected by the surface of the optical fiber microsphere. Therefore, the light beam entering the optical fiber microsphere is reflected by the cladding mode and the core mode, and is transmitted along the core and the cladding; when the core mode and the cladding mode returning along the original path meet the optical fiber cone again, the light in the cladding and the light in the core are coupled and converged to the core for transmission, and finally reach the spectrometer to form a reflection interference spectrum. The results are as follows Figure 3 shown.

[0056] (1) Build a pressure test device, which consists of a circulator, a broadband light source, a spectrum analyzer, and a cover glass / sample support. Fix the optical fiber sensing probe prepared in the embodiment on a glass slide with paper tape so that the optical fiber microsphere is in the center of the glass slide. Place a weight on the microsphere and keep the stress in the vertical direction. Figure 4 shown.

[0057] When studying the response characteristics of the optical fiber sensing probe to pressure, keeping other variables constant, applying pressure to the optical fiber sensing probe in the vertical direction by applying weights, the mass of each weight is 0.3g, corresponding to a pressure of 2.94N applied in the vertical direction, and the stress gradient is set to 2.94N, 5.88N, 8.82N, 11.76N, 14.70N, 17.64N, and each time a weight is placed, wait for 2 minutes and record the reflection spectrum under each pressure. The results are as follows: Figure 5 shown.

[0058] Depend on Figure 5 It can be seen that with the increase of pressure, the resonant wavelength of the interference trough moves toward the shorter wavelength direction. Figure 3 The interference peak near 1480nm, when the pressure changed by 17.64N, the troughs of the two interference peaks near 1500nm and 1550nm drifted to the long wavelength by 32.17nm and 35.74nm respectively. The interference peak was recorded at the central wavelength of each stress, and these data points were fitted, with sensitivities of 1.75666nm / N and 1.78371nm / N respectively.

[0059] (2) Build a temperature experimental device, which consists of a circulator, a broadband light source, a spectrum analyzer, and a temperature control box. Similarly, fix the optical fiber sensor probe prepared in the embodiment on a glass slide with paper tape, connect the end of the optical fiber sensor probe to the circulator, and place the connected structure on the sample table. Figure 4 As shown;

[0060] When studying the response characteristics of the optical fiber sensor probe to temperature, the temperature of the temperature control box was set to 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C respectively. After the temperature reached each set temperature value and stabilized for 1 minute, the reflection spectrum of the optical fiber sensor probe at each temperature was recorded. The results are as follows: Figure 6 As shown, the temperature sensitivities of the two interference peaks are 910.43 pm / °C and 680.53 pm / °C, respectively.

[0061] From the above, it can be seen that the reflective fiber optic sensing probe based on PDMS ball wrapped fiber cone proposed in the present invention realizes the simultaneous measurement of lateral stress and temperature by using fiber microspheres wrapped in PDMS layer and fiber cones in series. Compared with the fiber cone directly wrapped in PDMS layer, the former has much higher sensitivity to stress and temperature than the latter.

[0062] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A reflective optical fiber sensing probe, characterized in that: The invention comprises an optical fiber cone, an optical fiber microsphere melted on the conical end of the optical fiber cone, and a PDMS cladding attached to the surface of the optical fiber microsphere.

2. The reflective optical fiber sensing probe according to claim 1, characterized in that: The tapered region of the optical fiber taper has a length of 130-160 μm and a minimum cross-sectional diameter of 60-80 μm.

3. The reflective optical fiber sensing probe according to claim 1 or 2, characterized in that: The optical fiber microsphere is in the shape of a sphere with a diameter of 120-130 μm.

4. The reflective optical fiber sensing probe according to any one of claims 1 to 3, characterized in that: The PDMS cladding is formed by curing Dow Corning DC184 PDMS optical adhesive and has a thickness of 800-1000 μm.

5. A method for preparing the reflective optical fiber sensing probe according to any one of claims 1 to 4, characterized in that: The steps include: S1, using optical fiber taper technology to draw the optical fiber into a taper to obtain an optical fiber taper; S2, using optical fiber fusion technology to melt the front part of the tapered end of the optical fiber cone, and forming an optical fiber microsphere under natural surface tension after cooling; S3, using a coating process to coat PDMS optical glue on the surface of the optical fiber microsphere, and after curing, the reflective optical fiber sensing probe is obtained.

6. The method for preparing the reflective optical fiber sensing probe according to claim 5, characterized in that: Step S1 specifically includes: Two sections of single-mode optical fibers with their coating removed are fixed in the V-groove of an optical fiber fusion splicer, and the two sections of single-mode optical fibers are controlled to move closer to each other until their ends touch each other. After discharge to fuse the two sections of single-mode optical fibers, one section of the single-mode optical fiber is stretched unilaterally outward along the axial direction from the fusion point, and the other section of the single-mode optical fiber is stretched into a cone. After being broken, the optical fiber cone is obtained.

7. The method for preparing the reflective optical fiber sensing probe according to claim 6, characterized in that: Step S2 specifically includes: The optical fiber cone and the third section of single-mode optical fiber with the coating removed are fixed in the V-groove of an optical fiber fusion splicer so that the optical fiber cone does not contact the end of the third section of single-mode optical fiber. When discharge melts the front part of the tapered end of the optical fiber cone, the third section of single-mode optical fiber is controlled not to advance in the direction of the optical fiber cone. After cooling, the front part of the tapered end of the optical fiber cone forms an optical fiber microball under the action of natural surface tension.

8. The method for preparing the reflective optical fiber sensing probe according to any one of claims 5 to 7, characterized in that: Step S3 specifically includes: The PDMS optical glue and the curing agent are mixed evenly, and then coated on the surface of the optical fiber microsphere, and heated and cured to obtain the reflective optical fiber sensing probe.

9. Use of the reflective optical fiber sensing probe according to any one of claims 1 to 4 in an optical fiber sensor, characterized in that: The optical fiber sensor comprises a broadband light source, the optical fiber sensing probe and a spectrum analyzer; Wherein, the emission end of the broadband light source is connected to the input end of the optical fiber sensing probe through a circulator, and the output end of the optical fiber sensing probe is connected to the input end of the optical spectrum analyzer through a circulator.

10. The use of the reflective optical fiber sensing probe in an optical fiber sensor according to claim 9, characterized in that: The fiber optic sensor is used to monitor temperature and / or lateral pressure.

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