CN112595435B - High-sensitivity temperature measurement demodulation sensing system based on optical fiber strong evanescent field interferometer - Google Patents

Abstract

A high-sensitivity temperature measurement demodulation sensing system based on an optical fiber strong evanescent field interferometer comprises an optical fiber branching device, wherein one end of the optical fiber branching device is connected with a light source and a demodulator, the other end of the optical fiber branching device is connected with one end of an interferometer, the other end of the interferometer is connected with a light reflection device in series, a thermo-optic material wraps the middle of a cladding, when the system is applied, incident light emitted by the light source generates an interference spectrum through the interferometer, the thermo-optic material is sensitized simultaneously, after the interference spectrum passes through the light reflection device, a sensing peak in the interference spectrum can be reflected back to the interferometer, the thermo-optic material is sensitized again, the sensitized sensing peak is emitted to the demodulator through the optical fiber branching device, then the demodulator carries out peak searching processing on the reflection spectrum, and automatic demodulation is achieved. The design not only has the dual advantages of high sensitivity and easy demodulation, but also is convenient to encapsulate and fix and has stronger interference resistance.

Description

A high-sensitivity temperature measurement and demodulation sensing system based on optical fiber strong evanescent field interferometer

technical field

The invention relates to an optical fiber sensing temperature measurement system, which belongs to the field of optical fiber sensing technology, and also belongs to the intersecting field of material science and optoelectronic technology. sense system.

Background technique

Since the 1970s, optical fiber temperature measurement has become the most advanced technology for temperature detection. Due to its advantages of not being susceptible to electromagnetic interference, it is widely used in temperature detection work. Optical fiber temperature measurement technology is very easy to operate, and optical fiber not only has strong transmission performance, but also has the advantages of anti-electromagnetic interference, so it is widely used in various environments. Many developed countries in foreign countries are very fond of this technology, and gradually use it to replace the traditional temperature detection technology, and optical fiber technology has been widely used.

However, the existing optical fiber temperature sensor is difficult to have the advantages of high sensitivity and convenient demodulation, which has caused obstacles to its popularization and application.

The disclosure of information in this background section is only intended to increase the understanding of the general background of this patent application, and should not be considered as an acknowledgment or any form of suggestion that the information constitutes prior art known to those skilled in the art.

Contents of the invention

The purpose of the present invention is to overcome the defects and problems in the prior art that cannot have both high sensitivity and convenient demodulation, and provide a high-sensitivity optical fiber interferometer based on strong evanescent field interferometer that can have both high sensitivity and convenient demodulation. Temperature measurement and demodulation sensing system.

To achieve the above objectives, the technical solution of the present invention is: a high-sensitivity temperature measurement and demodulation sensing system based on an optical fiber strong evanescent field interferometer, which includes an optical fiber branching device, an outer cladding, an interferometer, a light reflection A device and a demodulator, the interferometer includes a cladding and a plurality of fiber cores arranged in it;

One end of the optical fiber branching device is connected to the light source and the demodulator, the other end of the optical fiber branching device is connected to one end of the interferometer, the other end of the interferometer is connected in series with the light reflection device, and the middle part of the cladding The outer wrapping layer is wrapped, and the outer wrapping layer is a thermo-optic material.

The optical fiber splitting device is a 2×2 coupler connected in parallel with a refractive index sensor, or a 2×1 optical switch.

The light reflection device is a fiber Bragg grating, a broadband Bragg grating or a surface-modified nano-silver reflective film.

The band selection width of the light reflection device is 1.1-1.6 times of the free spectrum width of the sensing peak of the interferometer.

The central wavelength range of the band of the light reflection device is 1.2-2.0 times the wavelength range of the sensing peak of the interferometer.

The absolute value of the thermo-optic coefficient of the thermo-optic material is greater than 3*10 ⁴ , the refractive index is 1.38-1.43, and the surface tension is 20.6-21.2 mN/m.

The thermo-optic material is polydimethylsiloxane, polyimide, magnesium fluoride or polyurethane.

The interferometer includes a left optical fiber section, a left tapered section, a straight waist section, a right tapered section and a right optical fiber section, one end of the left optical fiber section is connected to an optical fiber branching device, and the other end of the left optical fiber section is sequentially After the left tapered section, the straight waist section, the right tapered section, and the right optical fiber section, it is connected in series with the light reflection device; the diameters of the left optical fiber section and the right optical fiber section are consistent, and the diameter of the straight waist section is the left 1/10 to 1/20 of the diameter of the fiber segment;

The parts near the left tapered section on the left optical fiber section, the left tapered section, the straight waist section, the right tapered section, and the parts near the right tapered section on the right optical fiber section are jointly wrapped with the same outer wrapping layer .

There are seven fiber cores, including one central core and six peripheral cores, and all the peripheral cores are uniformly distributed in a regular hexagon around the central core.

The outside of the outer wrapping layer is wrapped with a capillary metal tube.

Compared with prior art, the beneficial effect of the present invention is:

1. In the high-sensitivity temperature measurement and demodulation sensing system based on the optical fiber strong evanescent field interferometer of the present invention, it mainly includes an optical fiber branching device, an outer cladding layer, an interferometer, a light reflection device and a demodulator, and an interferometer Including the cladding and multiple fiber cores set in it, wherein one end of the fiber branching device is connected to the light source and the demodulator, the other end of the fiber branching device is connected to one end of the interferometer, and the other end of the interferometer It is connected in series with the light reflection device, and the middle part of the cladding is wrapped with an outer cladding layer (thermo-optic material). After the interference spectrum passes through the light reflection device, the sensing peak in the interference spectrum is reflected back to the interferometer (the thermo-optic material simultaneously amplifies the influence of the ambient temperature on the wavelength of the interference spectrum), and is subsequently transmitted through the optical fiber splitting device. To the demodulator, then the demodulator performs peak-finding processing on the reflection spectrum, and performs automatic demodulation. Using mathematical analysis, the wavelength data can be converted into temperature data, which makes the measurement accuracy higher, more convenient to use, and easier to optical integration. Therefore, the present invention can not only improve the sensitivity of temperature measurement, but also can perform online real-time automatic demodulation, thereby having the dual advantages of high sensitivity and convenient demodulation.

2. In the high-sensitivity temperature measurement and demodulation sensing system based on the optical fiber strong evanescent field interferometer of the present invention, the middle part of the inner cladding of the interferometer is wrapped with an outer cladding layer, and the outer cladding layer is a thermo-optic material. , the temperature change of the external environment will cause a corresponding linear change in the refractive index of the thermo-optic material, and the change in the refractive index of the thermo-optic material will cause the wavelength of the interference spectrum generated by the interferometer to drift, so that the temperature of the external environment, the interference spectrum A linear relationship is constructed between the wavelengths of the bare fiber interferometer, thereby overcoming the defect of low temperature sensitivity of the bare fiber interferometer and achieving sensitivity enhancement. In addition, when the incident light passes through the interferometer for the first time and is reflected back into the interferometer by the light reflection device When the sensitivity is increased, double superposition, the sensing peak intensity of the interference spectrum is greatly increased, thereby greatly improving the sensitivity. Therefore, the invention not only can monitor the temperature of the environment, but also has high sensitivity.

3. In the high-sensitivity temperature measurement and demodulation sensing system based on the optical fiber strong evanescent field interferometer of the present invention, a capillary metal tube is wrapped outside the outer cladding layer. When applied, the capillary metal tube can not only Thermo-optic material) for protection and packaging, overcomes the shortcomings of thermo-optic material flexibility, and can reduce response time and avoid vibration or pressure interference on sensing, which is conducive to realizing online real-time high-precision demodulation. Therefore, the present invention is not only convenient for packaging and fixing, but also has strong anti-interference ability, which is beneficial to realize high-precision monitoring.

Description of drawings

Fig. 1 is a schematic structural view of the present invention.

Fig. 2 is a schematic structural diagram of the combination of the interferometer and the outer cladding layer in Fig. 1 .

FIG. 3 is a transverse sectional view of FIG. 2 .

FIG. 4 is a schematic structural diagram of the interferometer in FIG. 2 .

FIG. 5 is a transverse sectional view of FIG. 4 .

Fig. 6 is a comparative schematic diagram of the temperature sensitivity of Example 1 of the present invention.

Fig. 7 is a schematic diagram of comparison of sensing peak bands in Example 1 of the present invention.

In the figure: outer cladding layer 1, interferometer 2, cladding 21, fiber core 22, middle core 221, peripheral core 222, left fiber segment 23, left tapered segment 24, straight waist segment 25, right tapered segment 26 , right optical fiber section 27, light reflection device 3, capillary metal tube 4, light source 5, end-capping sleeve 6, thermo-optic material perfusion window 7, demodulator 8, fiber branching device 9.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Referring to Figures 1-5, a high-sensitivity temperature measurement and demodulation sensing system based on an optical fiber strong evanescent field interferometer includes an optical fiber branching device 9, an outer cladding layer 1, an interferometer 2, an optical reflection device 3 and A demodulator 8, the interferometer 2 includes a cladding 21 and a plurality of fiber cores 22 disposed therein;

One end of the optical fiber branching device 9 is connected to the light source 5 and the demodulator 8, the other end of the optical fiber branching device 9 is connected to one end of the interferometer 2, and the other end of the interferometer 2 is connected in series with the optical reflection device 3 , the middle part of the cladding layer 21 is wrapped with an outer wrapping layer 1, and the outer wrapping layer 1 is a thermo-optic material.

The optical fiber branching device 9 is a 2×2 coupler connected in parallel with a refractive index sensor, or a 2×1 optical switch.

The light reflection device 3 is a fiber Bragg grating, a broadband Bragg grating or a surface-modified nano-silver reflective film.

The band selection width of the light reflection device 3 is 1.1-1.6 times of the free spectrum width of the sensing peak of the interferometer 2 .

The central wavelength range of the band of the light reflection device 3 is 1.2-2.0 times the wavelength range of the sensing peak of the interferometer 2 .

The absolute value of the thermo-optic coefficient of the thermo-optic material is greater than 3*10 ⁴ , the refractive index is 1.38-1.43, and the surface tension is 20.6-21.2 mN/m.

The thermo-optic material is polydimethylsiloxane, polyimide, magnesium fluoride or polyurethane.

The interferometer 2 includes a left fiber section 23, a left tapered section 24, a straight waist section 25, a right tapered section 26 and a right fiber section 27, and one end of the left fiber section 23 is connected to the fiber branching device 9 , the other end of the left fiber section 23 is connected in series with the light reflection device 3 after the left tapered section 24, the straight waist section 25, the right tapered section 26, and the right fiber section 27; the left fiber section 23, the right fiber The diameter of segment 27 is consistent, and the diameter of described straight waist segment 25 is 1/10 to 1/20 of the diameter of left optical fiber segment 23; Section 24 , straight waist section 25 , right tapered section 26 , and right optical fiber section 27 near right tapered section 26 are wrapped with the same outer wrapping layer 1 .

The number of the fiber cores 22 is seven, including one central core 221 and six peripheral cores 222 , and all the peripheral cores 222 are uniformly distributed in a regular hexagon around the central core 221 . Preferably, the diameter of the core 22 is 9 μm, the distance between adjacent cores 22 is 35 μm, the diameters of the left fiber segment 23 and the right fiber segment 27 are both 125 μm, and the diameter of the straight waist segment 25 is 6 μm-15 μm.

A capillary metal tube 4 is wrapped around the outer wrapping layer 1 .

Principle of the present invention is described as follows:

The light reflective device in the present invention is a band-selective light reflective device. In application, by selecting a suitable band-selective optical reflection device to reflect the spectrum in the peak wavelength range of the interference spectrum sensing, it is beneficial for the demodulator to perform peak-seeking processing on the reflected spectrum and realize automatic demodulation.

In the present invention, the optical fiber is heated, melted and tapered into a micro-nano size, so that the surface of the optical fiber forms an evanescent field (including the left tapered section 24, the straight waist section 25, the right tapered section 26, especially in the straight waist section The surface of section 25 forms a strong evanescent field) to obtain an interferometer, and then make the interferometer contact with the thermo-optic material (that is, the outer cladding layer), and finally package it with a capillary metal tube. In application, when light passes through the interferometer, an interference spectrum will be generated. At this time, changes in the external temperature or refractive index will cause changes in the effective refractive index of the interferometer, resulting in a wavelength shift in the interference spectrum, thereby sensing the external temperature or refractive index. Variety. However, due to the small thermo-optic coefficient of silicon dioxide, the temperature sensitivity of the interferometer is low. Therefore, this design mainly focuses on the external refractive index change. Therefore, the thermo-optic material is wrapped outside the interferometer, that is, the thermal The relationship between the change of the refractive index of the optical material and the wavelength drift, and the change of the ambient temperature outside the thermo-optic material will cause the linear change of the refractive index of the thermo-optic material, thus establishing a relationship between the external ambient temperature and the wavelength drift linear correspondence.

In the present invention, the thermo-optic material preferably has a refractive index of 1.3907-1.4125 and a temperature of 10-60 degrees Celsius.

Example 1:

Referring to Figures 1-5, a high-sensitivity temperature measurement and demodulation sensing system based on an optical fiber strong evanescent field interferometer includes an optical fiber branching device 9, an outer cladding layer 1, an interferometer 2, an optical reflection device 3 and The demodulator 8 and the interferometer 2 include a cladding 21 and seven fiber cores 22 arranged therein (comprising an intermediate core 221 and six peripheral cores 222, all peripheral cores 222 are evenly distributed in a regular hexagon around the intermediate core 221 ), the interferometer 2 includes a left fiber section 23, a left tapered section 24, a straight waist section 25, a right tapered section 26 and a right fiber section 27, and one end of the left fiber section 23 is connected to the fiber branching device 9 The other end of the optical fiber branching device 9 is connected to the light source 5 and the demodulator 8, and the other end of the left optical fiber section 23 passes through the left tapered section 24, the straight waist section 25, and the right tapered section 26 successively. , the right fiber section 27 is connected in series with the light reflection device 3; the diameters of the left fiber section 23 and the right fiber section 27 are consistent, and the diameter of the straight waist section 25 is 1/10 to 10 of the diameter of the left fiber section 23 1/20; the position near the left tapered section 24 on the left optical fiber section 23, the left tapered section 24, the straight waist section 25, the right tapered section 26, the near right tapered section 26 on the right optical fiber section 27 The outside of the part is jointly wrapped with the same outer wrapping layer 1, and the outer wrapping layer 1 is a thermo-optic material (polydimethylsiloxane in this embodiment).

According to the experimental data, the sensitivity of the above-mentioned demodulation sensing system can reach 14338pm/°C, which is 500 times higher than that of the bare fiber MZI, and the accuracy can reach up to 0.001°C.

Please refer to FIG. 6 , which is a schematic diagram of the comparison of temperature sensitivity in Example 1. It can be seen from the figure that after polydimethylsiloxane wrapping, the sensitivity of the sensing system to temperature is greatly increased.

Please refer to Figure 7, which shows the interferometer transmission spectrum (dotted line) collected by the spectrometer at 15°C, and the reflection spectrum (solid line) collected by the demodulator in this design. The comparison of the two phases can be seen The amplitude of the interference spectrum in the reflection spectrum is significantly increased, which is more conducive to the demodulation of the demodulator, thereby facilitating the realization of real-time online automatic demodulation.

Example 2:

Basic content is the same as embodiment 1, the difference is:

The thermo-optic material is magnesium fluoride, and the interferometer 2 is a tapered single-mode fiber interferometer.

Example 3:

Basic content is the same as embodiment 1, the difference is:

The thermo-optic material is polyurethane, the interferometer 2 is a tapered seven-core optical fiber interferometer, and the optical fiber branching device 9 is a 2×1 optical switch.

Example 4:

Basic content is the same as embodiment 1, the difference is:

The optical fiber branching device 9 uses 2×2 couplers to connect the refractive index sensors in parallel to realize the high-sensitivity measurement of the dual parameters of the temperature and refractive index.

The above descriptions are only preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments, but all equivalent modifications or changes made by those of ordinary skill in the art according to the disclosure of the present invention should be included within the scope of protection described in the claims.

Claims (9)

1. A high-sensitivity temperature measurement demodulation sensing system based on an optical fiber strong evanescent field interferometer is characterized in that: the temperature measurement demodulation sensing system comprises an optical fiber branching device (9), an outer wrapping layer (1), an interferometer (2), a light reflecting device (3) and a demodulator (8), wherein the interferometer (2) comprises a wrapping layer (21) and a plurality of fiber cores (22) arranged in the wrapping layer;

one end of the optical fiber branching device (9) is connected with the light source (5) and the demodulator (8), the other end of the optical fiber branching device (9) is connected with one end of the interferometer (2), the other end of the interferometer (2) is connected with the light reflecting device (3) in series, the middle of the cladding (21) is wrapped with an outer wrapping layer (1), and the outer wrapping layer (1) is made of a thermo-optic material;

the interferometer (2) comprises a left optical fiber section (23), a left conical section (24), a straight waist section (25), a right conical section (26) and a right optical fiber section (27), one end of the left optical fiber section (23) is connected with the optical fiber branching device (9), and the other end of the left optical fiber section (23) sequentially passes through the left conical section (24), the straight waist section (25), the right conical section (26) and the right optical fiber section (27) and then is connected with the light reflection device (3) in series; the diameters of the left optical fiber section (23) and the right optical fiber section (27) are consistent, and the diameter of the straight waist section (25) is 1/10 to 1/20 of the diameter of the left optical fiber section (23);

the outer portions of the positions, close to the left conical section (24), on the left optical fiber section (23), the left conical section (24), the straight waist section (25), the right conical section (26) and the right optical fiber section (27), close to the right conical section (26) are wrapped by the same outer wrapping layer (1) together.

2. The high-sensitivity temperature measurement demodulation sensing system based on the optical fiber strong evanescent field interferometer as claimed in claim 1, wherein: the optical fiber branching device (9) is a 2 x 2 coupler parallel refractive index sensor or a 2 x 1 optical switch.

3. The high-sensitivity temperature measurement demodulation sensing system based on the optical fiber strong evanescent field interferometer as claimed in claim 1 or 2, wherein: the light reflection device (3) is a fiber Bragg grating, a broadband Bragg grating or a nano silver reflection film with a modified surface.

4. The high-sensitivity temperature measurement demodulation sensing system based on the optical fiber strong evanescent field interferometer as claimed in claim 1 or 2, wherein: the wave band selection width of the light reflection device (3) is 1.1-1.6 times of the free spectrum width of a sensing peak of the interferometer (2).

5. The high-sensitivity temperature measurement demodulation sensing system based on the optical fiber strong evanescent field interferometer as claimed in claim 4, wherein: the central wavelength range of the wave band of the light reflection device (3) is 1.2-2.0 times of the wavelength range of the sensing peak of the interferometer (2).

6. The high-sensitivity temperature measurement demodulation sensing system based on the optical fiber strong evanescent field interferometer as claimed in claim 1 or 2, wherein: the absolute value of the thermo-optic coefficient of the thermo-optic material is greater than 3 x 10 ⁴ The refractive index is 1.38-1.43, and the surface tension is 20.6-21.2 mN/m.

7. The high-sensitivity temperature measurement demodulation sensing system based on the optical fiber strong evanescent field interferometer as claimed in claim 6, wherein: the thermo-optic material is polydimethylsiloxane, polyimide, magnesium fluoride or polyurethane.

8. The high-sensitivity temperature measurement demodulation sensing system based on the optical fiber strong evanescent field interferometer as claimed in claim 1 or 2, wherein: the number of the fiber cores (22) is seven, the fiber cores comprise a middle core (221) and six peripheral cores (222), and all the peripheral cores (222) are uniformly distributed around the middle core (221) in a regular hexagon shape.

9. The high-sensitivity temperature measurement demodulation sensing system based on the optical fiber strong evanescent field interferometer as claimed in claim 1 or 2, wherein: the outer part of the outer wrapping layer (1) is wrapped with a capillary metal pipe (4).

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