Polydimethylsiloxane sensitization optical fiber temperature and strain simultaneous measurement sensor

Abstract

The utility model discloses a polydimethylsiloxane sensitization optical fiber temperature and strain simultaneous measurement sensor. The sensor comprises an incident optical fiber, an optical fiber coupler, an optical fiber patch cord, a transmission optical fiber, a sensing cavity, a reference cavity and an emergent optical fiber, an optical signal enters the optical fiber coupler through the incident optical fiber and is divided into two beams of equal-intensity light in the coupler, the two beams of light are respectively input into the transmission optical fiber through the optical fiber patch cord and then enter the sensing cavity and the reference cavity which are coated with the polydimethylsiloxane, and the light is reflected by the cavities to form interference; the interference light is transmitted back to the optical fiber coupler through respective transmission optical fibers, so that a vernier spectrum is formed; the emergent optical fiber transmits an optical signal containing temperature strain information to a spectrograph, trough drift is analyzed through a dual-wavelength matrix demodulation method, and simultaneous measurement is achieved. According to the utility model, the vernier effect, the structural advantages of the Fabry-Perot interferometer and the advantage of high thermo-optic coefficient of polydimethylsiloxane are combined, and the vernier interferometer has the advantages of low cost, high sensitivity, high stability and the like.

Description

TECHNICAL FIELD

[0001] The utility model relates to the field of optical fiber sensing technology, concretely relates to a polydimethylsiloxane sensitization optical fiber temperature and strain simultaneous measurement sensor. BACKGROUND

[0002] Temperature and strain are the most common physical quantities in practical applications, and have an important position in the fields of civil engineering, aerospace, industrial equipment, natural environment monitoring, etc. Their measurement is of great significance to ensure safety, improve efficiency and optimize performance.

[0003] Traditional temperature and strain sensors mainly include resistance thermometer, thermocouple, strain gauge and piezoelectric sensor, etc. These sensors sense the changes in the external environment through electrical or mechanical properties. Although traditional sensor technology is mature, the price is relatively low, and it has been widely used in many application scenarios, but they will be greatly affected in the face of electromagnetic interference, high temperature, corrosive environment, etc. At the same time, traditional sensors are difficult to monitor temperature and strain simultaneously, and if both parameters need to be measured, multiple independent sensors are required, increasing the complexity and cost of the system. Optical fiber sensors have excellent anti-electromagnetic interference capability, and the optical fiber material is corrosion-resistant, high-temperature-resistant and radiation-resistant, with high reliability in harsh environments, and can realize long-term stable monitoring. Researchers have developed various optical fiber sensors of different principles and structures for detecting temperature and strain. Including interferometric optical fiber sensors, fiber Bragg grating sensors, long-period fiber grating sensors, surface plasmon resonance sensors, etc. Some of these sensors require the use of some expensive special optical fibers, such as hollow core optical fibers, photonic crystal fibers, etc., and some also need to use instruments to process optical fibers. Various types of optical fiber sensors have their own limitations, such as complex manufacturing process of grating type sensors; surface plasmon resonance sensors not only have complex manufacturing process, but also high cost; and expensive special optical fibers. Optical fiber sensors mainly rely on optical fibers to sense external changes, and the main material of optical fibers is silica, which has high hardness, high rigidity, high compression and tensile strength, and only after special treatment or in special structure, can it have a large deformation, thereby improving the sensitivity. In addition, the thermal-optical coefficient and thermal-elastic coefficient of silica are very low, and under normal circumstances, it is less affected by temperature, so it is necessary to coat a heat-sensitive material, such as graphene oxide, metal nanomaterial, metal oxide, photosensitive polymer material, etc. in the sensing fiber area to improve the temperature sensitivity. Research has found that polydimethylsiloxane has excellent flexibility, optical transparency, chemical stability and easy processability, and is a multifunctional and high-performance material; and polydimethylsiloxane has a thermal-optical coefficient and a thermal-elastic coefficient that are one order of magnitude higher than silica, and is easy to prepare and can be stably attached to the surface of the optical fiber, which also plays a certain protective role for the optical fiber sensing structure, and is very suitable for manufacturing temperature-sensitive optical fiber sensors.

[0004] The Fabry-Perot interferometric fiber sensor realizes parameter measurement by forming phase modulation through interference measurement. It has many advantages compared with other types of fiber sensors, such as uniform spectrum, small structure that can be used for measurement in narrow space, low cost, etc. The utility model makes use of the advantage of uniform spectrum of Fabry-Perot interferometer, uses two Fabry-Perot interferometers with similar structure, one as a sensing instrument and the other as a reference instrument to generate vernier spectrum, and then realizes the function of sensitivity amplification; the structure of misaligned fiber splicing makes the sensor very sensitive to strain; at the same time, the polydimethylsiloxane is coated on the two misaligned structures by making use of its high thermal-optical coefficient, which protects the structure and also makes the sensing instrument sensitive to temperature. By monitoring the drift changes of the vernier spectrum envelope trough and the sensing instrument spectrum trough, and then using the double-wavelength matrix demodulation method, the simultaneous measurement of temperature and strain is realized. The sensor of the utility model has high sensitivity, stable structure and can realize multi-parameter measurement.

[0005] A C-type fiber vernier sensor and a manufacturing method (CN118190197A) are proposed in the prior art for measuring seawater temperature and salinity. A single-mode input fiber, a C-type fiber and a single-mode output fiber are sequentially fused to form two Fabry-Perot interferometers with the same structure, and the C-type fiber is made of a femtosecond laser etched hollow fiber. One of the interferometers is used as a salinity sensing cavity, and the other interferometer is filled with a temperature-sensitive polymer in the C-type fiber to form a temperature sensing cavity. The two interferometers are connected in parallel through a fiber coupler to realize vernier effect and sensitivity enhancement, and high-sensitivity temperature measurement is realized. However, the C-type fiber used in the sensor has high manufacturing cost, which is not conducive to practical application. A temperature and strain sensor based on a fiber over-coupling structure (CN111521290A) is proposed in the prior art, which is composed of a single-mode input fiber, a fiber over-coupling structure, a single-mode output fiber and a coupler. The fiber over-coupling structure is formed by fusing and tapering two coupled fibers through a fiber jumper. The coupled fiber is a single-mode fiber, a polarization maintaining fiber or a multi-mode fiber. The sensitivity of the over-coupling structure to the external environment is used to realize the measurement of temperature and strain. However, the manufacturing process of the sensor is relatively complex, and the sensitivity is not high. Utility model content

[0006] In view of the problems existing in the prior art, the utility model provides a polydimethylsiloxane sensitized fiber temperature and strain simultaneous measurement sensor, which has high sensitivity, stable structure, is easy to manufacture, has low cost and can realize multi-parameter measurement.

[0007] The purpose of the utility model is achieved at least by one of the following technical solutions.

[0008] The polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor comprises an incident optical fiber, an optical fiber coupler, a first optical fiber jumper, a second optical fiber jumper, a first transmission optical fiber, a second transmission optical fiber, a third transmission optical fiber, a fourth transmission optical fiber, a first polydimethylsiloxane coating, a second polydimethylsiloxane coating, a sensing cavity, a reference cavity and an outgoing optical fiber.

[0009] The output end of the incident optical fiber is connected with the input end of the optical fiber coupler, the output end on the left side of the optical fiber coupler is connected with the outgoing optical fiber, and the two output ends on the right side are respectively connected with the input ends of the first optical fiber jumper and the second optical fiber jumper, the output ends of the first optical fiber jumper and the second optical fiber jumper are respectively connected with the input ends of the first transmission optical fiber and the third transmission optical fiber, and the output ends of the first transmission optical fiber and the third transmission optical fiber are respectively connected with the sensing cavity and the reference cavity.

[0010] The incident optical fiber is used for inputting an optical signal, the optical fiber coupler divides the optical signal input from the incident optical fiber into two optical signals of equal intensity, and then the optical signals are transmitted to the first transmission optical fiber and the third transmission optical fiber through the first optical fiber jumper and the second optical fiber jumper respectively, the first transmission optical fiber and the third transmission optical fiber transmit the optical signals to the sensing cavity and the reference cavity respectively, the optical signals are reflected by the sensing cavity and the reference cavity to form a Fabry-Perot interference, and then a reflection spectrum including a plurality of resonance troughs is generated, the reflection signals of the sensing cavity and the reference cavity are transmitted back to the optical fiber coupler through the first transmission optical fiber and the third transmission optical fiber and the first optical fiber jumper and the second optical fiber jumper to be coupled, and then a vernier spectrum is formed, and the optical signal including temperature and strain information is output to the outgoing optical fiber.

[0011] The effective refractive index and the cavity length of the sensing cavity change under the influence of temperature and strain, the reflection spectrum drifts, the formed vernier spectrum drifts more, the outgoing optical fiber transmits the optical signal including the temperature and strain information to an external spectrometer, the wavelength drift change of the lower envelope line of the vernier spectrum is tracked to realize the measurement of the temperature and strain, the frequency spectrum of the vernier spectrum is analyzed through a fast Fourier transform data processing mode, the trough drift is analyzed through a dual-wavelength matrix demodulation method, and the simultaneous measurement is realized.

[0012] Further, the incident optical fiber is a single-mode optical fiber, and the input end is connected with an external broadband light source, and the output light of the broadband light source is transmitted into the single-mode optical fiber from the core.

[0013] Further, the optical fiber coupler divides the incident optical signal into two optical signals of equal intensity, and then transmits the optical signals out through the right output end, and the optical signals transmitted back by the right output end can be coupled.

[0014] Further, the first optical fiber jumper and the second optical fiber jumper are both single-mode optical fibers, and are used for transmitting optical signals.

[0015] Further, the first transmission optical fiber, the second transmission optical fiber, the third transmission optical fiber and the fourth transmission optical fiber are all single-mode optical fibers;

[0016] The first transmission optical fiber and the third transmission optical fiber are used for transmitting the light input from the first optical fiber jumper and the second optical fiber jumper and outputting the light back to the first optical fiber jumper and the second optical fiber jumper.

[0017] Further, the sensing cavity comprises a first reflecting surface, a first offset optical fiber and a second reflecting surface;

[0018] The first reflecting surface and the second reflecting surface are end surfaces of the first transmission optical fiber and the second transmission optical fiber respectively, and the first reflecting surface and the second reflecting surface are parallelly aligned; the first offset optical fiber is a thin-clad optical fiber, with a diameter of 79-81 μm and a length of 130-140 μm;

[0019] The sensing cavity is in an offset structure, formed by offset fusion splicing of the first offset optical fiber and the first transmission optical fiber and the second transmission optical fiber at two ends, with a core offset distance of 43-45 μm between the first offset optical fiber and the first transmission optical fiber and the second transmission optical fiber at two ends, so as to ensure that the light from the core of the first transmission optical fiber is not blocked, and a first polydimethylsiloxane coating is coated on the surface of the offset structure, so as to completely wrap the entire sensing cavity, so that the entire offset structure is stable and not easy to break; due to the high light transmission of polydimethylsiloxane, it will not block the transmission of the light signal; at this time, the effective refractive index of the sensing cavity is determined by the refractive index of the polydimethylsiloxane, and since the polydimethylsiloxane has a very high thermo-optic coefficient, the refractive index of the polydimethylsiloxane will change with the change of temperature, so that the sensing cavity is very sensitive to temperature change, and the measurement of temperature can be realized.

[0020] Further, the reference cavity comprises a third reflecting surface, a second offset optical fiber and a fourth reflecting surface;

[0021] The third reflecting surface and the fourth reflecting surface are end surfaces of the third transmission optical fiber and the fourth transmission optical fiber respectively, and the third reflecting surface and the fourth reflecting surface are parallelly aligned; the second offset optical fiber is a single-mode optical fiber, with a diameter of 120-125 μm and a length of 105-115 μm;

[0022] The reference cavity is a misaligned structure, which is formed by misaligned fusion of the second misaligned optical fiber and the third transmission optical fiber and the fourth transmission optical fiber at two ends, the core offset distance of the second misaligned optical fiber and the third transmission optical fiber and the fourth transmission optical fiber at two ends is 65-68 mu m, the light from the core of the third transmission optical fiber is not blocked, and the second polydimethylsiloxane coating is coated on the surface of the misaligned structure to form a second polydimethylsiloxane coating, so that the reference cavity is completely wrapped; here, the polydimethylsiloxane plays a role in protecting the misaligned structure, preventing it from breaking, and ensuring that the interference light intensity of the reference cavity matches the interference light intensity of the sensing cavity, so that the vernier spectrum is finally formed in the fiber coupler.

[0023] Further, the exit optical fiber is a single-mode optical fiber, and the output end is connected to a spectrometer to analyze the reflected spectrum including sensing information.

[0024] Further, the interferometer composed of the first transmission optical fiber, the first polydimethylsiloxane coating, the sensing cavity and the second transmission optical fiber has higher strain sensitivity, and a vernier sensing instrument is formed, which is placed in the environment to be measured to measure temperature and strain.

[0025] The interferometer composed of the third transmission optical fiber, the second polydimethylsiloxane coating, the sensing cavity and the fourth transmission optical fiber has relatively low strain sensitivity, and a vernier reference instrument is formed, which is placed in an isolated stable environment, and the temperature and strain in the stable environment are stable and unchanged.

[0026] Compared with the prior art, the beneficial effects of the utility model at least include:

[0027] The utility model is based on fabry -perot interferometer, through the modulation interference cavity, the light propagation state of core causes the phase of output light to change, can deduce the temperature and strain change of external environment through the wavelength shift of detecting output reflection spectrum. The two single mode optical fibers are used to form the reflecting surface, and the misaligned optical fiber in the middle is used to form the interference cavity, so that the structure is simple and the cost is low. In the sensor structure, light mainly propagates in the core and the cavity, and a phase difference is generated due to the distance between the two reflecting surfaces of the interference cavity, so that the reflected light can generate fabry -perro interference, and the phase difference is determined by the length of the cavity and the refractive index of the cavity. The misaligned structure makes the length of the cavity more susceptible to deformation, so that the sensor is more sensitive to strain. The refractive index of the cavity is determined by the polydimethylsiloxane coated on the surface of the misaligned structure, and the refractive index of the polydimethylsiloxane changes significantly with temperature, so that the sensitivity of the sensor to temperature is improved. Finally, two similar interferometers are manufactured by the above method, the strain sensitivity of the interferometer with the misaligned optical fiber as the fine core optical fiber is higher, and the interferometer is placed in the measuring environment as the sensing instrument; the strain sensitivity of the interferometer with the misaligned optical fiber as the single mode optical fiber is relatively low, and the interferometer is placed in the stable environment as the reference instrument; the two interferometers are connected in parallel by using the fiber coupler, so that the vernier effect is formed, the vernier spectrum is obtained, and the sensitivity is multiplied.

[0028] The utility model combines the structure advantages of vernier effect and fabry -perot interferometer, and the advantages of polydimethylsiloxane, such as high thermal optical coefficient, high light transmittance and high stability, and has the advantages of low cost, high sensitivity, multi-parameter measurement, high stability and the like. ACCURACY

[0029] In order to more clearly illustrate the technical scheme in the embodiments of the utility model, the drawings needed to be used in the embodiment description will be briefly introduced, and the drawings in the following description are only some embodiments of the utility model, and other drawings can be obtained by the drawings without creative labor for those skilled in the art.

[0030] Figure 1 It is the structural schematic diagram of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor of the utility model embodiment.

[0031] Figure 2 It is the frequency spectrum diagram of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor of the utility model embodiment.

[0032] Figure 3 It is the reflection spectrum schematic diagram of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor at different temperatures of the utility model embodiment.

[0033] Figure 4 is the linear fitting diagram of the relationship between the center wavelength of the envelope trough of the reflection spectrum of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor and temperature change.

[0034] Figure 5 is the reflection spectrum diagram of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor under different strains.

[0035] Figure 6 is the linear fitting diagram of the relationship between the center wavelength of the envelope trough of the reflection spectrum of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor and strain change.

[0036] Figure 7 is the vernier sensor reflection spectrum diagram of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor under 30-45 DEG C obtained through fast Fourier transform filtering.

[0037] Figure 8 is the vernier sensor reflection spectrum diagram of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor under 50-65 DEG C obtained through fast Fourier transform filtering.

[0038] Figure 9 is the linear fitting diagram of the relationship between the center wavelength of the envelope trough of the reflection spectrum of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor and temperature change.

[0039] Figure 10 is the vernier sensor reflection spectrum diagram of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor under 0-300με obtained through fast Fourier transform filtering.

[0040] Figure 11 is the vernier sensor reflection spectrum diagram of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor under 400-700με obtained through fast Fourier transform filtering.

[0041] Figure 12 is the linear fitting diagram of the relationship between the center wavelength of the envelope trough of the reflection spectrum of the polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor and strain change. DETAILED DESCRIPTION

[0042] The utility model discloses a further detailed description of the specific implementation of the utility model is made below in combination with the drawings and examples, but the implementation and protection scope of the utility model is not limited to this, the utility model makes the essential same equivalent replacement all belong to the protection scope of the utility model.

[0043] Embodiment:

[0044] Polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor, as shown in Figure 1 The output end of incident optical fiber 1 is connected with the input end of optical fiber coupler 2, the output end on the left side of optical fiber coupler 2 is connected with emergent optical fiber 13, and the input end of first optical fiber jumper 3 and second optical fiber jumper 8 is connected with the output end on the right side of optical fiber coupler 2 respectively, the input end of first transmission optical fiber 4 and third transmission optical fiber 9 is connected with the output end of first optical fiber jumper 3 and second optical fiber jumper 8 respectively, and the output end of first transmission optical fiber 4 and third transmission optical fiber 9 is connected with sensing cavity 6 and reference cavity 11 respectively, and the output end of sensing cavity 6 and reference cavity 11 is connected with second transmission optical fiber 7 and fourth transmission optical fiber 12 respectively.

[0045] Incident optical fiber 1 is used for inputting optical signals, optical fiber coupler 2 divides the optical signals input from incident optical fiber 1 into two optical signals with equal intensity, then the optical signals are transmitted into first transmission optical fiber 4 and third transmission optical fiber 9 through first optical fiber jumper 3 and second optical fiber jumper 8 respectively, and the optical signals are transmitted into sensing cavity 6 and reference cavity 11 through first transmission optical fiber 4 and third transmission optical fiber 9 respectively, the reflection of optical signals through sensing cavity 6 and reference cavity 11 forms Fabry-Perot interference, and further generates reflection spectrum including a plurality of resonance troughs, and the reflection of optical signals through sensing cavity 6 and reference cavity 11 is transmitted back to optical fiber coupler 2 through first transmission optical fiber 4 and third transmission optical fiber 9 and first optical fiber jumper 3 and second optical fiber jumper 8, and further forms vernier spectrum, and the optical signals including temperature and strain information are output to emergent optical fiber 13.

[0046] The effective refractive index and cavity length of sensing cavity 6 change under the influence of temperature and strain, so that the reflection spectrum drifts, and further makes the formed vernier spectrum drift more, emergent optical fiber 13 transmits the optical signals including temperature and strain information to external spectrometer, the wavelength drift change of the lower envelope line of vernier spectrum is tracked, the measurement of temperature and strain is realized, the frequency spectrum of vernier spectrum is analyzed through fast Fourier transform data processing mode, the trough drift is analyzed through double-wavelength matrix demodulation method, and the simultaneous measurement is realized.

[0047] The effective refractive index and cavity length of sensing cavity 6 change under the influence of temperature and strain, so that the reflection spectrum drifts, and further makes the formed vernier spectrum drift more, emergent optical fiber 13 transmits the optical signals including temperature and strain information to external spectrometer, the wavelength drift change of the lower envelope line of vernier spectrum is tracked, the measurement of temperature and strain is realized, the frequency spectrum of vernier spectrum is analyzed through fast Fourier transform data processing mode, the trough drift is analyzed through double-wavelength matrix demodulation method, and the simultaneous measurement is realized.

[0048] In one embodiment, the incident fiber 1 is a single-mode fiber, and the input end is connected to an external broadband light source, and the output light of the broadband light source is transmitted into the core of the single-mode fiber.

[0049] In one embodiment, the fiber coupler 2 divides the incident light signal into two beams of equal intensity, and transmits the light through the right output end, and can couple the light transmitted back through the right output end.

[0050] In one embodiment, the first fiber jumper 3 and the second fiber jumper 8 are both single-mode fibers, and are used to transmit light signals.

[0051] In one embodiment, the first transmission fiber 4, the second transmission fiber 7, the third transmission fiber 9, and the fourth transmission fiber 12 are all single-mode fibers.

[0052] The first transmission fiber 4 and the third transmission fiber 9 are used to transmit the light input from the first fiber jumper 3 and the second fiber jumper 8 and output the light back to the first fiber jumper 3 and the second fiber jumper 8.

[0053] The sensing cavity 6 includes a first reflecting surface 61, a first offset fiber 62, and a second reflecting surface 63.

[0054] The first reflecting surface 61 and the second reflecting surface 63 are respectively the end faces of the first transmission fiber 4 and the second transmission fiber 7, and the first reflecting surface 61 and the second reflecting surface 63 are parallel and aligned.

[0055] In one embodiment, the first offset fiber 62 is a thin-clad fiber with a diameter of 80 μm and a length of 135 μm.

[0056] The sensing cavity 6 is an offset structure formed by offset fusion splicing of the first offset fiber 62 and the first transmission fiber 4 and the second transmission fiber 7 at both ends, and the core offset distance of the first offset fiber 62 and the first transmission fiber 4 and the second transmission fiber 7 at both ends is 44.5 μm, which ensures that the light from the core of the first transmission fiber 4 is not blocked, and a first polydimethylsiloxane coating 5 is formed on the surface of the offset structure by coating polydimethylsiloxane, so that the entire sensing cavity 6 is completely wrapped, and the entire offset structure is stable and not easy to break. Due to the high light transmission of polydimethylsiloxane, it will not block the transmission of light signals. At this time, the effective refractive index of the sensing cavity 6 is determined by the refractive index of polydimethylsiloxane. Since polydimethylsiloxane has a very high thermo-optic coefficient, the refractive index of polydimethylsiloxane will change with temperature, making the sensing cavity 6 very sensitive to temperature changes, and enabling temperature measurement.

[0057] Further, the reference cavity 11 includes a third reflecting surface 111, a second offset fiber 112, and a fourth reflecting surface 113.

[0058] The third reflection surface 111 and the fourth reflection surface 113 are end surfaces of the third transmission optical fiber 9 and the fourth transmission optical fiber 12 respectively, and the third reflection surface 111 and the fourth reflection surface 113 are aligned in parallel;

[0059] In one embodiment, the second offset optical fiber 112 is a single-mode optical fiber with a diameter of 125 μm and a length of 110 μm;

[0060] The reference cavity 11 is an offset structure formed by offset fusion splicing of the second offset optical fiber 112 with the third transmission optical fiber 9 and the fourth transmission optical fiber 12 at two ends, the core offset distance of the second offset optical fiber 112 with the third transmission optical fiber 9 and the fourth transmission optical fiber 12 at two ends is 66.5 μm, which ensures that the light from the core of the third transmission optical fiber 9 is not blocked, and the second polydimethylsiloxane coating 10 is coated on the surface of the offset structure to completely wrap the entire reference cavity 11; the polydimethylsiloxane coating has the effect of protecting the offset structure and preventing it from breaking, and also ensures that the interference light intensity of the reference cavity 11 matches the interference light intensity of the sensing cavity, so that the vernier spectrum is finally formed in the fiber coupler 2.

[0061] In one embodiment, the exit optical fiber 13 is a single-mode optical fiber, and the output end is connected to a spectrometer to analyze the reflected spectrum containing sensing information.

[0062] The interferometer composed of the first transmission optical fiber 4, the first polydimethylsiloxane coating 5, the sensing cavity 6, and the second transmission optical fiber 7 has higher strain sensitivity and constitutes a vernier sensing instrument, which is placed in the environment to be measured to measure temperature and strain;

[0063] The interferometer composed of the third transmission optical fiber 9, the second polydimethylsiloxane coating 10, the sensing cavity 11, and the fourth transmission optical fiber 12 has relatively low strain sensitivity and constitutes a vernier reference instrument, which is placed in an isolated stable environment, and the temperature and strain in the stable environment are stable and unchanged.

[0064] The principle and feasibility analysis of the present embodiment: the reflected light signal intensities output by the vernier sensing instrument and the vernier reference instrument back to the fiber coupler are as follows:

[0065]

[0066] I sensor and I reference are the reflected light signal intensities output by the vernier sensing instrument and the vernier reference instrument back to the fiber coupler respectively, I M1 , I M2 , I M3 , I M4the reflected light intensity of the first, second, third and fourth reflecting surfaces 61, 63, 111 and 113, respectively, and the phase difference of the sensing cavity 6 and the reference cavity 11, respectively, and are expressed as:

[0067]

[0068] In the formula, n PDMS is the refractive index of the polydimethylsiloxane, λ is the wavelength of the light, L sensor and L reference are the cavity lengths of the sensing cavity 6 and the reference cavity 11, respectively; for the Fabry-Perot interferometer, the phase difference equals (2m+1)π in the m-th order mode, and then the wavelengths λ1 and λ2 of the reflection spectrum valleys of the sensing cavity 6 and the reference cavity 11 are expressed as:

[0069]

[0070] Since only the vernier sensing instrument is in the environment where the temperature and strain change, the refractive index n PDMS and the cavity length L sensor of the sensing cavity 6 change, and the wavelength of the reflection resonance valley will drift.

[0071] The free spectral ranges FSR1 and FSR2 of the sensing cavity 6 and the reference cavity 11 are expressed as:

[0072]

[0073] When the reflected light output of the vernier sensing instrument and the vernier reference instrument is coupled into the fiber coupler, the spectrum will be coupled, thereby forming the vernier spectrum; since the FSR1 and the FSR2 are very close but not equal, the vernier spectrum will form a periodic envelope, and the free spectral range FSR envelope of the envelope is expressed as:

[0074]

[0075] When the reflection spectrum valley of the vernier sensing instrument drifts, it will cause the envelope valley of the vernier spectrum to also drift, and the drift amount of the vernier spectrum envelope valley is M times the drift amount of the reflection spectrum valley of the vernier sensing instrument, thereby realizing sensitivity amplification, and is expressed as:

[0076]

[0077] After obtaining the vernier spectrum, the reflected spectrum data of the vernier sensing instrument is obtained by using the fast Fourier transform filtering, and the reflection spectrum valley λ envelope of the vernier sensing instrument is tracked by tracking the envelope valley λ sensor, the sensitivity coefficient matrix is obtained by using the two wave trough shift data, and the temperature and strain are measured simultaneously by combining the dual-wavelength matrix demodulation method, and the matrix is as follows:

[0078]

[0079] Wherein ΔT and Δε represent the change of temperature and strain respectively, K T1 , K T2 , K ε1 , K ε2 are the temperature and strain sensitivity coefficients of the wave trough λ envelope of the vernier spectrum envelope and the wave trough λ sensor of the reflected spectrum of the vernier sensor, and Δλ envelope and Δλ sensor represent the wavelength shift of the wave trough λ envelope of the vernier spectrum envelope and the wave trough λ sensor of the reflected spectrum of the vernier sensor.

[0080] In one embodiment, in the temperature measurement experiment, the vernier sensor is placed in a constant temperature and humidity box, and the vernier reference instrument is placed in the external stable environment. The relative humidity in the box is set to be consistent with the relative humidity of the external environment at that time, that is, 50% unchanged, the input end of the incident optical fiber 1 is connected to the external broadband light source, and the output end of the output optical fiber 13 is connected to the external spectrometer. As shown in Figure 3 , the temperature of the constant temperature and humidity box is adjusted, with a step of 5℃, from 30℃ to 65℃, and the wavelength shift of the vernier spectrum displayed by the spectrometer is obviously seen. As shown in Figure 4 , wherein the discrete points represent the wavelength change of the envelope trough under the vernier spectrum under different temperature environments, and the solid line represents the linear fitting of the discrete points. It can be seen that in the temperature range of 30℃-65℃, the sensitivity of the lower envelope trough is-2.098nm / ℃, and the linearity reaches 99%, which indicates that the accuracy is very high.

[0081] In one embodiment, in the strain measurement experiment, the vernier sensor is placed in the two parallel clamp platforms, the axial strain of the vernier sensor is applied by moving one of the clamp platforms, the input end of the incident optical fiber 1 is connected to the external broadband light source, and the output end of the output optical fiber 13 is connected to the external spectrometer. As shown in Figure 5 , the axial strain of the clamp platform is adjusted, with a step of 100με, from 0με to 700με, and the wavelength shift of the vernier spectrum displayed by the spectrometer is obviously seen. As shown in Figure 6 , wherein the discrete points represent the wavelength change of the envelope trough under the vernier spectrum under different strain, and the solid line represents the linear fitting of the discrete points. It can be seen that in the strain range of 0με-700με, the sensitivity of the lower envelope trough is 91.4pm / με, and the linearity reaches 99%, which indicates that the accuracy is very high.

[0082] In one embodiment, such as Figure 2 As shown, the vernier spectrum is processed using Fast Fourier Transform to obtain the spatial spectrum of the sensor. Based on the obtained frequency peak information, the vernier spectrum is filtered to separate the reflectance spectrum data of the vernier sensor, thus eliminating the need for separate measurements of the vernier sensor using a spectrometer. The processed reflectance spectrum data of the vernier sensor under different temperature and strain environments are obtained, as shown below. Figure 7 , Figure 8 , Figure 10 , Figure 11 As shown, the wavelength changes of the reflection spectrum troughs can be observed under different temperature and strain conditions. Figure 9 As shown, the vernier sensor exhibits a sensitivity of -0.369 nm / ℃ at the trough of the reflectance spectrum within a temperature range of 30℃-65℃, with a linearity reaching 99%. This indicates that the sensitivity amplification factor of the vernier envelope is 5.69. Figure 12 As shown, the sensitivity of the vernier sensor at the lower envelope trough in the strain range of 0με-700με is 17.1pm / με, and the linearity reaches 99%. It can be seen that the sensitivity amplification factor of the vernier envelope is 5.35, which is very close to the above theoretical basis.

[0083] When both ambient temperature and strain change simultaneously, the sensitivity coefficient matrix is ​​represented as follows:

[0084]

[0085] The above formula can be used to obtain the expressions for temperature and strain, enabling simultaneous measurement of temperature and strain.

[0086] The utility model discloses a polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor based on vernier effect and fabry-perot interference, with the help of two structure similar, free spectral range and interference intensity are similar fabry-perot interferometer, produce vernier spectrum, thereby realize sensitivity is multiplied amplification. Through the modulation of cavity length and the effective refractive index in the cavity of interference cavity, cause the phase change of output light, through the wavelength shift of monitoring output reflected light spectrum, can obtain the change of external environment temperature and strain. Utilize the optical fiber coupler to divide the input light average to vernier sensor and vernier reference instrument, and then couple the reflected light that they transmit back, thereby obtain vernier spectrum. In order to make the light intensity of vernier sensor and reference instrument similar, the similar staggered structure is selected, because the influence of staggered structure, make the interference cavity length more easily deform, make the sensor sensitive to strain, because the strain sensitivity of staggered fiber is higher, therefore use the interferometer of thin core fiber as sensor, use the interferometer of single mode optical fiber as reference instrument. Apply polydimethylsiloxane on the staggered structure, in addition to protect the staggered structure, utilize the characteristics of high thermal-optic coefficient of polydimethylsiloxane, improve the sensitivity of sensor to temperature.

[0087] Utilize the envelope trough shift of vernier spectrum, and then get the vernier sensor reflected spectrum trough shift that the vernier spectrum is handled by fast fourier transform filtering, constitute sensitivity coefficient matrix, realize the simultaneous measurement of temperature and strain through demodulation matrix.

[0088] The polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor of the utility model combines the advantages of vernier effect, fabry-perot interferometer structure and the advantages of high thermal-optic coefficient, good stability and good adhesion of polydimethylsiloxane, has the characteristics of low cost, high sensitivity and high stability.

[0089] The above embodiment is further detailed to the purpose, technical scheme and beneficial effect of the utility model, and it should be understood that the above is only the specific embodiment of the utility model, and is not used for limiting the utility model, and any modification, equivalent replacement, improvement etc. that is made within the spirit and principle of the utility model should be included in the protection scope of the utility model.

Claims

1. A polydimethylsiloxane sensitized optical fiber temperature and strain simultaneous measurement sensor characterized by: The incident optical fiber (1), the optical fiber coupler (2), the first optical fiber jumper (3), the second optical fiber jumper (8), the first transmission optical fiber (4), the second transmission optical fiber (7), the third transmission optical fiber (9), the fourth transmission optical fiber (12), the first polydimethylsiloxane coating (5), the second polydimethylsiloxane coating (10), the sensing cavity (6), the reference cavity (11) and the outgoing optical fiber (13) are included. The output end of the incident optical fiber (1) is connected with the input end of the optical fiber coupler (2), the left output end of the optical fiber coupler (2) is connected with the outgoing optical fiber (13), the right two output ends of the optical fiber coupler (2) are respectively connected with the input ends of the first optical fiber jumper (3) and the second optical fiber jumper (8), the output ends of the first optical fiber jumper (3) and the second optical fiber jumper (8) are respectively connected with the input ends of the first transmission optical fiber (4) and the third transmission optical fiber (9), the output ends of the first transmission optical fiber (4) and the third transmission optical fiber (9) are respectively connected with the sensing cavity (6) and the reference cavity (11), and the output ends of the sensing cavity (6) and the reference cavity (11) are respectively connected with the second transmission optical fiber (7) and the fourth transmission optical fiber (12). The incident optical fiber (1) is used for inputting optical signals, the optical fiber coupler (2) divides the optical signals input from the incident optical fiber (1) into two optical signals with equal intensity, and then the optical signals are transmitted to the first transmission optical fiber (4) and the third transmission optical fiber (9) through the first optical fiber jumper (3) and the second optical fiber jumper (8) respectively, the first transmission optical fiber (4) and the third transmission optical fiber (9) transmit the optical signals to the sensing cavity (6) and the reference cavity (11) respectively, the optical signals are reflected by the sensing cavity (6) and the reference cavity (11) to form a Fabry-Perot interference, and then a reflection spectrum including a plurality of resonance troughs is generated, the reflected optical signals of the sensing cavity (6) and the reference cavity (11) are transmitted back to the optical fiber coupler (2) through the first transmission optical fiber (4) and the third transmission optical fiber (9) and the first optical fiber jumper (3) and the second optical fiber jumper (8) again, and then the optical signals are coupled in the optical fiber coupler (2) to form a vernier spectrum, and the optical signals including temperature and strain information are output to the outgoing optical fiber (13).

2. The polydimethylsiloxane-sensitized fiber-optic temperature and strain simultaneous measurement sensor according to claim 1, characterized in that: The incident optical fiber (1) is a single-mode optical fiber, and the input end is connected with a broadband light source outside, and the output light of the broadband light source is transmitted into the single-mode optical fiber through the core.

3. The polydimethylsiloxane-sensitized fiber-optic temperature and strain simultaneous measurement sensor according to claim 1, characterized in that: The optical fiber coupler (2) divides the incident optical signals into two optical signals with equal intensity, and then transmits the optical signals through the right output end, and couples the optical signals transmitted back through the right output end.

4. The polydimethylsiloxane-sensitized fiber-optic temperature and strain simultaneous measurement sensor according to claim 1, characterized in that: The first optical fiber jumper (3) and the second optical fiber jumper (8) are single-mode optical fibers, and are used for transmitting optical signals.

5. The polydimethylsiloxane-sensitized fiber-optic temperature and strain simultaneous measurement sensor according to claim 1, characterized in that: The first transmission optical fiber (4), the second transmission optical fiber (7), the third transmission optical fiber (9) and the fourth transmission optical fiber (12) are single-mode optical fibers. The first transmission optical fiber (4) and the third transmission optical fiber (9) are used for transmitting the optical signals input from the first optical fiber jumper (3) and the second optical fiber jumper (8) and outputting the optical signals back to the first optical fiber jumper (3) and the second optical fiber jumper (8).

6. The polydimethylsiloxane-sensitized fiber-optic temperature and strain simultaneous measurement sensor according to claim 1, characterized in that: The sensing cavity (6) includes a first reflecting surface (61), a first offset optical fiber (62) and a second reflecting surface (63). The first reflecting surface (61) and the second reflecting surface (63) are end surfaces of the first transmission optical fiber (4) and the second transmission optical fiber (7) respectively, and the first reflecting surface (61) and the second reflecting surface (63) are aligned in parallel; The sensing cavity (6) is a staggered structure, and is formed by staggered fusion of the first staggered optical fiber (62) and the first transmission optical fiber (4) and the second transmission optical fiber (7) at two ends. The core offset distance of the first staggered optical fiber (62) and the first transmission optical fiber (4) and the second transmission optical fiber (7) at two ends is 43-45 μm, which ensures that the light from the core of the first transmission optical fiber (4) is not blocked, and a first polydimethylsiloxane coating (5) is coated on the surface of the staggered structure to completely wrap the entire sensing cavity (6).

7. The polydimethylsiloxane-sensitized fiber-optic temperature and strain simultaneous measurement sensor according to claim 6, characterized in that: The first staggered optical fiber (62) is a thin cladding optical fiber with a diameter of 79-81 μm and a length of 130-140 μm.

8. The polydimethylsiloxane-sensitized fiber-optic temperature and strain simultaneous measurement sensor according to claim 1, characterized in that: The reference cavity (11) comprises a third reflecting surface (111), a second staggered optical fiber (112), and a fourth reflecting surface (113). The third reflecting surface (111) and the fourth reflecting surface (113) are end surfaces of the third transmission optical fiber (9) and the fourth transmission optical fiber (12) respectively, and the third reflecting surface (111) and the fourth reflecting surface (113) are aligned in parallel; the second staggered optical fiber (112) is a single-mode optical fiber with a diameter of 120-125 μm and a length of 105-115 μm. The reference cavity (11) is a staggered structure, and is formed by staggered fusion of the second staggered optical fiber (112) and the third transmission optical fiber (9) and the fourth transmission optical fiber (12) at two ends. The core offset distance of the second staggered optical fiber (112) and the third transmission optical fiber (9) and the fourth transmission optical fiber (12) at two ends is 65-68 μm, which ensures that the light from the core of the third transmission optical fiber (9) is not blocked, and a second polydimethylsiloxane coating (10) is coated on the surface of the staggered structure to completely wrap the entire reference cavity (11).

9. The polydimethylsiloxane-sensitized fiber-optic temperature and strain simultaneous measurement sensor according to claim 1, characterized in that: The exit optical fiber (13) is a single-mode optical fiber, and the output end is connected to a spectrometer.

10. The polydimethylsiloxane-sensitized fiber-optic temperature and strain simultaneous measurement sensor according to any one of claims 1 to 9, characterized in that: The interferometer composed of the first transmission optical fiber (4), the first polydimethylsiloxane coating (5), the sensing cavity (6), and the second transmission optical fiber (7) is a vernier sensor, which is placed in the environment to be measured to measure temperature and strain. The interferometer composed of the third transmission optical fiber (9), the second polydimethylsiloxane coating (10), the reference cavity (11), and the fourth transmission optical fiber (12) is a vernier reference instrument, which is placed in an isolated stable environment.

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